24.3/1999

International Rice Reasearch Notes

Copyright International Rice Research Institute 1999

International Rice Research Institute IRRI home page: http://www.cgiar.org/irri Riceweb: http://www.riceweb.org Riceworld: http://www.riceworld.org IRRI Library: http://ricelib.irri.cgiar.org IRRN: http://irriwww/IRRIHome/irrn.htm http://www.cgiar.org/irri/irrn.htm

The International Rice Research Notes (IRRN) expedites communication among scientists concerned with the development of improved technology for rice and rice-based systems. The IRRN is a mechanism to help scientists keep each other informed of current rice research findings. The concise scientific notes are meant to encourage rice scientists to communicate with one another to obtain details on the research reported. The IRRN is published three times a year in April, August, and December by the International Rice Research Institute.

About the cover Wild rice species were collected in many countries in Asia. Mr. Makara Uok of the Cambodia-IRRIAustralia-Project collects wild rice Oryza nivara near a rice field in Kompong Speu, Cambodia. Inset: Different types of wild and weedy rice were found in Nepal and Lao. Cover photos: Baorong Lu

Editorial Board Michael Cohen (pest science and management), Editor-in-Chief Darshan Brar (plant breeding; molecular and cell biology) David Dawe (socioeconomics; agricultural engineering) Achim Dobermann (soil, nutrient, and water management; environment) Bao-Rong Lu (genetic resources) Len Wade (crop management and physiology)

Production Team Katherine Lopez, Managing Editor Editorial Bill Hardy and Tess Rola Design and layout The CPS Creative Services Team: Albert Borrero, Grant Leceta, Erlie Putungan, Juan Lazaro, Emmanuel Panisales Word processing Arleen Rivera

Contents4MINI REVIEW Taxonomy of the genus Oryza (Poaceae): historical perspective and current statusB.R. Lu

RESEARCH NOTESPlant breeding

9

Effect of planting time on outcrossing percentage in CMS line seed production of riceC. Lavanya, R. Vijaykumar, and N. Sreerama Reddy

11 Epistatic QTLs affecting hybrid breakdownin recombinant inbred populations derived from indica-japonica crossesZ.K. Li, L.J. Luo, H.W. Mei, D.B. Zhong, C.S. Ying, Q.Y. Shu, D.L. Wang, R. Tabien, J.W. Stansel, and A.H. Paterson

10 Association between simple sequence repeat(SSR) marker diversity, pedigree record, quantitative trait variation, and hybrid performance in riceW. Xu, S.S. Virmani, J.E. Hernandez, Z.K. Li, and E.D. Redoa

12 Molecular mapping of quantitative trait loci(QTLs) associated with whitebacked planthopper in riceP. Kadirvel, M. Maheswaran, and K. Gunathilagaraj

NEW14 WEB NOTESDecember 1999

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Pest science & management

15 Effect of organic manures on some predatorsin the rice ecosystemJ.C. Ragini, D. Thangaraju, and P.M.M. David

18 Predation rates of Atypena formosana on brownplanthopper and green leafhopperL. Sigsgaard and S. Villareal

16 Effect of culture nutrients on the productionof Rhizoctonia solani toxinsJ. Danson, K. Wasano, and A. Nose

19 A procedure for determining the mating statusof the yellow stem borerA.M. Dirie, M.B. Cohen, and J.S. Bentur

17 Susceptibility of some cereal crops to cystnematode Heterodera sacchari in West AfricaD.L. Coyne and R.A. Plowright

20 A genomic library of Xanthomonas oryzae pv.oryzae in the broad host range mobilizing Escherichia coli strain S17-1L. Rajagopal, S. Dharmapuri, A.T. Sayeepriyadarshini, and R.V. Sonti

Soil, nutrient, & water management

22 Dual cropping of Azolla substitutes for secondtopdressing of N in riceR. Thamizh Vendan, G. Gopalaswamy, and S. Antoni Raj

23 Tools for plant-based N management in differentrice varieties grown in southern IndiaR.M. Kumar, K. Padmaja, and S.V. Subbaiah

Crop management & physiology

25 Response of organic manures in a rice (Oryzasativa)chickpea (Cicer arietinum) crop sequenceG.R. Singh, S.S. Parihar, and N.K. Chaure

26 Effect of growth hormones on outcrossingof cytoplasmic male sterile linesR. Singh

28 NOTES FROM THE FIELD 32 RESEARCH HIGHLIGHTS

35 NEWS 39 INSTRUCTIONS TO CONTRIBUTORS

IRRI marks 40th yearIRRI will celebrate its 40th year of founding in April 2000 under the theme Rice Research for the New Millennium. During this time, the Institute will reflect on its research accomplishments and focus on new research thrusts that will ensure global food security in the new millennium. To mark the occasion, the Institute will host the International Rice Research Conference from 31 March to 3 April; a special Farmers Day on 3 April; and special events on the actual anniversary day of 4 April at which Philippine President Joseph Ejercito-Estrada has been invited. Other high-ranking government officials, representatives from other Consultative Group on International Agricultural Research (CGIAR) centers and nongovernment organizations, former IRRI staff, alumni, and other guests are expected to attend the anniversary celebration. The IRRI 40th anniversary logo (right) shows stylized leaves and panicles rising out of a rice bowl, symbolizing four decades of rice research that represents increasing quantity and quality of grain output. IRRI at 4040 years of achievement and 40 more years of challenges ahead!IRRN 24.3

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MINI REVIEW

Taxonomy of the genus Oryza (Poaceae): historical perspective and current statusB.R. Lu, Genetic Resources Center, IRRI

Dr Baorong Lu, germplasm specialist of IRRIs Genetic Resources Center (GRC), collects wild rice Oryza rufipogon in Eastern Nepal.

