ENLARGEMENT OF FmROUS ROOTS IN IeOMOeA Sv, CrlON B,4r,4ras (CoNVOLVULACEAE) 1

JAIME DiAZ, FERMIN DE LA PUENTE, AND DANIEL F. AUSTIN

Diaz, Ja ime and Fermin de la Puente (Departamento de Recursos Geneticos, Centro Interna- cional de la Papa, Apartado Postal 5969, Lima, PerfO, and Daniel F, Anstin (Department o f Biological Sciences, Florida Atlantic University, Boca Raton, FL 33431) ENLARGEMENT OF FIBROUS ROOTS IN IeOMOEA SECTION BarATAS (CoNVOLVULACEAE). Economic Botany 46(3):322- 329. 1992. The bank of sweet potato germplasm at the International Potato Center (CIP) in Lima, Peru, is made up of cultivated germplasm /Ipomoea batalas (L.) Lain.] and wiM germplasm collected in Latin America and the Caribbean. In the wild germplasm section Balatas is included because of its genetic importance in relation to its phylogenetic affinity with the cultivated sweet potato. In our study we have included 11 wild species of the section to identify and determine the primary factors that influence the enlargement of fibrous roots under greenhouse conditions. Thus, the study was divided into two sequential phases: a) identification of wild species with thickened fibrous roots; b) determination of the primary factors that influence the thickening of fibrous roots. The first phase began between 197 and 593 days after planting the 11 species by using a visual evaluation of the roots according to the gradual scale." 0 = fibrous roots; 1 = slightly thickened; 2 = moderately thickened; 3 = thickened," 4 = very thick. As a result four species were identified in categories three and four (1. balalas, I. cordato-triloba, I. tiliacea, and I. ramosis- sima). The second phase was begun between 123 and 669 days after planting of nine species identified with some category of enlargement according to an evaluation with a gradual quantified scale: 0 = <1.45 mm; 1 = 1.45-3.99 m; 2 = 4.0-6.99 ram; 3 = 7.0-9.0 ram; 4 = >9.0 ram. In this phase, two physiological factors were identified (vegetative period and volume of substrate) and a genetic factor (level of ploidy), which directly influence the thickening of fibrous roots. Considering the four species identified with thickened fibrous roots in categories three and four in the two phases of the study [I. balalas (4x), I. tiliacea (,Ix), I. cordato-triloba (2x) and I. ramosissima (2x)], we propose a plan for the use of wild germplasm in a program of systematic genetic improvement of the sweet potato.

Engrosamiento de Raices Fibrosas en el G6nero Ipomoea de la Secci6n Batatas (Convolvula- ceae). Engrosamiento de raices fibrosas en el g~nero Ipomoea de la secci6n Balatas (Convol- vulaceae). En el Centro Internacional de la Papa (CIP), el banco de germoplasma de camote, boniato o batata /Ipomoea balatas (L.) Lain.] esta constituido por material cultivado y silvestre colectados en America Latina y el Caribe desde 1985 a 1992. En el germoplasma silvestre, resalta la secci6n Balalas por su relaci6n filog~netica con la batata. El presente estudio incluye once especies de esta secci6n para identiftcar y determinar factores primarios que influyen en el engrosamiento de farces ftbrosas en condiciones de invernadero. Asf, el estudio fue dividido en dos fases secuenciales: a) Identificaci6n de especies silvestres con capacidad de formaci6n de rafces fibrosas engrosadas; b) Determinar los factores primarios que influyen en el engrosamiento de rafces fibrosas. La primera fase se inicio entre los 197 y 593 dfas despuOs de la siernbra de once especies siendo la evaluaci6n visual de rafces segfm la escala gradual." 0 = raices fibrosas; 1 = ligeramente engrosadas," 2 = moderamente engrosadas," 3 = engrosadas," 4 = muy engrosadas (Figura 1). Fueron identificados tres especies (I. batatas, I. cordato-triloba e I. tiliacea) con rafces f~rosas engrosadas con grado tres y cuatro. La segunda fase, se inicio entre los 123 y 669 dfas despu~s de la siembra de nueve especies identificadas con algfm grado de engrosamiento, siendo la evaluaci6n segfm una escala gradual cuantificada: 0 = <1.45 mm; 1 = 1.45-3.99 ram; 2 = 4.0-6.99 mm; 3 = 7.0-9.0 ram; 4 = > 9.0 ram. En esta fase, el engrosamiento de rafces fibrosas (grado tres y cuatro) continua manifestandose en las tres especies e iniciandose en I. ramosissima, a su vez, fueron identificados dos factores fisiol6gicos (periodo vegetativo de 638 dfas y volumen de substrato de 8") los cuales influyen directamente en el engrosamiento de las raicesfibrosas. Considerandose las tres especies [I. batalas (4x), I. tiliacea (4x) e I. cordato-triloba (2x)] iden-

J Received 3 June 1991; accepted 12 June 1992.

