Comparative Cytology of Rice Tungro Viruses in Selected Rice Cultivars

Ultrastructural studies were made using plants of five selected rice cultivars infected with rice tungro viruses. In all cultivars, rice tungro bacilliform virus (RTBV) was found in both xylem and phloem, while rice tungro spherical virus (RTSV) was observed only in the phloem. In tolerant cultivars Balimau Putih and Utri Merah, plants infected with RTBV and RTSV or RTBV alone, had fewer cells containing tungro viruses than plants of the sensitive cultivar Taichung Native 1. In RTBV-sensitive cultivars FK 135 and ASD 8 infected with both viruses or RTBV alone, electron-dense cytoplasm was observed in most cells of the phloem. Abundant phloem necrosis was also observed in FK 135. These observations were correlated with the reaction of each rice cultivar to tungro infection.