Introduction he genus Oryza L. is classified under the tribe Oryzeae, subfamily Oryzoideae, of the grass family Poaceae (Gramineae). This genus has two cultivated species (O. sativa L. and O. glaberrima Steud.) and more than 20 wild species distributed throughout the tropics and subtropics. The Asian cultivated rice (O. sativa) is an economically important crop that is the staple food for more than one-half of the worlds population. All the wild relative species in the genus Oryza, together with weedy rice and different rice varieties, serve as an extremely valuable genepool that can be used to broaden the genetic background of cultivated rice in breeding programs (Brar and Khush 1997, Bellon et al 1998). Fuller exploitation of the wild rice genepool will provide many more opportunities to significantly enhance rice productivity. More effective conservation management and more efficient use of the valuable genetic diversity in the rice genepool, however, largely rely on the development of an appropriate taxonomic and biosystematic framework for the genus Oryza. Species in Oryza have already attracted enormous attention from scientists worldwide because of their agronomic importance. Many studies on taxonomy, phylogeny, and genetic relationships of the Oryza species have been conducted (Roschevicz 1931, Sampath 1962, Tateoka 1963, Sharma and Shastry 1965, 1972, Chang 1985, Vaughan 1989, 1994, Morishima et al 1992, Wang et al 1992, Lu et al 1998). Diversity in Oryza is tremendous,

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which is reflected in the different genomes and genomic combinations in the genus, and in the significant morphological variation within and between species. On the other hand, the great morphological variation in this genus also causes certain taxonomic difficulties, leading to ambiguous delimitation between some Oryza taxa. In addition, different classification systems or taxonomic treatments have been proposed by authors who had access to herbarium specimens representing only certain geographic regions. This makes the taxonomy of Oryza species even more complicated. No single system has been generally accepted by scientists from different parts of the world to date. Historical perspective and species enumeration The genus Oryza was first described by Linnaeus (1753), who recognized only one species, O. sativa, based on the samples of cultivated rice from Ethiopia. During the past two centuries, more than 100 species were published in Oryza by different authors (for review, see Vaughan 1989), which gives this genus great taxonomic complexity. Baillion (1894) was the first who tried to make a more systematic classification of the genus. He recognized five Oryza species and divided them into four sections, i.e., Sect. Euoryza (O. sativa), Sect. Padia (O. meyeriana), Sect. Potamophila (O. parviflora), and Sect. Maltebrunia (O. leersioides and O. prehensilis). The latter two sections have been treated as independent genera in the current taxonomy of the tribe Oryzeae (Vaughan 1989). Roschevicz (1931) made a comprehensive review and detailed studies on Oryza species, which were considered as the greatest contribution to Oryza taxonomic research at that time. He established a classification system with 20 species in four sections, i.e., Sect. Sativa (with 12 species), Sect. Granulata (2 species), Sect. Coarctata (5 species), and Sect. Rhynchoryza (1 species). This system served as a foundation for Oryza taxonomic studies thereafter, although some species have been transferred to other genera of the Oryzeae. Since then, the genus has been extensively reviewed and revised by many taxonomists. Table 1 summarizes the number of species in the major taxonomic treatments of Oryza since its establishment by Linnaeus in 1753. The number of species varied from 5 to 27 in different systems established at different times. The delimitation of the genus Oryza also varied through time in different systems. The earlier taxonomists, such as Baillion (1894), Roschevicz (1931), Chevalier (1932), Chatterjee (1948), Sampath (1962), Tateoka (1963), Sharma and Shastry (1965, 1972), and Oka (1988), offered a wider generic delimitation. However, I recognize the same generic delimitation of Chang (1985) and Vaughan (1989), in which the genus Oryza is characterized by having a spikelet containing a single terminal fertile floret (composed of a lemma, palea, six stamens, and a bifid feathery stigma) and two sterile lemmas (sometimes referred to as glumes) connected to the base of the floret through a rachilla. O. coarctata is now in Porteresia; O. angustifolia, O. perrieri, and O. tisseranti are in Leersia, and O. sabulata is in Rhynchoryza.IRRN 24.3

Table 1. Species of Oryza as recognized by different taxonomists.The + indicates species recognized by the author(s). The italic epithets indicate commonly accepted taxa in modern literature; the bold italic epithets indicate taxa that are no longer included in the genus Oryza. Nonitalic epithets indicate names that are not valid anymore in the genus Oryza.Sharma & Shastry (1972) Ghose et al (1965)

Roschevicz (1931)

Linnaeus (1753)

Chevalier (1932)

Chatterjee (1948)

Prodoehl (1922)

Sampath (1962)

Tateoka (1963)

O. alta O. australiensis O. barthii O. brachyantha O. cubensis O. eichingeri O. glaberrima O. glumaepatula O. grandiglumis O. granulata O. latifolia O. longiglumis O. longistaminata O. malampuzhaensis O. meridionalis O. meyeriana O. mezii O. minuta O. nivara O. officinalis O. perennis O. punctata O. rhizomatis O. ridleyi O. rufipogon O. sativa + O. schlechteri O. stapfii O. angustifolia O. coarctata O. perrieri O. subulata O. tisseranti