Economic Botany 46(3) pp. 322-329. 1992 �9 1992, by The New York Botanical Garden, Bronx, NY 10458 U.S.A.

1992] DIAZ ET AL.: ROOTS IN I P O M O E A 323

tificadas en las dos fases con rafces fibrosas engrosadas (grado tres y cuatro) se apertura una alternativa para la utilizaci6n del germoplasma silvestre dentro de un programa de mejoramiento gendtico sistem(ttico de la batata. Finalmente, en I. cordato-triloba casi todas las entradas muestran un mayor porcentaje de plantas con grado tres y cuatro.

Key Words: fibrous roots, enlargement, section Batatas, wild species, ploidy level, volume, vegetative period.

The sweet potato [ I p o m o e a ba ta tas (L.) Lam.] is phylogenetically related to fifteen wild species in I p o m o e a , sec t ion B a t a t a s (Aus t in 1988; McDonald and Austin 1990). Of these sixteen taxa, the only cult ivated species is a hexaploid (6x = 2n = 90) that produces edible storage roots. There is, however, evidence of thickening in the fibrous roots to different degrees in the wild spe- cies (Nishiyama and Teramura 1962; Martin and Jones 1972; Nishiyama et al. 1975; Sakamoto 1976; Nishiyama 1982). The genetics of storage root formation and the physiological condit ions controlling them, are almost certainly the causes for the different degrees of thickening in fibrous roots (Jones and Deonier 1965; Nishiyama and Teramura 1962; Sakamoto 1970; Nishiyama et al. 1975; Nishiyama 1982). In a systematic pro- gram a imed at understanding and using the ge- netics of the sweet potato, wild species with de- sirable root traits should be included. This inclusion would help to improve the culinary quality and the disease resistance of sweet potato. In general, the fibrous nature of the roots in wild species l imits their direct util ization in improv- ing sweet potato (Iwanaga 1988), and negatively

affects their economic importance (Sakamoto 1976). The International Potato Center (CIP) has as a priority the identification of species in the section B a t a t a s with semituberous roots and the genetic incorporat ion of their desirable traits into the sweet potato. The objectives of this study were twofold: 1) to identify taxa in section Ba-

ta tas with the capacity to produce enlarged fi- brous roots, and 2) to determine the pr imary factors that influence the enlargement of fibrous roots.

MATERIALS AND M E T H O D S

This study was conducted under controlled greenhouse condit ions during summers and win- ters of the years 1988, 1989 and 1990, on the main grounds of CIP in Lima, Peru. The genetic material included eleven species of the I p o m o e a

section B a t a t a s with a polyploid series (diploid and tetraploid) and wide geographic and ecolog- ical distr ibution (Tables 1, 2). A soil mixture of humus, peat moss and sand mixed in the pro- port ion of 3:2:1 was used for the development of the root system in six and eight inch clay pots.

TABLE 1. ORIGIN AND PLOIDY LEVEL OF ELEVEN SPECIES IN IPOMOEA SECTION BATATAS PRESERVED IN THE GERMPLASM BANK AT CIP, 1990.

Level of Species ploidy Geographic origin

I. batatas (feral) 4 x I. tifiacea 4 • I. ramosissima 2 x L cordato-triloba 2 • L grandifolia 2 x I. trichocarpa* 2 x L cynanchifolia 2 x L lacunosa 2 x L x leucantha 2 x L tenuissima 2 x I. trifida 2 • I. triloba 2 x

Colombia and Ecuador. Mexico, Dominican Republic and Jamaica. Peru, Ecuador and Bolivia. Bolivia and Mexico. Brazil. Jekyll Island, Georgia, U.S.A.** Brazil. Southern Regional Plant Introduction Station, U.S.A.*** Ecuador, Peru, Venezuela, Mexico and Colombia. South Carolina, U.S.A.* Venezuela and Colombia. Eucador, Venezuela, Colombia, Peru, Mexico and Dominican Republic.

* Synonym of L cordato-triloba. ** Supplied by Dr. A. Jones.

