Pertanika 7(2), 61-66 (1984)

The flowering, pollination and hybridizationof groundnuts (Arachis hypogaea L.)

E. S. LIM and J. S. GUMPILDepartment of Agronomy and Horticulture

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

Keywords: Flowering; pollination; hybridization; groundnuts.

RINGKASANCiri-ciri pembungaan, teknik-teknik mengembirt dan pendebungaan kacang tanah telah diuji. Pem-

bungaan didapati berlaku antara 0645 hingga 0900 jam dengan kelewatan setengah jam pada hari-harimendungt Cepudebunga didapati matang satu jam sebelum bunga mengembang.

Kadar tumbesaran tiub debunga didapati lebih kurang 1 sm sejam dan persenyawaan dianggarkanterjadi di antara 5 hingga 6 jam selepas pendebungaan. Hasil lengai kacang tanah tidak bertambah denganteknik "tripping" walaupun didapati bahawa pendebungaan bantuan boleh menambah bilangan "tugal"berbanding dengan pendebungaan semulajadi.

Pengembirian boleh dilakukan dengan menggunakan pengepit atau sedutan pada waktu petang,sehari sebelum bunga-bunga berkembang dengan tidak menjejaskan kejayaan pengacukan. Didapati jugabeberapa kombinasi pengacukan dan induk-induk boleh memberi kejayaan pengacukan yang lebihdaripada yang lain.

SUMMARY

The flowering pattern, emasculation and pollination of locally grown groundnuts were studied.Flowering generally occurred between 0645 to 0900 h with a half hour delay on dull days. Antherdehiscence occurred in the bud about one hour prior to blooming.

Pollen tube growth was approximately 1 cm per hour and fertilization was estimated to take place5 to 6 hours after pollination. There was no improvement in pod set following tripping of the flowersalthough it was found that assisted pollination improved peg formation over natural self-pollination.

Emasculations can be carried out either using forceps or suction on the afternoon prior tothe day of anthesis without any detrimental effect on the success of cross-pollination. Some cross-com-binations and parents were capable of higher success in cross-pollinations than others.

INTRODUCTION

In the improvement of groundnuts (Arachishypogaea L.) information pertaining to theflowering, pollination, and seed set of the croprelevant to the local environment is necessary.For example, while it is generally known thatgroundnut flowers bloom early in the day, thetime of flowering differ from place to place.Flowering has been reported to occur as earlyas 0300 h in the Philippines (Jose, et al-> 1951)

and between 0600 to 0800 h in India (Dainiel,et a/., 1976). Dehiscence of the anthers has beenreported to occur early, prior to flower openingwhich enables self-pollination to take place withinthe closed petals (Culp et al.t 1968).

Groundnut, being a naturally self-pollinatedcrop would have little need for insect assistance.However, it has been reported that only less than10 percent of the numerous flowers produced,develop into mature pods (Othman, 1979; Lim

61

E. S. LIM AND J. S. GUMPIL

et al.t 1980). The low pod set may be due toinefficient self-pollination. In some legume crops(e.g. Medicago sativa, Vicia faba) the flowersneed to be tripped to effect pollination (Arm-strong, 1935; Lawes, 1972; Lim and Knight,1980).

Pod set can also be influenced by the effi-ciency of fertilization. The distance betweenthe stigma and the ovary ranges from 2.0 to6.0 cm (Othman, 1979) and slow pollen tubegrowth particularly where the style is long caninfluence the success of fertilization.

In the hybridization of groundnuts, thetechnique and time of emasculation as wellas the parental influence on the outcome ofthe cross-pollination are important conside-rations. Success from artificial cross-pollinationhas been reported to vary from 38 to 70 percentdepending upon the technique used and theefficiency of the operator (Halim and Ahmad,1980; Nigam et al.t 1981; Norden, 1980). Aseach successful cross-pollination only yields afew seeds, a high success rate is desirable.

The flowering behaviour, pollination andhybridization of groundnuts is investigated inthis study.

MATERIALS AND METHODS

was used to compare the relative merit of eachtreatment.

The tripping requirement and hybridizationstudies were carried out on four varieties ofgroundnuts. These were Alabama, Tainang No.1, Indonesian and Local. In the tripping studies,there was five replications with five plants each.On each plant an equal number of flowers weretripped or left as the untreated control. In thehybridization study the four varieties were crossedin all combinations including reciprocal crosses.All percentage data were transformed intoarcsine values prior to biometrical analyses.