+ +d +

+ +d +

+ + +d

+ +d + + +

+ + +d + + + +

+ + + + + + + +h + + + + + + + + + + + + + +

+ + +b +

+ + +b + +e

+ + + + +e

+ + + +

+ + +e +

+ + +e + +g + + +c + + + + + + + +

+ + + + + + + + + +b + + + + + + + + + + + + + + + +

Chang (1985)

+ + + + + + +i + + + + + + + + + + + + +i + +

+

+ + + + +c +

+ + + +c + + + + + + + + +c + + + + + + + +

+ + + + + + + + + + + + +

+ + + + +f + + + +

+

+ +

+ +

+ + + +

a Only includes species currently recognized in Oryza. bO. abromeitiana was recognized. cO. schweinfurthiana was recognized. dNamed as O. breviligulata by the author. eNamed as O. barthii by the author. fO. ubanghensis was recognized. gIncluding subsp. granulata and subsp. abromeitiana. hO. indandamanica was recognized. i Including O. perennis.

The subdivisional treatment The subdivision of Oryza into four sections by Roschevicz (1931) had a fundamental influence on subsequent rice taxonomists, although the sectional epithets have been modified because of the legitimacy of botanic nomenclature. Sect. Sativa and Sect. Granulata recognized by Roschevicz (1931) correspond to Sect. Euoryza and Sect. Padia published by Baillion (1894). According to the International Code of Botanical Nomenclature (ICBN), however, the type section should be named Oryza, which should replace both Sect. Euoryza and Sect. Sativa. Sect. Padia is a valid epithet because it was legally published by Baillion (1894) earlier5

Vaughan (1989)

Baillion (1894)a

+ + + + + + + + + + + + + + + + + + + + + + +

than Sect. Meyeriana named by Roschevicz (1931). Sect. Coarctatae and Sect. Rhynchoryza should no longer be included in Oryza, following the present generic delimitation by Chang (1985) and Vaughan (1989). Table 2 summarizes the subdivisional treatments of Oryza by different taxonomists at different times. Among these treatments, the ones by Sharma and Shastry (1965, 1972) and Vaughan (1989) have been more extensively accepted in different parts of the world. The subdivisional treatments by Sharma and Shastry (1965, 1972) seemed to be influenced by that of Roschevicz (1931), but with a significant revision in terms of the subdivisional ranks and their species inclusion. In the systems of Sharma and Shastry (1965, 1972), 26 species were recognized and included in eight (or nine) series of three sections. Species included in Sect. Oryza and Sect. Padia by Sharma and Shastry (1965) all conform to the present generic delimitation of Oryza, but most of the species (including the type species O. angustifolia) recognized by Sharma and Shastry (1965) in Sect. Angustifolia have no longer been included in Oryza. Only O. brachyantha remains in the genus. Therefore, the epithet Angustifolia should not be valid as a section in Oryza. Considering that O. brachyantha is morphologically and genetically very distinct from all other Oryza species, this species should be treated as a separate section. Vaughans classification of four complexes (1989) was obviously influenced by that of Tateoka (1962a). Based on an extensive morphological study of all Oryza species from different sources, Tateoka (1962a,b, 1963) made a comprehensive revision of the genus Oryza. He divided the Oryza species into two major categories, based mainly on morphological variation. The first group contained morphologically distinct species, such as O. schlechteri, O. australiensis, O. brachyantha, O. coarctata, O. angustifolia, O. perrieri, and O. tisseranti, whereas the second group included species with taxonomic difficulties. He placed all species belonging to the second group into five complexes, i.e., O. latifolia complex (7 species), O. sativa complex (3 species), O. glaberrima complex (3 species), O. ridleyi complex (2 species), and O. meyeriana complex (2 species). Species between

different complexes had a distinct morphological variation, but species within complexes had an ambiguous delimitation. Following this concept, Vaughan (1989) developed a classification system and recognized 22 species in four complexes (Table 2), with two species, O. brachyantha and O. schlechteri, outside of these four complexes. The significant change in this Oryza classification system is that, based on a thorough study of target plant materials from all over the world, Vaughan (1989) removed a few species from Oryza and made the delimitation of this genus more reasonable. He also provided distribution maps of all Oryza species and available genomic data for most species, which largely promoted a better understanding of the species relationships in the genus. In his later publication titled The wild relatives of rice: a genetic resources handbook, Vaughan (1994) provided further information for each Oryza species, such as morphological characterization, distribution, habitat, and species affinities within the genus. He also included his newly published species, Oryza rhizomatis Vaughan from Sri Lanka, in this handbook. A proposed taxonomic treatment Since the publication of Sharma and Shastrys taxonomic systems (1965, 1972), several newly described species, such as O. meridionalis Ng, O. rhizomatis, and O. neocaledonica Morat, have been added to Oryza. On the other hand, some species recognized by Sharma and Shastry (1965, 1972) in their systems, such as O. cubensis Ekman, O. malampuzhaensis Krish. et Chand., O. angustifolia Hubb., O. perrieri Camus, and O. tisseranti A. Chev., have been either considered as invalid epithets or moved from Oryza to other genera of the Oryzeae. The generic delimitation of Oryza by Sharma and Shastry (1965, 1972) therefore needs to be updated to respond to current changes in the genus. Vaughans classification (1989) better reflects the current circumscription and enumeration of the genus Oryza, but unfortunately the subdivisional rank complex that he adopted in his system has no legal standing in the International Code of Botanic Nomenclature (Art. 21.1, Greuter et al 1994). In addition, this classification system leaves two species outside of

