A Sampler to determine Available Guignardia citricarpa Inoculum on Citrus Leaf Litter

A sampler, the Kotzé-Quest Inoculum Monitor (K-QIM), was developed to determine the presence of dischargeable ascospores of Guignardia citricarpa, the causal agent of citrus black spot, on citrus leaf litter in the laboratory. Natural leaf litter from Eureka lemon and Valencia orange was rinsed and submerged in tepid water, secured between plastic grids and placed in the K-QIM. Different conditions for submerging leaves at 30, 35 and 40 °C for 5, 10 and 20 min were compared. After the 2-h K-QIM operation, dischargeable spores deposited over a 30 mm area of a silicone-coated microscope slide, were counted with a compound microscope. Effective capturing of ascospores was achieved from both Eureka lemon and Valencia orange leaf litter. This is the first sampler designed to capture fungal spores directly from plant material without environmental influences and it can be applied to establish the potential inoculum load available of G. citricarpa on a specific time or during a season.