Imaging the invasion of rice roots by the bakanae agent Fusarium fujikuroi using a GFP-tagged isolate

Fusarium fujikuroi (teleomorph Gibberella fujikuroi) is the main seed-borne pathogen of rice, the causal agent of bakanae, a disease that in the last years has become of increasing economical concern in many Italian rice growing areas. A virulent F. fujikuroi isolate was tagged with the green fluorescent protein (gfp) gene using Agrobacterium tumefaciens mediated transformation, and the virulence of the GFP isolate has been confirmed. Little is known about the early interaction of the pathogen with its host, in this work fungal development during the F. fujikuroi/root interaction was analysed by Laser Scanning Confocal Microscopy (LSCM), by using the GFP isolate obtained. The infection of rice roots was investigated from 48 h to 8 days post-inoculation both in resistant and susceptible cultivars. Roots of resistant genotype seem to trigger a hypersensitive response at the infection site and LSCM analysis of root sections allowed the visualization of fungal growth within host tissues. Fungal growth occurred both in the resistant and the susceptible cultivar, even if it was less abundant in the resistant one. Expression analysis of Chitinase1, a gene involved in fungal pathogenesis, was investigated by qPCR on the F. fujikuroi infected rice roots. Chitinase1 expression increased greatly upon infection in the resistant cultivar Selenio.