Table 2. Subdivisional treatments of Oryza by different rice taxonomists. Roschevicz (1931) Sect. Sativa Sect. Granulata Sect. Coarctataa Sect. Rhynchoryzaa Chevalier (1932) Sect. Euoryza Sect. Padia Sect. Sclerophylluma Sect. Rhynchoryzaa Ghose et al (1965) Sect. Sativa Sect. Officinalis Sect. Granulata Sharma & Shastryb (1965, 1972) Sect. Oryza Ser. Latifoliae Ser. Sativae Sect. Padia Ser. Schlechterianae Ser. Meyerianae Ser. Ridleyanae Sect. Angustifoliaa Ser. Brachanthae Ser. Perrierianae Tateokac (1963) O. latifolia O. sativa O. glaberrima O. ridleyi O. meyeriana Othersd Oka (1988) Sect. Oryzae Sect. Schlechterianae Sect. Granulatae Sect. Ridleyanae Sect. Angustifoliaea Sect. Coarctataea Vaughanc (1989) O. sativa O. officinalis O. ridleyi O. meyeriana Otherse

a All or some species in this section are no longer included in Oryza. bThe treatments by Sharma & Shastry in 1965 and 1972 were essentially the same. In the earlier treatment (1965), Sect. Oryza included the third Ser. Australienses. cThe entity complex was used as a subdivisional rank. dFive species were placed outside of any of the complexes. eTwo species were placed outside of any of the complexes.

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any of the complexes, which makes the classification incomplete. I therefore propose a taxonomic system of Oryza basically following the classification into three sections suggested by Sharma and Shastry (1965), but with certain modifications to match current changes in the genus. In my proposed system, 24 species are recognized and placed in three sections, i.e., Sect. Padia (with 3 series and 6 species), Sect. Oryza (3 series and 17 species), and the newly established Sect. Brachyantha (1 series and 1 species). This classification mirrors appropriately the enumeration of Oryza species and their relationships, and it also gains support through many morphological, cytological, and molecular studies of the genus. I. Sect. Padia (Zoll. et Mor.) Baill. (Type: O. granulata Nees et Arn. ex Watt). 1. Ser. Meyerianae Sharma et Shastry. (Type: O. granulata). O. granulata O. meyeriana (Roll. et Mor. ex Steud.) Baill. O. neocaledonica Morat 2. Ser. Ridleyanae Sharma et Shastry. (Type: O. ridleyi Hook. f.). O. longiglumis Jansen O. ridleyi 3. Ser. Schlechterianae Sharma et Shastry. (Type: O. schlechteri Pilger). O. schlechteri II. Sect. Brachyantha B.R. Lu, sect. nov. (Type: O. brachyantha Chev. et Roehr.). Plantae graciles, annuae; culmi tenues, erecti, glabri; folia linearia; inflorescentia erecta, racemosa; rami principes inflorescentiae flexui, nervosi; spicula linearia oblongaque, 8.5-9 0.8-1.8 mm; lemmata sterilia glabra, subulata, 1-2 8.5-9 mm, aliquando absentia; rachila curvata lunae instar; lemma fertilis mucronatum, 6-8 mm longum, 0.8-1.5 mm latum; aristae robustae, scabrae, 6-10 cm longae; antherae 1.8-2.5 mm longae. Plants gracile, annual; culms slender, erect, glabrous; leaves linear; inflorescence erect, racemose; main axes of inflorescence flexuous, ribbed; spikelets oblong-linear, 8.5-9 0.8-1.8 mm; sterile lemmas glabrous, subulate, 1-2 mm long, sometimes absent; rachilla bent in a comma-shape; fertile lemma mucronate, 6-8 0.8-1.5 mm; awns robust, scabrous, 6-10 cm long; anthers 1.8-2.5 mm long. 4. Ser. Brachyanthae Sharma et Shastry. (Type: O. brachyantha). O. brachyantha III. Sect. Oryza. (Type: O. sativa L.). 5. Ser. Latifoliae Sharma et Shastry. (Type: O. latifolia Desv.). O. alta Swallen O. eichingeri A. PeterIRRN 24.3

