MARKER ASSISTED SELECTION FOR RESISTANCE TO RICE YELLOW MOTTLE VIRUS IN FARMERS’PREFERRED RICE VARIETIES IN BURKINA FASO

ABSTRACT

Rice yellow mottle disease (RYMD), caused by Rice yellow mottle virus (RYMV), is a very damaging disease of rice in Sub-Saharan Africa. A participatory rural appraisal was conducted in Burkina Faso to assess farmers' awareness of rice production constraints with emphasis on rice yellow mottle disease (RYMD) and its management. RYMD was mentioned by farmers as the most important rice disease. Management practices included replacement of rice varieties and spray of pesticides. Farmers' choice for rice varieties was based on grain yield and taste as major criteria. Thirty four (34) farmers' rice varieties and 91 varieties from agricultural research institutions in Burkina Faso and Ghana were screened for resistance to RYMV. Partial resistance was found in 29.6% of the varieties, while all other varieieties were susceptible to the virus apart from the high resistance control. Well characterized non-resistance breaking (nRB) isolates of the virus was critical in identifying resistance sources. RYMV1 high resistance gene in Gigante and Bekarosaka (bearing rymv1-2 allele) was introgressed into both susceptible and partial resistant farmers' preferred varieties. Interspecific crosses involving Oryza glaberrima cultivar Tog5681 (bearing rymv1-3 allele of RYMV1 resistance gene) were successful but introgression of the resistance gene to RYMV failed. Recombinant lines were readily genotyped for the presence of the resistance gene at both homozygous and heterozygote states using SNP-markers. Genotypic characterization of recombinant lines was confirmed by assessment of their phenotypes through virus inoculation. Field evaluation of recombinant lines revealed high (77.29%) broad sense heritability estimates for grain yield. Path coefficient analysis indicated that grain yield was highly and positively correlated with plant panicle number (r=0.80), tiller number (r=0.76) and 1000-grain weight (r=0.61) but negatively to above-ground total biomass (r=-0.28). Per plant panicle number had the highest direct and positive effect on grain yield

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(0.94). Major indirect effects on grain yields were exerted by tiller number (0.76), number of days for first flowering (0.72) and above- ground total biomass (0.58). Most recombinant lines performed better than their parents with up to 27.5% highest increase compared to mid-parents. Best performing recombinant lines resulted from crosses involving high resistance donor Gigante or partial resistance donor Digang. From these recombinant lines, several high yielding lines are likely to be developed for release in the near future. By taking into account farmers' preferences, adequate varietal screening process and marker-assisted selection, it can be expected that the new rice varieties to be developed will make great impact in rice production in West Africa.

Keywords: rice, recombinant lines, rice yellow mottle virus, resistance, marker-assisted selection, farmers’ preferred varieties.