Hereditas 134: 21 1-217 (2001)

Genetic basis of variation of yield, and yield components in mungbean (Vigna radiata (L.) Wilczek)G. S. S. KHATTAK, M. A. HAQ2, M. ASHRAF3 and T. McNEILLY4

Nuclear Institute for Food and Agriculture (NIFA), Peshawar, PakistanNuclear Institute for Agriculture and Biology (NIAB), Faisalabad, Pakistan Department of Botany, University of Agriculture, Faisalabad, Pakistan Department of Plant Sciences, University of Liverpool, Liverpool, U.K.Khattak, G. S. S., Haq, M. A., Ashraf, M. and McNeilly, T. 2001. Genetic basis of variation of yield, and yield components in mungbean (Vignu rudiutu (L.) Wilczek).-Hereditas 134: 211-217. Lund, Sweden. ISSN 0018-0661. Received May 5, 2001. Accepted August 1, 2001Additive, dominance, and epistasis genetic basis of seed yields per plant, number of pods per plant, number of seeds per pod, and 1000 seed weight in mungbean (Vigna rudiata (L.) Wilczek) have been examined, using Triple Test Cross (TTC) analysis. The material for TTC test was evaluated in two seasons i.e., kharif (July-October) and spring/summer (March-June), at the research station of the Nuclear Institute for Agriculture and Biology (NIAB), Faisalabad, Pakistan. Epistasis was present significantly for number of pods per plant and number of seeds per pod when grown in the spring/summer season (March to June). Partition of epistasis showed that additive x additive (i type) interaction was an important component of number of pods per plant, and number of seeds per pod was found to be of both types i type, and additive x dominance, and dominance x dominance (j and 1 type) interactions. This indicated that epistasis might be a non-trivial factor in the inheritance of pods per plant, and seeds per pod in mungbean. The expression of epistasis was influenced differentially by particular genotypes, indicating that a limited number of genotypes may not be sufficient to detect non-allelic interactions for a trait in mungbean. Additive and dominance genetic components were significant for all four traits in kharif season (July to October) but only for seed yield and 1000 seed weight in spring/summer season. This suggests that the genes controlling seed yield per plant, and 1000 seed weight are equally sensitive to the environment. The predominance additive gene action in those traits is not significantly influenced by epistasis, suggesting that improvement of the traits can be achieved through standard selection procedures.

G. S . S. Khuttuk, Nucleur Institute for Food and Agriculture (NIFA), P. 0. Box 446, Peshuwar, Pakistan. E-mail: nifa@psh.paknet.com.pk

INTRODUCTION Mungbean (Vigna radiata (L.) Wilczek) is an important short-duration grain legume crop with wide adaptability, low input requirements, and the ability to improve the soil by fixing atmospheric nitrogen. Mungbean is well suited to a large number of cropping systems and constitutes an important source of protein in the cereal-based diets of many people in India, Pakistan, Thailand, Indonesia, the Philippines and China, among other countries (JANSEN et al. 1996). The primary yield components in mungbean are pods per plant, seeds per pod and 1000 seed weight. The improvement of these components mainly depends upon the suitable breeding method and proper generation of selection in the segregating populations. The estimates of genetic components of variance would be very useful to adopt suitable breeding method and to find the best selection stage (generation) for the improvement of these traits. Most genetic models, particularly those for second-degree statistics, which have been developed to estimate the components of continuous variation

have the absence of epistasis (SINGH and SINGH 1976) as one of their simplifying assumptions. This assumption may be true for some characters in some populations but not for others. However, very few analyses provide a valid test for this. A good genetic model is that which enables the breeder to have precise and unbiased estimates of all the components of genetic variance. The triple test cross design, which is a simple extension of the design 111 of COMSTOCK ROBINSON and (1952), was proposed by KEARSEY JINKS and (1968). This design provides not only a precise test for epistasis but also gives unbiased estimates of additive ( D ) and dominance ( H ) components if epistasis is absent. Further more, this approach is independent of both the gene frequencies and the mating system of the populations to be investigated. In the present study, the detection of epistasis, additive, and dominance components of seed yield and primary yield components was carried out in two seasons in a set of mungbean genotypes using the TTC model suggested by KETATA al. (1976) in et which the testers L,, L,, and L,, were crossed to a