O. grandiglumis (Doell) Prod. O. latifolia O. minuta J.S. Presl. et C.B. Presl. O. officinalis Wall. ex Watt O. punctata Kotechy ex Steud. O. rhizomatis Vaughan 6. Ser. Australienses Tateoka ex Sharma et Shastry. (Type: O. australiensis Domin.). O. australiensis 7. Ser. Sativae Sharma et Shastry. (Type: O. sativa L.). O. barthii A. Chev. O. glaberrima Steud. O. glumaepatula Steud. O. longistaminata Chev. et Roehr. O. meridionalis Ng O. nivara Sharma et Shastry O. rufipogon Griff. O. sativa ReferencesBaillion N. 1894. Histoire des plantes. Vol. XII, Paris. Bellon MR, Brar DS, Lu BR, Pham JL. 1998. Rice genetic resources. In: Dowling NG, Greenfield SM, Fischer KS, editors. Sustainability of rice in the global food system. Davis, Calif. (USA): Pacific Basin Study Center and Manila (Philippines): International Rice Research Institute. p 251 283. Brar SD, Khush GS. 1997. Alien introgression in rice. Plant Mol. Biol. 35:35 47. Chang TT. 1985. Crop history and genetic conservation: rice a case study. Iowa State J. Res. 59:425455. Chatterjee D. 1948. A modified key and enumeration of the species of Oryza L. Indian J. Agric. Sci. 18:185192. Chevalier A. 1932. Nouvelle contribution a letude systematique des Oryza. Rev. Bot. Appl. Agric. Trop. 12:10141032. Ghose RLM, Ghatge MB, Subramanyan V. 1965. Rice in India. New Delhi (India): Indian Council of Agicultural Research. 507 p. Greuter W, Burdet HM, Chaloner WG, Demoulin V, Nicolson DH, Silva PC, editors. 1988. International Code of Botanic Nomenclature. Adopted by the Fourteenth International Botanical Congress, Berlin, July-August 1987, Regnum Vegetabile. Linnaeus C. 1753. Species Plantarum. Vol. I. Stockholm. Facsimile edition. Lu BR, Naredo MEB, Juliano AB, Jackson MT. 1998. Taxonomic status of Oryza glumaepatula Steud. III. Assessment of genomic affinity among AA genome species from the New World, Asia, and Australia. Genet. Resour. Crop Evol. 45:205214. Morishima H, Sano Y, Oka HI. 1992. Evolutionary studies in cultivated rice and its wild relatives. Oxford Surv. Evol. Biol. 8:135184. Oka HI. 1988. Origin of cultivated rice. Tokyo: Japan Science Society Press. 254 p. Prodoehl A. 1922. Oryzeae monographice describuntur. Bot. Arch. 1:211 224, 231256. Roschevicz RI. 1931. A contribution to the study of rice. Turdy Prikl. Bot. Genet. Selek. 27(4):3133. Sampath S. 1962. The genus Oryza: its taxonomy and species interrelationships. Oryza 1(1):129. Sharma SD, Shastry SVS. 1965. Taxonomic studies in the genus Oryza. VI. A modified classification of genus. Indian J. Genet. 25(2):173178.

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Sharma SD, Shastry SVS. 1972. Evolution in genus Oryza. Advancing frontiers in cytogenetics. Proceedings of the National Seminar, 1972. New Delhi (India): Hindustan Publishing Corporation. p 520. Tateoka T. 1962a. Taxonomic studies of Oryza. I. O. latifolia complex. Bot. Mag. Tokyo 75:418427. Tateoka T. 1962b. Taxonomic studies of Oryza. II. Several species complex. Bot. Mag. Tokyo 75:455461. Tateoka T. 1963. Taxonomic studies of Oryza. III. Key to the species and their enumeration. Bot. Mag. Tokyo 76:165173.

Vaughan DA. 1989. The genus Oryza L. Current status of taxonomy. IRRI Res. Pap. Ser. Vaughan DA. 1990. A new rhizomatous Oryza species (Poaceae) from Sri Lanka. Bot. J. Linn. Soc. 103:159163. Vaughan DA. 1994. The wild relatives of rice: a genetic resources handbook. Los Baos (Philippines): International Rice Research Institute. Wang ZY, Second G, Tanksley SD. 1992. Polymorphism and phylogenetic relationships among species in the genus Oryza as determined by analysis of nuclear RFLPs. Theor. Appl. Genet. 83:565581.

4th International Rice Genetics Symposium set for October 2000The Fourth International Rice Genetics Symposium (IRGS) will be held at IRRI on 22-27 October 2000. The first IRGS was held in 1985. It led to the birth of the Rice Genetics Cooperative (RGC), which aimed to promote international cooperation in rice genetics. The same year, the Rockefeller Foundation organized the International Program on Rice Biotechnology, which has played a major role in advancing the frontiers of rice science, international collaboration, and human resource development in rice. During the second IRGS (held in 1990), a unified numbering system for rice chromosomes and linkage groups was established. More than 500 scientists from 31 countries participated in the third IRGS (held in 1995). Correct orientation of classical and molecular linkage maps was one of the symposium highlights. Major advances in the genetics and molecular biology of rice have become apparent during the past 15 years. A high-density molecular genetic map of more than 2,300 DNA markers has been developed and several genes of economic importance as well as quantitative trait loci (QTL) have been tagged with molecular markers. Synteny relationships between genomes of rice and several other cereals have been established. Molecular markeraided selection is being used to move genes from one varietal background to another and to pyramid genes. Scientists have developed BAC and YAC libraries and are using them in the physical mapping of the rice genome. A map-based cloning strategy has been used to isolate agronomically important genes. Regeneration from protoplasts of many indica and japonica varieties has allowed researchers to introduce novel genes into elite germplasm through transformation. More recently, biolistic and Agrobacterium-mediated transformation procedures have become available. International programs on rice genome sequencing and functional genomics have been established. These developments have opened new frontiers in rice molecular biology, particularly for understanding the genetic architecture of traits and their manipulation, modifying gene expression, genome sequencing, functional genomics, and gene discovery. Researchers are using these breakthroughs to develop rice varieties with higher yield potential and yield stability for feeding 50% more rice consumers by 2025. The fourth IRGS will feature plenary sessions, oral presentations, and poster sessions. Participants will discuss the latest developments in rice systematics and evolution, cytogenetics, classical genetics, tissue and cell culture, molecular markers, genetic engineering, and genomics. The proceedings will be published. Scientists interested in attending the symposium should send a registration form indicating their name, academic title, address (phone, fax, email), and tentative presentation title to Dr. G.S. Khush at IRRI, MCPO Box 3127, Makati City 1271, Philippines (fax: 0063-2-761-2404; email: g.khush@cgiar.org or to Dr. T. Kinoshita, Faculty of Agriculture, Hokkaido University, Kita 9, Nishi 9, Sapporo 060, Japan (fax: 0081-11-706-4934; email: Takamure@abs.agr.hokudai.ac.jp). Important dates 1 April 2000 30 June 2000 Deadline for abstracts Deadline for full papers

