Effect of Temperature on Seedling Traits, Genetic Analysis of Seedling Traits and Their Influence on Seed Yield in Mungbean [Vigna radiata (L.) Wilczek] Genotypes

Mungbean is also known as green gram, an ancient pulse crop widely cultivated under different agro-ecological situations in India mainly during Kharif and summer seasons (Kumar et al., 2024). It is a diploid species having chromosome number (2n=22) belongs to family Leguminosae (Fabaceae), sub-family Papilionaceae and is botanically recognized as Vigna radiata (L.) Wilczek (Anita et al., 2022). Mungbean is a native of South Asia (India). Vigna radiata var. sublobata is the possible progenitor of mungbean. It is basically a self-pollinated crop (Singh et al., 2015).
       
Mungbean is widely cultivated in tropical and subtropical regions for its nutritional value and adaptability to diverse environmental conditions. As a vital source of plant-based protein, mungbean contributes significantly to human diets, especially in developing countries. The optimum temperature for green gram growth is 28-30^oC temperature; however, the successful cultivation of mungbean is highly sensitive to environmental factors, specially, temperature playing a pivotal role in influencing various growth stages, from germination to seedling development.
       
Temperature is one of the most critical abiotic factors that affect seed germination, seedling growth and overall plant development. Optimal temperature conditions ensure efficient physiological processes, such as water uptake, enzyme activity and metabolic reactions, which are crucial for seedling vigour and survival. However, deviations from the optimal temperature range can result in growth inhibition, physiological stress and even plant death. For mungbean, understanding the temperature thresholds that promote or hinder early seedling growth is essential for improving agricultural productivity, especially in regions facing temperature fluctuations due to climate change (Haj Sghaier  et al., 2022).
       
In Mungbean, low temperatures can delay germination and restrict seedling growth, while excessively high temperatures may induce heat stress, affecting the overall plant health and yield. Despite its resilience, mungbean is not immune to such temperature extremes, which can cause physiological damage at critical early growth stages. Therefore, understanding the effect of different temperature regimes on mungbean seedlings is crucial for optimizing growing conditions and ensuring successful crop establishment.
       
Genetic variability serves as the cornerstone of plant breeding. Screening diverse genotypes for traits such as higher seed yield and its components under high-temperature stress is essential. Identifying heat-tolerant genotypes enables the transfer of this tolerance into high-yielding varieties through suitable breeding strategies. Germination studies conducted under controlled conditions provide a reliable means to validate findings from field screenings. This additional support of field screening validates high temperature tolerant genotypes (Begna and Teressa, 2024).
       
This study aims to investigate the influence of varying temperature conditions on the germination and seedling development in mungbean to assess the extent of genetic variability and character association on seedling traits to increase the yield in mungbean.

The experimental material consisting of thirty five genotypes was procured from NBPGR, Regional Station, Jodhpur; Rajasthan Agricultural Research Institute, Durgapura, Jaipur; Agricultural Research Station, Sriganganagar and Agricultural Research Station, Mandor, Jodhpur as given in Table 1. The field experiments were conducted with 35 genotypes of mungbean in a randomized block design with three replications, accommodating three meter long two rows per replication at 30 cm spacing at the College of Agriculture, Bikaner and Swami Keshwanand Rajasthan Agricultural University, Bikaner, Rajasthan during summer 2019 and Kharif 2019-20 with temperature range from 28 to 43^oC temperature. All the recommended practices were adopted to raise a good crop. Observation for seed yield were recorded on an individual plant basis from five randomly selected plants in each genotype of each replication. Harvested seeds from each genotype were used for further study of seed germination and seedling traits under controlled conditions.


      
In laboratory experiment, ten seeds from each thirty-five mungbean genotypes were germinated for seed germination at two different temperature gradients (optimal temperature 30^oC and high temperature 40^oC). The experiment was followed a completely randomized design with three replications for each genotype. It was conducted in a plant growth chamber using seed germination paper (Gsm: 145) in petri-dishes (9 cm in diameter), which were moistened and kept at the respective temperature gradients (30^oC and 40^oC). Glass petri-dishes were used and the germination papers served as the matrix for seed germination. Ten sterilized seeds from each of the thirty-five mungbean genotypes were placed on sterilized seed germination papers in petri-dishes in plant growth chamber. Each germination paper was moistened with 3 ml of double distilled water. Seed germination was recorded on 7^th day after seeding. For seedling parameters, ten seeds of each thirty five mungbean genotypes were sown in 200 ml volumetric pot-tray containing solarite in plant growth chamber at two different temperature gradients (optimal temperature 30^oC and high temperature 40^oC). The experiment was conducted in completely randomized design with three replications of each genotype. Observations were recorded for different seedling characteristics on 15^th day of seed planting. Five seedlings were randomly selected from each pot-tray to record the data on seedling length, seedling fresh weight, seedling dry weight and seedling vigour index. The data on seedling dry weight was recorded after drying in hot air oven for 48 hours at 65^oC. The observations were recorded for following characters.
 
