RICE BACTERIAL LEAF-BLIGHT - FIELD EXPERIMENTS, SYSTEMS-ANALYSIS AND DAMAGE COEFFICIENTS

Bacterial leaf blight (BLB) is an important vascular disease in irriga ted rice, that is difficult to manage and that can cause up to 50% yie ld reduction. A systems analytical approach was adopted to increase un derstanding of damage and to develop a tool that generates disease man agement recommendations. Field experiments were conducted at three loc ations in India and The Philippines during the dry and wet seasons fro m 1991 to 1995, to assess the consequences of various epidemics for gr owth and production. On the whole, higher and longer epidemics reduced amounts of green leaf area, leading to reduced total above-ground dry matter production and grain yield. Higher nitrogen application rates caused greater grain yields, but also greater grain yield reduction du e to BLB. The BLIGHT crop simulation model, incorporating the effects of BLB on area and photosynthetic rate of green leaf area at three can opy levels, was successfully tested against three field experiments, a nd used in scenario studies to quantify the grain yield reduction at h arvest due to a certain amount of disease spread earlier in the season . This reduction, defined as damage coefficient (DC), was determined f or various crop development stages and for a wide range of environment s, epidemics and leaf nitrogen contents. The 216 data sets resulting f rom the scenario studies were structured by approximation by the 'hat' -curve, which is characterized by the maximum DC for a certain scenari o, the crop development stage at which this occurs, and a scale parame ter that determines the width of the curve. On the average, the DC rea ched a maximum of 266 kg grain ha(-1) leaf about mid-way through grain filling. It is concluded that in addition to traditional disease mana gement options such as use of tolerant cultivars and optimizing transp lanting dates, careful nitrogen management is a possible tool to limit spread of the disease. (C) Published by Elsevier Science B.V.