An adventure in applied science - IRRI books - International Rice ...

Early research and training results 129tible varieties served as checks and ensured that there would be abundantspores of the blast disease in the nursery so that no variety could escapeexposure to the disease.That first year, Ou not only screened thousands of varieties from the worldcollection but helped the Varietal Improvement Department set up its ownnurseries so that it could test the many genetic lines from the breedingprogram.Beginning in 1963, Ou made arrangements to establish rice blast testingnurseries in many cooperating countries. Furthermore, during an internationalsymposium on the blast disease at IRRI that year, FAO asked theInstitute to take full responsibility for its international rice blast testingprogram, which Ou had originally started. That year, also, Ou and cooperatingscientists in other countries selected 250 rice varieties for wide screening tests.Included were 38 differential varieties from Japan, the US., and Taiwan and100 varieties that had been tested in 1962 in the FAO program. The rest of the250 varieties had been selected by IRRI because of their resistance to thephysiologic races that existed in the Los Baños area. Forty sets of the uniformblast nurseries were sent to 15 cooperating countries in 1963. The followingyear, the number of cooperating countries increased to 20 and remained atabout that level through 1967. The varietal composition of the nurserieschanged greatly as resistant cultivars were identified.According to the results sent back to IRRI, several varieties proved to beresistant to all but two or three of the races of blast encountered in the entiretesting program. Such varieties as Tetep, Carreon, and Tadukan were widelyused in IRRI’s breeding program, as well as in national programs, to incorporatebroad-based resistance to blast in the improved varieties.Without doubt, Ou’s research on the rice blast disease was the mostthorough and comprehensive of any such studies in the tropics and subtropics.He not only screened many thousands of varieties to identify superior breedingmaterials but conducted countless fundamental studies of the disease,such as the effect of nitrogen nutrition on the severity of disease attack, themode of inheritance of blast resistance, methods of culturing the causalorganism, the correlation between leaf blast and neck rot resistance, thedistribution of airborne spores, the chemical control of the disease, the standardizationof race numbers, the seasonal variation in physiologic races atIRRI, and the races originating from single lesions.During the early years, Ou did considerable work as well on two otherfungal diseases of rice — stem rot and sheath blight.IRRI pathologists (as mentioned in Chapter 2) recognized the presence ofviral diseases during the first year of the research program. Ou had demonstrated,as early as 1962, that leafhoppers of the genus Nephotettix were vectorsof a viral disease that he tentatively called orange leaf. In 1963, he describedfour viral diseases that occurred on IRRI’s experimental fields: orange leaf,tungro, yellow dwarf, and dwarf diseases. By 1964, after many studies andobservations, he concluded that the disease he had called yellow dwarf in 1963was instead a tropical viral disease transmitted by the brown planthopper