RICE RATOONING - IRRI books - International Rice Research Institute

ALTERNATIVE TO DOUBLE CROPPING IN TROPICAL ASIA 11Table 6. Grain yield and blast reaction performance of three semidwarf rice varieties, main andratoon crops, Ponnampet, Karnataka, 1986. aVarietyBlast ratingMain crop Ratoon crop of main cropDays to Plant Yield Days to Plant Yield Leaf blast Neck50% flowering height (t/ha) 50% flowering height (t/ha) (plant crop) blast(cm)(cm)IET 9667IET 9668IET 9670868994Mean 89% height reduction –13312511412446.6.083nil111–3638419996911.71.71.638 95 1647% reduction in days to flowering –201–42.69010090–a Source: Naidu et al (17).In the cultivar reaction to blast at Ponnampet, Naidu et al (17) noted that of 57entries in the National Screening Nursery, which suffered 100% blast incidence onmain crop, 3 — IET 9667, IET 9668, and IET 9670 — could regenerate a vigorousratoon crop. They produced an average yield of 1.64 t/ha, compared to negligible orno yield for the main crop, with a 42.6% reduction in duration. Plant height was alsoreduced 46.6% (Table 6). No effect on seed viability and germination was recordedHowever, in the same experiment, cultivar Intan, used as control, suffered100% blast incidence and could not establish itself as a ratoon crop because theratoon rice was also attacked by leaf blast.These findings suggest that there could be cultivars that have a disease in themain crop but can withstand it in the ratoon crop and produce satisfactory grainyields.In studies on yellow dwarf disease of rice, Muniyappa and Ramakrishnan (14)observed that infestation level was much higher (1.05-35.89%) on the ratoon cropthan on the main crop (0.33-22.5%). They also noted variability in resistance toyellow dwarf among the cultivars studied; cultivars CH2, CH45, CR126-33-11,IR127-80-1-10, and MR278 had zero incidence in both main and ratoon crops.WeedsWeeds are reported to cause as much as 11% rice grain yield loss in Asia. Manydevices have been worked out for effective control of weeds in irrigated rice undervarious climates, soil types, weed flora, etc. Such studies are limited to ratoon riceweed management. However, the effects of tillage practices on both main and ratooncrops were studied by Bahar and De Datta (2). Tillage clearly helps produce higherratoon crop yields. Plowing followed by harrowing gave the highest yields of mainand ratoon crops, the most panicles/m 2 , and the lowest percentage of unfilled grains.Thus, weed management is essential for better yields. More studies are necessary towork out cheaper weed management practices.SEED QUALITYReddy and Pawar (23) observed that seed from the ratoon crop of a number ofcultivars showed no defect in productive capacity or viability. Several studies