PertanikaJ.Trop.Agric.Sci. 18(3): 193-199(1995) ISSN: 0126-6128© Universiti Pertanian Malaysia Press

Influence of Seed Ripeness, Sarcotesta, Drying and Storage on Germinabilityof Papaya (Carica papaya L,) Seed

U.R. SANGAKKARAFaculty of Agriculture

University of Peradeniya, Sri Lanka

Keywords: papaya, seeds, germination, fruit maturity, sarcotesta, drying

ABSTRAK

Betik (Carica papaya L.) adalah buah-buahan tropikal terkenal yang dibiakkan oleh biji benih. Walaubagaimanapun, percambahan dan cara mendapatkan anak benih yang baik dalam spesis ini adalah rumitkerana keadaan biji benihnya. Sehingga kini, satu siri kajian untuk menilai kesan kematangan buah, sarkotestadan kekeringan terhadap percambahan dan penghasilan anak benih yang baik masih diteruskan. Ciri-ciri bijibenih buah betik bertukar bersama kematangan buah. Kecepatan percambahan meningkat bersama kematanganbuah, Setakat ini, biji benih yang terbaik untuk percambahan dan untuk pemerolehan anak benih yang suburdi dapati dari buah-buah masak atau yang terlebih masak. Kewujudan sarkotesta mengurangkan percambahandan meningkatkan bilangan anak benih yang luar biasa. Gabungan sarkotesta dalam kesederhanaanpercambahan biji benih betik atau padi tidak menghalang percambahannya. Ini bermakna bahawa halanganlebih berpunca dari sarkotesta yang tidak tersentuh bukan dari penghalangpenghalang yang diperolehidaripadanya. Mengering biji benih betik di bawah suhu berudara dan teduh, akan mengekalkan prosespercambahan ke darjah yang lebih tinggi daripada bila biji benih dikeringkan di dalam oven. Penurunankelembapan biji benih di bawah 10% yang mengurangkan percambahan, menunjukkan corak sifat yangsederhana untuk biji benih betik dibandingkan biji benih ortodok atau degil

ABSTRACT

Papaya (Carica papaya L.) is a popular tropical fruit which is propagated by seed. However, germination andthe procurement of good seedlings are difficult in this species due to the nature of the seed. Thus a series of studiesto evaluate the influence of fruit maturity, sarcotesta and drying on germination and production of healthyseedlings was carried out The characteristics of papaya seed change xvith fruit maturity. Speed of germinationincreases with fruit maturity. Thus, the best seed for germination and for the the procurement of healthy seedlingsis obtained from ripe or over-ripe fruits. The presence of the sarcotesta reduces germination and increases thenumber of abnormal seedlings. Incorporation of the sarcotesta in the germination medium of papaya or rice seedsdid not inhibit their germination. This suggests that inhibition is caused by the intact sarcotesta rather thaninhibitors derived from it. Drying papaya seeds under shade and ambient temperature maintained germinabilityto a greater degree than when seeds were desiccated in ovens. The reduction of seed moisture below 10% reducedgermination significantly, indicating an intermediate behaviour pattern for papaya seeds in contrast to orthodoxor recalcitrant seeds.

INTRODUCTION

Seeds are a primary source of plant propagationin agriculture, horticulture and forestry, as theyare dispersal units consisting of an embryo, foodreserves and protective structure (Roberts andKing 1989). Seeds of most cultivated species canbe dehydrated and stored under conditions oflow humidity and temperatures for varying

lengths of time, without loss of germinability(Ellis 1991). Such seeds are classified as orthodoxtypes (Roberts and King 1989; Hofmann andSteiner 1989).

Another group of seeds retains highmoisture contents during maturation. Theseseeds do not withstand desiccation and need tobe stored at a high moisture content. The seed

U.R. SANGAKKARA

moisture content at which germinability is lostvaries from species to species and according tothe drying regime (Farrant et al 1988). Theseseeds are classfled as recalci trant and arecommon among tropical and subtropicalperennial species (Chin and Roberts 1980;Roberts et al 1984).

An intermediate category of seed has beenidentified (Ellis et al 1990); these survivedesiccation to approximately 10% moisturecontent, but further drying reduces germinability(Ellis 1991). Seeds of several important foodcrops, e.g. coffee (Ellis et al 1990) are of thistype.

Papaya seeds have been classified asrecalcitrant (Chin et al 1984; Hofmann andSteiner 1989) and more recently as theintermediate type (Ellis et al 1990).

Propagation of papaya by seed is difficultdue to rapid seed deterioration after harvest.This is attributed to microbial degeneration ofthe sarcotesta, which reduces viability (Begumetal 1987), although Gherardi and Valio (1976)had reported the presence of growth-inhibitingsubstances in the mucilage covering the seed.However, these studies do not clearly identifythe influence of fruit maturity and the presenceor the sarcotesta on the germinability of papayaseeds, before and after drying. Thus threeexperiments were carried out with the objectiveof determining the importance of fruit maturity,the sarcotesta and the process of drying on thegerminability of papaya.

