Study On The Effects Of Magnaporthe Oryzae On Photosynthesis Characteristics And Yield Of Rice Plants

To understand the impact of Magnaporthe oryzae on photosynthetic characteristics and yield of rice, the susceptible rice plants were collected from the paddies of Yucheng District of Ya’an, Pujiang County of Chengdu, and Jiangyou city of Mianyang.Then, physiological races were identificated after separation and purification, and selection of the pathogenic physiological races of rice varieties R725, R720 and R727. At tillering and booting stage,the spore suspension of pathogenic physiological races were inoculated on the leaves, and photosynthetic pigment content, gas exchange parameters and chlorophyll fluorescence parameters were investigated after seven days to study the effect of different physiological races of M.oryzae on photosynthesis indexes of rice leaves. In addition, inoculation spore suspension at booting stage and observation the yield components in laboratory after harvest to study the effect of different physiological race on rice yield. The results were showed as follows:After separation, purification and identification, nine different physiological races of M.oryzae were obtained, named ZA5, ZA10, ZA14, ZA17, ZA18, ZC8, ZC11, ZG1 and ZF2. Among of them, ZA5, ZA17, ZC8, ZG1 and ZF2 are pathogenic physiological races of R725, R720 and R727.M.oryzae had varying degrees of impact to the photosynthetic parameters of tested rice varieties at tillering and booting stage.Except E and NPQ, the M.oryzae on Pn, Gs, Ci, Fv/Fo, Fv/Fm,Fv’/Fm’, ΦPSII, q P, Chl a, Chl b and Car of photosynthetic ind exes were Basically the same degree of impact.M.oryzae could significantly reduce the Chl a and chl a/b of R725, R720 and R727, resulting in reducing the light absorptionand transmission efficiency, then inhibiting the photosynthesis.Otherwise, the reduction degree of Chl a content s significantly higher than Chl b, showed Chl a was more sensitive to M.oryzae.M.oryzae had different degrees of inhibition on Car of R725, R720 and R727, resulting in reducing light absorption and free radical scavenging capacity of Car, decreasing the protection to chlorophyll, and affecting the photosynthetic efficiency.After treatment of M.oryzae, the Pn, Gs and E of plants were reduced, and Ci was increased to a given extent. It showed that the decreased photosynthesis was the decline of Gs resulting in reduing of CO2 and photosynthetic pigment content, and the decline of photosynthetic enzyme or other non-stomatal factors resulting in reducing of CO2 utilization. In addition, in the experiment we found there were little asymptomatic leaf tissues, but Pn also significantly reduced, indicating blast severity is not an acceptable indicator for predicting M.oryzae-induced reductions in Pn.After treatment of M.oryzae, chlorophyll fluorescence parameters Fv/Fo, Fv/Fm, ΦPSII, q P and NPQ were significantly reduced, suggesting that M.oryzae and its biotoxins may destroy the PSII reaction centers of test rice variety, so that the photosynthetic system could not be used to increase the light protection by increasing the proportion of heat dissipation.The sensitivity of tested rice varieties was different to the different physiological races of M.oryzae. The strongest toxic effect on the R725 was ZA5, the strongest toxic effect on the R720 was ZC8, and the strongest toxic effect on the R727 was ZG1. After treatment of different physiological races of M.oryzae, the main factor limiting rice yield was different, The main limited factors of ZA5, ZA17, ZC8, ZG1 and ZF2 were panicles number and Chl a/b, ΦPSII,Fv/Fo, 1000-grain weight, panicles number and Ci, respectively.After infection of M.oryzae, not only the leaf photosynthetic structures was destroyed, causing damage to the optical system,also the leaf sheath related cells and enzyme activity were toxic.Then serious ly hindered normal photosynthesis and the assimilation of material decreased. It means Source significant ly reduced, then the transportation to light assimilates panicle of photosynthate reduced, grain number and seed rate were decreased,resulting in capacity reducing. M.oryzae may also metabolize some certain complexes, hindered rice-related physiological responses of the late filling, resulting in significant reduction of 1000-grain weight caused by inadequate filling, ultimately, causing rice production.