Association of Leafhopper Feeding Behavior with Transmission of Rice Tungro to Susceptible and Resistant Rice Cultivars. G. Dahal, Former research fellow, International Rice Research Institute, P.O. Box 933, Manila, Philippines, Present address: Institute of Agriculture and Animal Science, G.P.O. Box 984, Kathmandu, Nepal; H. Hibino(2), and R. C. Saxena(3). (2)Plant virologist, International Rice Research Institute, P.O. Box 933, Manila, Philippines, Present address: National Agriculture Research Center, Kannondai, Tsukuba, 305 Japan, (3)Entomologist, International Rice Research Institute, P.O. Box 933, Manila, Philippines. Phytopathology 80:371-377. Accepted for publication 5 September 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-371.
To evaluate selected rice cultivars for their resistance to tungro disease and to the leafhopper Nephotettix virescens, a vector of tungro, the feeding behavior of tungro-viruliferous leafhoppers on rice seedlings during an inoculation access was monitored by honeydew tests and electronic recording. Tested seedlings were indexed by enzyme-linked immunosorbent assay for the presence of rice tungro bacilliform virus (RTBV) and rice tungro spherical virus (RTSV). The ninhydrin test monitored leafhopper excretion of ninhydrin-reactive honeydew, indicating leafhopper feeding from the phloem. The safranin test monitored leafhopper excretion of honeydew containing safranin that was absorbed into the xylem elements. The bromocresol-green test monitored leafhopper excretion of basic and acidic honeydew, indicating leafhopper feeding from the phloem and xylem, respectively. The electronic recording monitored waveform patterns, indicating sustained leafhopper feeding from the phloem and xylem. On leafhopper-resistant cultivars, leafhoppers fed mainly from the xylem and, during the feeding, transmitted predominantly RTBV alone. The virus transmission efficiency on the resistant cultivars was high for ASD7, Palasithari 601, and Gam Pai 30-12-15, whereas it was low for ARC 11554 and Ptb 18. On susceptible cultivars IR22 and Taichung Native 1 (TN1), feeding was mainly from the phloem, and transmission was predominantly for both RTBV and RTSV together in high efficiency. On Utri Rajapan and Habiganj DW8, feeding was mainly from the phloem, but virus transmission efficiency was low, indicating their resistance to virus infection. Correlation analysis indicated that differences in the degree of phloem or xylem feedings between virus transmitter and nontransmitter leafhoppers in each cultivar were not significant. In the electronic recording, durations of phloem and xylem feeding of leafhoppers were not significantly different between those that successfully transmitted the viruses on TN1 and those that failed to transmit. There were also no qualitative differences in waveforms between virus transmitter and nontransmitter leafhoppers on each cultivar. Correlations between phloem feeding and virus transmission by leafhoppers and leafhopper survival were significant among cultivars with various resistances to leafhopper. The correlations were not significant within individual leafhoppers in each cultivar. The negative correlation was probably due to variability of leafhoppers in feeding behavior in each cultivar. Nevertheless, resistances of rice cultivars can be differentiated by testing feeding activities of leafhoppers during an inoculation access. The bromocresol-green test was the most appropriate test for this purpose.
Additional keywords: rice green leafhopper, vector resistance.