Pertanika 7(3), 25 -31 (1984)

The Reproductive Characters of Four Varietiesof Groundnuts (Arachis hypogaea L.)

E.S. LIM and OTHMAN HAMDANDepartment of Agronomy and Horticulture,

Faculty of AgricultureUniversiti Pertanian Malaysia,Serdang, Selangor, Malaysia..

Key words: Reproductive characters; groundnuts.

RINGKASAN

Ciri-ciri pembiall-an bagi 4 jenis kacang tanah iaitu, Nudong, V-13, Matjam dan Alabama telah dikaji.Kesemua jenis menunjukkancorak yang sama bagi pembungaar:, pembent~kant~galdan hasil ~enggai. Hanyasebanyak 15 peratus bunga-bunga yang dikeluarkan menghaszlkan lengaz-lengaz matang. Haszl yang rendahini adalah disebabkan oleh pendeb1./-ngaan yang kurang cekap dan pengguguran biji muda akibat pengaruhalam sekeliling yang kurang baik.

SUMMARY

The reproductive characters of 4 groundnut varieties, Nudong V-13, Matjam and Alabama. werestudied. All varieties showed similar patterns of flowering, pegging and podding. Only 15 percent of theflowers produced developed mature pods. The .low yield ,was attributed to inefficient pollination andabortion of developing kernels due to adverse envzronmental mfluences.

INTRODUCTION

Groundnuts is an important short term croplocally grown in rotation with rice and othercrops. Yields of the crop vary from location tolocation and from season to season. There hasbeen no significant improvement in yields despitemany years of cultivation and the introduction ofnew varieties. Due to the inconsistent yieldsof the local and introduced varieties, it is difficultto identify superior material. The inconsistencyin yields can be due to many factors, one of themost important being the basic fertility of thecrop. Many yield studies on the groundnut cropwere based upon the final yield and yield compon­ents. However, in order to understand more fullythe reasons for the low yield, the reproductivecharacters of the crop at each stage of develop­ment from flowering up to pod maturity needto be studied. The various reproductive charactersof two local and two introduced varieties wereinvestigated in this study.

MATERIALS AND METHODS

Four varieties of groundnuts were used inthe study. They consisted of two locally adopted

25

varieties (V-13 and Matjam) and two introducedvarieties (Nudong and Alabama). The plantswere grown in a randomised complete blockdesign with four replications. Within each plot,25 plants were labelled for the collection offlower, peg and pod production data. Another5 plants within each plot were used for destructivestudies such as the determination of hypanthiumlengths, the number of ovules in the ovary and thenumber of developing kernels in the pegs. Pollenstudies were also based upon these plants. Collec­tion of the pollen samples were made during thesecond and third week of flowering with viabilitytests conducted on agar culture media using theperspex block technique (Lim, 1978). Podswere harvested 105 days after planting for thedetermination of pod and kernel number.

RESULTS

Flowering

In all VarIetIes, flowering commenced 25days after sowing. The daily flower productionincreased progressively with alternations of highand low production. The main flowering periodspanned about 40 days after which sporadic

E.S. LIM AND OTHMAN HAMDAN

flowering was observed. The flowering patternwas similar for all the varieties studied and con­sisted of two peak flowering periods, one occurr­ing during the first 3 weeks of flowering and thesecond in the later period of flowering. Rainfallappeared to stimulate flower~;lg and generallypreceded the period of high flower production(Figure 1).

The number of flowers produced duringthe first three weeks of flowering did not differsignificantly from that produced in the laterthree weeks except in the variety, Matjam. Thisvariety produced twice as many flowers in thefirst half of the flowering period than in thesecond half (Table 1).

50 Nudong

20

"0 oj

The total number of flowers produced bythe plants varied, ranging from a low of only 18flowers to a maximum of 142 flowers. Due to thewide variation in flower numbers, the varietieswere not significantly different for the numberof flowers produced. An overall mean of 57flowers per plant was obtained.

