Mycena citricolor isolates from diverse hosts in Costa Rica: Colony aspect, growth dynamics, reproduction in vitro and aggressiveness on Coffea arabica

Abstract

The basidiomycete fungus Mycena citricolor hosts on about 80 plant families. The asexual morph causes the disease known as American leaf spot of coffee (Coffea arabica). We isolated and characterized 15 isolates of M. citricolor collected from coffee plants, shade trees and weeds. Cultures on potato-dextrose-agar + yeast extract (PDAY) medium were kept for a week in complete darkness. The cultures were then exposed to light for 7 weeks and co-cultivated with coffee foliar discs, to stimulate the production of gemmifers. We evaluated the speed of growth, appearance, colour of the mycelium and gemmifers production capacity. All isolates conformed to the typical cultural characteristics of M. citricolor, with beige/white thin and slightly aerial mycelium. The whitest isolate was from Persea americana, which had the slowest growth rate in vitro (6.4 mm/day), while the isolate from weed Kalanchoe pinnata was the fastest, with a speed of 9 mm/day. The most gemmifer-producing isolates were those isolated from the coffee cultivar Catimor-Costa Rica 95, Citharexylum donnell-smithii and Cissus verticillata, with over 200 gemmifers per Petri dish. Isolates from Erythrina and Ipomoea nil produced <50 gemmifers on average. The Composite Aggressiveness Index (CAI) was determined on 2-year-old detached coffee branches of the Caturra variety foliage. The least aggressive isolate was from Erythrina poeppigiana (CAI = 0) and the most aggressive was from Kalanchoe pinnata (CAI = 18.87). The isolate from the coffee cultivar Catimor-Costa Rica 95 was more aggressive than that from the cultivar Caturra (CAI = 9.94 vs. CAI = 3.66). Moreover, successful infection occurred only when the apex of gemmae made direct contact with the coffee leaf when using the inoculum derived from C. verticillata and Anredera cordifolia. These results show the variability in the population of the pathogen. This is the first study that characterizes the growth, morphology, reproduction and aggressiveness of M. citricolor obtained from hosts other than coffee. In addition, it is the first to report the use of coffee foliar discs to induce gemmifer production in vitro and to assess and quantify the effect of gemma position when inoculating coffee leaves.