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Table 1. Distinctive characteristics of genotypes used in TTC studiesGenotypes 6601 NM 92 NM 51 NM 89 Pak 22 RC 71-27 Pusa Baisakhi ML-5 VC 1560D vc 2272 VC 3902A Sr.No.61 Growth habit Indeterminate Semi-determinate Semi-determinate Semi-determinate Indeterminate Indeterminate Semi-determinate Indeterminate Semi-determinate Semi-determinate Semi-determinate Indeterminate Maturity Late Early Medium Late Late Late Medium Medium Medium Early Medium Late1000 seed weight (8)

*MYMV resistance Tolerant Highly resistant Resistant Resistant Tolerant Tolerant Moderately susceptible Moderately susceptible Susceptible Moderately susceptible Susceptible Moderately susceptible

34 54 45 40 32 30 30 32 60 28 70 34

* Mungbean yellow mosaic virus.number of varieties instead of random F, individuals as suggested by KEARSEY JINKS(1968). and MATERIALS AND METHODS Two genotypes, 6601 and NM 92, were used as testers with designation L, and L,, respectively. They were the two extreme high and low mungbean genotypes for most of the traits selected from the existing mungbean germplasm. They were hybridized in a combination of 6601 x NM 92 during kharif (JulyOctober) 1997. The resulting F, was the third tester designated as L,. Ten true breeding genotypes/accessions, NM 51, NM 89, Pak 22, RC 71-27, Pusa Baisakhi, ML-5, VC 1560D, VC 2272, VC 3902A, and Sr.No.61 were crossed with the three testers ( L l , L,, and L,) during spring/summer (March- July) 1998. The distinctive characteristics of all the genotypes used are presented in Table 1. The testers were used as females in the entire Triple Test Cross combinations. The experiment thus consisted of 12 inbred lines (2 testers and 10 inbred lines), 20 single crosses, and 10 three-way crosses. The material was planted in a randomized complete block design with three replications at the research station of Nuclear Institute for Agriculture and Biology, Faisalabad, Pakistan, during kharif 1998 (planted on 15th July) spring/summer 1999 (planted on 10th March). Kharif and summer/ spring are normally humid and dry seasons, respectively. The mean photoperiod and mean temperature was 1321 h and 39.8C in kharif and 1254 h and 41C in spring/summer season. A plot size of 0.6 m2 (single row plot of 2-meter length) was assigned to each entry in each replication. The plant-to-plant spacing between and within rows was kept 30 cm and 10 cm, respectively in both seasons. The experimental material was bordered by standard mungbean variety NM 92 to avoid border effect. The experimental field soil was sandy loam. Fertilizer was applied at sowing at the rate of 20N: 60P Kg/ha (one bag of DAP per acre). Weeds were removed manually. In spring/summer season experimental crop was irrigated three times (1st irrigation after third week of sowing, 2nd at the initiation of flowering and 3rd at the pod filling stage). In kharif no irrigation was required due to monsoon (rainy season). The trial conducted during kharif 1998 was protected from whitefly invasion and hence from mungbean yellow mosaic virus (MYMV) infection, by spraying insecticide Polo [chemical name Diafenthiuron and active ingredients are 3-(2,6di isopropyl-4phenoxyphenyl- 1-tert.butyl)] at a rate of 250 ml/ha at five days intervals regularly from 15 days after sowing to complete pod formation. Thus the MYMV susceptible parents and crosses .were evaluated in an MYMV disease-free environment. The data were collected from 10 randomly selected plants per replication for the following traits: i) Number of pods per plant at maturity. ii) Seeds per pod at maturity (average of 10 randomly selected pods of each plant). iii) Seed yield per plant (g) at maturity. iv) 1000 seed weight (g).Analysis of variance

The analysis of variance was performed following the (1985) method described by SINGHand CHAUDHARY to determine the significance of treatments, and to partition the treatment effect so as to determine the significance variation among hybrids, parents, lines, testers, P, P, vs. F,, P, vs. P,, lines vs. testers, and hybrids vs. parents for each trait using the TTC technique.

