Mutation breeding for rice improvement in Tanzania.

Abstract

The mutation breeding program based at Sokoine University of Agriculture (SUA), Morogoro, Tanzania aims at reducing plant height and maturation period of popular indigenous cultivars while maintaining some of the good qualities of the parents. Dry seeds of the indigenous popular cultivars were irradiated with 170, 210, 240 and 250Gy Gamma-rays from 60 Co at IAEA Seibersdorf Laboratories in Vienna in 1987, 1994 and 2001. The irradiated seeds and controls were sown at SUA. M 1 panicles were harvested, and planted as M 2 panicle-to-row progenies. M 2 plants were selected and advanced to M 3 and subsequent generations using pedigree selection method using plant height, early maturity and grain type as selection criteria. In another procedure, Single Seed Descent (SSD) method was used, whereby one seed was randomly selected from each M 2 plant to raise the M 3 generation. Apart from this, some improved mutants have been used in the cross breeding program. The selected variants with improved plant type have been evaluated in multi-locational trials and on farmers’ fields. Mutants that were selected using single seed descent were found to be very early in maturity and were resistant to rice yellow mottle virus (RYMV). After several years of multilocation and on-farm trials, SSD 35 was released in 2005 as a new variety under the name of Mwangaza. On the other hand, the improved mutants originating from cultivar ‘Salama’ also combined high yield potential and resistance to RYMV. Semi-dwarf Supa mutant, M-100 was backcrossed to ‘Supa’ variety and one high-yielding line selected from this cross has been recommended for cultivation in Zanzibar. Other lines originating from crosses between mutants and other varieties have been found to be resistant to rice yellow mottle virus and also combine high yield potential and acceptable grain quality.