Race Identification Of Setosphaeria Turcica, Ultrastructural Changes When The Pathogen And Host Interaction And Gene Differential Expression

Northern corn leaf blight (NCLB) is the most serious disease for maize production all over the world. In China, NCLB mainly occurred in Northeastern China and Northern China, and the cool mountain areas in Southwestern China. The serous occurrence of NCLB causes severe yield loss, even up to 50%. The dissemination of resistant cultivars is the most economical and effictive strategy to control this disease. This paper focuses on race identification of Setosphaeria turcica in Yunnan, Guizhou and the three northeastern provinces, and the interaction between NCLB and maize by scanning and transmission microscopy. The differential expression of maize resistant gene Ht3 was measured using differential display reverse transcription PCR (DDRT-PCR). The major results were as follows:1. Forty-five isolates were identified as eight races, i.e.12,13,3N,123,12N,13N,23N and 123N in Yunnan Province and four races such as 123,13N,23N and 123N in Guizhou Province. The virulence frequencies of isolates against resistance genes Htl, Ht2, Ht3 and HtN were 73.3%,73.3%,90.0%and 80.0%in Yunnan isolates respectively, and 80.0%,80.0%, 100% and 93.3% in Guizhou isolates respectively. The more complex composition by simple resistance gene, the lower virulence was found in the isolates population. The virulence to composition of four single resistance genes was lowest to 30.0% and 53.3% in Yunnan and Guizhou respectively. But the races in Yunnan were more complex than in Guizhou and the isolate virulence is higher in Guizhou than in Yunnan. Nineteen isolates were identified as seven races,i.e. 1,13,123,2N,12N,13N,123N in three northeast Provinces. The virulence frequencies of isolates against resistance genes Htl, Ht2, Ht3 and HtN were 84.2%,84.2%, 68.4% and 78.9%, respectively. The more complex composition by simple resistance gene, the lower virulence was found in the isolates population. The virulence frequency of isolates against all four resistance genes was 47.4%.2. The NCLB spores began to invade the internal leaves of maize after inoculation 9 h; in the early stages of germination, the germination form of the spores in the maize leaves of disease resistant and susceptible did not have difference. The mycelium of NCLB spread rapidly in susceptible varieties; the mycelium spread from epidermal cells to cortex, vascular tissue and even to the vascular bundle. The cell wall next to the infected cells had grown mastoids, had folded and thickened in the disease resistant varieties; and the NCLB mycelium were trapped by dense material and mesh structure. The mycelial growth is limited. The infected host secreted phenols which were harmful to NCLB to inhibit the spread of mycelium; and the disease resistance host response was significantly stronger than the susceptible host.3. Maize gene fragments related to resistance to Setosphaeria turcica was cloned by DDRT-PCR. It was presumed that gene Ht3 induced the gene expression which participated the photosystem repair.