MATERIALS AND METHODS

The experiments used seeds of commonlyavailable papaya ecotypes in Sri Lanka, whichare a mixture of the Hawaiian and Indianvarieties.

Experiment 1. Influence of Fruit Maturity and thePresence of the Sarcostesta on Germination of PapayaSeeds

Seeds were removed from mature, ripe andover-ripe papayas. These stages corresponded togreen fruits with a yellow tinge, with hard pinkflesh (mature), yellow-green fruit with soft ediblered flesh (ripe) and yellow fruit with pulpy redflesh not suitable for consumption (over-ripe)respectively.

Soon after extraction, four replicates of 100seeds from each maturity stage were planted at

a depth of 2 cm in washed river sand (diameter0.5-0.6 mm). Similar replicates of seeds from thethree maturity stages were planted in the samemanner after removal of the sarcotesta by rubbingwith sand. The fresh and dry weights of seed andsarcotesta were recorded. Germination and thepercentage of abnormal seedlings weredetermined beginning from day 5 after planting,up to day 30.

Experiment 2. Effects of Drying on Storability andGermination of Papaya Seeds

Based on the results of the experiment, eightreplicates, each of 600 seeds of ripe and over-ripe fruits, 50% with the sarcotesta removed asdescribed above were dried either under partialshade at a mean ambient temperature of 28°C ±2.6° or oven dried at 40°C ± 1.5°.

Subsamples (150 seeds) from each replicatefor each of the four treatments were dried tomoisture contents of 25, 10 and 5% and storedin sealed containers. Germination wasdetermined at 0, 30 and 90 days after storageusing 50 seeds per replicate.

Experiment 3. Influence of the Sarcotesta on theGermination of Papaya and Bice SeedsSeeds obtained from ripe and over-ripe papayafruits were divided into nine seedlots, eachcontaining 300 seeds. The sarcotesta of seeds ineach seedlot were carefully separated and placedin individual petri dishes, while the clean seedswere washed in distilled water.

Within the same maturity category, thesarcotesta from one seedlot were mixed withclean seeds of another sample, which wereplanted in trays and germination determined asdescribed in Experiment 1. This was carried outon all six groups.

The sarcotesta of the remaining threeseedlots were mixed with three replicates of riceseeds (variety BG 34-8), each containing 300seeds, and planted in sand at a depth of 2 cm.Another three replicates of rice seeds wereplanted without mixing with the papayasarcotesta. Control treatments of seeds with andwithout the sarcotesta were also maintained forcomparison. Germination and numbers ofabnormal seedlings were determined on day 21after planting.

The data of all experiments were analysedstatistically to determine the significance of thedifferent treatments.

194 PERTANIKAJ. TROP. AGRIC. SCI. VOL. 18 NO. 3, 1995

INFLUENCE OF SEED RIPENESS, SARCOTESTA, DRYING 8c STORAGE ON GERMINABILITY OF PAPAYA SEED

RESULTS AND DISCUSSIONThe stage of maturity of papaya fruits had asignificant influence on seed characteristics(Table 1). Seeds of mature unripe fruits had thelowest fresh weight. The sarcotesta accountedfor 50% of fresh weight, and the seeds had avery high moisture content. Thus in comparisondry weight was low.

Fresh weight of seeds increased in ripe fruitsbut did not change significantly in over-ripefruits. The weight of the sarcotesta also increasedin seeds of ripe fruits, but this constituted only45% of the seed fresh weight, and it was lowerthan in seeds of mature fruits. Further ripeningdid not change these parameters.

Seed moisture content declined with fruitmaturity, and the dry weights increased,culminating in a 100-seed dry weight of 2.41 g inripe fruits. Accumulation of photosynthates inthe endosperm and loss of seed moisture arecharacteristic of seed maturity (Hanson 1984).

Stage of maturity and the presence of thesarcotesta had a significant impact ongermination and development of abnormalseedlings (Table 2). The interaction betweenthese two variables was significant in allsamples.

Germination of seeds from mature fruitswas lowest and the percentage of abnormalseedlings was the highest. In contrast, therewere no differences in these parameters betweenseeds obtained from ripe and over-ripe fruits.This clearly shows the importance of stage offruit maturity in determining the germinabilityof papaya seeds and the procurement of healthy

normal seedlings. It also confirmed theunsuitability of using seed from mature butunripe fruit for the propagation of papaya. Thiscould be attributed to incomplete developmentand high moisture content of the seeds, both ofwhich affect germination and seedlingdevelopment.