The members of the organizing committee are J. Bennett, D.S. Brar, S.K. Datta, B. Hardy, M.T. Jackson, G.S. Khush, H. Leung, and Z. Li. For more information, contact D.S. Brar Chair, Organizing Committee 4th International Rice Genetics Symposium International Rice Research Institute MCPO Box 3127, Makati City 1271, Philippines Tel.: (63-2) 845-0563 ext. 709 Fax: (63-2) 891-1292, 761-2406, 845-0606 E-mail: d.brar@cgiar.org IRRI Web site: http://www.cgiar.org/irri

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Plant breeding

Effect of planting time on outcrossing percentage in CMS line seed production of riceC. Lavanya, R.Vijaykumar, and N. Sreerama Reddy, Agricultural Research Station (ARS), Maruteru 534122, West Godavari District, Andhra Pradesh, India E-mail: ravi_lavanya@hotmail.com

Commercial exploitation of hybrid rice depends on the identification of suitable heterotic combinations; their stable cytoplasmic male sterile (CMS), maintainer, and restorer lines and economically viable seed production technology; seed distribution infrastructure; and other factors. Although several heterotic combinations with stable CMS lines of IRRI origin were developed at the ARS, seed production is yet to be perfected. A higher outcrossing rate is one of the major factors contributing to higher seed yield in hybrid rice. Seed yield depends on several cultural and environmental factors such as planting time and weather parameters from flowering to maturity. This study identifies suitable seasons for effective and economically viable hybrid seed production. A trial was carried out at monthly intervals from 1 November 1993 to 1

October 1994 at ARS following standard seed production practices. IR62829A was sown on the first of every month followed by staggered sowing of IR62829B at 2-d intervals, i.e., on the fifth and seventh of every month. Twenty-eight-day-old seedlings were transplanted in each plot of 40 m2 consisting of 24 rows with a row ratio of 4A: 2B lines and a spacing of 15 20 cm. During transplanting, seedlings of B lines sown during different dates (D1 and D2) were planted alternately. Two rows of B lines were planted at the end of each set as border rows. At initial flowering, flag leaves of CMS lines were clipped from the top half to one-third to facilitate free movement of pollen. Supplementary pollination techniques such as pulling a long nylon rope (5 mm diam) back and forth every 30 min or shaking the pollen parent with a bamboo pole were followed at peak anthesis for about a week to increase outcrossing percentage.

Data on yield, yield components, and daily meteorological information for 10 d from the initial flowering date are presented for each set of sowing dates (see table). A simple correlation was estimated between outcrossing percentage, seed yield, and weather parameters. Results revealed that June flowering (April sowing) was the most favorable time, followed by August and September flowering periods. An increasing trend was observed between wind velocity and outcrossing percentage (r = 0.95**) and seed yield (r = 0.97**). In this study, maximum temperature (cv 6.7%), minimum temperature (cv 13.3%), and relative humidity (cv 5.2%) were less variable than wind velocity (cv 56.5%). Both maximum and minimum temperatures within a range of 28.9/19.6 C to 36.2/29.4 C, however, were not correlated with outcrossing (r = 0.27, 0.56) and seed yield (r = 0.08, 0.56). Relative

Weather parameters affecting outcrossing percentage in CMS line seed multiplication. Temperature (%) Max June July Aug Sep Oct Nov Dec Jan Feb Mar Apr May Mean 23 Aug 93 17 Sep 93 15 Oct 93 23 Nov 93 24 Dec 93 31 Jan 94 3 Mar 94 24 Mar 94 28 Apr 94 24 May 94 22 June 94 19 July 94 t calculated 22.8 12.4 9.5 11.9 15.0 11.8 12.3 13.5 15.4 17.9 24.6 23.3 15.9 1.37 819 408 327 374 492 347 434 459 498 514 912 861 554 0.29 31.9 30.9 32.9 31.4 28.9 30.5 33.2 33.4 36.2 35.8 34.9 32.2 32.7 Min 27.5 26.2 27.3 21.7 19.9 19.6 21.7 22.8 25.8 27.1 29.4 25.8 24.6 85.0 91.7 92.3 88.3 86.1 90.6 89.5 91.9 78.3 80.0 86.2 87.3 87.3 2.20 1.60 0.60 0.90 1.40 0.70 0.80 0.98 1.40 1.70 3.14 3.08 1.54 Relative humidity (%) Wind velocity (m s-1)

Month of sowing

Initial flowering

Outcrossing (%)

Seed yield (kg ha-1)

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Association between simple sequence repeat (SSR) marker diversity, pedigree record, quantitative trait variation, and hybrid performance in riceW. Xu, IRRI and Plant Breeding and Biotechnology Division (PBBD), Philippine Rice Research Institute (PhilRice), Nueva Ecija; S.S.Virmani, IRRI; J.E. Hernandez, Department of Agronomy, University of the Philippines Los Baos; Z.K. Li, IRRI; and E.D. Redoa, PBBD, PhilRice, Philippines E-mail: s.s.virmani@cgiar.org

