Identification Of Citrus Succosa Anthrancnose And Its Control

Bendizao mandarin (Citrus succosa Hort. ex Tanaka) is an excellent local citrus species with characteristics of stuitable taste of sweet, little sour, juicy, and ready to be processed for canned orange petals. It is popular in Taizhou, Zhejiang, China. However, anthracnose is one of the important diseases of bendizao mandarin. It affects mainly fruits, causes the loss of fruit yield and quality. A few research on anthracnose of Bendizao mandarin has been carried out so far. In this study,59isolates of Colletotrichum sp. were obtained from the bendizao mandarin fruits showing anthracnose-like symptoms. The pathogenic fungal species was identified based on both morphological and molecular characteristics, Resistant frequency to Thiophanate-Methyl of C. gloeosporioides population from different regions in Taizhou was assayed, in vitro toxicity against C. gloeosporioides and the field controlling effects of six fungicides were studied.. The results were followed:1. In total,59Colletotrichum iolates were obtained, they could be designed as Group A and Group B based on the characteristics of isolate’s colony. Group A (36isolates) formed white or gray-white colony, produced orange conidial mass in the later stage. Group B (23isolates) formed white to gray-white colony, which turned to black the culture period extended. Conidial mass was not obsevered on colony of group B. The conidia of both Groups were oval to short cylindrical shape, single-cell, collour-less with a size of12to18.9μ,×3～8.9μm. Pathogenicity test indicated that both Groups were pathogenic to citrus fruits, caused100%inoculated fruits infected. A fragment of about500bp was amplified from all islates by using the C. gloeosprioides-specific primers Cglnt/ITS4, but no fragment could be obtatined by using C.acutatum-speccific primers Calnt/ITS4. ITS sequence was amplified from one selected isolates by using the general primer ITS4/ITS5and sequences. It is99%identical to that reported for C.gloeosprioides (JQ580528.AJ301988.1). Collectively, we concluded that the causal agent of anthracnose of Bendizao mandarin is C. gloeosprioides.2. Resistance to Thiophanate-methyl of these59isolates were tested by the method of distinguishing dosage method. The results showed that12strains isolated of14isolates (86%) from Sanjian farm in Jiaojiang district were resistant to thiophanate-methyl. All45isolates from Huangyan were thiophanate-methyl-resistance.3. In vitro toxicity of six fungicides are tested by using the mycelial growth rate. The results showed that the half maximal effective concentrations (EC50) for pyraclostrobin, azoxystrobin, prochloraz, pyraclostrobin· me-tiram, Thiophanate-Methyl and iprovalicarb in inhibiting the mycelial growth of C. gloeosporioides were0.81,2.58,0.066,4.97,1555.15and237.98μg/ml, respectively. While the EC50in inhibiting for pyraclostrobin, azoxystrobin, prochloraz and pyraclostrobin· me-tiram in inhibiting the spore germination were0.93,14.34,4.47and5.29μg/ml, respectively.4. The field controlling experiments of fungicides pyraclostrobin· me-tiram60%WG, pyraclostrobin25%EC, iprovalicarb70%WP, azoxystrobin25%SCand prochloraz25%EC, in controlling Bendizao mandarin anthracnose were conducted in2011and2012. The results showed that the controlling efficiencies of azoxystrobin, prochloraz, iprovalicarb and pyraclostrobin· me-tiram with the recommended concentrations on citrus anthracnose were all above95%. the controlling efficiencies in2012was less than2012, the trend is consistent with each other, suggesting that azoxystrobin, prochloraz, iprovalicarb and pyraclostrobin· me-tiram is effective in controlling Bendizao mandarin anthracnose.