New methods of screening deepwater rice for yellow stemborer resistance
1988
Catling, H.D. | Islam, Z. | Pattrasudhi, R. (International Rice Research Inst., Los Banos, Laguna (Philippines))
Deepwater rices were screened for resistance to yellow stemborer Scirpophaga incertulas (Walker) at the stem elongation stage; reaction was based on the number of damaged stems. In Bangladesh, 189 genotypes were screened in large field plots (5 x 5 m) exploiting natural populations of borers, or by a method of inoculating small plots (80 x 60 cm) in a deepwater pond. In Thailand, 470 cultivars and advanced lines from 6 breeding programs in Asia were screened by a method using potted plants in oil drums. The number of damaged stems did not correlate with dead heart and whitehead symptoms, nor with stem thickness. The two new methods were an improvement on conventional field screening in that growth conditions were more regular, the load of stem dissection was reduced, and inoculation gave a more uniform borer pressure. The small plot technique requires a controlled deepwater pond, whereas the potted plant method requires only a screenhouse and a supply of oil drums. The pot method is simple and rapid, and two or more annual cycles are possible. The cultivar Leb Mue Nahng III was an effective susceptible check in Thailand, but no resistant check has yet been found. No strong source of resistance emerged from the screening, but several Bangladesh genotypes showed signs of low to moderate resistance: two headrow selections of Habiganj Aman 4, two BR232 lines, and a BR308 line. The search for varietal resistance should continue, but it is also becoming increasingly clear that a method is needed to screen for varietal tolerance.
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