Salt tolerance QTLs of an endemic rice landrace, \u3ci\u3eHorkuch\u3c/i\u3e at seedling and reproductive stages

Salinity has a significant negative impact on production of rice. To cope with the increased soil salinity due to climate change, we need to develop salt tolerant rice varieties that can maintain their high yield. Rice landraces indigenous to coastal Bangladesh can be a great resource to study the genetic basis of salt adaptation. In this study, we implemented a QTL analysis framework with a reciprocal mapping population developed from a salt tolerant landrace Horkuch and a high yielding rice variety IR29. Our aim was to detect genetic loci that contributes to the salt adaptive responses of the two different developmental stages of rice which are very sensitive to salinity stress. We identified 14 QTLs for 9 traits and found that most are unique to specific developmental stages. In addition, we detected a significant effect of the cytoplasmic genome on the QTL model for some traits such as leaf total potassium and filled grain weight. This underscores the importance of considering cytoplasm-nuclear interaction for breeding programs. Finally, we identified QTLs co-localization for multiple traits that highlights the possible constraint of multiple QTL selection for breeding programs due to different contributions of a donor allele for different traits

The ecology and evolution of life history trait divergence in Panicum hallii

Exploring the process of local adaptation is important to understand how environmental variation can drive phenotypic and genetic differentiation as a response to selection. One hypothesis is that local adaptation results from genetic trade-offs in which locally favored alleles reduce fitness elsewhere to provide environment specific fitness advantage. However, studies that aimed to explain local adaptation in plants were mostly done by transplanting seedlings and avoided the important aspects of divergence in earlier life stages. In this thesis, I assess local adaptation from seed and seedling perspective using Panicum hallii, a C4 perennial grass endemic to North America. This is a wonderful system to study local adaptation as it spreads to a wide range of climatic conditions. By combining field and lab-based experiment, I showed that the seed and seedling transition is important for adaptation. The pattern of genetic architecture at seed and seedling traits suggests that the differentiation was primarily due to genetic pleiotropy or linkage disequilibrium. I also discovered the evidence of antagonistic pleiotropy at two loci for seed size and dormancy traits (Chapter-1). I later tested whether the seed size and dormancy trait combination evolved as correlational selection by doing a complex reciprocal transplantation at two representative habitats. My data showed that both seed size and dormancy traits are important for adaptation to native habitats, suggesting that correlational selection is important for adaptation to different habitats. I also showed that soil surface disturbance had a significant effect on the recruitments, plants adapted to high competitive habitat was favored in undisturbed plot and the opposite was observed for the plants adapted in dry, calcareous soil (Chapter-2). Finally, I looked at natural diversity population to estimate the impact of different seed size strategies for adaptation in different habitats. Our data exhibited that the ecotypic differentiation in P. hallii were strongly associated with seed size and seed size was under strong selection pressure for adapting at variable sites (Chapter-3). Overall, this dissertation showed that seed and seedling traits are extremely important for adaptation in different habitats and the variation in these traits significantly impact life history strategies in P. hallii.Plant Biolog

Supplementary File 2 from Seed size variation impacts local adaptation and life-history strategies in a perennial grass

Field recruitment (seedling and adult count) data for the genotypes from lowland, upland and sympatric grou

Supplementary File 1 from Seed size variation impacts local adaptation and life-history strategies in a perennial grass

Genotype information, collection site, bioclim variables and mean phenotypes collected from the greenhouse experimen

Supplemenatry_Information.docx from Seed size variation impacts local adaptation and life-history strategies in a perennial grass

Seed mass is an ecologically important trait that often differs considerably among ecotypes. Yet, because few studies examine the impacts of seed mass on adult life-history traits, its role in local adaptation is unclear. In this study, using accessions of Panicum hallii that spanned the two major ecotypes, we examined whether covariation between seed mass, seedling and reproductive traits impacts ecotypic divergence and local adaptation. The perennial grass P. hallii has two distinct ecotypes—a large-seeded upland ecotype adapted to xeric environments and a small-seeded lowland ecotype adapted to mesic environments. In the greenhouse, seed mass varied greatly across P. hallii genotypes in a manner consistent with ecotypic divergence. Seed mass covaried significantly with several seedling and reproductive traits. At field sites representing the habitats of the two ecotypes, seed mass had different impacts on seedling and adult recruitment: selection favoured large seeds in upland habitat and small seeds in lowland habitat, which was consistent with local adaptation. By demonstrating the central role of seed mass in ecotypic differences in P. hallii and its importance to seedling and adult recruitment under field conditions, these studies show that early life-history traits can promote local adaptation and potentially explain ecotype formation