Abstract:

The determination of disease resistance of Casuarina clones to Pseudomonas solanacearum is subject to the variations of plant and bacterial materials, inoculation condition as well as rating method of disease severity. It was demonstrated in this study that the infected clonal ramets and excised twigs exhibited same wilting symptom and similar disease progressing pattern; their relative disease intensities were positively correlated under the same set of inoculum densities, but the ramets were more resistant. Among three types of excised twigs, the lignified brown had highest disease rating, followed by the partially lignified green, and the tender was least susceptible.The bacteria could be consistently cultured for at least 14 days without losing its virulence.While the disease severity of clones under sunshine, fluorescence or in shade were not significantly different, it increased as the inoculum density increased. It was suggested that using the excised brown twigs with relatively low or moderate inoculum densities inside laboratory to detect the bacterial resistance of Casuarina clones would be an efficient and reliable approach.

Key words: Casuarina clone, Pseudomonas solanacearum, Excised twig, Resistance determination