Break-down of Resistance of a Rice Line MR118 to Rice Tungro Disease in Peninsular Malaysia

Abstract

Rice lines MR114, MR118 and MR119 were resistant to rice tungro disease (RTD) at Permatang Bendahari, Penang, Peninsular Malaysia during the off season of 1989. However, MR118 was rated as susceptrble at Bukit Merah, Penang in 1990 and at Kuala Muda, Kedah and Bumbong Lima, Penang in 1991. The mechanism of resistance involved in MR118 was suspected to the resistance to green leaffLopper (GLH) that was similar to that of IR42. IR42 which was generally cultivated as RTD resistant variety in the Peninsular Malaysia since 1981 also lost its resistance at Kuala Muda in 1991. Therefore, the break-down of MR118 before its official release was believed to be due to the development of the GLH population which acquired infestivity on IR42, resulting from the prolonged large scale planting of IR42 in the area.