Study on Crown Rot of Strawberry in thailand

Abstract

During 1992-1993, Strawberry (Fragaria x ananassa Duchesne) crown rot of cultivars Tioga and Florida 90 were observed and collected at the fruit production fields in Chiang Mai province (Mae Rim and Samoeng District) and Chiang Rai province (Mae Sai District). Infected plants were studied the symptom and ioslated in laboratory. Potato dextrose agar (PDA) medium for isolating general fungi, selective medium N5ARP (cornmeal agar amended with 5 ppm nystatin, 250 ppm sodium ampicillin, 10 ppm rifampicin and 100 ppm PCNB) and RNV (cornmeal ager amended with 500 ppm sodium ampicillin, 10 ppm rifampicin, 10 ppm benomyl, 25 ppm PCNB and 50 ppm nystatin) for isolating pythiaceous fungi were used. The infected plants, after being planted in fruit production fields, grew normally for some time, then wilted suddenly and died. A reddish brown, firm rot or reddish brown streaking occured in portions of the interiors of crowns of wilted plants. Isolations of the fungi with PDA medium from crown rot, the predominant fungal genera were Colletotrichum and Fusarium, the frequency of Colletotrichum associated with crown rot tissue were high. Isolations of the fungi from crown rot and root with N5ARP medium, predominantly without fungal growth but found some collectotrichum and Pythium. Whith RNV medium, either no fungal growth but also found some Pythium. Pathogenicity tests of the fungi isolated from crown rot, Colletotrichum 3 isolates on strawberry cv. Tioga confirmed the pathogenicity of Colletortrichum. the methods were plant spray with condidial suspensions and putting mycelial disc on the side of unwounded stem tissue. Some morphological studies of Colletortrichum, the causal organism of strawberry crown rot was Colletotrichum gloeosporioides (Penz.) and Sacc.