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Etiology

Biological Variants of Rice Tungro Viruses in the Philippines. P. Q. Cabauatan, International Rice Research Institute, P.O. Box 933, Manila, Philippines; R. C. Cabunagan(2), and H. Koganezawa(3). (2)(3)International Rice Research Institute, P.O. Box 933, Manila, Philippines; (3)Present address: Shikoku National Agricultural Experiment Station, Zentsuji, Kagawa 765, Japan. Phytopathology 85:77-81. Accepted for publication 20 July 1994. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/Phyto-85-77.

Tungro is a composite disease of rice induced by dual infection with rice tungro bacilliform virus (RTBV) and rice tungro spherical virus (RTSV). Four strains of RTBV, designated L, G1, G2, and Ic. were isolated on the basis of their characteristic symptoms on rice cultivars FK135 and Taichung Native 1 (TN1). On FK135, strain Ic caused severe stunting, reduced tillering, narrow leaves, and distinct interveinal chlorosis (striping and/or mottling) on the leaf blades, while G1 and G2 caused only mild stunting and foliage was a normal green. On TN1, G1 and Ic caused mild stunting but no discoloration of the foliage; G2 caused severe stunting and yellow to orange discoloration similar to that caused by the type strain L. Thus, G1 and Ic can be readily differentiated by the reaction of cultivar FK135, while G1 and G2 can be differentiated by that of TN1. Cross-inoculation experiments showed that strains G1 and Ic were cross protective. In other studies, a virulent strain of RTSV (Vt6) was isolated from tungro-infected plants collected from Mindanao, Philippines. The cultivar TKM6, like many other cultivars resistant to type strain A, was susceptible to strain Vt6. TKM6 plants infected with both RTBV and strain Vt6 showed severe stunting and discoloration.