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.

Macrophomina phaseolina is the causal agent of charcoal rot disease of melons and causes significant losses worldwide and causes significant losses worldwide The use of resistant cultivars is a desirable method for controlling this disease, but there is no information about the influence of temperature on the resistant behavior found in melon accessions. The purpose of the present study was to assess the effect of temperature on the reaction of six melon accessions selected previously for their resistant response to M. phaseolina. They were inoculated with the M. phaseolina isolate CMM-1531 and grown under accurately controlled environmental conditions at different temperature regimes (25, 28, 31, and 34 ºC) in a replicate experiment. The increase in temperature increased the severity of symptoms in most genotypes, but this effect was less pronounced in the highly susceptible control, the cultivar 'Piel de sapo', and in the most resistant accession, the wild African agrestis Ag-15591Ghana 2 that remained resistant even at 34ºC. The use of several screening temperatures allowed a better characterization of accessions that behaved similarly as highly resistant at 25ºC (Con-Pat81Ko, Dud-QMPAfg, Can-NYIsr and Ag-C38Nig), but in which resistance breaking was observed with temperature rise. Temperatures of 28ºC and 31ºC were sufficient to make Dud-QMPAfg, Ag-C38Nig and Can-NYIsr moderately resistant, whereas Con-Pat81Ko remained highly resistant. All these genotypes were susceptible at 34ºC, which suggest that are not suitable for hot-climate growing areas. The most promising accession was Ag-15591Ghana, whose resistance was confirmed in two greenhouse experiments under stressful temperatures (>34ºC). The behavior of these sources should be confirmed in naturally infested fields, but the controlled screening methods presented here are essential to characterize new resistance sources and to conduct genetic studies when a high number of plants must be managed under controlled environmental conditions.

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‘Piel de Sapo’ is one of the most consumed market class of melons in the Mediterranean area and it represents an important economic crop in Spain. The ‘Mini PS’ melon breeding line, which bears two main introgressions from the dudaim ‘Queen’s pocket’ melon in the Piel de Sapo genetic background, was evaluated for its fruit quality traits in three environments. Some interesting commercial characteristics were detected, such as a notable decrease in the fruit weight and a rounder shape, compared with Piel de Sapo, while the other quality traits were not altered. Thus, this mini melon line, ideal as a personal melon, may be useful in the development of new melon cultivars.