RICE RATOONING - IRRI books - International Rice Research Institute

Diseases and disease managementin rice ratoon cropsT. W. Mew and N.G. FabellarInternational Rice Research InstituteP.O. Box 933, Manila, PhilippinesLittle has been reported on diseases and disease management in relation to ratoonrice. Two aspects of disease management are important considerations in ratoon ricecrop production.First, the speculation is that ratoon rice will manifest a disease problem becausethe inoculum is likely to be perpetuated from main crop to ratoon crop; available hosttissues for continuous infection are also prolonged. Few data and reliable informationhave been reported in the literature. The general belief among plant pathologists isthat, like volunteer rices or stubble left in fields, a ratoon crop will provide amplereservoir for diseases to continue to cause damage and for the inoculum to perpetuate,ready to cause secondary and tertiary infection.Second, with the development of genetic resistance to diseases in many ricecultivars, it is assumed that the ratoon crop will possess the same degree of resistance.This paper examines these issues. The sources of information are predominantlyour own observations over the past several years of monitoring disease development inmain crops and ratoon crops on IRRl farms. Experiments on the effects of diseasemanagement in main crops on ratooning and on disease development in ratoon cropare also reported.DISEASES OF MAIN AND RATOON CROPSThe diseases commonly observed in main rice crops can also be found in ratoontillers. Also, the diseases to which a rice cultivar is known to be resistant are absent inthe ratoon rice. Yellow dwarf, caused by a mycoplasma-like organism which has a1-3 mo latent period in rice plants, depending on the temperature (4), is oftenobserved in ratoon rice (Fig. 1, Table 1). Yellow dwarf is transmitted by Nephotettixcincticeps, N. virescens, and N. nigropictus. In addition to the long latent period inthe plants, the incubation period in the vector insect body is usually 25-30 d. Yellowdwarf was observed on ratoon crops of susceptible cultivar IR32.Rice ragged stunt is a new virus disease, found in South and Southeast Asia1977-79. The spherical virus is transmitted only by nymphs and adults ofNilaparvata lugens (Stål). Symptoms of the systemic disease are also manifested inratoon rice (2). In a survey of ratoon rice on 9,000 ha of ricefields in Malaysia afterthe main crop had been harvested, Ooi (3) reported finding a low level of rice raggedstunt. He attributed the low incidence on ratoon rice to the absence of disease onoff-season rice, when the vector was prevalent.