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Test for epistasis

The detection of epistasis was performed according to SINGHand CHAUDHARY (1985). The test of significance of the difference, L,j + L, - 2L, (i = geno-

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types/accession), provides information about the presence or absence of epistasis. Therefore, the L,, L, - 2L3, for each line (genotype) and each replication was first computed (a replication thus consisted of 10 values each for a genotype) and then tested. The total epistasis for 10 degrees of freedom was calculated as uncorrected genotypes (lines) sums of on square [C (LIJ L, - 2L3J)2]/n the total of replications. The total epistasis was partitioned into two components. The correction factor c.f. = [C (LIJ+ L, - 2L3,)I2/n measures mainly the epistasis of the additive by additive type (i type) for one degree of freedom and corrected genotypes sums of square [C (LIJ L, - 2L3,)2/n- c.f.1 mainly the j + 1 type (additive by dominance and dominance by dominance) for 9 degrees of freedom. The sum of square due to interaction of epistasis with blocks (replications) was calculated as the difference between total sum of squares and type of epistasis (total s. s. - total epistasis/i type epistasis/j 1 type epistasis). Each of the three types of epistasis were tested against their respective interaction with blocks. However, before testing individual epistasis, the homogeneity of the interaction was first tested. As there were only 2 variances (i x block and j + 1 x block) homogeneity was first tested as:

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calculated replication-wise and subjected to an analysis of variance as given in appendix I.Estimation o dominance component (H) f

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The difference of L,, - L, for each genotype/accession was calculated replication-wise and subjected to an analysis of variance as given in appendix 11.Average degree o dominance f

Average degree of dominance was .calculated as ( H / D)'12, where H and D are the dominance and additive variance components, respectively.Direction o dominance f

+

(rs,d

+

Direction of dominance was determined by calculating the linear correlation coefficient rs,d between the sums (LIJ L2,) and the corresponding difference (L,,- L2,) for all genotypes/accessions. Significant positive and negative correlation would indicate a predominant direction of dominance towards decreasing and increasing values of the trait, respectively (JINKS et al. 1969). All triple test cross calculations were performed using the MSTAT-C package (Michigan State University and Agricultural University of Norway).

+

F(2, 18) = Mean square of i type interaction Mean square of j and 1 type interaction Where the homogeneity of interaction variances was not significant the i and j 1 types of epistasis were then also tested against the pooled error, i.e., total epistasis x block interaction.

RESULTS AND DISCUSSIONAnalysis o variance f

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Individual genotypic epistasis

The individual contribution of each line to total epistasis was determined and tested for significance according to KETATAet al. (1976) for those traits in which the total epistasis was significant. The mean value (C LIj L, - 2L3j)/r (where r is total replications) of each genotype for a trait was tested using a 't' test with 20 degrees of freedom as follows:

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t = Mean/S.E. S.E. = (Error mean square/replication)''2Additive-dominance model

The analysis of variance of seed yield and yield components in mungbean are presented in Table 2 and 3 for kharif and spring/summer plantings, respectively. All traits showed highly significant differences among treatments (F, hybrids and parents) and between first parent (L,) and second parent (LJ in both seasons. The highly significant differences among treatments indicated that considerable genetic variation existed in the lines, testers, and hybrids, included in the present study. The significant differences between first parent L, (6601) and second parent L, (NM 92) clearly show that the L , and L, testers are extremely high vs. low selections from the population, and would provide estimate of additive and dominance variation with equal precision (KEARSEY and JINKS 1968).Detection o epistasis f

The traits where total epistasis effects were not detected by either test, an additive-dominance model and was fitted to the data as outlined by KEARSEY JINKS (1968) and JINKS et al. (1969).Estimation o additive variance component ( 0 ) f

