Genetic diversity,population structure and validation of SSR markers linked to Sw-5 and I-2 genes in tomato germplasm

Tomato is the world’s second largest cultivated vegetable crop. Tomato spotted wilt virus (TSWV) and fusarium wilt (FW) are the two major biotic stresses in India limiting tomato production. Identification and utilization of resistant lines to realize the full genetic potential of varieties for yield gain is an eco-friendly approach. The present research work involved genetic diversity study of 48 genotypes, augmented from different exotic, and indigenous sources belonging to three species using SSR markers. A total of 195 alleles were generated by employing 84 polymorphic markers. The PIC value was ranged from 0.12 to 0.93. Two sub-populations (K = 2) were revealed by model based structure analysis. The cluster analysis using the UPGMA method classified the genotypes into 6 clusters. Pusa Ruby, EC-310310 and EC-620452 were found to be highly diverse. Molecular characterization of 48 genotypes with SSR markers divulged seven genotypes with Sw-5 gene and nine genotypes with I-2 gene showing resistance to TSWV and FW, respectively and further, on artificial screening, they were found to be phenotypically resistant. Out of 195 alleles generated from 84 polymorphic SSR markers, 43 alleles from 26 SSR markers were identified with positive average allele effect distributed across nine chromosomes and positive average allele effect was identified for the average weight of the fruit, the number of fruits formed per plant, and fusarium wilt PDI score. Fruit weight and fruit yield per plant registered a significant and positive correlations. The identified genotypes with varied backgrounds and performances will be very useful as diversified sources in resistant breeding programs of tomato.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12298-021-01037-8.     

Characterization of backcross introgression lines derived from <Emphasis Type="Italic">Oryza nivara</Emphasis> accessions for photosynthesis and yield

Improvement of photosynthetic traits is a promising strategy to break the yield potential barrier of major food crops. Leaf photosynthetic traits were evaluated in a set of high yielding Oryza sativa, cv. Swarna?×?Oryza nivara backcross introgression lines (BILs) along with recurrent parent Swarna, both in wet (Kharif) and dry (Rabi) seasons in normal irrigated field conditions. Net photosynthesis (P_N) ranged from 15.37 to 23.25 µmol (CO₂) m^?2 s^?1 in the BILs. Significant difference in P_N was observed across the seasons and genotypes. Six BILs showed high photosynthesis compared with recurrent parent in both seasons. Chlorophyll content showed minimum variation across the seasons for any specific BIL but significant variation was observed among BILs. Significant positive association between photosynthetic traits and yield traits was observed, but this association was not consistent across seasons mainly due to contrasting weather parameters in both seasons. BILs 166s and 248s with high and consistent photosynthetic rate exhibited stable high yield levels in both the seasons compared to the recurrent parent Swarna. There is scope to exploit photosynthetic efficiency of wild and weedy rice to identify genes for improvement of photosynthetic rate in cultivars.     

Expression Dynamics of Genes and microRNAs at Different Growth Stages and Heat Treatments in Contrasting High Temperature Responsive Rice Genotypes

The global warming-driven climate change is becoming a major challenge for rice cultivation in Asia and Africa. High-temperature stress impairs the physiology and growth of rice plant, and ultimately results in reduced grain yield. This study was aimed to decipher the physiological and molecular changes occurring during different growth stages of heat-tolerant (N22) and -susceptible (Vandana) rice cultivars under three different heat treatments. Chlorophyll content, membrane integrity, gas exchange parameters and expression of genes and miRNAs were analyzed in N22 and Vandana at seedling, vegetative, and reproductive growth stages after exposing to short and long duration of high temperature stress, and recovery. A number of genes and miRNAs showed dynamic changes in their expression patterns at different growth stages and heat treatments, highlighting the necessity to understand gene regulation before employing the genes for modification through transgenic or gene editing approaches. Predominantly N22 showed distinct and unique capability to reprogram its physiological and molecular machinery during prolonged heat stress at reproductive stage, suggesting that the dynamics in gene regulation is crucial to determine its heat tolerant ability. The study has larger implications in deploying genes for the development of heat tolerant rice cultivars through breeding, transgenic, and genome editing approaches.