Abstract:

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．Malicolaisolates by ironing wound，the small canker were developed and conidiomata were formed 8～9 days after inoculation on aDpie cuhivar‘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．

Key words: Malus pumila, morphologic characteristics, rDNA&mdash, ITS, pathogenicity