Germination (%)
 
The germination capacity of seeds, determined by a binary outcome (germinated or non-germinated), was converted into quantitative attribute, expressed as germination percentage. Ten seeds from each genotype were used to calculate germination percentage based on the number of seeds germinated out of the total seeds used the germination test at different temperatures (30^oC and 40^oC). A seed was considered to have germinated at the emergence of both radicle and plumule up to 2 mm length (Chartzoulakis and Klapaki, 2000). The number of germinated seeds was recorded 7^th day after planting in petri-dishes and the germination percentage was determined by using the following formula (Aniant  et al., 2012).
 

Seedling length (cm)
 
The seedling length of germinated seeds was recorded on the 15^th day of planting in pot trays. Five seedlings from each genotype that was grown in the pot tray were randomly selected from each replication. The seedling length (the distance from root tip to shoot tip) was measured by using a measuring scale in centimetres and averaged.
 
Seedling fresh weight (mg)
 
The fresh weight of seedling from the five seedlings which were selected already from each replication was measured in milligram by using a sensitive electronic balance and averaged.
 
Seedling dry weight (mg)
 
The seedlings which were taken for fresh weight were kept into paper bags. The abbreviations of varieties were written on paper bags by the marker for further identification. After taking the fresh weight of seedlings these were kept in the oven at 65^oC for 48 hours for drying. After drying, the dried seedlings were weighed using the sensitive electronic balance in milligram and the average was recorded.
 
Seedling vigour index
 
The seedling vigour index was determined by multiplying the seedling length with concerned germination percentage by the following formula (Iqbal and Rahmati, 1992). 
 

Analysis of variance was done by subjecting the data to the statistical method described by Panse and Sukhatme (1985). The statistical analysis was performed using INDOSTAT 8.1 and XLSTAT 2021.2.2 software. Genotypic variances and phenotypic variances were calculated according to Johnson et al., (1955); Comstock and Robinson (1952), respectively from the expectations of mean squares by using an ANOVA table for each character. Heritability in a broad sense was calculated as suggested by Burton and Devane (1953). The expected genetic advance for each character was calculated as suggested by Johnson et al., (1955). Phenotypic correlation and path coefficients of variation were computed as per the method given by Dewey and Lu (1959).

The analysis of variance revealed significant differences among thirty five genotypes of mungbean for all seedling traits except germination at 30^oC which indicate the presence of good amount of variability in the genotypes and scope of selection for genetic improvement of mungbean (Table 2). The results confirmed the findings of Adlan (2019) in mungbean, Get  et al. (2019) in lentil, Pal et al. (2020) and Meena (2021) in mothbean.


       
At 30^oC temperature (Table 3), the mean germination percentage was 99.68%, with a narrow range of 96.67% to 100%. The genotypic coefficient of variation (GCV) was 0.51%, while the phenotypic coefficient of variation (PCV) was 1.29%, indicating low variability. Broad-sense heritability was moderate (15.66%), with a genetic advance of 0.42, which accounts for 0.42% of the mean. The mean seedling length was 18.48 cm, ranging from 15.77 cm to 21.25 cm. GCV (6.52%) and PCV (6.76%) were closely aligned, signifying minimal environmental influence on this trait. High heritability (92.80%) was observed, coupled with a genetic advance of 2.39, contributing to 12.93% of the mean. The mean seedling fresh weight was 270.18 mg, with a wide range of 215.56 mg to 385.87 mg. GCV (10.49%) and PCV (10.66%) were close, indicating high genetic control over the trait. Heritability was very high (96.80%), with a substantial genetic advance of 57.44, contributing to 21.26% of the mean. The mean seedling dry weight was 32.57 mg, with a range of 22.02 mg to 43.47 mg. GCV (12.22%) and PCV (12.43%) showed strong genetic control and low environmental influence. Heritability was very high (96.60%), with a genetic advance of 8.06, accounting for 24.75% of the mean. The mean seedling vigor index was 1839, ranging from 1558 to 2125. GCV (7.08%) and PCV (7.11%) were almost identical, suggesting negligible environmental impact. The trait exhibited extremely high heritability (99.20%) and a genetic advance of 267.33, contributing to 14.54% of the mean. Traits such as seedling fresh weight, seedling dry weight and seedling vigor index exhibit very high heritability (above 95%) and substantial genetic advance. These traits are likely controlled predominantly by additive gene action and can be improved effectively through simple selection methods such as mass selection or pedigree selection. These traits showed high heritability and genetic advance, indicating strong genetic control with minimal environmental influence. These can be prioritized for direct selection in breeding programs aimed at improving heat tolerance. These results are accordance with the earlier finding of Adlan (2019) in mungbean, Get  et al. (2019) in lentil, Pal  et al. (2020) and Meena (2021) in mothbean.