Germination of seeds of mature fruits waslow on the 10th day, but increased significantlythereafter (Table 2), in contrast to that of theother two categories. Stage of fruit maturity hada direct impact on speed of germination.Although the number of abnormal seedlings wasgreater from seeds of mature fruits, theincrements in number between the 10th and30th day was similar (approximately 72%) in allseedlots. Thus development of abnormalseedlings was not affected by fruit maturity, incontrast to germination.

The presence of the sarcotesta reducedgermination, and echanced the number ofabnormal seedlings (Table 2). This confirmsearlier reports of the detrimental effects of thesarcotesta on germination of papaya seeds(Gherardi and Valio 1976; Begum et al 1987).However, the effect of the sarcotesta in reducinggermination and enhancing the number ofabnormal seedlings differed with fruit maturity,having a greater inhibitory effect on thegermination of seeds from ripe and over-ripefruit, while the number of abnormal seedlingswas greatest in seeds of mature fruits on the30th day. Reyes et al (1980) have suggested thepresence of growth inhibitors in the sarcotestaas the causal agent.

TABLE 1Characteristics of seeds obtained from mature, ripe and over-ripe papaya

Characteristic

Fresh wt. per 100 seeds (g)

Fresh wt. of sarcotesta of100 seeds (g)

Dry wt. per 100 seeds withoutsarcotesta (g)

Moisture content (%)

MatureFruit

9.45

4.81

1.15

76.0

RipeFruit

11.84

5.42

1.94

64.2

Over-npeFruit

11.59

4.99

2.41

51.7

LSD

0.152

0.029

0.008

2.619

PERTANIKAJ. TROP. AGRIC. SCI. VOL. 18 NO. 3, 1995 195

U.R. SANGAKKARA

TABLE. 2Influence of fruit maturity and presence of sarcotesta on germination and occurrence of

abnormal seedlings in papaya

Fruit Type

Mature

Ripe

Over-ripe

LSD (P=0.05)

Sarcotesta

AbsentPresentAbsentPresentAbsentPresentFruit typePresence ofSarcotestaInteraction

A

30.1%24.2%75.4%37.4%78.2%39.5%9.592.51

Observation (Days after planting)

10

B

10.6%22.6%

8.4%12.5%9.0%

14.0%14.248.55

*

A

42.5%36.0%82.0%46.0%84.5%50.2%

4.981.95

*

20

B

16.2%32.0%9.5%

17.2%7.2%

18.0%9.072.80

*

A

48.2%42.1%87.5%56.8%89.0%57.0%

6.911.92

30

B*

18.5%38.0%10.0%21.0%

7.0%24.5%

2.914.90

•

A - Percentage germination; B - Percentage abnormal seedlings.

The influence of the sarcotesta and methodof drying on storability and germinability ofpapaya seeds is presented in Table 3. Seeds fromripe and over-ripe fruits were used due to thepoor germinability of those from mature fruit(Table 2). The germination response was similarin both types of seed and drying significantlyreduced germination, confirming the poorresponse of papaya seeds to desiccation (Chin etal. 1984). Thus the highest percentagegermination was observed at a seed moisturecontent of 25%, irrespective of other treatments.Lowering of seed moisture to 10% reducedgermination in both categories of seed, althoughthe decrease was not excessive. In contrast, dryingseeds to 5% moisture decreased germinationsignificantly. Thus, as reported by Ellis et al(1990), seeds of ripe and over-ripe papaya fruitsseen to tolerate desiccation to 10% seed moisturecontent without considerable loss of germination.Thus, these seeds could be dried to a greaterdegree than most recalcitrant seeds, which loseviability at approximately 30% moisture content,thereby exhibiting intermediate characteristics,as suggested by Ellis et al (1990).

The absence of the sarcotesta increasedgerminability significantly irrespective of fruitmaturity, drying regime or seed moisture content.This confirms earlier results of the adverse effectsof the sarcotesta on germination, due to thepresence of inhibiting compounds (Begum et al

1987). However, when compared with germinationvalues at 25% moisture content, its effect inreducing germination is lower at reduced seedmoisture contents. This indicates that drying,ecpecially to 5% seed moisture content, may de-activate the germination inhibitors. However,drying to this low seed moisture level reducedgermination of all seeds significandy. Thus thebeneficial impact of removing the inhibitory effectof the sarcotesta is minimal in dried seeds. Storageof seeds does not negate the adverse effect of thesarcotesta, thus illustrating the value of removingit prior to planting.

Oven drying decreases germinationirrespective of fruit maturity and the presence ofthe sarcotesta (Table 3). This is due to thehigher temperature regime, which could destroythe embryo and/or cause detrimental changesto the endosperm reserves. Drying at moderatetemperatures under shade allows the process ofdesiccation to progress gradually, thus causingminimal changes to the seed. However,germination decreases with length of storage forboth categories of seed dried to three moisturelevels. The decline in germination is mostsignificant in seeds dried to a moisture contentof 5%. This again confirms the adverse effect oflow moisture in papaya. The decline ingermination with length of storage is greaterwhen seeds are dried with the sarcotesta, againshowing the importance of removing it.

