Disease Survey, Pathogen Identification And Disease Control Methods In Morella Rubra In Cixi, Zhejiang Province

Red bayberry(Myrica rubra Seib.&Zucc.) is a specialty fruit tree in China, with high economic importance. Red bayberry native in Yuyao and Cixi, Zhejiang Province, and now is planted in southern provinces of China. Diseases such as dead branches, leaf loss, fruit rot, and even tree death are often observed in red bayberry trees. However, little is known about these diseases. In order to effectively control diseases and guarantee healthy growth of red bayberry, it is essential to understand the diseases and the causal agents.During the disease survey, a stem disease-" Red bayberry canker" which causes the stem death is observed in the region. The disease incidence of this disease is38.3%, of which13.2%are severer,25.1%are less severe. Koch’s postulation was fulfilled to determine the pathogens. The pathogenic isolates were identified as Pseudomonas syringae pv. myricae by the morphological and165rDNA sequence analyses. Through the toxicity measurement during lab trials, streptomycin was found to be the top effective fungicide against P. syringae pv. myricae. During the field experiments, streptomycin exerted the best control efficacy against the canker disease with the disease recurrence rate of8.3%. Through the screening of bio-control bacteria against P. syringae pv. myricae, one strain YZF3was found to exert the highest bacteriostatic effect, which is the same as streptomycin. Based on the morphology and16S rDNA sequence analysis, YZF3is tentatively identified as Streptomyces flavotricini.There are reportedly several kinds of arbutus fungal disease. A survey of diseases on red bayberry was conducted in Cixi, Zhejiang Province in2011.’Red coat disease’, with the incidence rate of31.7%, among which7.5%is the most serious, causes the red spot in basis of trunks.However, it barely causes trees to death. Typical symptoms often observed in leaves were red to red-brown necrotic lesions on the leaf tips or margins. Three strains were isolated from the leaf lesions, of which2strains were identified as Pestalotiopsis sydowiana and Pestalotiopsis disseminata respectively on the basis of morphological characteristics and analysis of rDNA of internal transcribed spacer (ITS). Another disease observed in leaves was anthracnose. Six strains were obtained, and were identified as Colletotrichum gloeosporioides based on ITS analysis. However, the colony morphology between them was different. Two of strains were identified as Colletotrichum gloeosporioides using the species specific primers. In this study,4strains were isolated from rotting fruit and identified as Penicillium citrinum, Aspergillus clavatus, Trichoderma sp. and Botryosphaeria dothidea. Other diseases caused by unknown causal agents have also been found in this study, such as:1) A leaf disease with50%incidence rate demonstrated leaf chlorisis, and mainly distributed on tender branches. Neither fungi or bacteria have been isolated, so it is not fungal or bacterial disease.2) Only one tree was found totally dead without fungal or bacterial infection.3) Cortex of branches was found cyclic cracking but without fungal or bacterial infection.4) Green algae was found in the leaves under shadow.