Light and scanning electron microscopy studies on the infection of oriental lily leaves by Botrytis elliptica

Light, scanning electron and fluorescent microscopy were used to observe th e infection process of Botrytis elliptica on leaves of oriental lily (cv. S tar Gazer). At 20 degreesC and 100% relative humidity, conidia germinated o n both adaxial and abaxial foliar surfaces, but germ tubes failed to invade epidermal cells on the adaxial surface. On abaxial surfaces, short (< 20 m um) swollen germ tube appressoria penetrated through stomatal openings (19% ), through the epidermis near guard cells (52%), or directly through epider mal cells (29%). Esterase activity was detected on germ tubes and conidia a fter 6 h of incubation, and deformation of the cuticle on abaxial surfaces of lily was observed surrounding infection sites. By 3 h after inoculation, almost 70% of the conidia had germinated, but no penetration was observed. At 6 h after inoculation, almost one-third of germinated conidia had penet rated epidermal cells, and water-soaked lesions were associated with 20% of the penetrations. By 9 h after inoculation, approximately 60% of the germi nated conidia had penetrated plant tissues, and water-soaked lesions were a ssociated with 60% of the infections. Fluorescent microscopy with a specifi c fungal stain allowed assessment of successful infection and visualization of sub-epidermal hyphae. We conclude that penetration of abaxial foliar su rfaces of oriental lilies by B. elliptica occurs via short swollen germ tub e appressoria mostly near stomata.