Variability analysis in f2 populations of blackgram (Vigna Mungo (L.) Hepper) for yield and its attributing traits

Introduction

Pulses are an indispensable source of dietary protein, particularly for the predominantly vegetarian population of India. Besides their nutritional importance, they improve soil fertility through biological nitrogen fixation, thereby enhancing the productivity of succeeding crops. Among the pulse crops, black gram (Vigna mungo (L.) Hepper; 2n = 22) is one of the most important grain legumes cultivated in tropical and subtropical regions, especially in India. Commonly known as urdbean, urid, or mash, it is a selfpollinated crop belonging to the family Fabaceae and subfamily Papilionoideae. India is recognized as the primary centre of genetic diversity for black gram (Zeven et al., 1982) [13] , highlighting its significance in the origin and diversification of this crop. Black gram is popularly referred to as the "King of Pulses" because of its excellent culinary qualities, wide adaptability, and high nutritional value. It is an erect, semi-erect, or trailing annual herb with a well-developed tap root system bearing numerous root nodules that facilitate atmospheric nitrogen fixation. The crop produces narrow, cylindrical pods and is valued for its seeds, which are rich in protein, carbohydrates, vitamins, and essential minerals while being naturally free from cholesterol. The seeds contain approximately 24% www.extensionjournal.com protein, 1.4% fat, 3.2% minerals, and 57.3% carbohydrates (Aykroyd and Doughty, 1964) [3] . In addition, black gram is an excellent source of essential amino acids such as lysine and tryptophan, which are deficient in cereal grains, thereby improving the biological value of cereal-based diets. It is also rich in potassium, calcium, magnesium, iron, copper, and manganese, making it an important component of a balanced human diet (Goyal et al., 2010) [13] . Black gram can be cultivated successfully under a wide range of agro-climatic conditions and soil types, although sandy and sandy loam soils are considered most suitable for its cultivation. Owing to its heat-loving nature, photoinsensitivity, and short duration, the crop can be grown throughout the year under suitable conditions. It is widely cultivated in arid, semi-arid, and subtropical regions and plays an important role in sustainable agriculture by improving soil organic matter and contributing biologically fixed nitrogen to the soil. Despite the availability of improved varieties, the productivity of black gram in India remains relatively low compared with its genetic potential. The crop is often grown under rainfed conditions on marginal lands with poor soil fertility, inadequate irrigation, suboptimal nutrient management, and limited plant protection measures. Furthermore, the availability of quality seed of improved cultivars is often inadequate, compelling farmers to rely on local landraces that are generally low yielding and susceptible to major diseases such as Mungbean Yellow Mosaic Virus (MYMV), powdery mildew, and leaf crinkle disease. These constraints substantially reduce productivity and profitability. Genetic improvement through the development of highyielding, disease-resistant, and widely adaptable cultivars remains one of the most effective strategies for enhancing black gram productivity. Successful crop improvement depends on the availability of sufficient genetic variability and a thorough understanding of the inheritance of economically important traits. Estimation of genetic parameters such as variability, heritability, genetic advance, correlation, and path coefficient provides valuable information for identifying superior genotypes and formulating efficient selection strategies. Therefore, the present investigation was undertaken to assess the genetic variability and character association in segregating F₂ populations of black gram, with the objective of identifying promising traits and genotypes for effective yield improvement through selection. Technology in our country. The real yield potential of the crop can be exploited through varietal improvement programme which needs the information pertaining to range of existing genetic variability and its relationship with various economically important characters present in the promising available genetic stocks. Keeping these important points in consideration, the present study targeted on the genetic variability, heritability and genetic advance studies, genotypic and phenotypic correlation between seed yield and its related characters and to analyze path coefficient for assessing the direct and indirect effects of individual characters on seed yield.

