Biological control represents a sustainable alternative that can be used to reduce the impacts of soilborne diseases in melon cultivation, which are major constraints to productivity. This study evaluated the effectiveness of four biological products formulated with Bacillus and Trichoderma species in suppressing symptoms caused by root pathogens in melon crops, including Fusarium spp., Macrophomina phaseolina, Monosporascus cannonballus, and Rhizoctonia solani. Two greenhouse experiments were conducted to simulate successive crop cycles using two naturally infested soils (A and B). Bombardeiro/Lastro, Quality^®, TrichobiolMax, and TrichonemateMax were applied using two management strategies: (1) a tray application 8 days after sowing (DAS) + four pot applications at 7-day intervals, totaling five applications, and (2) a tray application 8 DAS + two pot applications at 14-day intervals, totaling three applications. The yellow melon cultivar ‘Goldex’ was used in the experiments. Forty-five days after transplanting, the treatments showed statistically significant differences compared to the positive control (naturally infested soil without products), both in disease incidence and severity and in plant growth parameters. In Soil A, three applications of Quality^® and TrichobiolMax resulted in 50% and 60% disease incidences, respectively. In Soil B, five applications of Lastro and TrichobiolMax led to 60% of plants showing disease symptoms. These products also reduced disease severity in both soils, and TrichonemateMax showed potential for nematode control. Additionally, these products resulted in a 21% reduction in the frequency of Fusarium spp. in Soil A. These findings are valuable for developing sustainable practices in melon cultivation, promoting more efficient and environmentally sound management of root diseases.

Macrophomina phaseolina is a major phytopathogen linked to root rot and vine decline in melon plants in northeastern Brazil. Managing this pathogen is difficult due to its polyphagous nature and adaptation to the semi-arid conditions of the region. In this study, we inoculated 10 isolates each of M. phaseolina (Ph) and M. pseudophaseolina (Ps) onto two melon hybrids, 'Beloro' and ‘Natal RZ’, to assess their pathogenicity. Sixty days post-planting, we measured disease incidence (INC) and severity (SEV), shoot (SL) and root length (RL), fresh shoot and root weight (FSW and FRW), and dry shoot and root weight (DSW and DRW). The hybrid 'Beloro' exhibited a 100% INC across all tested isolates. The ‘Natal RZ’ hybrid showed INC ranging from 14.3 to 100.0%, with the Ph-A6P5 and Ps-A10P16 isolates causing no disease (INC and SEV of 0.0). Average SEV indicated that Ph isolates were more aggressive, causing severe damage to both 'Beloro' (4.58) and ‘Natal RZ’ (3.18), compared to Ps isolates, which showed lower severity scores in 'Beloro' (2.56) and ‘Natal RZ’ (0.70). Given the limited information on the pathogenicity of Ps in melon, further research is essential to determine the infectious potential of this fungus.