Resistance in melon to Monosporascus cannonballus and M. eutypoides: Fungal pathogens associated with Monosporascus root rot and vine decline

The fungal species Monosporascus cannonballus and M. eutypoides have been described as the causal agents of Monosporascus root rot and vine decline disease (MRRVD), which mainly affects melon and watermelon crops. Resistance to M. cannonballus has been reported in some melon cultivars (ssp. melo). Moreover, melon ssp. agrestis accessions have proven to be better resistance sources. This is the case of the Korean accession ‘Pat 81’, highly resistant under field and artificial inoculation. The objective of the work here presented was the evaluation of the resistance to MRRVD of different accessions representing the variability of Cucumis melo ssp. agrestis, against both, M. cannonballus and M. eutypoides, in a multiyear assay under different infection conditions. In general, M. eutypoides was less aggressive than M. cannonballus in the different environmental conditions. There was a strong influence of temperature on MRRVD, with more severe symptoms with higher temperatures and with variable effect of infection on plant development depending on the fungal species considered. Resistance to MRRVD has been confirmed in ‘Pat 81’ and in its derived F1 with a susceptible Piel de Sapo melon. Among the new germplasm explored, African accessions (both wild agrestis and exotic cultivated acidulus) showed good performance in artificial inoculation assays and in field conditions. These sources do not present compatibility problems with commercial melons, so they can be introduced in backcrossing programs. The accession assayed of the wild relative Cucumis metuliferus, also resistant to Fusarium wilt and to root‐knot nematode, was highly resistant to MRRVD. The interest of this accession mainly relies in its advantages as a rootstock for melon. Roots scanned for the WinRhizo root image analysis system (2015 artificial inoculation assay). For each genotype three roots representative of each treatment, the non‐inoculated control, the inoculation with Monosporascus cannonballus and the inoculation with M. eutypoides, are provided.