Study On Evaluation Indexes For High Temperature Stability Of Photosynthesis In Rice

Rice (Oryza sativa L.) is one of the most important crops in the world, and an immense progress has been made in the utilization of dwarfing gene and heterosis. From now on, the major aim is to increase its yield per acreage, because it is very difficult to increase area due to the smaller and smaller agricultural acreage per capita resulted from the increasing population and scarcity of water resource. Among all kinds of approach increasing yield per acreage, raising efficiency for solar energy utilization (Eu) is the most efficient one. Remarkably, that has a bigger potential of raising Eu because the ideal Eu of rice could reach 3%-5%, not only 1%-1.5% of high yield variety. Currently, the eifect of high temperature on rice yield has attracted people's attention, owing to the aggravated global greenhouse effect. The results showed: midday depression of photosynthesis would more or less occur at midday with high temperature and highlight, which is one of the most important reasons for the loss of light energy while rice is growing. Research on increasing Eu by appreciable breeding and culture technique that is the most staple method for high and stable yield has drawed the crucial attention. The high temperature stability of photosynthesis (HTSP) is the main part of high photosynthetic efficiency in rice physiological breeding,however, there has been no appreciate evaluation index for it. In this study, we put forward a simple and useful evaluation index for the high temperature stability breeding in rice by the appraisement on HTSP of different varieties and genetic analysis of extreme materials on HTSP, to direct the screening and identification of variety resources and breeding offsprings. The major results are as follows:1,Midday depression of photosynthesis had been observed,but the decrease extent of net photosynthetic rate (Pn) had significant difference in all of the rice varieties tested under natural high temperature sunny conditions. Based on this, we identified several varieties which possessed the worse and better HTSP including Texianzhan and Shuhui527, respectively.2,Changes of flag leaf Pn in rice under a series of different temperatures: the daily changes of flag leaf Pn showed a kind of double-peaks' curve, the maximum and minimum of Pn mostly appeared at about 09:00 and 13:30h ,respectively, at natural temperatures, thus the difference value (D-value) of which could be regarded as the evaluation index for HTSP. Simultaneously, the Pn would begin decreasing when the leaf...