Variations in the Molecular and Physiological Characteristics and the Virulence of Monilinia fructicola, M. fructigena and M. laxa Isolates

Twenty-three Monilinia isolates of various origin were identified and compared by morphological means and by biomolecular protocols based on random amplified polymorphic DNA (RAPD) analysis, and on PCR detection by species-specific primer pairs. The identification of most Monilinia isolates by PCR and RAPD confirmed the identification by morphological criteria, although two isolates initially identified as M. fructigena by morphological means were attributed to M. fructicola by the biomolecular techniques. Monilinia isolates were also compared in terms of their in vitro pectolytic activity and isoenzyme patterns. All the isolates produced polygalacturonase and pectin methylesterase, but pectin lyase activity was found only in M. fructicola and M. fructigena, and not in most M. laxa isolates. The Monilinia isolates differed significantly in their isoenzyme patterns. Based on RAPD-PCR and PCR amplification and pectolytic isoenzymes, the isolates analysed clustered in three major groups, each corresponding to a Monilinia species. Artificial inoculations in peach and pear fruits revealed differences in virulence between the Monilinia species and within isolates. No correlation was found between the amount of pectolytic enzymes produced in vitro and virulence. Variations between and within the Monilinia species may depend at the physiological level on variations in the isoenzyme patterns of the pectolytic enzymes

Involvement of Olpidium bornovanus and O. virulentus in the occurrence of melon root rot and vine decline caused by Monosporascus cannonballus in central Italy

[EN] Monosporascus root rot and vine decline (MRRVD), caused by Monosporascus cannonballus, has become one of the most important diseases of melon worldwide. Recent evidences suggest that M. cannonballus is not the sole cause of MRRVD, but other pathogens, Olpidium spp. and Melon necrotic spot virus (MNSV) are also involved. The aim of this study was to ascertain the potential concomitant involvement of these pathogens in the development of MRRVD of melon in Central Italy analyzing a soil sampled from a greenhouse with a known history of this disease. O. bornovanus and O. virulentus along with M. cannonballus were identified from the sampled soil. Bait melon plants grown in the contaminated soil were colonized by both Olpidium species and by M. cannonballus, showing roots browning and foliage wilt. No infection by MNSV was detected in bait plants. In the tripartite pathogenicity test, O. bornovanus alone was found to be a virulent pathogen, capable of colonizing roots with a high percentage of colonization intensity, resulting in root browning and foliage wilting. Both disease severity and intensity of Olpidium colonization determined by the co-inoculation of ascospores of M. cannonballus and Olpidium spp. were statistically similar to that resulted by Olpidium or by ascospores separately inoculated. Root symptoms were accompanied by a gradual vine decline and foliage wilting. Root rot and vine decline, which was previously attributed in Central Italy primarily to M. cannonballus, needs to be reattributed, since O. bornovanus and O. virulentus are also involved without apparent synergistic effect among the pathogens.The research was supported by the Department for Innovation in Biological, Agro-food and Forest systems (DIBAF), Viterbo, internal grant. Part of the research was performed by Diana Martignoni within the Lifelong Learning Programme (LLP) - Erasmus Staff Training Work Programme at the Instituto Agroforestal Mediterraneo, Universitat Politecnica de Valencia, Valencia, Spain.Aleandri, M.; Martignoni, D.; Reda, R.; Alfaro Fernández, AO.; Font San Ambrosio, MI.; Armengol Fortí, J.; Chilosi, G. (2017). Involvement of Olpidium bornovanus and O. virulentus in the occurrence of melon root rot and vine decline caused by Monosporascus cannonballus in central Italy. JOURNAL OF PLANT PATHOLOGY. 99(1):169-176. doi:10.4454/jpp.v99i1.3787S16917699

Fungi associated with root rot and collapse of melon in Italy

Melon represents the most widespread cucurbit in Italy. In recent years melon has been subjected to significant losses in yield and quality due to an increasing number of soil-borne fungal diseases. The collapse of melon, caused by a complex of fungal pathogens, including Monosporascus cannonballus, Acremonium cucurbitacearum, Plectosporium tabacinum and Rhizopycnis vagum, represents one of most destructive diseases worldwide. The purpose of this study was to determine the occurrence of collapse throughout melon-producing areas in Italy in recent years, to verify the identification of isolates collected, and to test their pathogenicity on melon and other cucurbits. Several fungi were isolated from symptomatic roots of melons in the Italian production areas. The identification was supported by PCR with a species-specific primer and DNA sequence data. RFLP and sequence analyses showed the existence of a substantial homogeneity among Italian M. cannonballus isolates. Given the self-incompatibility of these isolates it is impossible to ascertain vegetative compatibility groups (VGC) and consequently genetic relatedness cannot be studied. The frequency of isolation of fungal species varied with geographic locations, M. cannonballus being present mainly in Central Italy, while A. cucurbitacearum and P. tabacinum were most common in Apulia. In pathogenicity tests under greenhouse conditions M. cannonballus, A. cucurbitacearum and P. tabacinum caused collapse symptoms and root rots, whereas R. vagum was found to be a weak pathogen