Studies On Dynamics Of Maize Sheath Blight And Screening Resistance Of Maize To The Pathogen

Physiological and pathological changes of Phenylalanine ammonia-lyase(PAL) activity were tested. The effects of temperature on the mycelial growth of Rhizoctonia solani AG-l-IA and on its infection in maize were also studied. The dynamics of maize sheath blight was monitored under field conditions by interval sowing. Fifty-two cultivars or lines of maize were identified for the resistance to the disease by inoculation. The results are as follows:1. PAL activity increased more highly in resistant variety or at earlier growth stage or upper sheathes. The increase rate and degree of PAL activity in resistant variety were rapider and higher than that in susceptibile variety when infection occurred.2. The temperature range for mycelial growth of Rhizoctonia solani AG-l-IA in maize was 10-35℃,and the optimum temperature was 25-30℃. The sclerotia germinated over a temperature of 18-35℃, with an optimum at 25-30℃. Infection could occur in the temperature range 15-35℃, optimum 25-30℃. Incubation period of the disease was shorter in susceptible optimal temperature than in other temperatures, and its relative lesion area developed more largely at the same condition. Under every temperature, the relative lesion area of the disease of medium growth stages and sheathes was shorter than that of other growth stages and sheathes.3. The dynamics of the disease in field condition includes horizontal expansion and vertical expansion. The horizontal development appeared Logarithmic curve function. The disease curve of vertical development was differment with varying disease target.The growth stage and climate factors influenced the dynamics of the disease. There was a close relation between growth stage and disease development. Temperature was a key climate factor in horizontal development and rainday rate could strengthen occurrence of the disease. Relative humidity was a key factor in vertical development and rainday rate was required for rapid development of the disease only when relative humidity was above 80%.4. Five high resistance cultivars(lines) were found among fifty-two evaluated cultivars(lines). The ratio of the lesion height to the height of corn ear could be used to identify the resistance of corn to maize sheath blight.