STUDIES ON CROP LOSS CAUSED BY STRIPE RUST ON WINTER WHEAT (II)——EFFECT OF DISEASE ON THE LEAF PHOTOSYNTHESIS

Winter wheat was used to investigate the effect of stripe rust (Puccinia striiformisWest.) on the photosynthesis of leaves with different disease severity. The rates of CO_2 uptakeof leaves were measured with an infrared gas analyzer. The results showed that on the dis-eased leaves the maximum rate of photosynthesis of the uncolonized part (P'_(max)) was negative-ly proportional to the disease severity and could be described as P'_(max)=P_(max)*(1- 0. 826*S).The photosynthsis model was built as P = I*@*P_(max)* (1 - b*S)/(P_(max)* (1- b*S) + I*@).From this model two relative photosynthesis reduction models were deduced: L_(photo) = A*S~n,where n = f(P'_(max)/P_(max)), and L_(photo) = 1 - (1 - S)*(1-b*S)*(P_(max) + I*@)/(P'_(max) + I*@).The relationship between the critical point crop loss model and these models was discussed.