Changes in Germination and Seedling Traits of Sesame under Simulated Drought

Drought is considered one of the leading abiotic constraints to agricultural crop production globally.Present study was conducted to assess the effects of different drought treatments(viz.Control,10%PEG,and 20%PEG)on seed germination,germination indices,seedling traits,and drought tolerance indices of sesame.Our results showed that maximum reduction in the studied parameters was observed at higher PEG concentration(i.e.,20%PEG).As compared to control,the drought treatments viz.10%and 20%PEG decreased the values for germination indices,such as germination percentage,coefficient of variation of germination time,germination index,and seedling vigor index.Similarly,for seedling traits,the values were decreased for root length,shoot length,root shoot ratio,root fresh weight,shoot fresh weight,root dry weight and shoot dry weight under 10%and 20%PEG treatments significantly in comparison with control.Furthermore,relative to control,the values for drought tolerance indices,such as germination drought tolerance index,root length drought tolerance index,shoot length drought tolerance index,total seedling length drought tolerance index,root fresh weight drought tolerance index,shoot fresh weight drought tolerance index,total fresh weight drought tolerance index,root dry weight drought tolerance index,shoot dry weight drought tolerance index and total dry weight drought tolerance index were also reduced under 10%and 20%PEG treatments,respectively.Our results confirms that drought impact on seed germination and seedling traits could be quantified by using different indices which can further help to design drought adaptation and mitigation strategies.Based on these results it can be concluded that germination indices,seedling traits,and drought tolerance indices have great potential to simulate drought stress impacts on different crop traits thus they should be used in all kinds of stress related studies.

Genetic Components of Heterosis for Seedling Traits in an Elite Rice Hybrid Analyzed Using an Immortalized F2 Population

Utilization of heterosis has greatly contributed to rice productivity in China and many Asian countries. Superior hybrids usually show heterosis at two stages： canopy development at vegetative stage and panicle development at reproductive stage resulting in heterosis in yield. Although the genetic basis of heterosis in rice has been extensively investigated, all the previous studies focused on yield traits at maturity stage. In this study, we analyzed the genetic basis of heterosis at seedling stage making use of an ＂immortalized F2＂ population composed of 105 hybrids produced by intercrossing recombinant inbred lines （RILs） from a cross between Zhenshan 97 and Minghui 63, the parents of Shanyou 63, which is an elite hybrid widely grown in China. Eight seedling traits, seedling height, tiller number, leaf number, root number, maximum root length, root dry weight, shoot dry weight and total dry weight, were investigated using hydroponic culture. We analyzed single-locus and digenic genetic effects at the whole genome level using an ultrahigh-density SNP bin map obtained by population re-sequencing. The analysis revealed large numbers of heterotic effects for seedling traits including dominance, over- dominance and digenic dominance （epistasis） in both positive and negative directions. Overdominance effects were prevalent for all the traits, and digenic dominance effects also accounted for a large portion of the genetic effects. The results suggested that cumulative small advantages of the single-locus effects and two-locus interactions, most of which could not be detected statistically, could explain the genetic basis of seedling heterosis of the F1 hybrid.