New insights into the infection process of Rhynchosporium secalis in barley using GFP

Through the use of a Rhynchosporium secalis isolate transformed with the green fluorescent protein gene and LASER scanning confocal microscopy (LSCM), fungal development during the R. secalis/barley interaction was analysed. Each infection stage was investigated from 0.5 h to 14 days post-inoculation (p.i.) with extensive sampling within the first 48 h p.i. Early germination events were observed that had not been previously described. A specific time of germination was noted, with germ tube formation appearing as early as 1 h p.i. Conidia were observed within anticlinal grooves of epidermal cells and the formation of bubbles within these pectin-rich regions was observed within 24 h p.i. The study reports R. secalis pectinase production and suggests degradation of these pectin-rich regions. Reactive oxygen species were present during early penetration, 3 h p.i. and co-localised with fungal development. LSCM allowed the visualisation of fungal growth deep within tissues at the later stage of the infection.