Materials and Methods

The present investigation was conducted at the Pulses and Castor Research Station, Navsari Agricultural University (NAU), Navsari, Gujarat, during the late kharif season of 2020 to assess the genetic variability, heritability, correlation, and path coefficient among segregating populations of black gram (Vigna mungo L. Hepper). The experimental field consisted of medium black soil with medium to poor drainage, good water-holding capacity, and a soil pH ranging from 7.5 to 7.8. The prevailing weather conditions during the crop growth period were normal and favourable for successful crop establishment and development. The experimental material comprised three F₂ populations developed from the crosses NUK-15-02 × NUK-15-07, NUK-15-02 × NUK-15-09, and NUK-15-02 × GU-1, which were maintained at the Pulses and Castor Research Station, Navsari Agricultural University, Navsari. The important characteristics of the parental lines used in the study are presented in Table 1.1. Parent NUK-15-02 is resistant to Mungbean Yellow Mosaic Virus (MYMV); NUK-15-07 is a high-yielding genotype resistant to MYMV, powdery mildew, and leaf crinkle disease; NUK-15-09 possesses moderate resistance to MYMV, leaf crinkle virus, leaf curl virus, and powdery mildew; while GU-1 is a late-maturing genotype with moderate resistance to powdery mildew. The three F₂ populations, along with their respective parents and F₁s, were grown in a non-replicated trial during late kharif 2020. Each parent and F₁ was sown in two rows comprising approximately 40 plants, whereas each F₂ population was planted in ten rows consisting of about 200 plants at a spacing of 45 cm between rows and 30 cm between plants. All recommended agronomic and plant protection practices were followed uniformly throughout the crop season to ensure healthy crop growth. Random sampling was employed for recording observations on the experimental material. Ten competitive plants were randomly selected from each parent and F₁ generation, whereas 100 plants were selected from each F₂ population after excluding three border plants from both ends of each row to eliminate border effects. Observations were recorded on twelve quantitative characters, namely days to flowering, plant height (cm), branches per plant, clusters per plant, pods per plant, pod length (cm), seeds per pod, 100-seed weight (g), seed yield per plant (g), days to maturity, chlorophyll content, and harvest index. These observations were subjected to statistical analyses for estimating genetic parameters and determining the association among yield and its component traits.

Results and Discussion

The segregating populations exhibited improved mean performance over the parental means for several economically important traits, indicating the effectiveness of hybridization in generating useful variability. The cross NUK-15-02 × NUK-15-09 recorded higher mean values for pods per plant, 100-seed weight, days to maturity, and chlorophyll content, while NUK-15-02 × GU-1 showed superiority for pods per plant and chlorophyll content. In contrast, NUK-15-02 × NUK-15-07 exhibited a desirable reduction in days to flowering, suggesting its potential for developing early-maturing genotypes. Considerable variation was observed among the F₂ populations for most of the characters studied. The cross www.extensionjournal.com NUK-15-02 × NUK-15-07 exhibited higher variance for days to flowering, plant height, branches per plant, clusters per plant, pods per plant, pod length, 100-seed weight, seed yield per plant, days to maturity, and chlorophyll content. Similarly, NUK-15-02 × NUK-15-09 showed high variance for days to flowering, plant height, branches per plant, clusters per plant, pods per plant, seed yield per plant, chlorophyll content, and harvest index, whereas NUK-15-02 × GU-1 recorded higher variance for days to flowering, plant height, clusters per plant, pods per plant, seed yield per plant, chlorophyll content, and harvest index. The high variance observed for these traits indicates the presence of substantial genetic variability, providing ample opportunity for effective selection in subsequent generations. The phenotypic coefficient of variation (PCV) and genotypic coefficient of variation (GCV) showed wide variation across the studied traits. In all populations, GCV values were generally close to the corresponding PCV values, indicating that the expression of these traits was largely controlled by genetic factors with comparatively lower environmental influence. High GCV and PCV values were recorded for branches per plant, clusters per plant, pods per plant, seed yield per plant, and chlorophyll content, suggesting greater scope for improvement through selection. Moderate GCV and PCV values were observed for plant height and 100-seed weight, whereas days to flowering and days to maturity exhibited low variability. Moderate GCV was also observed for pods per plant, harvest index, and pod length in most crosses, although exceptions were noted in specific populations. The low to moderate variability for these traits indicates comparatively limited scope for improvement through direct selection. Broad-sense heritability estimates were generally high for most of the traits across the three F₂ populations. High heritability was observed for days to flowering, plant height, branches per plant, clusters per plant, pods per plant, pod length, seeds per pod, and seed yield per plant, indicating that these traits were predominantly governed by genetic factors. However, broad-sense heritability includes both additive and non-additive genetic effects; therefore, high heritability alone may not guarantee effective selection. The cross NUK-15-02 × NUK-15-07 and NUK-15-02 × GU-1 exhibited high heritability for 100-seed weight, while NUK-15-02 × NUK-15-09 showed moderate heritability. Days to maturity exhibited low, moderate, and high heritability in NUK-15-02 × NUK-15-09, NUK-15-02 × GU-1, and NUK-15-02 × NUK-15-07, respectively. Chlorophyll content and harvest index also showed varying levels of heritability among the populations. Traits with low to moderate heritability were more susceptible to environmental influence, making genetic improvement through selection comparatively difficult.

