Developing drought tolerant rainfed lowland rice (Oryza sativa l.) genotypes using marker assisted back crossing technique

Thesis

With an objective of developing high yielding drought tolerant rice genotypes, marker assisted selection was employed in the selection of suitable donor parents and subsequent introgression of the drought tolerant alleles in the background of susceptible high yielding variety (TXD 306). Twenty genotypes were evaluated in well irrigated, moderate and severe stress conditions to select drought tolerant donors. They showed differences in agronomic and physiological performances. Yield under drought stress was positive and significantly correlated with spikelet fertility, number of panicles m'2, grain weight, and plant height, and negatively correlated with number of days to flowering. Fifty SSR markers were employed to characterize 21 genotypes for drought tolerance. Polymorphism information content (PIC) values varied from 0.00 to 0.67. Cluster analysis revealed three clusters. The drought susceptible rice, TXD 306 formed its own cluster. The results showed substantial levels of genetic diversity sufficient to suit selection of drought tolerant donors for the breeding programme to improve TXD 306 for drought tolerance. Combination of markers assisted selection and agro-morpho-physiological performances were able to identify two drought tolerance donors viz; Mwinula and Moroberekan. Crosses were done to develop Fi and then BCiFi generations. Foreground selection was done on 108 BCiFi plants with SSR markers linked to drought tolerance. The heterozygous BCiFi were selfed to generate BC1F2 seeds. The results of single marker analysis revealed that SSRs RM 252, RM 264 and RM 566 had significant association with grain yield and leaf rolling under reproductive stage drought stress. The proportions of phenotypic variation explained by the markers ranged from 45.9% to 14.0% for tolerance to leaf rolling and 10.9% to 5.5% for grain yield. Chi-square results observed significant segregation distortion for the three markers used across the populations studied. In most cases marker distortion skewed towards susceptibility (74.4%) followed by heterozygosity (17.9%) and tolerance (7.7%). All BC1F2 populations performed essentially better than theiii recurrent parent under reproductive stage drought stress. The BC j F j lines should undergo further evaluation and selection to develop drought tolerant varieties which can be used to replace the popular high yielding but susceptible varieties in the drought prone rainfed ecologies.

The Commission for Science and Technology-Tanzania (COSTECH)