ASSESSING THE REPRESENTATIVENESS OF DATA ON YIELD LOSSES DUE TO RICE DISEASES IN TROPICAL ASIA

The representativeness of information on yield losses due to rice dise ases in tropical Asia was studied. Published studies involving differe nt groups of diseases (viral, bacterial, and fungal) and conducted in different rice production ecosystems were compared to help identify re search gaps, the filling of which could improve current disease manage ment in rice and help in developing strategies that fit the management needs of fast-evolving rice production systems in the future. Four cr iteria of representativeness of yield loss information were used: repr esentativeness over time (the proportion of studies conducted over mor e than one crop cycle), representativeness over space (the proportion of studies conducted in more than one location), representativeness of scale (the proportion of studies conducted on the scale of plots or f ields), and representativeness of injury (the standard deviation of th e proportion of studies using inoculation, spontaneous infection, or c hemical control). A strong imbalance in both the number and the repres entativeness of studies dealing with fungal, viral, and bacterial dise ases was found. Most of the few studies of yield loss due to viral dis eases (mainly rice tungro disease) were conducted on the scale of indi vidual (potted) plants or were based on one-year data sets, often refl ecting strong epidemics only. Studies of bacterial diseases were condu cted in single locations only, and whether such results can be extrapo lated still needs to be addressed. There is an acute need to better do cument yield losses in rice ecosystems other than the irrigated ecosys tem. While studies conducted in the upland, rain-fed lowland, and deep -water rice ecosystems seem to have a high degree of representativenes s, this cannot compensate for their small number in View of the great diversity of these environments. Studies of irrigated rice tend to con centrate on one year and one location. This approach may be based on t he erroneous view that the irrigated ecosystem is homogeneous, and pos sible extrapolation of data from these studies needs to be examined.