Baruah, Akhil RanjanBora, Smriti Shyamolee2024-06-252024-06-252023https://krishikosh.egranth.ac.in/handle/1/5810210880Rice (Oryza sativa L.) is a staple food crop for half of the world’s population and it has been grown as major cereal crop in three distinct seasons in Assam. Out of various constrains of rice production, abiotic stresses such as drought, low temperature (LT), salinity adversely affect crop growth and development. Low temperature stress at the early growth and reproductive stages in rice are critical, and the present study was conducted to screen low temperature tolerant genotypes at the booting stage (intermediate stage of reproductive phase) and study gene expression for cold responsive genes in tolerant and susceptible rice genotypes. A total of 30 rice cultivars collected from Regional Agricultural Research Station, Karimganj, AAU were subjected to low temperature stress at the booting stage in a growth chamber maintained at 12- 12.5C for seven days. The recovery and low temperature tolerance of plants after stress were evaluated based on pollen fertility, number of panicle emerged, number of seeds set and grain yield. The results revealed that the phenotypes of C-59 and IET-9097 were superior for all the traits under study whereas Costco and IET-8687 showed lowest trait values, indicating varied levels of low temperature tolerance at the booting stage. These four cultivars, C-59 and IET- 9097 as low temperature tolerant; Costco and IET-8687 as low temperature susceptible were chosen to study gene expression analysis using six cold responsive genes (OsCOLD1, OsDREB2A, OsCTB1, OsLTT1, OsAPX1, OsNAC9) through real time quantitative reverse transcriptase polymerase chain reaction (RT-qPCR). The results showed that all the genes were up-regulated in the cold tolerant cultivars, C-59 and IET-9097 and down regulation in the other two cold susceptible cultivars, Costco and IET-8687. After performing qRT-PCR analysis, correlation between the gene expression data and phenotypic observations followed by path analysis was performed to detect associations between the genes and phenotypes. Path analysis revealed that out of six genes used in the study, three genes showed direct positive effect over grain yield (OsDREB2A, OsCTB1 and OsNAC9) and three genes showed indirect effect for grain yield (OsCOLD1, OsLTT1 and OsAPX1). The study is preliminary with respect to low temperature tolerance at the booting stage using rice collection of AAU and hence, further validation is required.EnglishThesis