Genetic variability and trait association for morphological and yield parameters of mungbean ( Vigna radiata L . )

Genetic variability in existing germplasm is mandatory before commencement of a successful breeding program. To estimate genetic variability and correlations among mungbean genotypes, an experiment was conducted at The University of Agriculture, Peshawar during 2014. Fourteen mungbean genotypes were sown in RCB design with three replications. Data were recorded on days to maturity (days), plant height (cm), pod length (cm), pods plant(no.), grains pod(g), 1000 grain weight (g), biological yield (tons ha) and grain yield (tons ha). Analysis of variance showed highly significant differences (P≤0.01) among mungbean genotypes for all the studied traits. Mean value for the said traits ranged between 67-76.3, 48.7-105.7, 7.2-9.7, 15.2-22.5, 9.312.0, 42.6-55.6, 8.888-13.111 and 2.022-3.401 for days to maturity, plant height, pod length, pod plant, grains pod 1000 grain weight, biological yield and grain yield, respectively. Genotype Mung NM11 performed better for yield and yield associated parameters under agro-climatic conditions of Peshawar. Significant negative phenotypic correlation for grain yield was observed with pods plant (r =-0.51) whereas, significant positive correlation was observed with 1000 grain weight (r = 0.60). Based on the results of current study, genotype “Mung NM11” could be disseminated directly among growers for the commercial production of mungbean or may be included in a cultivar development program to produce transgressive segregants.


Introduction
Mungbean (Vigna radiata L.) is an important pulse crop due to its adaptation to short growth duration, low water requirement and soil fertility [1].It is native to Indian subcontinent but it is also grown in Pakistan, China, Thailand, Philippines, Indonesia, Burma, Bangladesh and in hot and dry regions of South Europe and Southern USA [2].Thailand has been the world's largest mungbean exporter (approx.30-50%) for the last 20 years or so.Mungbean is highly praised for its rich protein content, minerals and vitamins with outstanding digestibility and low production of flatulence as compared to other beans [3].In general, mungbeans contain 22-28% protein, 60-65% carbohydrates, 1-1.5 % fat and 3.5-4.5% fibers [2].Mungbeans also contain certain essential amino acids like lysine [4].Furthermore, it is a tropical and subtropical crop and requires a warm temperature of 30°C to 35°C.It has strong tap root system with nodules to fix atmospheric nitrogen.In Pakistan, it is one of the major pulse crop and ranks second to chickpea (Cicer arietinum L.) where it is cultivated on an area of 130.9 thousand hectares with an annual production of 92.9 thousand tons, yielding 710 kg ha - 1 [5].In Khyber Pakhtunkhwa, mungbean has covered an area of 8.6 thousand hectares with the total production of 5.4 thousand tons having an average yield of 628 kg ha -¹ [5].Knowledge of genetic variability in existing germplasm is imperative in crop improvement [6].The greater genetic variability offers more liberty to the plant breeder to produce a cultivar with broadened genetic base, such cultivars are then remain viable for a longer period of time and have the capability to resist and tolerate the biotic and abiotic stresses [7].Direct selection for seed yield is difficult and often deceptive because of the complex nature of the trait.Hence, it is an important practice to explore the relationship among morphological and yield parameters in mungbean germplasm and then make selections based on the knowledge obtained from these correlations.This experiment was therefore, designed to investigate genetic variability and ascertain relationship among various plant traits with seed.

Materials and methods
The study was carried out at the research farms of The University of Agriculture, Peshawar during 2014.Fourteen mungbean genotypes viz., KM-

