Pathogenicity of a Psychrotolerant Fungus Monilinia laxa in Prunus armeniaca L. Plantations of Intramontane Dagestan

Abstract

A comprehensive study of brown rot causal agents of Prunus armeniaca L. has been first carried out in plantations of Intramontane Dagestan located along the altitudinal gradient (690–1130 m above sea level (a.s.l.)). Pure cultures of Monilinia spp. have been isolated from symptomatic shoots and fruits. Species identification based on morphological, cultural, and molecular-genetic characteristics has revealed the dominance of a single species, Monilinia laxa (Aderh. & Ruhland) Honey. The temperature limits for the growth of Dagestan M. laxa isolates are determined as 0–32°C, with the optimum at 24–26°C. The maximum level of conidiogenesis is observed at the temperature drop to 12–16°C. Isolates collected at the altitude of 1070–1130 m a.s.l. exhibit higher growth rates at low temperatures (0–8°C) compared to isolates from 690 m a.s.l. All isolates demonstrate high pathogenicity towards fruits (especially stone fruits) and moderate pathogenicity on shoots at optimal temperatures. Pathogenicity remains high at 10°C and moderate at 3–5°C, with the necrosis expansion rate being significantly higher in high-altitude isolates (0.11–0.16 cm2 day–1). Given the responsiveness of M. laxa to even slight temperature increases, its aggressiveness is expected to rise under current climate change trends. An insignificant increase in the frequency and duration of droughts will not provide the infection severity reduction, since the primary driver of aridization is an increasing evapotranspiration during a minor increase in precipitation. The potential of the endophytic bacterium Paenibacillus sp. and the mycoparasitic fungus Trichoderma atroviride as biocontrol agents for the brown rot management has been demonstrated.