Colonization of Fusarium solani isolate in Troyer citrange seedlings

A research was carried out to investigate whether the association with the rolABC genes of A. rhizogenes could modify the susceptibility of Troyer citrange to Fusarium solani, the causal agent of dry root rot. F. solani strain 1A was inoculated in cuttings and leaves of Troyer citrange seedlings modified by rolABC genes and wild type (WT). Interveinal chlorosis of leaf, wilt and defoliation, observed both on rolABC and WT were more severe on transgenic line. Two months after root inoculation with the pathogen, root weight was significantly reduced in rolABC seedlings, but no root rot was recorded. F. solani was always reisolated from artificially inoculated cuttings, midribs and roots without differences between wild types and transgenic lines. The pathogen was never recovered from not inoculated plant tissues. Cell-free fungal culture filtrates induced leaf wilt and defoliation within 10 days from inoculation, without any significant difference between rolABC and WT shoots. Scanning electron microscopy (SEM) of infected roots, carried out at 3 and 6 days after inoculation, showed the penetration and colonization of the hyphae. Evidence is presented that F. solani infects Troyer citrange tissues without differences between wild type and transgenic lines in the early phase of colonization and in absence of visible specific disease symptoms. The tests here described could be used to evaluate rootstocks sensitivity to the pathogen.