Results and Discussion
Days to maturity (days) Plant breeder's main aim is to develop early maturing genotypes, which yields more in short period of time.Short duration varieties of mungbean can efficaciously avoid yield reducing diseases like mungbean yellow mosaic virus (MYMV) and Cercospora leaf spot (CLS).Harvesting losses can also be alleviated by developing short duration cultivars in mungbean.Therefore, early maturity is desirable in mungbeans.Highly significant differences (P≤0.01) were displayed among the genotypes for days to maturity (Table 1).Similar results were also reported by Ali et al., Begum et al. and Gul et al. [8,9,10].Days to maturity among mungbean genotypes ranged from 67.0 to 76.3 (Fig. 1).Earliest maturity was exhibited by KM-1 (67.0) whereas; genotype VC-6369 took maximum days to maturity (76.3) with an average value of 72.6 days.Days to maturity had significant positive correlation with plant height (r=0.62)whereas, it showed non-significant association with other traits.These findings were confirmed by Derya et al. and Singh et al. [11,12], who observed negative correlation between days to maturity and seed yield among mungbean genotypes.They implied that high temperature was the key factor responsible for longer reproductive phase resulting in more yield.

Pod length (cm)
Mean squares for pod length exhibited highly significant differences (P≤0.01)among mungbean genotypes suggesting the existence of reasonable genetic variability among tested germplasm (Table 1).Similar findings have been reported earlier by Tabasum et al. [6].Longer pods provide more room for seeds and as a result the dream of high productivity is more likely to be realized.Mean values for pod length among mungbean genotypes ranged from 7.2 to 9.7 cm (Fig. 3).Genotype KM-1 produced shortest pods and longest pods were produced by genotype Mung NM-06 with a mean value of 8.8cm.Pod length had nonsignificant positive correlations with days to maturity (r=0.46),plant height (r=0.51),1000grain weight (r=0.33) and grain yield (r=0.39) whereas, non-significant negative correlations with pods plant -1 (r=-0.04)and grain pod -1 (r=-0.07)were observed.Our results are in agreement with those of Singh et al. and Dhuppe et al. [12,15], who reported positive correlation between plant height and grain yield in wheat.However, Naidu and Satyanarayana [16] reported contradictory results to those of present finding.This vague deviation might be due to the differences in climatic conditions and genetic material.

