Pathogenicity of novel Monosporascus species in accessions of four melon botanical groups

The Monosporascus root rot and vine decline (MRRVD) can be caused by the fungal species Monosporascus cannonballus and M. eutypoides. The Monosporascus species recently described in Brazil (M. brasiliensis, M. caatinguensis, M. mossoroensis, M. nordestinus and M. semiaridus) are potentially causal agents of the MRRVD. This work was made to evaluate them comparing to M. cannonballus pathogenicity, and to evaluate melon accessions reaction in four botanical groups of melon. MRRVD was evaluated by the severity of the damages in the roots and by the root dry matter reduction index (RIDM). On average, the studied species caused damage to melon accessions. After all, only M. brasiliensis, M. caatinguensis and M. nordestinus were virulent according to the accessions evaluated (A-16, C-32 syn. Pat 81, Goldex and HBJ), i.e., accession-species interaction occurred, and among them, M. caatinguensis was the most virulent. The accession A-16 (acidulus group) showed higher resistance (<10 % of root dry mass loss) to M. cannonballus, M. caatinguensis and M. nordestinus. The accession C-32 was susceptible to M. caatinguensis and moderately resistant to the others. The accession A-16 was the most promising one and can be used as a donor of resistance alleles or as a rootstock.