Varietal improvement for rainfed lowland rice in South and Southeast Asia: results of survey
1986
Mackill, D.J. (International Rice Research Inst., Los Banos, Laguna (Philippines))
A survey of rice breeders in nine countries in South and Southeast Asia was conducted to document current work on rainfed lowland rice improvement. Disease and insect susceptibility is regarded as the major weakness of current varieties; this is followed by poor drought and flood tolerance and low yield potential. The major diseases are bacterial blight, blast, brown spot, sheath rot and tungro virus. The major insect pests are stem borer, brown planthopper, and gall midge. Drought and flash floods are the important environmental stresses, followed by stagnant flooding, salinity, P deficiency, and Zn deficiency. Long or medium slender grains with intermediate amylose are favored. The cultural types "shallow, favorable" and "shallow, drought-prone" represent about 30% each of the rainfed lowland area. "Drought- and submergence-prone" and "medium-deep, stagnant water" are present in almost equal amounts. "Submergence-prone" rainfed lowland rice is less common. Breeding objectives for disease and insect resistance and adverse soils tolerance are apparently not strongly related to cultural type. Information from the survey should facilitate exchange of germplasm among programs with similar objectives.
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