Rice tungro disease management - IRRI books - International Rice ...

Rice tungro disease in the PhilippinesX.H. Truong, E.R. Tiongco, E.H. Batay-an, S.C. Mancao, M.J.C. Du, and N.A. JuguanThe rice tungro disease scenario in the Philippines, research trends, andcurrent extension activities are briefly explained and discussed in this paper.Farmers’ perceptions and knowledge on the subject were also includedbecause farmers make decisions for sustaining farm income and protectingthe agroecosystem. Some farmer groups have used green leafhopper(GLH)-resistant varieties for the past several years through the SeedNetand Farmers' Field School, yet rice tungro disease (RTD) remains a majorconstraint to rice production. For the first time in rice technology development, rice tungro virus (RTV)-resistant advanced breeding lines were identified.A few farmers in RTD-endemic areas evaluated these lines on theirfarms. Seeds of these lines with yields of 3.5–4.5 t ha -1 are being increasedand will be deployed as stopgap materials for farmers during thewet season. Some progress had been made in understanding the genotypesof tungro viruses present during recent RTD outbreaks, and the roleof cropping practices and infective GLH or virus inoculum during the pastRTD outbreak in Mindanao. More collaborative efforts in research andextension have to be undertaken to strengthen farmers’ decision makingfor appropriate RTD management in the context of a sustainable farmingsystem.RTD outbreaksThe early outbreaks of rice tungro disease in the 1940s in major rice-growing regionsin the Philippines had reduced yield by 1.4 million t annually (Serrano 1957), longbefore the causal organism of the disease was known (Hibino et al 1978, 1991), Majoroutbreaks in 1962, 1969, 1971, 1975, 1977, 1984, 1986, and 1989 in areas associatedwith intensive cultivation of early recommended varieties were reported by municipalagricultural officers (MAO) of the Department of Agriculture (DA), and reviewedby Baria (1997). Recent outbreaks occurred sporadically during 1993-98, affectingareas from 900 to 2,700 ha yearly in Mindanao (Table 1). In addition, about700 ha were affected in Negros Occidental in 1998. Crop loss estimated by the DAprovincial agricultural office from the outbreak in Davao del Norte in 1993 alonereached – P10.6 million (US$406,494). Most of the affected locations commonly reportedwere irrigated lowlands under climatic types III and IV. Dry and wet seasonsin type III are not pronounced; it is relatively dry from November to April and wetduring the rest of the year, whereas rainfall in type IV (>150 mm monthly) is more orless evenly distributed throughout the year. In most cases, rice tungro disease (RTD)outbreaks were attributed to insufficient irrigation water, which prompted farmers topractice staggered planting. The consolidated report of the DA-MAO showed thatearly infection at the vegetative stage of IR64 and IR60, BPI Ri10, PSB Rc4, 6, 8, 12,20, Masipag, and Bugos induced severe crop losses varying from 39% to 65%.No comprehensive information on the agroecosystem during the reported RTDoutbreaks was available. The only known fact was that recent outbreaks occurredduring August-October. The average monthly rainfall during the same period recorded