Floral Morphology

The groundnut flower consists of the usualstandard, wing and fused keel petals of a legumeflower. However, an unusual feature is the pre­sence of an elongated calyx tube known as thehypanthium which resembles a flower stalk.The ovary is located at the ba.se of the hypanthiumand is attached to a filamentous style which isas long as the hypanthium. The length of thehypanthium ranged fram 2 to 6 cm. No relation­ship was observed between the hypanthiumlengths and the location of the flower. The averagehypanthium length was 3.85 cm and not signi­ficantly different among the varieties studied(Table 2).

>10 V-13 Within the petals, at anthesis the stigmawas observed to be located slightly above the ringof anthers. The position of the stigma relativeto the anthers may be disadvantageous to naturalself-p ollination.

Pollen Production and Viability

oJ 40 Alabama

No differences were found among VarIetIesfor the mean number of pollen produced and theviability 0f the pollen grains. The average pollenproduction pel' plant was 8200 pollen grains.Viability was also high with an average of 89.8percent germination (Table 3).

Ovule Number

Fig. 1. Mean daily flower production per plot (25plants)

Following syngamy, "pegs" were formed.The peg is a stalk-like structure (the gynophore)that develops from the base of the ovary andcarries at its tip the fertilized ovules that even­tually develop into kernels as the pod matures.

Peg and Food Development

The varieties V-13, Matjam and Alabama hada high frequency of ovaries containing 2 ovules.Very few ovaries had up to 3 ovules which wasalso the maximum number observed (Table 4).Variety Nudong, however, had a large number ofovaries with 3 and 4 ovules. No ovary was foundwith only one ovule; the minimum numberobserved was 2 ovules.

5545~5

Daily Rainfall

25

20

20

26

THE REPRODUCTIVE CHARACTERS OF FOUR VARIETIES OF GROUNDNUTS

TABLE 2The distribution of groundnut flowers for the lergth of hypanthium

Frequency (% flowers studied)Hypanthium

length(cm) Nudong V-13 Matjam

2.0 2.4 3 3 4

2.5 2.9 6 8 8

3.0 - 3.4 20 16 22

3.5 3.9 24 18 22

4.0 4.4 34 31 23

4.5 4.9 11 15 12

5.0 5.4 1 5 7

5.5 5.9 1 2 2

6.0 and above 0 2 0

Mean hypanthium 3.8 3.9 3.9

length (cm)

Alabama

4

9

12

25

32

16

o

o

3.8

The number of pegs and pods produced werenot significantly different among the vadetiesstudied. An average of 50 percent of the flowersdeveloped into pegs and out of these only 30percent continued development into maturepods (Table 5). Based upon the number of flowers

27

available, only 15 percent of the yield potentialwas realised.

Further loss of yield potential was evidentfrom the limited development of the fertilizedovules (developing kernels) to maturity. The

E.S. LIM AND OTHMAN HAMDAN

TABLE 3Pollen viabili ty of groundnu t flowers

Po lIen Production Pollen Viability

VarietyNo. Per 0/0Flower S.£. Germination S.£.

Nudong 7750 125 88.7 2.09

V~13 8250 205 90.6 2.12

Matjam 8700 215 90.5 2.17

Alabama 8125 250 89.3 2.48

TABLE 4Percentage of ovaries with 1, 2, 3 and 4 ovules

Percentage of ovaries Mean no.of ovules

Variety per ovaryovules 2 ovule 3 ovule 4 ovule

Nudong 0 8 48 44 3.24

V---13 0 95 5 0 2.08

rVlatjam 0 97 3 0 2.01

Alabama 0 97 3 0 2.13

Variety

Nudong

V-13

Matjam

Alabama

Mean

TABLE 5Peg and pod production of groundnuts

Pegs Mature Pods

Mean Percent of Mean Percent of Percent ofNo./plant flowers No./plant Pegs Flowers

27.4 49.2 6.0 22.2 11.0

31.4 51.8 10.0 32.8 17.2

29.2 47.2 10.3 35.0 16.9

25.3 52.0 7.8 31.2 16.2

28.3 50.0 8.5 30.3 15.3

Differences between the varieties not significant at P = 0.05

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THE REPRODUCTIVE CHARACTERS OF FOUR VARIETIES OF GROUNDNUTS

number of developing kernels within the pegsvaried. With the exception of the variety Nudong,the other varieties generally contained 2 develop­ing kernels in the peg. The Nudong variety hadmany pegs with 3 and 4 developing kernels (Table6).

