Phytopathology. 2014 Jan;104(1):34-9. doi: 10.1094/PHYTO-01-13-0024-R.
Blast, caused by Pyricularia oryzae, has become an economically important disease in wheat in Brazil, but little effort has been devoted to understanding the wheat-P. oryzae interaction. This study was intended to determine the effects of P. oryzae infection on the photosynthetic process in wheat plants using a susceptible (BR 18) and a partially resistant cultivar (BRS 229). It was found that the net carbon assimilation rate (A), stomatal conductance (gs), and transpiration rate were dramatically reduced in both cultivars due to P. oryzae infection but to a lesser degree in BRS 229. Photosynthesis was impaired in asymptomatic leaf tissues, indicating that blast severity is not an acceptable indicator for predicting P. oryzae-induced reductions in A. The proportionally larger decreases in A than in gs, in parallel with increases in internal CO2 concentration (Ci), suggest that the lower influx of CO2 into the diseased leaves caused by stomatal closure was not a prominent factor associated with the reduction in A. Additional support for this conclusion comes from the nonsignificant correlation between A and gs, the negative correlation between A and Ci and the positive correlation between blast severity and Ci. Both the maximum rate of carboxylation and the maximum rate of electron transport were dramatically depressed at advanced stages of P. oryzae infection, mainly in BR 18, although the reduction in A was not closely related to the decrease in the electron transport rate. In conclusion, biochemical limitations likely related to the reduced activity of Rubisco, rather than diffusive limitations, were the main factor associated with decreases in A during the infection process of P. oryzae on wheat leaves.
稻瘟病引起的穗枯病已成为巴西小麦的一种重要经济病害，但对小麦与稻瘟病菌相互作用的研究甚少。本研究旨在利用感病（BR18）和部分抗性品种（BRS229）确定稻瘟病菌感染对小麦植株光合作用过程的影响。结果表明，由于稻瘟病菌感染，两个品种的净碳同化率（A）、气孔导度（gs）和蒸腾速率均显著降低，但 BRS229 降低程度较小。在无症状叶片组织中，光合作用受到损害，表明穗枯病严重程度不能作为预测稻瘟病菌引起 A 降低的可靠指标。A 的比例下降大于 gs 的比例下降，与内部 CO2 浓度（Ci）的增加平行，表明由于气孔关闭导致 CO2 进入患病叶片的通量减少不是与 A 降低相关的突出因素。A 与 gs 之间无显著相关性、A 与 Ci 之间呈负相关、Ci 与穗枯病严重程度之间呈正相关，为这一结论提供了额外支持。在稻瘟病菌感染的后期，羧化的最大速率和电子传递的最大速率均显著降低，主要在 BR18 中，尽管 A 的减少与电子传递速率的降低没有密切关系。综上所述，与 Rubisco 活性降低相关的生化限制而不是扩散限制可能是与稻瘟病菌感染过程中 A 降低相关的主要因素。