196 PERTANIKAJ. TROP. AGRIC SCI. VOL. 18 NO. 3, 1995

INFLUENCE OF SEED RIPENESS, SARCOTESTA, DRYING & STORAGE ON GERMINABIUTY OF PAPAYA SEED

TABLE 3Influence of sarcotesta and drying regime on storability and germinability of papaya

seed at various levels of seed moisture content

Fruit Type

25% Seed Moisture

Ripe

Over-ripe

10% Seed Moisture

Ripe

Over-ripe

5% Seed Moisture

Ripe

Over-ripe

Sarcotesta

absent

present

LSD (P=0.05)

absent

present

LSD (P=0.05)

absent

present

LSD (P= 0.05)

absent

present

LSD (P • 0.05)

absent

present

LSD (P = 0.05)

absent

present

LSD (P = 0.05)

MethodofDrying

shadeovenshadeoven

shadeovenshadeoven

shadeovenshadeoven

shadeovenshadeoven

shadeovenshadeoven

shadeovenshadeoven

Storage

0

Period

30Germination

84655034

2.1

856747360.9

74604030 ,

1.3

766445350.8

272216100.3

22181690.2

75524127

3.8

76554427

1.13

64473224

0.4

70574030

1.2

18141081.1

2612960.4

(days)

90(%)

70423620

1.9

70443521

0.7

614026200.3

65423224

2.9

168960.3

127550.2

PERTANIKAJ. TROP. AGRIC. SCI. VOL. 18 NO. 3, 1995 197

U.R. SANGAKKARA

The adverse effect of the sarcotesta ininhibiting seed germination of other seeds inseen in Table 4. Application of extractedsarcotesta of a similar quantity as the papayaseed of the same maturity stage or to rice seeddid not reduce germination or result in abnormalseedlings. This clearly illustrates that theinhibitory effect of the sarcotesta occurs onlywhen kept intact. Thus, the possibility that thesarcotesta acts as a barrier to germination andhealthy seedling development cannot be ignored,although the presence of germination inhibitorshas been reported (Begum et al 1987).

CONCLUSIONFruit maturity affects seed quality in papaya.Seed development is complete at fruit ripeningand not at maturity as was observed from seeddry weight and the contribution of the sarcotestato this parameter.

The stage of maturity, the presence ofsarcotesta and drying method affected seed quality.Seeds of ripe and over-ripe fruits are most suitablefor propagation purposes. As in recalcitrant seeds(e.g. Sangakkara 1993), drying under shade atambient temperatures maintains germinability in

contrast to forced desiccation in ovens. Desiccationof seeds to a moisture content of less than 10%reduces germination significantly. Length ofstorage also decreased germination, especiallywhen seeds were oven-dried.

Presence of the sarcotesta, which could beconsidered a protective cover, significantlyinhibits germination of papaya seeds andincreases the number of abnormal seedlings.Thus, removal of the sarcotesta increasesgermination. Addition of the extracted sarcotestawas only inhibitory when left intact; this aspectrequires elucidation. High rates of germinationand development of healthy seedlings can beobtained by using seeds from ripe or over-ripefruits and from which sarcotesta is removed. Ifdesiccation is required, this process should becarried out gradually under ambienttemperatures.

ACKNOWLEDGEMENTS

Gratitude is expressed to Ms N Mendis and MrE R Piyadasa for research assistance, and Ms S NWerellagama Meegahakumbura for secretarialwork. The project was partially funded by theUniversity of Peradeniya.

TABLE 4Influence of sarcotesta of seed from ripe and over-ripe papaya fruits on

germination of rice or other papaya seeds

Seed Type Treatment Germination (%)at 21 Days

AbnormalSeedlings (%)

21 Days

Ripe Papaya

Over-ripe Papaya

Rice

with sarcotesta intactwithout sarcotestawith sarcotesta from other seedsLSD (P= 0.05)

with sarcotesta intactwithout sarcotestawith sarcotesta from other seedsLSD (P = 0.05)

with sarcotesta from ripe papaya seedswith sarcotesta from over-ripe papaya seedswithout sarcotestaLSD (P = 0.05)

47.285.680.4

4.03

51.788.083.6

2.77

91.694.295.1

1.23

31.04.55.65.73

37.65.86.11.84

4.863.964.221.04

198 PERTANIKAJ. TROP. AGRIC. SCI. VOL. 18 NO. 3, 1995

INFLUENCE OF SEED RIPENESS, SARCOTESTA, DRYING & STORAGE ON GERMINABILITY OF PAPAYA SEED

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(Received 27 July 1994)(Accepted 11 January 1996)

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