RESULTS

Flowering and Anther Dehiscence

Flower buds were seen one day prior toanthesis. The buds developed rapidly and mostbuds reached maximum size by the earlyafternoon (1430 h Malaysian Standard Time).Flowering occurred on the morning of thefollowing day. Flowering was observed to beginfrom 0645 h on a fine morning with maximumblooming around 0730 ha. On dull and wetmornings, the flowering was delayed by halfan hour (Figure -1).

A locally grown Spanish variety of ground-nuts, "Local", obtained from Telok Chengaiin Kedah, was observed for the time of floweropening and anther dehiscent. The crop wasgrown in the Universiti Pertanian Research Areain 1982.

The pollen tube growth rate was determinedthrough pistil decapitation of pollinated flowersat various time intervals after pollination and atdifferent distances from the stigma. Decapitationwas carried out hourly up to five hours afterpollination and the style excised at distances vary-ing from 1 to 4 cm. Each treatment combinationconsisted of 15 flowers replicated three times.

In comparing emasculation techniques, theanthers were removed using either (a) forceps or(b) suction. Selected flower buds were emas-culated in the later afternoon and pollinated thefollowing morning. In a separate study,emasculations were carried out at two differenttimes, (a) between 1430 and 1530 h and (b)between 1730 and 1830 h, on the day prior toflowering. In these studies, the success ofpollination, as indicated by the peg formation,

07 30 0800

TIME (M.S.T,)

Fig. 1 - Time of opening of groundnut flowers

The dehiscence of the anthers were indicatedby the presence of pollen within the keel petals.The anthers were found to dehisce beginning from0545 h until 0715 h M.S.T. Most anthers dehiscedat 0615 h. Flowering followed about one hourafter pollen was released (Table 1).

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THE FLOWERING, POLLINATION AND HYBRIDIZATION OF GROUNDNUTS

TABLE 1Time of anther dehiscent and anthesis in groundnuts

Number of flowersA 11 1 IV

(M.S.T)

0545

0600

0615

0630

0645

0700

0715

0730

0745

0800

0815

With Anthers dehisced

3

23

64

87

95

98

100

100

100

100

100

Opened

0

0

0

0

0

5

20

57

89

97

100

Growth Rate of Pollen TubesThe formation of pegs after decapitation of

the pistil indicated that the pollen tube had grownbeyond the point of decapitation and fertilizationhad been achieved. The number of pegs formeddecreased when the pistil was decapitated furtheraway from the stigma and when the time betweenpollination and decapitation was reduced (Table2). Flowers with pistils decapitated 5 hoursafter pollination at 1 cm from the stigmaproduced the largest number of pegs while few orno pegs were formed when the pistils weredecapitated two hours after pollination at distancesof more than 2 cm from the stigma.

TABLE 2

Methods and Time of EmasculationIn the two emasculation methods studied

there was no significant difference betweenemasculation using forceps or by suction. Thenumber of pegs formed from pollinations follow-ing the emasculations were similar with bothmethods. The proportion of pegs >rmed fromthe pollinated emasculated flowers wassignificantly more than the untreated controlflowers suggesting that both the emasculationtechniques used did not adversely affect theflower buds in their ability to form pegs (Table3).

TABLE 3Percentage of successful pollinations in two methods

of emasculation

Emasculation method Percentsuccess

Angularvalues

ControlForceps

Suction

(Not emasculated) 60.6

78.6

80.6

51.29

64.14

66.79

LSD (P = 0.05) 9.49

In the comparison between flower budsemasculated in the early and in the late afternoonthere was no significant difference in their abilityto form pegs. The difference of 2 hours in thetime of emasculation was not critical (Table 4).

TABLE 4The effect of emasculation time on the percentage

of successful pollinations in the afternoon.

Mean rercen

Time afterpollination(hours)

1

2

3

4

5

ixage oi nower^ wiuiforming pegs

Distance

1

5.3bc

16.6de

72.4gh

94.5j

ucuapuaicu piMus

of decapitation point fromstigma (cm)

2

Oa

0.8a b

35.2f

77.6gh

86.4 h l j

3 4

Oa Oa

Oa Oa

27.7ef 11.6cd

70.6g 25.5ef

79.5ghi 78.8ghi

Time of emasculation

Control (Undisturbed)

Early emasculation(1430 - 1530 h)

Late emasculation(1730 - 1830 h)

LSD (P - 0.05)

Percent

success

59.7

70.3

79.7

-

Angular

value

50.80

57.68

65.93

8.85

Mean values having the same leter are not significantlydifferent at P = 0.05 based on the New DuncanMultiple Range Test.

Tripping RequirementThe tripped and untripped flowers for all

four varieties were not different in their abilityto form pods (Table 5). There is no evidence,

63

E. S. LIMANDJ.S.GUMPIL

therefore, to suggest the presence of a trippingrequirement in groundnuts.

