Preliminary results on the evaluation of the effects of elicitors of plant resistance on Chrysanthemum yellows (CY) phyto-plasma infection

Delay of syndrome development and of plant death has been used to evaluate the activity of 1) the arbuscular mycorrhizal fungi Glomus mosseae and G. intraradices, 2) the rhizobacteria Pseudomonas putida S1PF1, Pseudomonas aureofaciens 30-84 and Streptomyces sp. SB20, 3) chitosan and 4) benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester (BTH) as inducers of resistance against chrysanthemum yellows phytoplasma infection. While G. mosseae and P. putida S1PF1 slightly reduced the number of CY-infected plants and extended the life span of the affected plants, only 2.4 mM BTH provided some protection from the disease and a delay of the syndrome. Two concentration of chitosan (0.1 and 0.2%) dissolved in acetic or chloride acids were not effective, although some protection from the disease was present in plants sprayed only with acetic acid. Both acids induced phytotoxic effects on the daisy plants