*** Supplied by Dr. R. Jarret.

324 ECONOMIC BOTANY [VOL. 46

TABLE 2. GENETIC MATERIAL USED IN A STUDY OF ENLARGEMENT OF FIBROUS ROOTS IN SECTION

B A TA TAS.

No, geno- Ploidy Accession types Species level Geographic origin

DLP 657 5 L batatas 4x DLP 1818 9 L batatas 4 •

DLP 1843 1 L batatas 4 •

DLP 1874 5 1. batatas 4 x

DLP 1270 11 L batatas 4x DLP 1640 3 L cordato-triloba 2 •

DLP 2761 2 L cordato-triloba 2• DLP 2762 4 L cordato-triloba 2 •

DLP 2934 6 L cordato-triloba 2 •

DLP 2936 6 L cordato-triloba 2 x

DLP 3001 2 L cordato-triloba 2 x

DLP 2554 1 I. cynanchifolia 2 x

DLP 2611 1 I. grandifolia 2 •

AC 67.43 6 L trichocarpa 2 x AC 63.36 1 L lacunosa 2 x

D L P 431 1 DLP 521 4 DLP 780 2 DLP 1289 1 DLP 2931 1 DLP 3004 1 DLP 3007 1 DLP 671 5 D L P 1173 2 DLP 1339 8 DLP 1656 6 DLP 2760 10 DLP 2765 1 DLP 2766 4 DLP 2814 6 DLP 2819 9 AC 87.4 2 DLP 2917 3 DLP 2925 1 DLP 2926 1 DLP 2928 4 DLP 2964 3 DLP 2971 1 D L P 2972 10 DLP 2974 2 DLP 2981 10 DLP 2986 6 DLP 2964 3 DLP 3179 5 DLP 3186 2 DLP 3187 6 DLP 3188 3 DLP 3201 4 DLP 3204 2 DLP 3251 1 DLP 3252 4 DLP 3253 9

L x leucantha

I. x leucantha

L x leucantha

L x leucantha

L x leucantha

L x leucantha

L x leucantha

L ramosisslma

L ramostsslma

L ramoslsslma

L ramostsslma L ramostsstma

L ramoslsslma L ramoslsstma

L ramostsstma L ramostsstma

L tenuisslma 1. tiliacea

1. tiliacea

L tiliacea

L tiliacea

L tiliacea

L tiliacea

L tiliacea

L tiliacea

I. tiliacea

L tiliacea

L tiliacea

1. tiliacea L tiliacea

1. tiliacea

L tiliacea

L tiliacea

L tiliacea

L tiliacea L tiliacea

L tiliacea

2 x

2x 2x 2x 2x 2x 2x 2x 2x 2x 2x 2x 2x 2x 2x 2x 2x 4x 4x 4x 4x 4x 4x 4x 4x 4x 4x 4x 4x 4x 4x 4x 4x 4x 4x 4x 4x

P e r u

Colombia Colombia Colombia Ecuador Bolivia Bolivia Bolivia Mexico Mexico Colombia Brazil Brazil Jekyll Island, Georiga, U.S.A. Southern Regional Plant Introduction

Station, U.S.A. Ecuador Peru Venezuela Ecuador Mexico Colombia Colombia Peru Ecuador Bolivia Bolivia Bolivia Bolivia Bolivia Peru Peru South Carolina, U.S.A. Mexico Mexico Mexico Mexico Dominican Republic Dominican Republic Dominican Republic Dominican Republic Dominican Republic Dominican Republic Dominican Republic Jamaica Jamaica Jamaica Jamaica Jamaica Jamaica Jamaica Jamaica Jamaica

1992] 325 DiAZ ET AL.: ROOTS IN I P O M O E A

TABLE 2. CONTINUED.