Knowledge of genetic diversity among prospective parental lines is important for the success of a hybrid breeding program. Genetic diversity is usually measured using pedigree information, plant phenotypic data, and molecular markers. In this study, we determined the relationship between various genetic diversity measures and hybrid performance in rice. The materials used in this study were 37 maintainer and 44 restorer lines of the WA-CMS (wild abortive-cytoplasmic male sterile) system, which represented germplasm of different origins (IRRI, Philippines, and China) used in our tropical hybrid rice breeding program. The pedigrees of these parental lines could be traced back to ultimate ancestors that had no known pedigree information based on published pedigree records (IRRI 1985, 1995) and PhilRice technical notes. Of these lines, 10 maintainer and 18 restorer lines were randomly selected to produce 34 F1 hybrids in 1997. The hybrids and their parents were evaluated at three field locations in the Philippines from the 1997 dry season to 1998 dry season. Coefficients of coancestry were calculated for the parental lines using the pedigree information. D2 estimates were

derived using data on 11 quantitative characters: days to flowering, flag leaf length and width (cm), plant height (cm), number of productive tillers, panicle length (cm), 100-grain weight (g), grain yield per plant (g), grain length and width (mm), and panicle weight (g). SSR assays with 37 primer pairs were made at PhilRices Genetic Laboratory. Nei and Li (1979) coefficients were then derived. Correlation analysis between various diversity measures and hybrid performance or midparent heterosis on six measured traits (plant height, grain yield, total plant weight, 100-grain weight, grain length and width) was performed. In the analysis of variance across three locations, significant to highly significant differences were observed for all quantitative traits under investigation, except for flag leaf width. The mean number of alleles per SSR locus was 4.24 1.71, ranging from 2 to 9. There was one locus where more than 5 alleles were resolved. There was no or poor correlation between different measurements of diversity and the pedigree records for both B and R lines (Table 1). These results suggested that the methods for measuring

genetic diversity are not consistently associated with each other. This confirms previous reports in durum wheat (Autrique et al 1996) and barley (Shut et al 1997). No correlation was observed between the diversity measures based on all SSR markers and F1 performance or midparent heterosis for all quantitative traits measured (Table 2), indicating that molecular diversity in a random set of SSR markers is not useful in predicting midparent heterosis. Prediction power should be improved if selected markers are linked to quantitative trait loci affecting heterosis. Genetic diversity measured by the pedigree-based coefficient of coancestry was significantly correlated with the F1 mean performance but not with midparent heterosis for highly heritable traits, inluding 100-grain weight, grain length, and plant height. Therefore, pedigree information can be useful in tracing genes of additive action. D 2 estimates based on quantitative trait differences between parents were significantly associated with F1 performance for plant height and midparent heterosis for total plant weight, plant yield, and 100grain weight.

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humidity was negatively correlated with outcrossing (r = 0.47) and seed yield (r = 0.5). The study indicates that seed production can be taken up in areas of artificial irrigation with tube wells or bore wells during summer months (April and May) without hindering the normal crop season.

The outcrossing potential in CMS lines, however, was higher in semiarid zones such as Warangal (43.9%) and Palem (40.2%) than in a humid zone such as Maruteru (19.4%) in Andhra Pradesh. This may be due to the relatively higher humidity (80-90%) and low wind velocity

(mean 1.54 m s -1) prevailing at ARS, Maruteru. Seed production of hybrid rice may thus be more efficient and economical in semiarid zones of the country.

Table 1. Correlation coefficients among genetic diversity measures in maintainer (B) and restorer (R) lines of rice.a Quantitative trait Pedigree record Quantitative traita

ReferencesAutrique E, Nachi MN, Monneveux P, Tanksley SD, Sorrels ME. 1996. Genetic diversity in durum wheat based on RFLPs, morphological traits and coefficient of parentage. Crop Sci. 36:735742. Nei M, Li W. 1979. Mathematical model for studying genetic variance in terms of restriction endonucleases. Proc. Natl. Acad. Sci. USA 76:52695273. Shut JW, Qi X, Stam P. 1997. Association between relationship measures based on AFLP markers, pedigree data and morphological traits in barley. Theor. Appl. Genet. 95:11611168.

SSR 0.092* (B) 0.033 (R) 0.025 (B) 0.047 (R)

0.061 (B) 0.216**(R)

*, **indicate significance levels of P 5% and 1%, respectively.

Table 2. Correlation between hybrid performance (F1), midparent heterosis (HMP), and different diversity measures of parental lines.a Basis for diversity SSR markers F1 HMP Pedigree record F1 HMP Quantitative traits F1 HMPa

Plant height Total plant (cm) weight (g) 0.03 0.30 0.34* 0.30 0.40* 0.12 0.02 0.06 0.19 0.14 0.03 0.38*

Grain yield per plant (g) 0.07 0.06 0.07 0.10 0.18 0.40*

100-grain weight (g) 0.04 0.06 0.43** 0.01 0.16 0.42*

Grain length Grain width (mm) (mm)

0.01 0.05 0.43** 0.26 0.05 0.23

0.09 0.01 0.26 0.05 0.32 0.01

*, **indicate significance levels of P 5% and 1%, respectively.