TABLE 5Mean number of pegs and pods produced per plant

plant from tripped and untreated flowers

TABLE 6Percentage successful cross-pollination from among

four varieties

Number of pegs Number of pods

Alabama

Tainang

Indonesian

Local

Untreated

48.6

42.6

47.2

41.2

Tripped

51.2

41.2

49.4

44.0

Untreated

29.0

27.6

28.0

35.6

Tripped

32.6

25.2

40.0

38.2

Treatment means for untreated and tripped are notsignificantly different at P = 0.05 for all varieties.

HybridizationAll the four varieties studied were found to

cross readily in all parental combinations withan average success of 31.6%. There was generallyno significant difference among the cross-com-binations for the proportion of successful cross-pollinations (Table 6). However, when each pairof crosses were compared, significant differenceswere found depending upon whether the varietywas used as the pollen or seed parent (Table 7).The Tainang variety was found to be a betterpollen parent than Alabama when crossedwith the seed parent, Local. In crosses whereAlabama was the seed parent, both theTainang and Indonesian varieties were betterpollen parents than variety, Local. Amongbetter pollen parents than variety, Local. Amongseed parents, the variety Alabama formed morepods than Tainang when cross-pollinated with acommon pollen parent, Indonesian. The varietyAlabama was also found to be a better seedparent than a pollen parent when crossed withIndonesian (Table 8).

DISCUSSION

Flowering and EmasculationThe flowering characteristics of the groundnut

plants determine the time that is suitable forcarrying out emasculations and cross-pollinations.Flowering commenced just after day-breakwith a delay of half an hour duringdull or wet days. Peak flowering occuredabout 0730 h. M.S.T. and most flowers openedby 0900 h.

Cross combinationMean Percent success

(pod set)

Local and Alabama

Local and Indonesian red

Local and Tainang

Alabama and Indonesian

Alabama and Tainang

Indonesian and Tainang

24.425.142.7

33.0

35.8

28.8

AD. mean values were not significantly differentat P - 0.05.

The anthers were found to dehisce before theflower opened. Emasculation must, therefore,be carried out in the bud stage. The groundnutflower buds only appeared one day beforeflowering and developed to its maximum size onthe same day. In order to allow the buds todevelop sufficiently for handling, emasculationwas carried out in the later part of the day.

The results have shown that the emasculationof flower buds during the afternoon prior to theday of anthesis was not detrimental to the successrate following pollination and there were alsono differences in the success of cross-pollinationfollowing emasculation either by using forcepsor by suction. Thus bud emasculations maybe carried out as early as 15 hours prior to anthesisusing either method. The ability to carryout bud emasculation early also has significancein terms of labour costs reduction and theconvenience of working hours.

Pollination and FertilizationIn groundnuts, self-pollination is the rule.

The release of pollen from the anthers evenbefore the flowers open excluded the entry ofpollen from other plants. However the efficiencyof self-pollination was questioned. The resultsin the emasculation and pollination study haveshown that manually pollinated flowers are capa-ble of producing more pegs than naturallyself-pollinated flowers. This indicated that naturalpollination by itself is not adequate for theoptimum production of pegs.

The possibility of the presence of a trippingrequirement to enhance pod set was also investi-gated. Although tripping of the staminal column

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THE FLOWERING, POLLINATION AND HYBRIDIZATION OF GROUNDNUTS

TABLE 7

Percentage of successful cross-pollinations among crosses withcommon male and female parents

Group Parent A Parent B

Mean % crosses producingpods (female x male)

A X B

26.5b

33.9 a b

44.9a

42.2a

42.i a

22.4b

35.3a

27.9a

24.4a

40.6a

29.8a

22.7a

B X A

22.4a

27.9a

40.6a

24.4a

29.8a

26.5a

22.7b

33.9ab

42.2a

44.9a

42.1a

35.3ab

2

3

4

Local

Alabama

Indonesian

Tainang

Alabama

Indonesian

Tainang

Indonesian

Tainang

Local

Tainang

Local

Alabama

Local

Alabama

Indonesian

Means values with the same letter are not significantly different at P - 0.05 based upon the New DuncanMultiple Range Test.

is necessary in Medicago sativa and Vicia fabato promote seed set (Armstrong, 1935; Lawes1972); Lim and Knight, 1980), a similar require-ment was not evident in this study. The fourvarieties used did not differ in pod yield whetherflowers were tripped or untreated.

