Primary Study On The Biochemical Resistant Mechanisms Of Curvularia Lunata Leaf Spot In Maize

The changes of defensive enzyme activities and isoenzyme patterns and phenolics were studied in maize leaves infected by Curvularia lunata within one week after inoculation. In addition, the influence of leaf extract on pathogen spore germination was studied. The results are as follows.1. The leaf extract of both Mol7(resistant) and Chuandanl3(susceptible) can influence germination of pathogen spore. The influence was greater in Mol7(resistant) than in ChuandanlS. The extract was presumed to contain some inhibitory substances against pathogen spore germination . Infection of pathogen might result in the increase of the substances,and the phenomenon was more remarkable in the resistant cultivar.2. The changes of phenolics were correlated with pathogen infection. Phenolics in both Mo 17 and ChuandanlS accumulated after the inoculation with Curvularia lunata. Furthermore, the accumulation of phenolics in Mo 17 (resistant) was not only faster, but also greater than in Chuandanl3 (susceptible) . It can be deduced that infection of pathogen may stimulate the increase of phenolics. Resistant cultivar is more sensitive to the stimulation.3. The activity of Pnylalanine Ammonia-lyase (PAL) increased in both resistant and susceptible cultivars after inoculation. The activity of PAL in resistant cultivar increased faster and greater than that in susceptible one. The results indicate that PAL may have an important function in the resistance of Maize to Curvularia lunata.4. Pathogen infection resulted in the increase of peroxidase (POD) activity and the change of isoperoxidase patterns. POD activity increased rapidly in the early and middle30infection stages, but decreased a little in the late infection stage in both resistant and susceptible cultivars. The increase of POD activity was greater and earlier in the resistant cultivar than in the susceptible one. Three new isoperoxidase bands (e,f,g) appeared in Chuandan 13 (susceptible) after inoculation. There is no new isoperoxidase band in Mo 17 (resistant), but the activities of many isoperoxidase bands of Mo 17 increased rapidly with the infection of pathogen. The changes of POD activity and isoperoxidase patterns suggest that the increase of POD activity is related to the resistance in the early and middle infection stages.5. The esterase (EST) and catalase (CAT) isozymes were analysed by electrophoretic methods. The changes of isozyme patterns in both cultivars were similar. Therefore, it indicates that there must be some other factors, which affect the activities of EST and CAT.