ISHS Acta Horticulturae 658: I International Symposium on Rootstocks for Deciduous Fruit Tree Species
SIMPLE EXCISED TWIG ASSAY OF MALUS SPECIES FOR DETERMINING RESISTANCE TO VALSA CANKER |
| Authors: | H. Bessho, S. Komori, J. Soejima |
| Keywords: | Malus, Valsa canker, disease resistance, excised twig assay, inoculation condition |
| Abstract:
Valsa canker is the most economically important wood rot disease of apple in Japan. A simple excised twig assay for determining resistance to Valsa canker was developed. Dormant shoots were cut into 80 mm lengths. The center of each twig segment was burned with a soldering iron. A piece of agar with actively growing Valsa ceratosperma was inoculated onto the burned part of the twig. Twig segments were incubated in 100ml plastic containers with cotton containing moisture. After 5 to 7 days incubation, the length of the necroses were measured. Several factors associated with lesion development of Valsa ceratosperma were examined. Lower moisture content in the container accelerated the development of lesions. Optimum moisture content in the container was 1 ml for determining the resistance to Valsa canker. The burning time of the twig segments using the heated iron also affected lesion length. Optimum burning time was 5 sec to determine the resistance. Lesion length was longer on 1-year-old shoots than on 2-year-old shoots. The susceptibility to canker of twigs cut from the base of shoots was lower than that of those cut from the top of the shoots. The simple excised twig assay was used to evaluate Valsa canker resistance of several Malus species. Most of apple cultivars belonging to M. x domestica were considered to be susceptible to Valsa canker. Most of genotypes belonging to M. baccata, M. sieboldii, M. fusca and M. prunifolia were resistant to Valsa canker. | |
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