No. geno- Ploidy Accession types Species level Geographic origin

DLP 3262 4 L tiliacea 4 x Jamaica DLP 703 1 I. triflda 2 x Venezuela DLP 741 3 I. trifida 2 x Venezuela DLP 749 1 1. trifida 2 x Venezuela DLP 781 1 I. trifMa 2 x Venezuela DLP 870 1 L triftda 2 x Venezuela DLP 875 1 1. trifMa 2 x Venezuela DLP 1048 2 L triftda 2x Colombia DLP 1054 1 L trifMa 2x Colombia DLP 1055 1 L trifida 2 x Colombia DLP 1859 7 I. triftda 2 x Colombia DLP 2083 4 I. trifida 2 x Colombia DLP 2894 2 I. triftda 2 x Venezuela DLP 2991 1 I. triftda 2 x Colombia DLP 2993 1 I. triflda 2 x Colombia DLP 2999 2 I. trifida 2 x Colombia DLP 623 1 I. triloba 2 x Ecuador DLP 748 7 L triloba 2 x Venezuela DLP 751 5 1. triloba 2 x Venezuela DLP 1679 6 L triloba 2 x Colombia DLP 1822 1 L triloba 2 x Colombia DLP 1895 6 I. triloba 2 x Colombia DLP 2057 7 I. triloba 2 x Colombia DLP 2139 1 I. triloba 2 x Colombia DLP 2429 9 I. triloba 2 x Peru DLP 2837 1 I. triloba 2 x Mexico DLP 2865 4 I. triloba 2 • Venezuela DLP 2926 2 I. triloba 2 x Mexico DLP 2928 4 1. triloba 2 x Mexico DLP 2937 6 I. triloba 2 x Mexico DLP 2942 4 I. triloba 2 • Mexico DLP 2943 1 I. triloba 2 x Mexico DLP 2977 2 I. triloba 2 • Dominican Republic DLP 2982 6 I. triloba 2 x Dominican Republic DLP 2987 3 1. triloba 2 x Dominican Republic DLP 2937 1 1. triloba 2 x Mexico DLP 2942 1 1. triloba 2 x Mexico DLP 3003 I 1. triloba 2 x Colombia NCSU. 12 5 I. triloba 2 x NSSL, Ft. Collins, CO, U.S.A.

The s tudy w a s d iv ided into p lanning and eval-

uat ion phases.

A) Pre l iminary planning: The p r imary se- quence was carr ied out be tween 197 and 593

days after planting. Presence o f f ibrous root en-

l a rgement in the e leven species was eva lua ted by

visual rat ing on the fol lowing scale: 0 = fibrous

roots; 1 = slightly enlarged; 2 = modera te ly

th ickened; 3 = enlarged; 4 = greatly th ickened

(Fig. 1).

B) Quan t i t a t ive evaluat ion: Af ter the ident i -

fication o f n ine taxa wi th s o m e w h a t th ickened

fibrous roots , the second phase was begun. This

phase cons i s ted o f a pe r iod o f 123 to 669 days

after plant ing. In this phase, the poss ible factors responsible for differences in root thickening were

invest igated. These factors were: vegetat ive pe-

r iod, and v o l u m e o f subs t ra te wi th in the six and

eight inch clay pots. In this phase, the d i ame t e r

o f root th ickening was meas u red according to the

scale: 0 = <1 .45 m m ; 1 = 1.45-3.99 m m ; 2 =

4.0-6.99 m m ; 3 = 7 .0-9 .0 m m ; 4 = > 9 . 0 m m .

RESULTS AND DISCUSSION

In the first phase the root sys tems o f 703 plants were evaluated. These plants inc luded 290 ge-

326 ECONOMIC BOTANY [VOL. 46

Fig. 1. Examples of enlargement in the tetraploid Ipomoea batatas accession De La Puente 657. A. Scale 0 = fibrous roots; B. Scale 1 = slightly enlarged; C. Scale 3 = enlarged; D. Scale 4 = greatly thickened. All plants grown in eight inch pots.

1992] DtAz ET AL.: ROOTS IN IPOMOEA 327

TABLE 3. PERCENTAGE OF PLANTS WITH ENLARGED FIBROUS ROOTS IN ELEVEN SPECIES IN IeOMOEA

SECTION BArArAS. LA MOLINA, OCTOBER 1988 TO JUNE 1990, LIMA, PERU.

No. % Plants with fibrous roots/class* acces- Total

Species sions 0 1 2 3 4 plants

L batatas (L.) Lam. 5 36.4 14.6 12.2 24.4 12.2 41 L cordato-triloba Dennstedt** 6 20.7 22.6 34.0 15.1 07.6 53 L tiliacea (Willd.) Choisy 16 57.6 31.3 07.6 02.5 01.0 198 L trifida (H.B.K.) Don 12 76.1 18.2 05.7 00.0 00.0 8 L triloba L. 19 93.2 06.2 00.6 00.0 00.0 161 L tenuissima Choisy 1 00.0 100.0 00.0 00.0 00.0 2 L lacunosa L. 1 75.0 25.0 00.0 00.0 00.0 4 L ramosissima (Poir.) Choisy 8 99.2 00.8 00.0 00.0 00.0 132 L cynanchifolia Meisn. 1 100.0 00.0 00.0 00.0 00.0 1 1. grandifolia (Dammer) O'Don. 1 100.0 00.0 00.0 00.0 00.0 1 L x leucantha Jacq. 7 100.0 00.0 00.0 00.0 00.0 22

