The rice varieties selected for diversity and association studies were effective as they displayed variation for six different physiological traits. Therefore, these varieties were distinct from each other in terms of the studied traits. Among the characters studied seed vigour index I exhibited the highest phenotypic and genotypic coefficients of variance followed by seed vigour index II and very useful for selection of the trait. Other characters like germination percentage shoot length, root length and seedling dry weight recorded had moderate to low variability. Similar results were obtained in soybean (Mehetre et al. 1997 and Aditya et al. 2011), blackgram (Shanmugam and Sree Rangasamy 1983) and green gram (Sree Rangasamy and Shanmugam 1984). Germination percentage and seed vigour index-I had the highest heritability with the highest GAM for the varieties studied. The results are consistent with previous research that has shown all the characters except shoot length, dry shoot weight and dry root weight had high heritability together with high genetic advance, indicating that variability was due to additive gene effects (Panse, 1957).Heritability estimates were more than 60% for all the characters studied which indicate that these characters were less influenced by environmental conditions and phenotypic selection would be effective for these characters. Shoot length, root length, seedling dry weight and seed vigour index II had the low GA and germination percentage and seed vigour index-II had the high GA. The GAM value for SVI was higher than all the seed physiological traits. This indicates that SVI has a higher potential for genetic improvement compared to the other seed vigour traits. On the other hand, SDW had the lowest GAM value, suggesting that there is little scope for genetic improvement in this trait. The GAM coupled with heritability for a character provides a reliable and meaningful indication for affective utilization in selection programmes (Allard, 1960). Similar high PCV, GCV combined with high heritability for seedling vigour trait such as shoot length, root length, coleoptile length and mesocotyl length were reported by Akshaya et al., (2020); Akshitha et al., (2020). Availability of high genetic variations and heritability for the target traits were useful for improvement of the traits in rice reported in many previous studies (Singh et al. 2012; Pradhan et al. 2019a; Mohapatra et al. 2021). Varieties with superior value for multiple physiological traits such as Satabdi (RL, and SVI-I) and IR68897B (SDW and SVI-II) are useful donor parents in the breeding for improvement of seed vigour in rice.Based on the UPGMA dendrogram generated using genetic similarity values, the study found a significant genetic variation among the 44 rice varieties studied. The varieties were grouped into five major clusters: I, II, III, IV, and V, with different maturity periods ranging from early to very late maturity. The occurrence of maximum intra-cluster distance indicated the possibility of high genetic diversity among the genotypes within the cluster (Tejaswini et al. 2016). Furthermore, the genetic diversity observed among the rice varieties studied could be used in crop improvement programs for developing high-yielding, stress-tolerant, and disease-resistant rice varieties (Ellur et al. 2016).The identification of the early, mid, late, and very late maturity groups within the clusters is important for rice breeders, as it provides information on the appropriate growing conditions and management practices for each variety. Early maturity varieties are suitable for areas with short growing seasons, while late maturity varieties are suitable for areas with long growing seasons (Fazily et al. 2021). The study also highlights the need for conservation of rice genetic resources for sustainable agricultural production.The study investigated the association between SSR markers and seed vigour traits in rice using GLM in TASSEL5 software. Out of 41 SSR markers, 29 were significantly associated with root length, shoot length, seedling dry weight, germination percentage, seed vigour index-I, and seed vigour index-II.For seedling dry weight, 12 SSR markers namely RM 250, RM 1353, RM 85, RM 204, RM 1339, RM 229, RM 230, RM 20, RM 221, RM 240, RM 5389 and RM 16 were significantly associated with the trait but Huang et al. (2004) reported that Markers RM336, RM19 and RM21 located on chromosome7, 2 and 11, respectively were significantly associated with QTL controlling shoot dry weight trait.RM 16 on chromosomes 3 was also associated with seedling dry weight (Zhang et al. 2005a). The QTLs for seedling dry weight at initial seedling stage qFV-5-1 (Zhou et al. 2007); qSDW5–1 and qDW5 (Cui et al. 2002); qSDW4.2 and qSDW8.2 (Cheng et al. 2013); qSDW2 (Han et al. 2007) and qTDW 12–1 (Kanbar et al. 2006) was reported. For germination percentage, 11 SSR markers were highly significantly associated with the trait. In our investigation, for seed vigour index-I, 11 SSR markers were highly significantly associated with the trait.SRR markers can be used for the marker-assisted selection of rice varieties with desired seed vigour traits.qVI on chromosome 5 was linked with these traits(Diwan et al. 2013). Anandan et al. 2016 detected association of seed vigour index with marker, RM341 on chromosome 2. Markers RM336 and RM19 located on chromosome7 and 12, respectively were significantly associated with QTL controlling root length, shoot length, seedling dry weight, germination percentage, seed vigour index-I, and seed vigour index-II are different from the genes reported by (Huang et al. 2004).In our study RM315, RM 334 and RM 224 on chromosomes 1, 5 and 11 were significantly not associated QTL controlling seedling dry weight (Cairns et al. 2009, Zhang et al. 2005a and Anandan et al. 2016). RM 1353, RM 250 and RM 229 on chromosomes number 7, 2 and 11 were significantly associated with all seed physiological traits which is used for our study. RM 223, RM 3428 and RM 240 was significantly associated only with seedling dry weight. RM 9 present on chromosomes number 1 was significantly only associated with shoot length (Sanghamitra 2021).
To enhance the seed vigor trait in high-yielding varieties, it is possible to utilize robust markers identified through marker-assisted breeding programs that are associated with physiological parameters. The traits identified and markers detected in the association analysis will be useful for improvement of seed vigour in rice.