During the development of the pegs into podsmany of the developing kernels aborted. In allthe varieties studied, most of the pods contained2 kernels. The Nudong variety had, in addition,many 3-kerneled pods. Single-kerneled pods werealso found (Table 7).

The distribution of pegs for the number ofdeveloping kernels was not significantly differentfrom the distribution of ovaries for the number ofovules present. However, significant differences

were obtained when the distribution of pegswas corn.pared with that of pods for kernelnumbers (Table 8). All varieties exhibited asimilar pattern of an increase in the number ofpods with 1 and 2 kernels. Thus, in addition tothe low pod set, the low number of fertilizedovules that developed into mature kernels furtherreduced the yield.

DISCUSSION

In all seed crops, yield is dependent to alarge extent upon the hasic reproductive unitsavailable. In groundnuts the basic reproductiveunits constitute the flowers. The productionpattern of the groundnut flowers favour podsetting. The extended period of flowering is anadvantage when conditions are less than favourable

TABLE 6Percentage of pegs with 1, 2, 3 and 4 developing kernels (DK)

Percentage of pegsVariety Mean Nnmber

DK/peg1 DK ? DK 3 DK 4 DK

Nudong 0 7 62 31 3.24

V-13 0 92 8 0 2.08

Matjam 0 91 9 0 2.09

Alabama 0 87 13 0 2.13

TABLE 7Percentage of pods with 1, 2, 3 and 4 kernels

Percentage of podsVariety Mean Number

kernels/pod1 kernel 2 kernels 3 kernels 4 kernels

Nudong 11.2 50.6 35.8 2.4 2.29

V-13 12.2 86.8 1.0 0 1.89

Matjam 13~1 85.7 1.2 0 1.91

Alabama 11.5 86.4 2.1 0 1.91

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~.s. LIM AND OTHMAN HAMDAN

TABLE 8Summary of Chi-square values for comparisons betweendistributions for the number of ovaries, pegs and podsaccording to the number of ovules, developing kerbels

or seeds present

Distributionscompared Nudong

Variety

V-I3 Matjam Alabama

Ovaries vs. Pegs

Ovaries vs. Pods

Pegs vs. Pods

ns = P ~ 0.05

** ;: P < 0.01

4.10 ns

81.24 **

75.71 **

0.74 ns

15.24 **

17.80 **

3.19 ns

16.32 **

21.70 **

6.79 ns

12.27 **

19.37 **

to pollination and fertilization. The floweringpeaks observed in all varieties to follow rainfallare also plant responses to match favourableweather conditions with flower production.However, very late flowers would not have ade­quate time for pod development before theharvest. Pods take about 8 weeks to mature fromthe time of flowering and therefore, only the first3 weeks of flowering may be considered to beuseful. The number of flowers produced duringthe first 3 weeks varied among the varieties butwere more than 3 times the number of podsproduced.

Pollination and fertilization are necessarybefore further development can take place. Thegroundnut flower had no shortage of pollen inall the varieties studied. There were over 8000pollen grains per plant of very high viability.The only problem that may arise is the pollina­tion process. Only about 50 percent of the flowersdevelop pegs indicating that in half the flowersproduced, pollination or fertilization was notachieved. The location of the stigma was observedto be slightly above the anthers. This can preventnatural self-pollination. The crop cannot rely oncross-pollination. A low level of natural cross­pollination of less than 2 percent has been re­ported (Culp et at., 1968). It has also been foundthat manual pollinations resulted in more pegsbeing produced than when groundnut flowerswere left undisturbed (Lim and Siegfred, 1'84).Inadequate pollination may, therefore, cause thelow peg formation.

Peg development follows fertilization (Smith1956). However, pollination need not result inthe fertilization of ovules. Many factors can delaythe growth of pollen tubes and failure of ferti­lization. High temperatures and soil moisture

30

stress have been cited (Ono and Ozaki, 1974).The length of the style as indicated by the hypan­thiuIIl length can also influence the success offertilization. The hypanthium length was foundto range from 2 to 6 em. The rate of pollentube growth has been estimated at 1 em perhour after an initial lag period of 2 hoursfor pollen germination (Lim and Siegfred,1984). Thus, the flowers would require from 4 to8 hours for fertilization to be affected. Althoughno study was made to relate the length of thehypanthium to peg formation, it is possible thatfertilization of the ovules would be more likelyto be achieved for flowers with short styles.

