Amylovorin-Induced Shoot Wilting: Lack of Correlation with Susceptibility toErwinia amylovora

Abstract

Amylovorin, a polysaccharide isolated from ooze produced on the surface of E. amylovora-infected apple and pear fruit, has no host-specificity and cannot be used to screen plant material for resistance to fire blight. The cut ends of excised shoots of Cotoneaster pannosa, Spiraea vanhouttei and 19 Malus pumila (apple) cultivars were placed in aqeuous solutions of amylovorin under controlled environmental conditions and observed for wilting for up to 12 h. There was no significant difference in the mean time required for wilting of C. pannosa and S. vanhouttei shoots, although only C. pannosa was susceptible to E. amylovora. When shoot tips (6 cm long) of apple cultivars were placed in amylovorin solution and evaluated hourly for degree of wilting, there were significant differences in mean wilt indices of the cultivars. However, the differences were not correlated with the susceptibility of the cultivars to infection by E. amylovora. Shoot flexibility of both C. pannosa and M. pumila shoots was significantly correlated with sensitivity to wilting after placement in amylovorin solutions.