Study On The Lesion Expansion Valsa Canker On Apple Tree And The Pycnidium Development Of Valsa Mali

Apple tree Valsa canker (Valsa mali var. mali) is one of the three kinds of importantapple tree disease, which is widely distributed in apple producing areas of China. With theapple cultivation area continues to expand, the disease has appeared five times ofepidemics in the country, which always cause destruction of many orchards, seriousproblems with our apple industry health and sustainable development. To understand thelesion expansion dynamics and the development progress of the pycnidium of the pathogenin different seasons is beneficial for the control disease. The above problems were studiedby means of artificial inoculation test in field and investigation in the laboratory. The mainresults are as follows:1) The time duration from artificial inoculation to a visible lesion (lesion radialexpansion to5mm) was variable in different seasons. The shortest time duration occurredin spring with average of7.7days, followed by10.2days in summer, and12.5days in fall.2) The expansion of lesions formed in different seasons had a common characteristic:all the lesions showed a rapid expansion process during the early stage of about2monthsand then the expansion of the lesion was very slow or nearly stopped for2-5months,another rapid expansion process would be seen again afterwards. The second rapidexpansion process would appear in spring or autumn no matter the artificial inoculationwas made in which season.3) The pycnidium development progress stages of Valsa mali var. mali can be dividedinto: pycnidium primordium, immature pycnidium, mature pycnidium and senescentpycnidium, and establish a method for rapid identification by naked eyes.4) In the field, the lesion of apple tree Valsa canker formed in different growingseasons will produce pycnidium within one month after “symptom appearance”. Theshortest time duration occurred in summer, the same was for the formation of maturepycnidium. The lesion occurred in late October of autumn did not produce maturepycnidium until April of the following year.5) During the period from April to October, the lesions of apple tree Valsa canker willproduce mature pycnidia, these pycnidia can release conidia at any time in suitable condition. From November to March of the next year, the pycnidium on lesions developedquite slowly and the numbers on lesion was rather stable.