       
At 40^oC temperature (Table 4), the mean germination percentage was 85%, with a range of 67-100%. Genotypic and phenotypic coefficients of variation (GCV and PCV) were relatively close at 8.39% and 9.00%, respectively, indicating minimal environmental influence on this trait. High heritability (86.90%) coupled with moderate genetic advance as a percentage of the mean (16.12%) suggests that this trait is under substantial genetic control and amenable to selection. The mean seedling length was 6.53 cm, ranging from 4.25-9.79 cm. The GCV (19.79%) and PCV (20.00%) values were nearly identical, implying strong genetic control with negligible environmental influence. Extremely high heritability (97.80%) and substantial genetic advance as a percentage of the mean (40.32%) suggest that seedling length is a reliable trait for selection under heat stress. The mean fresh weight was 111.64 mg, ranging from 52.33-148.35 mg. The GCV (24.03%) and PCV (24.06%) were nearly equal, indicating robust genetic control. Very high heritability (99.70%) and significant genetic advance (49.43%) suggest the trait can be effectively improved through direct selection. The mean dry weight was 14.12 mg, with a wide range of 3.53-35.33 mg. GCV (60.49%) and PCV (60.53%) showed negligible environmental influence, emphasizing strong genetic control. Exceptionally high heritability (99.90%) and genetic advance (124.53%) make this trait an excellent candidate for selection. The mean vigor index was 561.56, ranging from 355.83-819. GCV (22.19%) and PCV (22.35%) were nearly identical, confirming the strong genetic influence. High heritability (98.60%) and substantial genetic advance (45.40%) indicate the potential for significant genetic improvement. The study highlights the potential for improving heat tolerance in crops through the selection of traits with high heritability and genetic advance. Key traits such as seedling length, seedling fresh weight and seedling vigor index are highly heritable and can serve as reliable indicators for breeding programs aimed at developing heat-tolerant varieties. These results are accordance with the earlier finding of Adlan (2019) in mungbean, Get  et al. (2019) in lentil, Pal  et al. (2020) and Meena (2021) in mothbean.


       
Character association analysis specify that significant correlations among germination percentage, seedling traits and seed yield at 30^oC (Table 5). Germination percentage showed a significant positive correlation with seedling vigor index but a negligible association with seed yield per plant. This suggests that while higher germination may enhance early seedling growth, it does not necessarily translate into higher yield. Seedling length exhibited a strong positive correlation with seedling vigor index, fresh weight and dry weight  indicating that longer seedlings tend to be more vigorous and healthier. Similar trends were observed by Rahman  et al. (2020), who reported that seedling vigor is a key indicator of early-stage growth potential. Seedling fresh and dry weights were positively correlated with seed yield per plant suggesting that heavier seedlings contribute to better yield performance. This aligns with findings by Singh  et al. (2018), who emphasized the role of seedling biomass in enhancing crop productivity.



The correlation analysis at 40^oC revealed that germination percentage had a positive correlation with seedling vigor index but was not significantly associated with seed yield (Table 6). This suggests that while high germination enhances early vigor, it does not directly contribute to productivity under heat stress, as also observed by Sharma  et al. (2020). Seedling length showed a strong positive correlation with seedling vigor index but was negatively correlated with seed yield. This indicates that excessive elongation may lead to weaker plants, which could negatively impact final yield, supporting the findings of Rahman  et al. (2019). Seedling fresh weight had a negative correlation with seedling dry weight, suggesting that increased water retention under heat stress may limit dry matter accumulation, similar to the findings of Singh  et al. (2018). However, seedling dry weight was positively correlated with seed yield emphasizing that dry matter accumulation is a key factor for productivity as reported by Kumar  et al. (2021). An unexpected negative correlation between seedling vigor index and seed yield suggests that highly vigorous seedlings may not always translate into higher yields under high-temperature conditions. This could be due to excessive energy allocation toward early growth at the cost of reproductive development, as highlighted by Ahmed  et al. (2022).


               
Path analysis reveals that the highest positive direct effect on seed yield per plant was observed for seedling vigour index at 30^oC followed by seedling dry weight at 40^oC, seedling dry weight at 30^oC, seedling length at 40^oC, seedling fresh weight at 30^oC and germination percentage at 40^oC at phenotypic level (Table 7 and 8). These findings are in accordance as reported by Adlan (2019) in mungbean, Pal  et al. (2020) and Meena (2021) in mothbean.




 

Seedling traits like seedling dry weight, seedling fresh weight and seedling vigour index exhibited high degree of genetic variability along with high heritability and high genetic advance as per cent of mean at 40^oC. Therefore, screening of genotypes on the basis of seedling traits may be conducted at 40^oC. Among seedling traits, seedling fresh weight, seedling dry weight and seedling vigour index had positive correlation with seed yield at 30^oC and directly contributed towards seed yield, therefore, these traits can be used for future mungbean breeding programme.

The present study was supported by Prof. (Dr.) N.K. Sharma, SKRAU, Bikaner; for the best guidance and support. I am also extremely grateful to Dr. Om Veer Singh, Principal Scientist and Officer-In-Charge, NBPGR, RS, Jodhpur; Prof. (Dr.) B.R. Chaudhary, Hon’ble Vice-Chancellor, Agriculture University, Jodhpur and Prof. (Dr.) O.P. Khedar, O/I, MULLaRP, RARI, Durgapura, Jaipur for providing valuable research material for my Ph.D. research experimentation.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.

The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish, or preparation of the manuscript.