Etiology And Control Of Walnut(Juglans Regia) Leaf Spot Caused By Phoma Herbicola

A new walnut disease occured recent years in Yichang City, Hubei province:leaf spot of Juglans regia, this disease has some impact on yield and quality of walnut and reduces the economic effect of walnut growing. In this paper, the pathogen of J. regia leaf spot was identified based on etiology and biological characteristics of the pathogen, the pathogenicity to different cultivars of walnut, the indoor screening of pesticides that cause the inhibition of mycelial growth and spore germination and the control efficiency of different pesticides applied in different ways were also studied. The above study provide theoretical basis for further understanding of the disease and drawing up of cultivation measures. The results are as follows:Leafs and stems had typical symtoms were collected from J. regia fields in Yichang city, Hubei province. Regular pathogen-isolation method was used and Phoma sp. isolates were obtained. When fungal plugs or conidia suspensions were inoculated on healthy leaves of J. regia, black spot symptom was seen obviously after a few days on all leaves. According to the size and other descriptions of the colony, NaOH test, pycnidia and conidia of the isolate, the pathogen was identified as Phoma herbicola with reference to Phoma identification manual. The ITS sequences of the isolate Phol was obtained and being compared with sequences in GenBank, the result showed that it had similarity at98%with accession No. FJ827141Phoma sp.BJ-CH-2008, and E-value was zero. After the construction of the phylogenetic tree of the ITS sequences, it was confirmed that the isolate had the nearest genetic distance and were clustered together with some species of phoma sp.The biological characteristics of isolate Phol which induced the leaf spot of J. Regia was also studied. Its mycelia could grow in temperatures between5℃and35℃and in pH between4and11,while25℃and pH at5were the best conditions. In the test of utilization of nitrogen and carbon sources, results showed that mycelial could grow the fastest in lactose and KNO3and grow the slowest in starch and NH4Cl.Cultivar resistance was tested indoor by inoculating mycelial plugs of P. herbicola on leafs of different cultivars of J regia. Among8tested cultivars, xiang ling, present No.2and luhe were moderate resistant cultivars, liaoheNo.2and shennongjia wild walnut were susceptible cultivars, present No.3, liaohe No.1and present No.1were highly susceptible cultivars. In the test of inhibition effect for mycelial growth and spore germination of P. herbicola in vitro, eight fungicides were used, the result showed that5%Validamycin A SP and70%Thiophanate-Methyl WP had respectively the highest inhibitory effect with EC500.5825μgml-1and0.0282μg ml"1.5%Validamycin A SP and70%Thiophanate-Methyl WP were used for indoor prevention test, the result showed that, the control efficiency of70%Thiophanate-Methyl WP was higher than5%Validamycin A SP, control efficiency when pesticide sprayed before mycelial inoculating was higher than when mycelial was inoculated before pesticides were sprayed.