The development of pegs into pods did not. always follow peg formation. Only one-third

of the pegs reached maturity. The failure of pegsto develop into pods was largely due to theabortion of the developing kernels. Unfavourabletemperature and moisture regimes followingfertilization, nutritional deficiencies, especiallycalcium and the failure of double fertilizationcan result in the abortion of the young kernel(Ono and Ozaki, 1974; Shibuya and Suzuki,1956; Singh et at., 1980; Smith, 1954). Fora peg to develop to maturity there must be at leastone developing kernel within it.

Further losses in the yield potential wasevident in the number of kernels within thepod. Abortion of the developing kernels resultedin fewer kernels being present in the pod than inthe pegs. Comparisons between the distributionof the ovaries for ovule number, pegs for develop­ing kernel number and pods for kernel numbershow no significant differertces for the distributionof ovaries and pegs indicating that fertilizationand kernel development at the early pegging stagewere complete. However, differences were signi-

THE REPRODUCTIVE CHARACTERS OF FOUR VARIETIES OF GROUNDNUTS

ficant on comparing the distribution of pegs andpods. Therefore further loss of the yield potentialoccurred after pegging. Due to the abortion ofdeveloping kernels, there were only a few podswith 3 or 4 kernels. Many pods were found with2 kernels. Single-kerneled _pods were also foundwhen originally no ovary or peg contained onlyone ovule. The death of one or more fertilizedovule resulted in these pod categories. Theselosses in yield were found in all the varietiesstudied.

The vanetles studied were similar in theirflower production and reproductive charactersup to pod maturation. In these varieties, inspite ofmany flowers being produced, only 15 percent ofthe flowers de:veloped into mature pods. Thenumber of ovules that developed into maturekernels were even fewer, representing only 12.7percent of the ovules available. These losses inthe reproductive potential of the crop was attri­buted to adverse environmental influences. Thusany improvement in environmental conditionscan bring about yield improvement up to thelimits of the basic fertility which if> about 6 timesthe present yield obtained. The consistency inwhich all varieties suffer losses at each stage ofreproduction suggest that the environmentalfactors greatly influence the outcome of thecrop. Therefore, it is not surprising that incon­sistent results have been obtained in field trials.From the results it is evident that conditions thatcan improve pollination and reduce abortion canresult in large gains in yield improvement. Themanipulation of planting dates to coincide withfavourable conditions, supplementary irrigationand the supply of adequate nutrients are factorsto consider.

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REFERENCES

CULP, T.W., BAILEY, W.K. and HAMMONS, R.O.(1968) : Natural hybridization of peanuts (Arachishypogaea L.) in Virginia. Crop Sci., 8: 109-110.

LIM, E.S. (1978) : A technique for pollen studies. Per­tanika. 1: 59-61.

LIM, E.S. and SIEGFRED, 1. (1984) : The flowering,pollination and hybridization of groundnuts (Ara­chis hypogaea L.) In press.

ONO, Y. and OZAKI, K. (1974) : Effect of temperatureon pod development and yield of groundnut plants.Proc. Crop Sci. Soc. Japan., 43: 242-246.

SHIBUYA, T. and SUZUKI, M. (1956) : Morphologicaland physiological studies on subterranean fructi­fication of legume crops - occurrence of abortionof fertilized seed in peanut. Proc. Crop Sci. Soc.Japan, 25: 17-18.

SINGH, SURJIT, LIM, E.S. and RAJAN AMARTHA­LINGAN. (1980) : Effects of lime and its place­ment on the growth and yield of groundnuts Ara­chis hypogaea L.). Proc. Legumes in the Tropic1979, Univ. Pertanian Malaysia. pp 379-388.

SMITH, B.W. (1964) : Arachis hypogaea L. Reproduc­tive efficiency. A mer. J. Bot., 41: 607-616.

SMITH, B.W. (1956): Arachis hypogaea L. Normalmegasporogenesis and syngamy with occasionalsingle fertilization. A mer. J. Bot., 43: 81-89.

(Received 26 March, 1984)