Performance analysis of Sub 1 pyramided F5 population in rice

Abstract

Rice (Oryza sativa L.) is the most important primary food crop that provides food to about half of the population. The cultivated species of rice are semi aquatic plants of normal height ranging from 0.90m – 1.8m, but some can grow up to 5 metres in deep water. In lowlands and deep-water rice field, over 16 million hectares of the world’s rice lands are unfavourably impacted by floods due to total submergence and one of the major constraints in rice cultivation worldwide is submergence stress. This mainly affects flood prone areas like kuttanadu, pokkali as well as low lying paddy fields in Kerala. Even though hundreds of high yielding varieties were developed in the nation, they are not suitable for cultivation in the problematic areas affected by various abiotic stresses. The easiest way is to incorporate the abiotic stress tolerant (Quantitative Trait Loci) QTLs into the already bred high yielding varieties without altering any of the characters through molecular breeding. Sub1 is a major quantitative trait locus (QTL) representing a cluster of three ethylene responsive factor (ERF) genes: Sub1 A, Sub1B and Sub1C that confers submergence tolerance to rice genotype. Submergence tolerant rice variety is credited with maintaining energy and alcoholic fermentation which require high levels of carbohydrates. Sub1 locus contain Sub1A, Sub1B and Sub1C, all of which encode ethylene responsive factor and are up regulated under submergence, but only Sub1A is responsible for flash flood tolerance. The near isogenic lines generated by the introgression of the Sub1 from FR13A into to susceptible cultivar shows restricted shoot elongation similar to FR13A. The present study was undertaken for the performance assessment of Sub 1 QTL in the BC3F5 progenies of submergence susceptible rice varieties Jaya, Jyothi and Uma. The research was conducted in the Department of Plant Breeding and Genetics, Rice Research Station, Vyttila during the period 2021-2022. The experimental material used for the study included 50 accessions of BC3F5 progenies of Jaya, Jyothi and Uma obtained from Rice Research Station, Vyttila. 47 SSR markers distributed across the rice genome were used for polymorphism survey between recurrent parents Jaya, Jyothi and Uma and Swarna Sub-1 96 Progenies of BC3F5 was evaluated in the field to assess the submergence tolerance of Sub-1 introgressed lines. In-vitro screening of BC3F5 progenies were performed by pot culture experiment. 14 days old seedlings were subjected to complete submergence and the pots were desubmerged after 14 days. The survival percentage and elongation percentage were scored based on the observation. Most of the selected lines have shown good recovery percentage resembling its Sub-1 donor Swarna Sub-1. Rice varieties with the Sub1 gene were shown higher survival rate with better yield even after 2 weeks of submergence stress. The advancement of marker assisted selection (MAS) have striking impacts on developing improved Sub1 varieties that can meet the increasing demands of consumers along with the population hike. In this present study, 31 rice genotypes were observed with the Sub1 QTL using SSR markers through molecular characterisation in order to find out the best submergence tolerant lines. More over this finding lays the foundation for further researches with Sub1 QTL for crop improvement. 2 SSR markers ART-5 and Sub1BC2 were used as foreground markers to identify the Sub-1 QTL. Background markers are used to identify the recurrent parent marker allele. A total of 45 polymorphic background markers were used for background screening. 9