Total 77 703

* scale: 0 = fibrous; 1 = slightly thickened; 2 = moderately thickened; 3 = thickened; 4 ffi greatly thickened. ** Including percentages of plants of synonym L trichocarpa.

notypes which cor responded to 77 accessions o f e leven species (Table 3). As a result, it was pos- sible to distinguish different proport ions o f plants in the four classes o f root thickening. In the fi- brous root class, there were 73.26%; in the slight- ly enlarged class 15.64%; in the modera te ly thickened class 6.26%; in the enlarged class 3.27%; and in greatly th ickened 1.56%. In the last two classes the species that gave the best results were I. bata tas (L.) Lam, [3(27.3%), 4(12.1%)], I. cor-

dato- tr i loba Denns ted t (syn. L tr ichocarpa Ell.) [3(15.1%), 4(7.6%)] and L ti l iacea (Willd.) Choi- sy [3(2.5%), 4(1.0%)].

In the second phase, 825 plants o f 273 geno- types which cor responded to 64 accessions o f nine species were eva lua ted (Table 4). The dis-

t r ibut ion o f plants by degree o f en la rgement was: 0 = 60.72%; 1 = 16.99%; 2 = 11.81%; 3 = 8.07%; and 4 = 2.41%. The percentages o f plants in scales three and four were: I. ba ta tas [3(23.5%), 4( 13.7%)], L cordato- t r i loba [3(19.2%), 4(5.8%), L ti l iacea (Willd.) Choisy [3(11.3%), 4(2.4%)], I. r a m o s i s s i m a (Poir.) Choisy [3(2.5%), 4(0.5%)] I. tr i loba L. [3(1.2%)], and L trifida (H.B.K.) D o n [3(1.1%)]. In L cordato- tr i loba all accessions had a high n u m b e r o f plants with scale three and four.

In scales three and four o f en la rgement o f fi- brous roots, the high values are probably favor- ably inf luenced by the in teract ion o f long vege- ta t ive per iod (638 days) and a large v o l u m e o f substrate (8 inch pots) (Nish iyama and T e r a m u r a 1962) (Table 5). Expression o f the physiological

TABLE 4. PERCENTAGE OF PLANTS WITH THICKENED FIBROUS ROOTS IN NINE SPECIES OF IPOMOEA

SECTION BATATAS. LA MOLINA, OCTOBER 1988 TO OCTOBER 1990, LIMA, PERU.

% Plants with fibrous roots* No. a c ~ e s -

Species sions 0 1 2 3 4 Total plants

1. batatas 5 21.6 17.6 23.5 23.5 13.7 51 I. cordato-triloba 6 17.3 25.0 32.7 19.2 05.8 52 I. tiliacea 19 49.1 21.3 15.8 11.3 02.4 328 1. rarnosissima 9 84.7 08.4 04.0 02.5 00.5 203 I. trifida 8 7 ! .7 19.6 07.6 01.1 00.0 92 1. triloba 10 87.8 11.0 00.0 01.2 00.0 82 L x leucantha 5 71.4 28.6 00.0 00.0 00.0 14 L tenuissima 1 00.0 100.0 00.0 00.0 00.0 1 L lacunosa 1 100.0 00.0 00.0 00.0 00.0 2

Total 64 825

*Scale: 0 = <1.45 mm; 1 = 1.45-3.99 mm; 2 = 4.00-6.99 mm; 3 = 7.00-9.00 mm; 4 = >9.00 mm.

328 ECONOMIC BOTANY [VOL. 46

TABLE 5. INFLUENCE OF THE VEGETATIVE PERIOD AND DIAMETER OF POTS ON THE THICKNESS OF

FIBROUS ROOTS IN SIX SPECIES OF IPOMOEA SECTION BATATAS. L A M O L I N A , NOVEMBER 1 9 8 8 TO O C T O B E R

1990, LIMA, PERU.

