Screening of Rice Accessions For Resistance to Rice Yellow Mottle Virus

Rice yellow mottle virus (RYMV) is responsible for the most damaging virus disease of rice in Africa. The objective of this study was to assess the reaction of rice accessions to RYMV, for better control of the virus. Rice accessions including landraces and collections from research institutes were collected from 2010 to 2013 in Burkina Faso and Ghana. Two viral inoculums composed of non-resistance-breaking RYMV isolates (inoculum-1) on the one hand and of resistance-breaking isolates (inoculum-2) on the other hand were used for the screening experiments in the greenhouse. A subset of rice accessions were exposed to field isolates under field conditions of virus transmission. Experimental designs were randomized complete blocks with three replicates. Of 117 rice accessions challenged with inoculum-1, 69.2% were susceptible to RYMV and expressed disease symptoms between 10 and 13 days post-inoculation (DPI). Partial resistance was found in 30.7% of the accessions which expressed symptoms between 15 and 17 DPI. When inoculum-2 was used, the proportion of susceptible accessions was higher (84.6%) and symptoms appeared earlier (7-10 DPI). High resistance was not found in any accession. Leaf virus content allowed a clear distinction between susceptible, partially resistant and highly resistant accessions.

Altogether, these results indicated that the choice of virus isolates is critical when screening rice germplasm for resistance to RYMV. Non-resistance-breaking isolates should be used for successful detection of resistance in screened accessions