The sum of L,,

+ L,

for each genotype/accession was

Evidence for the presence of epistasis (total epistasis, i, and j 1 types) is indicated in Table 4 and 5 for kharif and spring/summer seasons, respectively. Total epistasis was significant only in the spring/summer season for pods per plant and seeds per pod. Further partitioning of total epistasis into overall epistasis (i, and j + 1 types) revealed that only additive x additive

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Table 2. Analysis o variance (mean squares values) o seed yield and primary yield components in mungbean f f under kharif plantingSource of variation df Mean squares Seed yield per plant Replications Treatments (F, hybrids and parents) Hybrids Parents Lines Testers P, + P, vs. F, PI vs. P, Lines vs. Tester Hybrids vs. parents Error 2 42 29 12 9 2 1 1 1 1 84 2.54 58.50** 38.95** 24.19** 26.47** 24.65** 0.002 49.31** 2.80 1037.30** 1.06 Pods per plant Seeds per pod 1000 seed weight 2.53 219.80** 120.70** 52.88** 66.55** 15.24 6.48 74.00** 5.12 5096.70** 8.29 0.02 1.46** 0.67** 2.40** 2.96** 0.96 0.80 3.23** 0.29 12.89** 0.33 0.93 155.71** 109.04** 278.89** 301.87** 265.98** 5.56* 526.41** 97.93** 31.27** 0.92

.

** = Significant at 0.01 level.Table 3. Analysis o variance (mean squares values) o seed yield and primary yield components in mungbean f f under spring /summer plantingSource of variation df Mean squares Seed yield per plant~~~~~~~~~~

Pods per plant Seeds per Pod 0.07 23.00** 20.28** 25.25** 24.25** 41.02** 12.00** 70.04** 2.69 74.73** 1.49 0.70 1.27** 1.40** 1.oo** 1.09** 0.96** 1.45** 1.48** 0.21 0.70 0.23

1000 seed weight 9.54 243.93** 159.12** 468.12** 551.72** 282.52** 0.50 564.54** 86.90** 13.31 8.43

Replications Treatments (F, hybrids and parents) Hybrids Parents Lines Testers P,+P, vs. F, PI vs. P, Lines vs. Tester Hybrids vs. parents Error

2 42 29 12 9 2 1 1 1 1 84

0.82 13.90** 11.51** 15.22** 18.91** 2.89** 1.28** 4.51** 30.41** 67.33** 0.22

. ,

** = Significant at 0.01 level.Table 4. Analysis of variance for the test of epistasis for mungbean seed yield and its primary yield components in kharif seasonSource df Mean squares Seed yield per plant (8) Pods per plant Seeds per pod 1000 seed weight (g) Total epistasis Epistasis (i type) Epistasis (i and 1 type) Epistasis (i type) x Blocks Epistasis (i and 1 type) x Blocks Total epistasis x Blocks 10 1 9 2 18 20 3.77 20.14 1.95 3.00 1.69 1.82 1.36 9.52 0.46 8.97 3.68 4.21 6.13 0.24 6.79 3.68 3.36 3.39 2.97 19.2 1.16 1.77 2.23 2.18

(i) interaction (homozygous x homozygous) was significant for pods per plant, while both i, and j + 1 (homozygous x heterozygous heterozygous x heterozygous) type of interactions were significant for

+

seeds per pod. Epistasis for number of seeds per pod in mungbean has been shown previously by MALIK and SINGH(1983) and recently for pods per plant by SINGHand SINGH(1996) and RAM (1997). Epistasis

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Table 5. Analysis of variance Jor the test of epistasis for mungbean seed yield and its primary yield components in springlsummer seasonSource df Mean squares Seed yield per plant (8) Pods per plant Total epistasis Epistasis (i type) Epistasis (i and 1 type) Epistasis (i type) x Blocks Epistasis (i and 1 type) x Blocks Total epistasis x Blocks 10 1 9 2 18 20 5.52 28.07 3.02 4.94 4.17 4.24 54.86** 536.69** 1.33 1.57 1.42 1.43 Seeds per pod 1000 seed weight (g) 6.59** 17.48* 5.38* 0.44 0.31 0.33 2.74 0.28 3.01 3.94 4.05 4.04