Epistatic QTLs affecting hybrid breakdown in recombinant inbred populations derived from indica-japonica crossesZ.K. Li, IRRI and Department of Soil and Crop Sciences, Texas A&M University, College Station, Texas 77843 USA; L.J. Luo, H.W. Mei, D.B. Zhong, C.S.Ying, China National Rice Research Institute (CNRRI), Hangzhou; Q.Y. Shu, D.L. Wang, Department of Agronomy, Zhejiang Agricultural University, Hangzhou, China; R. Tabien, J.W. Stansel, IRRI; and A.H. Paterson, Department of Soil and Crop Sciences, Texas A&M University, USA E-mail: Z.Li@cgiar.org

Inbreeding depression (ID), the depressive effect on the expression of traits, arises primarily from increasing homozygosity in outcrossing species. Heterosis (H), the superiority of F1 performance relative to parental performance, is associated with heterozygosity (Allard 1960, Filho 1999). In quantitative genetic theory, ID and H are due to nonadditive gene actions and are considered as two aspects of the same phenomenon (Mather and Jinks 1982). Recently, Li et al (1997) suggested that hybrid breakdown (HB) in rice is part of ID due largely to additive epistasis. In this study, we examined HB in a recombinant inbred (RI) population of rice and mapped main-effect and epistatic quantitative trait loci (QTLs) associated with grain yield and

biomass, which appeared to shed some light on the genetic basis of HB in rice. A set of 254 F10 recombinant inbred lines (RILs) derived from a cross between Lemont (japonica) and Teqing (indica) was used. The parents and RILs were evaluated for grain yield (GY) and biomass (BY) per plant in a replicated trial conducted at CNRRI in 1996. Genotyping was conducted at Texas A&M University, USA. A complete linkage map of 182 markers spanned 1,918.7 cM and covered 12 rice chromosomes with an average interval of 11.3 cM between markers (Li et al 1999). The values of HB (RILs MP) for GY and BY were used as input data, where MP was the mid-parent value. A mixed linear model was used for mapping epistatic QTLs using

QTLMAPPER v. 1.0 based on a threshold of LOD >2.5 (Wang et al 1999). The mean HB of the RILs was 2.7 -1 t ha (54.6%) and 3.7 t ha-1 (37.7%), ranging from 4.5 t ha-1 (90.8%) to 2.5 t ha-1 (50.8%) for GY and from 7.6 t ha-1 (78.4%) to 4.1 t ha-1 (42.2%) for BY. The segregation of the RILs for BY and GY could be largely explained by four main-effect QTLs and seven pairs of epistatic loci (see table). Four main-effect QTLs affecting both GY and BY were mapped to chromosomes 2, 3, and 9, which unlikely contributed to HB since the effects of two alleles at each QTL tend to cancel each other. On the other hand, all but one pair of the epistatic QTLs had significant positive epistatic effects on GY

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and/or BY. According to Mather and Jinks (1982), this indicated that most interactions between alleles from the same parents generally resulted in increased GY and/or BY, whereas those between alleles from different parents resulted in reduced GY and BY. These results indicated that disharmonic interactions between the japonica (Lemont) alleles and the indica (Teqing) alleles at these epistatic loci were largely responsible for HB observed in the RI population.

ReferencesAllard RW. 1960. Inbreeding depression and heterosis. In: Principles of plant breeding. New York: John Wiley & Sons. p 213223. Filho JBM. 1999. Inbreeding depression and heterosis. In: Coors JG, Pandey S, editors. Genetics and exploitation of heterosis in crops. Madison, Wisconsin (USA): American Society of Agronomy and Crop Science Society of America. p 6980. Li ZK, Luo LJ, Mei HW, Paterson AH, Zhao XH. 1999. A defeated rice resistance gene acts as a QTL against a virulent strain of Xanthomonas oryzae pv. oryzae. Mol. Gen. Genet. 261:5863.

Li ZK, Pinson SRM, Paterson AH, Park WD, Stansel JW. 1997. Genetics of hybrid sterility and hybrid breakdown in an inter-subspecific rice (Oryza sativa L.) population. Genetics 145:11391148. Mather K, Jinks JL. 1982. Biometrical genetics. London: Chapman and Hall. Wang DL, Zhu J, Li ZK, Paterson AH. 1999. Mapping QTLs with epistatic effects and QTL environment interactions by mixed model approaches. Theor. Appl. Genet. (in press)

Main-effect QTLs and digenic epistatic loci affecting hybrid breakdown of biomass (BY, in t ha-1) and grain yield (GY, in t ha-1) in the Lemont/ Teqing RILs of rice. Trait BY GY BY GY BY GY BY GY BY GY BY GY BY GY BY GY BY GY BY Chromosome 2 3 3 9 5 1 7 8 2 1 Marker interval i C624xG45 C515RG348 G249RG418 RG451RZ404 gl1Y1049 R210RZ382 G20RG30 CSU754G104 RG654RG256 RZ382RG532 11 5 12 10 9 11 L457bG2132b RG556gl1 G402RG20q CDO98RG752 CDO82CDO226b RG1109RZ537b Chromosome Marker interval i LOD 2.65 2.26 9.81 8.37 5.50 5.87 3.53 2.29 3.80 4.66 2.58 3.98 5.10 2.52 2.86 3.95 4.24 2.66 2.50 a ia 1.08*** 0.55*** 1.86*** 0.84*** 1.54*** 0.82*** 1.03*** 0.43*** 0.29* 0.73** 0.29* 0.57* aj aij

0.56* 0.42** 0.68** -

0.76*** 0.44*** 0.42** 0.31*** 0.65*** 0.23** 0.52*** 0.28*** 0.51*** 0.23** 0.54**

a ai and aj were the main effects of the epistatic loci associated with the Lemont allele, and aij was the epistatic effect between loci i and j. *, **, *** represent the significance levels of P