Characterization of Paramyrothecium roridum (Basionym Myrothecium roridum) causing leaf spot of strawberry

Strawberry plants showing symptoms of leaf spots and petiole lesions were collected from El Qalubya governorate, which is one of the most famous areas that extensively grows strawberry in Egypt. The objectives of this study were to isolate and characterize the causal pathogen of the disease. The isolated pathogen was identified as Paramyrothecium roridum (formerly known as Myrothecium roridum) based on its morphological characteristics and sequencing the partial rDNA internal transcribed spacer (ITS). A pathogenicity test using detached leaf assay revealed that P. roridum is a potential pathogen of strawberry. Symptoms started as small necrotic areas which expanded rapidly to macerate whole leaflets and petioles. In advanced stages of infection, dark olive green sporodochia were clearly distinguished on the infected tissues. Six strawberry cultivars showed different levels of susceptibility to P. roridum. Florida was the most resistant cultivar while Beauty, Camarosa, Fortuna and Sweet Charlie were susceptible. Festival showed a moderate level of susceptibility. An in vitro assay on the effect of the liquid culture filtrate of P. roridum on strawberry leaves showed that the filtrate caused damage to tissues and clear necrotic symptoms were developed. High performance liquid chromatograph (HPLC) analysis on the filtrate of 10 day old P. roridum culture revealed the presence of various mycotoxins. The two major toxins detected were 8-alpha-hydroxyroridin H and myrothecin A in addition to other trichothecenes. Data also revealed the capability of P. roridum to produce polygalacturonase (PG) and cellulase (Cx) enzymes in liquid cultures. The activity of PG was found to be significantly correlated with the age of the growth culture. This is the first record of P. roridum on strawberry in Egypt.