Study On Identification, Resistance Evaluation And Control Of Pestalotiopsis Eriobotrifolia In Chongqing

Gray leaf spot has become one of the most common and widely spread diseases in loquat production. Now, this disease caused disastrous influence on orchards, not only reduce fruit yield but also affect the quality of loquat. In this paper, pathogens of loquat gray leaf disease and their diversity were identified in Chongqing areas by using molecular marker technology, and the resistance to gray leaf disease of94loquat germplasms was evaluated. Meanwhile effective fungicides were screened which could provide basis for controlling gray leaf spot. The main conclusions were as followed:1.6strains from samples of gray leaf spot were identified to be Pestalotiopsis eriobotrifolia based on characteristics of morphology of conidia, PCR amplification of rDNA-ITS and β-tubulin sequence. They all could infect loquat leaves and cause significant disease spot. Phylogenetic tree based on sequence of ITS and β-tubulin gene showed that there were greater differentiation in Pestalotiopsis eriobotrifolia because of the different origin regions. Strains with significant difference may be different physioogical races.2. In order to evaluate virulence of different P. eriobotrifolia, loquat leaves and fruits were used to inoculated with isolate XZ-CQBB after making different wounds. Results showed lesions were significant in treatments of wounds on back of leaves and equator fruits. And lesions were more apparent and spread faster in wounded leaves than fruits. Inoculations of different virulent strains showed that the sizes of lesions on the leaves as the same as lesions on other materials. It could be quick and stable method. Inoculations of ’XZ-CQBB’ strain in different loquat cultivars showed that the sizes of lesions were able to reflect different resistant ability. This method could be used for evaluation resistance of different Loquat germplasms.3. The resistance to loquat gray leaf diseases of94loquat germplasms were investigated in continuous two years. Combined with the indoor inoculation result then grade the resistant level of different loquat resources by investigation and the indoor inoculation result. Screening and established the evaluation method of loquat was resistant ability. Comprehensive comparison indicated that medium resistance germplasms accounted for larger proportion in the whole test strains. About10germplasms showed stable and strong resistance that means looking for disease-resistant materials is feasible. We found that disease-resistant material originated from different areas, and the resistance of wild resources was extremely higher than that of cultivars and red flesh germplasms had better resistance than the white flesh. That means plant disease resistance may be associated with long-term natural selection and differences of botany properties. Natural triploid loquat showed abundant resistance changes which could be new breeding source in future. The experiment also showed that loquat resistance has great relationship of tree vigor, management level, environment and climate.4.11fungicides indoor research showed that all kinds of fungicides could differently inhibit growth of strain "XZ-CQBB" under different concentration. Virulence regression equation and EC50values showed sensitivity and toxicity of fungicides to P. eriobotrifolia strains. Some traditional fungicides such as prochloraz, flusilazole, propiconazole showed significant inhibition, EC50values were0.0378mg/L,0.8732mg/L,1.6363mg/L. New type fugicides, like azoxystrobin, thiophanate-methyl also strongly inhibited the growth of strain. Comprehensive comparison of control effect infield, these fungicides’control efficiency were all50%. The experiment also showed that plant may have drug resistance of Carbendazim.