Pods plant -1 (pods)
Pods plant -1 is an important yield contributing trait that has direct influence on the seed yield in mungbean.Analysis of variance displayed highly significant differences (P≤0.01)among the mungbean genotypes for pods plant -1 (Table 1) suggesting the presence of sufficient variability among this set of genotypes.Similar results have been reported by Zaid et al. [2] in wheat.Mean value for Pods plant -1 among mungbean genotypes ranged from 15.2 to 22.5 (Fig. 4) where minimum pods plant -1 were produced by VC-6368 and maximum pods plant -1 were recorded for genotype Mung NM-11 with an average value of 18.7.Current results are in line with the findings of Jalilian et al. [17], who observed significant difference among mungbean genotypes for pod plant -1 .Pods plant -1  showed significant positive correlation with grain yield, whereas, nonsignificant correlation was observed with days to maturity (r=0.19),plant height (r=0.45),pod length (r=-0.04),grains pod -1 (r=0.27)and1000 grain weight (r=-0.52).Ali et al. [8] also reported significant correlation of pods plant -1 with yield and yield components.Grains pod -1 (grains) Mean squares values exhibited highly significant differences (P≤0.01)among the mungbean genotypes for grains pod -1 (Table 1).Similar results were also reported by Abna et al. [18].Mean value for grains pod -1 among mungbean genotypes ranged from 9.3 to 12.0 (Fig. 5).Minimum grains pod -1 was recorded forNM-92 while, maximum mean value for grains pod -1 NM-19-19 with an average mean value of 11.2 grain pod -1 .Grain pod -1 had non-significant correlation with days to maturity (r=-0.47),plant height (r=0.34),pod length (r=-0.07),pods plant -1 (r=0.27),1000 grain weight (r=-0.12),grain yield (r=0.25) and harvest index (r=-0.60).Current findings are contradictory with the results of Abna et al. [18], who observed significant association with the yield and yield related traits.1000 grain weight (g) Mean square values displayed highly significant differences (P≤0.01)among the genotypes for 1000 grain weight (Table 1) indicating acceptable amount of variation.Similar results were also reported earlier by Begum et al. [9].Mean value for 1000 grain weight among mungbean genotypes ranged from 42.6 to 55.6 (Fig. 6) whereas, minimum 1000 grain weight was recorded for genotype Mung Chakwal-06 while maximum 1000 grain weight was displayed by genotype Mung NM-11 with a mean value of 46.2 g. 1000 grain weight had significant association with grain yield (r=0.60) whereas, it showed non-significant correlation with rest of the traits (Table 2).Significant correlation between 100-grain weight and seed yield was also reported by Patil and Deshmukh  Mean squares for biological yield exhibited highly significant variance (P≤0.01)among the genotypes (Table 1) indicating the presence of acceptable amount of variation.Similar results were also reported by Tiwari et al. [20].Mean value for Biological yield among mungbean genotypes ranged from 8.888 to 13.111(Fig.7).Minimum Biological yield was recorded for genotype KM-1 (8.888 tons ha -1 ) while maximum Biological yield (13.111 tons ha -1 ) was recorded for NM-92.Biological yield had significant positive correlation with days to maturity (r=0.56)while, non-significant association was observed by biological yield with rest of the traits.Our results are in conformity with Talebi et al. [21], who suggested that biological yield and harvest index could be used as base for selecting genotypes with high grain yield.Grain yield (tons ha -1 ) Mean square data revealed highly significant (P≤0.01)differences among mungbean genotypes for grain yield (Table 1).Our findings are in line with the results reported by Zaid et al. and Begum et al. [2,9].Mean value for grain yield among mungbean genotypes ranged from 2.022 to 3.401 tons ha -1 (Fig. 8) where genotype KM-1 displayed minimum grain yield and NM-92 produced maximum grain yield.Average mean value across genotypes was 2.656 tons ha -1 .Current results were similar to the earlier findings of Soltani and Hammer [22], who reported significant differences for grain yield in mungbean genotypes.Grain yield exhibited significant negative correlation with pod plant -1 (r=-0.51)whereas, it showed significant positive association with 1000 grain weight (r=0.60)(Table 2).Similar results have been reported earlier by Dhuppe et al. and Pun and Villarreal [13, 14], who observed significant correlation among mungbean genotypes for yield and its contributing traits.Harvest index (%) Analysis of variance expressed highly significant variation (P≤0.01)among mungbean genotypes for harvest index (Table 1).Our findings are in line with the earlier reported results of Tabasum et al. [6].Mean value for harvest index among mungbean genotypes ranged from 17.7 to 36.5 % (Fig. 9).Minimum harvest index was recorded by genotype NM-92 whereas; maximum harvest index was recorded for genotype Mung NM11 with an average mean value of 25.5%.Harvest index had significant positive correlation with 1000-grain weight (r=0.75) and grain yield (r=0.84) whereas, non-significant association was observed with rest of the traits.Our results are in conformity to the earlier findings of Tabasum et al.   be recommended for general cultivation under Peshawar conditions.Seed yield had significant positive correlation with 1000 grain weight and significant negative association was observed with pods plant -1 , therefore special attention should be given to the mentioned traits in selection process to attain high productivity.

Figure 1 .
Figure 1.Mean days to maturity (days) of 14 mungbean genotypes, during 2014Plant height (cm)Mean squares for plant height among mungbean genotypes were significantly different (Table1) indicating the presence of sufficient genetic variability among the tested germplasm for the said traits.Similar results were also reported by[2,9].Mean values for plant height ranged from 48.7 to 105.7 cm (Figure2).Genotype KM-1 produced the shortest plants while, genotype VC-6321 attained maximum plant height.Average

Table 2 . Correlation among yield and yield associated traits in Mungbean Conclusion and recommendations
On the basis of current investigation following results can be concluded: Sufficient amount of variability was recorded among genotypes for all the studied traits thus providing adequate scope for the breeder to start a cultivar development program.Genotype Mung NM11displayed maximum mean value for 1000grain weight, harvest index and grain yield, therefore could be selected as a parent in a breeding plan to achieve transgressive segregants.It can also