*, ** = Significant at 0.05 and

0.01 levels, respectively.

has been found for both number of seeds per pod and number of pods per plant in peas also (SINGHet al. 1997). Presence of epistasis for pods per plant and seeds per pod in springlsummer season, and its absence for these traits in kharif season, further shows that presence or absence of epistasis may depend upon the environment in which the plant material has been examined, and thus, it may not always be related to the inherent capacity per genotype. The components of variance have been reported to different extents over environments, if different kinds of gene actions are not equally sensitive to the environments (JINKS and PERKINS 1970). Such conclusions regarding environment influences have also been reported in pearl millet (BURTON1968a), winter wheat (KETATA al. et 1976), spring wheat (SINGH1980; SINGHet al. 1992; PAWAR al. 1994), and mungbean (SRINIVES et and TANGBUNITIVONG 1991). The i type epistasis is a linear directional and fixable component, and thus the standard hybridization and selection procedures could be of value for additive x additive interaction for pods per plant in mungbean, being a self-pollinating crop. The j and 1 type epistasis are non-directional and unfixable by selection under self-fertilization, and would therefore not be favorable for developing pure lines of mungbean for more number of seeds per pod. However, the greater magnitude of i type epistasis than that of j and 1 type epistasis for seeds per pod has a special significance in mungbean, being a selffertilized crop where a fixable component of genetic variation can be most easily exploited. Further, i type epistasis has been found to be more important than j and 1 type epistasis in wheat by SINGH and SINGH(1976). The individual line analysis for epistatic effects of pods per plant and seeds per pod is presented in Table 6. All lines made significant contributions to

the total epistasis of these two traits, except VC1560D for pods per plant, and Pak 22, Rc 71-27 and VC 2212 for seeds per plant, which had non-significant contribution in non-allelic interaction. The line ML-5 contributed a major portion of non-allelic interaction to pods per plant, whereas the line ML-5 and NM 51 played positive and negative roles, respectively, in influencing the non-allelic interaction for seeds per pod. These results, as well as similar findings of BURTON (1968b) and KETATA et al. (1976), indicate that epistasis is determined to some extent by the genotypes of the lines employed. Therefore, several lines should be used in studies designed for the detection of epistasis through TTC analyses.Additive and dominance components

The estimates of additive and dominance variance components, degree of dominance and direction of dominance for those traits not significantly affected

Table 6. Epistatic deviations of individual mungbean genotypes for pods per plant and seeds per pod exhibiting signlJicant differences among genotypes tested in springlsummer seasonGenotypes NM 51 NM 89 Pak 22 RC 71-27 Pusa Baisakhi ML-5 VC 1560D VC 2272 VC 3902A Sr.No.61 SE Pods per plant 3.13** 2.17** 2.37** 2.13** 2.07** 3.37** 1.07 1.70* 2.53** 2.63** 0.69 Seeds per pod 1.40** 1.93** - 0.40 -0.60 1.60** 2.47** 1.20** -0.47 1.70** 1.60**-

0.31

*, ** = Significant at 0.05 and 0.01 levels, respectively.

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Table 7. Estimates of additive ( 0 ) and dominance (H) variance components, degree of dominance (HID)"' and direction of dominance (r.7,Jf o r seed yield and primary yield components showing non -signiJicant epistasis in kharif and springlsummer seasonTrait Kharif season Seed yield per plant (g) Pods per plant Seeds per pod 1000 seed weight (g) D 123.92** 702.71** 3.07** 354.82** 57.63** 422.26** level. H 87.85** 347.73** 2.88** 20.42** 4.01** 54.39** (HID)"' 0.84 0.70 5.58 0.24 0.26 0.36rs,d

0.31 1 0.368 0.234 -0.535-0.118 -0.61 1

SpringlSummer season Seed yield per plant (g) 1000 seed weight (8)

** = Significant at 0.01

by epistasis in either or both seasons (kharif and spring/summer) are shown in Table 7. Additive and dominance gene effects were significant (all p