Recent finding on the chromosomal locations of GLH and RTSV resistance genes in ARC11554 rice cultivar and the effectiveness of the genes in preventing RTSV infection

Rice tungo disease (RTD) is considered as the most serious viral disease in the Philippines. RTD is caused by Rice tungo bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV) transmitted by green leafhoppers (GLH, Nephotettix virescens). RTSV alone rarely causes distinctive symptoms in rice, but it mediates transmission of RTBV, which enhance disease symptoms. Indian rice cultivar ARC 11554 has been found resistant to GLH and RTSV. The associations of GLH and RTSV resistance with genotypic variations in populations derived from ARC 11554 were examined to clarify the chromosomal locations of the loci controlling the resistance traits. GLH resistance was confirmed to be a dominant trait controlled by a locus (GLH14) near 4.4 Mb of chromosome 4. On the other hand, the identification of a locus associated with RTSV resistance was carried out using populations which are susceptible to GLH to avoid masking of RTSV resistance with GLH resistance. RTSV resistance was found to be controlled by a single recessive gene (tsv1) in chromosome 7, containing a non-susceptible allele of the translation initiation factor 4-gamma gene, which has been known conferring RTSV resistance in other rice cultivars. To assess the effectiveness of the two genes in prevention of RTSV, ARC 11554 - derived plants with GLHL14, with tsv1, and with combination of both genes were inoculated with RTSV by forced-tube method using 5, 10 and 15 GLH. The frequencies of RTSV infections were compared. RTSV was not detected in plants carrying only the the tsv1 whereas at least 50% of the plants carrying only the GLH14 were infected. Result suggests that the use of resistance to GLH alone does not assure the prevention of RTSV infection while the use of tsv1 gene is much effective, although the combination of GLH14 and tsv1 might prolong the durability of rice plants against RTD in fields.