Average* Vegetative** period Diameter of pots Slxcies No. accessions diameter (mm) (days) (inches) Total plants

L cordato-triloba 3 05.83 518; 638 8 12 L cordato-triloba 6 04.55 335; 365 6 40 I. tiliacea 19 03.96 335; 579 8 110 I. tiliacea 13 01.78 335 6 218 L trifMa 4 02.57 365; 579 8 7 I. trifida 8 00.91 335; 365 6 85 L ramosissima 9 02.03 579; 610 8 58 L ramosossima 8 00.12 335; 365 6 145 I. x leucantha 5 01.56 426; 669 8 9 L x leucantha 2 00.20 335 6 5 L trifoba 9 01.00 335; 638 8 20 I. triloba 10 00.27 335; 579 6 62

Total 96 771

* All values of the grading scale. ** Where there are two figures, one set of plants was grown for the first number of days, and another set of plants was grown for the second number

of days. The length of time grown depended on the size of the pot.

factors related to total diameter such as vegeta- tive period and volume of substrate may be ob- served in I. cordato-triloba, I. tiliacea, L trifMa, L ramosissima, I. x leucantha and L triloba (Ta- ble 5). This influence is most notable in I. ra- mos iss ima and I. tiliacea where it produced a change of almost three degrees of diameters (Ta- ble 5). Based on visual evaluation, the influence of accessions and genotypes appeared to be sig- nificant within each species. No statistical anal- ysis was performed.

CONCLUSIONS AND RECOMMENDATIONS

In the first phase three species were identified which produced enlarged fibrous roots of be- tween 7 and 15 mm. These species are L batatas, L cordato-triloba and I. tiliacea. The same three species from the first phase were identified in the second phase along with a fourth species, L ra- mosissima. Factors influencing enlargement in- clude the vegetative period, especially the time between 335 and 669 days, and the diameter of the growing pots (8 inch). The inclusion of L batatas (4x), L cordato-triloba (2x) (DLP 1640, DLP 2762, DLP 2934 and DLP 2936), and I. tiliacea (4x) in a program of systematic genetic improvement should assist in the evaluation and inclusion of desirable traits from the germplasm of wild species into the sweet potato. This germ- plasm appears to hold promise for future im- provement of sweet potato cultivars. Finally, the

interaction of the three primary factors deter- mined as responsible for the enlargement of fi- brous roots was not analyzed statistically because of the preliminary nature of the study. However, we interpreted the presence of enlarged fibrous roots of scales three and four as a direct result of the action of these factors.

ACKNOWLEDGMENTS

Publication support was provided by the Centro International de la Papa. We thank Dr. Peter Scmiediche and Ted Carey for suggestions.

LITERATURE CITED

Austin, D. F. 1988. The taxonomy, evolution and genetic diversity of sweet potatoes and related wild species. Pages 27-59 in International Potato Center 1988. Exploration, Maintenance, and Utilization of Sweet Potato Genetic Resources, Proc. Planning Conf., Centro Internacional de la Papa, Lima, Peru.

lwanaga, M. 1988. Use of wild germplasm for sweet potato breeding. Pages 199-210 in International Potato Center 1988. Exploration, Maintenance, and Utilization of Sweet Potato Genetic Resources, Proc. Planning Conf., Centro Internacional de la Papa, Lima, Peru.

Jones, A, and M. T. Deonier. 1965. Interspecific crosses among Ipornoea lacunosa, I. ramoni, L trichocarpa and L triloba. Bot. Gaz. 126:226--232.

Martin, F. W., and A. Jones. 1972. The species of Ipomoea closely related to the sweet potato. Econ. Bot. 26:201-215.

McDonald, J. A., and D. F. Austin. 1990. Changes

1992] DIAZ ET AL.: ROOTS IN IPOMOEA 329

and additions in Ipomoea section Batatas (Con- volvulaceae). Brittonia 42:116-120.

Nishiyama, I. 1982. Autohexapioid evolution of the sweet potato. Pages 263-274 in R. L. Villareal and T. D. Griggs (ed.). Sweet Potato-Proceedings of the Sakamoto, S. First International Symposium, Asian Vegetable Research and Development Center.

- - , T. Mayazaki, and S. Sakamoto. 1975. Evo- lutionary autoploidy in the sweet potato [Ipomoea

batatas (L.) Lam.] and its progenitors. Euphytica 24:197-208.

- - , and T. Teramura. 1962. Mexican wild forms of sweet potato. Econ. Bot. 16:304-314.

1970. Utilization of related species on breeding of sweet potato in Japan. JARQ 5(4).

- - . 1976. Breeding of a new sweet potato variety, Minamiyutaka, by the use of wild relatives. JARQ 10(4).