ASSOCIATION OF FUSARIUM SOLANI WITH ROLABC AND WILD TYPE TROYER CITRANGE
S. Spina, V. Coco, A. Gentile, A. Catara, G. Cirvilleri
To determine if rolABC genes of Agrobacterium rhizogenes could modify the susceptibility of Troyer citrange to dry root rot, conidial suspensions of a Fusarium solani strain isolated from citrus roots (PVCT1A) were used in cutting, leaf midrib and root inoculation assays of wild type (wt) and rolABC Troyer citrange. In all assays, the pathogen was reisolated equally well from wt and transformant. Interveinal chlorosis, wilt and defoliation of inoculated cuttings and leaf midribs, observed both in rolABC and wt, were more severe in transgenic lines. Two months after root inoculation with the pathogen, root weight was significantly reduced in transgenic lines. No root rot symptoms were observed on rolABC or wt lines, but wilting was more severe on wt. Cell-free fungal culture filtrate induced leaf wilt and defoliation within 10 days from immersion in the filtrate, without any significant difference between rolABC and wt lines. Scanning electron microscopy observations of infected roots showed that fungal penetration and colonization was similar in both lines. Evidence is presented that F. solani colonizes Troyer citrange tissues even in absence of visible symptoms and without differences between wt and rolABC lines.