苹果树Valsa malicola的发现及其致病性研究

The Occurrence of Valsa malicola on Apple Trees and Its Pathogenicity

从苹果树腐烂病病斑上分离得到分离物,其在PDA培养基上菌落颜色为乳白色,30d未形成产孢体,在37℃高温下不能生长。在20%苹果树皮煎汁培养基(ABA)上于25℃培养6d即可形成大量微小(直径0.1～0.5mm)的产孢体,每皿(直径9cm)数量平均达140～250个。根据其在枝条上产生的有性型和无性型子实体的形态特征,鉴定为Valsa malicola Z.Urb.及其无性型Cytospora schulzeri Sacc.&P.Syd。进一步的ITS序列聚类结果也表明,陕西各分离株与美国和南非的V.malicola聚为一类。采用菌丝块接种烫伤的离体苹果枝条(秦冠、富士),发现其在伤口部位扩展缓慢、病斑面积很小,但8～9d后仍可形成大量产孢体,而常见的致病种V.ceratosperma形成的病斑面积很大,在接种后20d才能在接种枝条上形成产孢体。

Valsa canker is a distructive disease on apple trees and causes severe economic losses. Five isolates showing different colony color, as compared with common species of Valsa canker pathogen, were found in Shaanxi among 150 isolates from China. The colony color of the isolates on PDA were milk white and no growth under 37℃. A conidiomata was not found in the culture period （30 d） on PDA. But many small conidiomata were produced at 6 d on 20% ABA medium and yellow to brown cirrhi was secreted. There were about 140 - 250 conidiomata in one plate （diameter 9 cm） and the average size were 0.1 - 0.5 mm. The isolates were identified as Valsa malicola （anamorph C. schulzeri ） by fruiting body morphological characters, such as ascostromata and conidiomata. Furthermore, the ITS sequence analysis showed that 5 isolates from Shaanxi were clustered to the same group with V. malicola from USA and South Africa. After inoculating 2-year-old twigs with V. malicola isolates by ironing wound, the small canker were developed and conidiomata were formed 8 - 9 days after inoculation on apple cultivar ＇Qinguan＇ and ＇Fuji＇ The disease developed very slow, compared to that caused by V. ceratosperma, which developed much more faster and caused large, typical canker symptoms and produced conidiomata after 20 days after inoculation.