The growth rate of pollen tubes wasbased upon the formation of pegs followingdecapitation of the style. Fertilization,which is indicated by peg development, canonly occur when the tip of the pollen tubebearing the generative nucleus has grown pastthe point of decapitation. The range of treat-ments applied allowed the hourly growth of thepollen tube to be monitored. Based on theformation of pegs, most of the pollen tubes hadgrown more than 1 cm in the first 3 hours afterpollination, 2 to 3 cm after 4 hours and 4 cmafter 5 hours. The results suggest that theaverage pollen tube growth is approximately1 cm per hour. The inital 3 hours required for thepollen tube growth of 1 cm was due to the lag

period for pollen germination, which tookapproximately 2 hours. Therefore, dependingupon the length of the style, fertilization isestimated to occur 5 to 6 hours after pollinationfor styles 3 to 4 cm in length.

HybridizationIn the hybridization of groundnuts, a high

success T-ate from the cross-pollinations isdesirable. The male and female parents are oftenchosen based upon traits such as pod yield, seedquality and pest and disease resistance. However,it is also necessary that the parents be able to setseed well on cross-pollination. The number ofseeds that can be recovered from each successfulpollination may be only one or two. Therefore,when success from cross-pollination is low, alarge number of crosses need to be made requiringmuch time and expenses.

The selection of parents and the crossingsystem, where possible, should consider the seedset ability of the cross-combination. The results

65

E. S. LIMANDJ.S. GUMPIL

TABLE 8Mean percent successful cross-pollination among

reciprocal crosses

Reciprocal crosses Percent pod set

Local x Alabama

Alabama x Local

Local x Indonesian

Indonesian x Local

Local x Tainang

Tainang x Local

Alabama x Indonesian

Iindonesian x Alabama

Alabama x Tainang

Tainang x Alabama

Indonesian x Tainang

Tainang x Indonesian

ns

ns

ns

ns

ns

ns

n,s. P > 0.05* P < 0.05

did not reveal any completely incompatiblecross-combinations among the varieties used.However, some combinations of parentsproduced significantly fewer seeds from cross-pollinations than others. In a particular com-bination, some varieties were more successfulthan others when used as the seed parents thanas the pollen parent. There was also an instancewhere one cross was better than its reciprocalcross for the percent pod set. The availabilityof pollen, the ease of emasculation and pollina-tion are possible causes for the low pod set inspecific combinations. The choice of parentsin a particular cross-combination as wellas the hybrid combination should beconsidered for this character.

CONCLUSION

Anthesis in groundnut plants occurs between0730 and 0900 h M.S.T. and'bud emasculationfor hybridization can be carried out inihe afternoon prior to trie day ot anthesis usingeither forceps or suction.

Natural pollination was found to beinadequate and there is a need for supplementarypollination. Tripping of the flowers does notassist the pollination process.

The duration from pollination to fertilizationis estimated to be 5 to 6 hours depending uponthe length of the style.

In general the varieties studied hybridizedreadily in all combinations. In a few cross-combinations, the choice of a variety for the seedor pollen parent influenced the success of thecross-pollinations.

REFERENCES

ARMSTRONG, J.M. and WHITE, W.J. (1935): Factorsinfluencing seed setting in alfalfa. /. Agric. Set. 25:161-179.

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

DAINIEL, D.S. and THULASIADA, G. (1976): PeanutIn: Botany of Field Crops. Macmillan Co. India,pp. 244-263.

HALIM HAMAT and AHMED AZHAR JAAFAR (1980):Pengacukan Kacang Tanah. Teknologi Pertanian,Malaysian Agricultural Research and DevelopmentInstitute 1: 24-32.

JOSE, M.C. and V.F. GUEVARA (1951): The floralbiology and fruitification of peanut (Arachishupogaea L.) Philippine Agriculturist 35: 137-142.

LAWES, D.A. (1972): The development of self-fertilefield beans. Welsh Plant Breeding Station, Abery-stwyth Rpt. pp. 739-751.

LlM, E.S. and KNIGHT, R. (1980): The effect ofinbreeding and hybridization on the seed set abilityof Vicia faba L. SABRAO J. 12: "99-108.

LIM,E.S. SURJIT, S. and AMARTALINGAM, A. (1980):Reproductive efficiency of groundnuts. Proc. Legumesin the Tropics, pp. 87-96.

NlGAM, S.N., SWIVEDI, S.L., and GIBBONS, R.W.(1981): Groundnut Breeding at 1CRISAT. Proc.Intl. Workshop on Groundnuts, ICRISAT, 1 3 - 1 7October 1980, Patancheru, India.

NORDEN, AJ. (1980): The hybridization of cropplants. Amer. Soc. Crop Sci, pp 443-436.

OTHMAN HAMDAN (1979): Reproductive efficiencyof groundnuts (Arachis hypogaea L.) Project paper,Univ. Pertanian Malaysia 1978/79.

Received 18 February 1984

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