Genetic advance expressed as a percentage of the mean was high for plant height, branches per plant, clusters per plant, pods per plant, 100-seed weight, seed yield per plant, and chlorophyll content across the populations. High genetic advance coupled with high heritability suggests the predominance of additive gene action and indicates that selection for these traits would be highly effective. Moderate genetic advance was observed for pod length, seeds per pod, and harvest index in some populations, whereas days to flowering and days to maturity generally exhibited low genetic advance. These results suggest that non-additive gene action predominates for these traits, thereby reducing the effectiveness of simple phenotypic selection. The combined assessment of heritability and genetic advance provides a more reliable estimate of the expected response to selection than heritability alone. In the present investigation, plant height, branches per plant, clusters per plant, pods per plant, 100-seed weight, seed yield per plant, and chlorophyll content exhibited high heritability coupled with high genetic advance in all three populations, confirming the predominance of additive gene action and indicating good prospects for improvement through pure-line selection. Conversely, high heritability associated with moderate or low genetic advance for days to flowering, pod length, and seeds per pod suggested a greater contribution of non-additive gene effects or environmental influence. Low heritability coupled with low genetic advance for days to maturity in NUK-15-02 × NUK-15-09 and NUK-15-02 × GU-1 further indicated the importance of non-additive gene action in controlling this trait. Since seed yield is a complex quantitative trait influenced by several component characters, correlation and path coefficient analyses were undertaken to identify the most important yield determinants. In all three F₂ populations, seed yield per plant showed strong and positive associations with plant height, clusters per plant, and pods per plant, indicating that simultaneous improvement in these traits would result in enhanced seed yield. Positive and significant correlations were also observed between seed yield and branches per plant in NUK-15-02 × NUK-15-09 and NUK-15-02 × GU-1, and between seed yield and harvest index in NUK-15-02 × NUK-15-07 and NUK-15-02 × GU-1. Among all the component traits, pods per plant exhibited the highest positive correlation with seed yield, followed by clusters per plant and plant height. Path coefficient analysis further revealed that pods per plant exerted the highest positive direct effect on seed yield in all three populations, followed by clusters per plant and plant height. These findings clearly indicate that emphasis on these characters during selection would be highly effective in improving seed yield in greengram breeding programme www.extensionjournal.com

Acknowledgement

AcknowledgementThe authors sincerely express their gratitude to the Department of Plant Breeding and Genetics, N.M. College of Agriculture, Navsari Agricultural University, Navsari, Gujarat, for providing the necessary research facilities, experimental materials, and technical support for conducting this study. The authors also acknowledge the staff of the Pulses and Castor Research Station for their assistance during the field experimentation and data collection.

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