RICE RATOONING - IRRI books - International Rice Research Institute

BREEDING, AGRONOMIC PRACTICES, AND SEED PRODUCTION 179Field and laboratory screening for virus and MLO epidemiology have beenreported (14, 15, 16, 17). The need is for further standardization of simple andefficient screening techniques.Until now, ratoon crop experiments were based on cultivars not bredspecifically for ratoon cropping. Little work has been done to select genotypesespecially adapted to high ratoon yields. Many wide crosses are needed tounderstand the nature of ratooning ability inheritance and characters attributing toratoon yield.AGRONOMIC MANAGEMENTMain crop planting timeThe planting time of the main crop cannot be fixed in many rice growingenvironments, especially in tank and rainfed rice areas where the start of rains iserratic. This results in varying harvest times for the main crop. Delayed or very earlyharvests may lead to subsequent problems in the ratoon crops, such as floweringcoinciding with low temperatures, harvest coinciding with heavy rains, and delayedharvest overlapping planting time for a subsequent crop (3, 11). Bird pests also causeheavy damage to ratoon crops at the grain ripening stage if the ratoon plots are indifferent growth stages.To solve these problems, it is important to identify varieties with goodratooning ability for different main crop planting dates. In Karnataka, if the seasonis late for Intan, early-maturing Mingolo has been found to come to timely harvest inboth the main and the ratoon crops. However, if Mingolo is planted early, its ratoonflowers in severe winter and fails to set any seed (23).Selecting the main crop plot for ratooningA good uniform plant stand with a vigorous root system in the main crop is aprerequisite to a successful ratoon crop (4, 10). The growing period available for theratoon crop and the weather conditions (temperature and rainfall) that prevailduring ratoon growth also determine whether a particular plot is worth selecting forratooning. A main crop plot that lodged because of rain, wind, and other factors oran overmature plot may not be fit for ratooning. A plot located near the day roostsof birds during the active growth season may pose problems. Specific varieties,locations, and seasons need to be identified for a main crop-ratoon crop system.Stage and height of cutting main cropEarly results suggest that the best time to cut the main crop is when it is fully ripe, butbefore the green disappears. However, because senescence is a varietal character, thestage has to be fixed in reference to the variety recommended for the specificsituation. The effect of cutting height on ratoon crop performance has beenprofusely studied (4, 10, 21). Varieties differ markedly in their ratoon tillerproduction. Some are unaffected by the cutting height (30). Stubble height also isreported to influence ratoon growth duration. Variety by location-specific study isimportant. The relationship between cutting height and disease needs to be