RICE RATOONING - IRRI books - International Rice Research Institute

RATOON RICE RESEARCH IN KARNATAKA 107Grain yield and related charactersVarietal differences in grain yield and other related characters are also quite large.Ratoon crop yields of 6-140% of main crop yields have been reported. Main cropyields ranged from 0.8 to 7.5 t/ ha, the related ratoon crop yields ranged from 0.1 to8.7 t/ha. Average yields of main and ratoon crops were 3.7 and 2.1 t/ha. In a fewcases, ratoon crop yields exceeded main crop yields.In 1985-86, IET9667, IET9668, and IET9670 produced ratoon crop yields of1.7 and 1.6 t/ha at Ponnampet Farm; the main crop failed due to low or hightemperature (25). Higher ratoon crop yields also have been reported in sorghum andcotton (15). Others (7, 13, 27) reported ratoon crop yields 20-60% of main cropyields. Haque (6) reported ratoon crop yields of 65 IR lines ranging from 7 to720 kg/ha, accounting for 0.33-13% of the main crop yields. Main crop plus ratooncrop yieids in Karnataka ranged from 2.9 to 9.8 t/ha, main crop 2.44-6.11 t/ ha, andratoon crop 0.23-3.22 t/ha. Per day production in main crop plus ratoon crop was14.8-33.0 kg/ha, which could be increased through improved management (5).Ratoon crop yield was more variable than main crop yield (6). It is possible toreduce high fluctuations in ratoon crop yields by breeding stable ratooning anduniformly flowering varieties and adopting improved management practices. In aplanting date study at Bangalore (India), Basavaraju et al (1) reported that Mangalaplanted in August and harvested at the end of November produced the highestratoon yields among early maturing Mangala, CT1351, and Halubbalu. Jones (8)reported that cultivar selection had more effect on ratoon crop yields than didcutting height.RESISTANCE TO STRESSVarieties susceptible to virus diseases are not suitable for ratoon crops. AtBangalore, only 15 of 260 genotypes tested were unaffected by yellow dwarf orgrassy stunt in the ratoon growth; the rest had to be immediately plowed under, evenif they possessed ratooning ability. In the cold tolerance nursery, 86 of 232 genotypestested in the 1984-85 winter were unaffected by viruses in ratoon growth. Among theaffected ratoon growths, incidence was 5.0-20.0%. Diseases like blast, brown leafspot, and glume blight occurred at the same intensity on both main and ratooncrops. Resistance to viruses is a requirement of varieties to be fitted into a rice ratooncropping system.Varieties currently under study for their suitability for ratoon cropping inIndia are those that are resistant to viruses (Intan, Mingolo, Intan mutant,Mangala). Recent work at the Main Research Station, Bangalore, to selectgenotypes combining cold tolerance, ratooning ability, and desirable growthduration for planting the main crop in Sep-Oct and harvesting the ratoon crop inApril, identified seven that possess all three characters: KBCPI, CT51, NR10073-167-3-1-1, IR18476-55-2, IR15599-135-3, B2983-6-SR-85-3-24, and CT19. Thesegenotypes have been screened for several seasons for different stresses and are beingadvanced to prerelease farm trials in southern Karnataka.Cultivars that flower before the end of winter (night temperature less than18 °C) may fail even if they have good ratoon potential unless cold tolerance is bred