REACTION OF MELON GENOTYPES TO THE ROOT´S ROT CAUSED BY Monosporascus

Abstract

Monosporascus root rot and vine decline (MRRVD) is an important disease in the melon crop in Brazil. In our research, we evaluated the reaction of 45 melon genotypes to M. cannonballus in two successive cropping seasons in a greenhouse. Melon seedlings were transplanted into naturally infested soil. The evaluation of the genotypes was performed after 55 days, using a score scale to group each genotype into one of five classes and to calculate the disease severity index. None of the genotypes showed an immune reaction to M. cannonballus, regardless of the season. In the first cycle, only 28.9% ('AF 464', 'Auraprince', 'DRG 2278', 'Estoril', 'Guaporé', 'Kousto', 'Mabel', 'Magisto', 'Massaï', 'Nectar', '8530', 'RZ 34130' and 'RZ 34292') had a similar reaction to the high resistance to the MRRVD. Most genotypes (66.7%) behaved as moderately resistant while 4.4% were susceptible and none were highly susceptible. Conversely, in the second cycle, no genotype showed a reaction similar to high resistance while 42.2% behaved as moderately resistant, 48.9% as susceptible, and 8.9% as highly susceptible. The severity levels ranged from 7.5 to 60% and 27.5 to 92.5% for the first and second cycles, respectively. The genotypes 'DRG 2278', 'Estoril', 'Guaporé', 'Kousto', 'Mabel', 'Massaï', 'RZ 34130' and 'RZ 34292' were identified as highly resistant and moderately resistant in the first and second cycles of cultivation, respectively. Therefore, these genotypes are promising sources of resistance to M. cannonballus and should be preferred in commercial fields infested with the pathogen.

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

“…Another important look of this work is that the species have a different behavior due to accessions. Despite this, it was found that the species M. cannonballus , notoriously the agent of MRRVD worldwide (Sarpeleh 2008; Al-Mawaali et al 2013; Yan et al 2016; Markakis et al 2018; Sales Júnior et al 2019) and the novel species M. mossoroensis was the least virulent since none of the accessions was classified as susceptible to both species. Particularly, the accession A-16 was highly resistant to M. cannonballus , and of moderate or high resistance when inoculated with each of these species.…”

“…Consequently, the following classes of genotypes were separated. 0: like immune; 0.1-1.0: highly resistant; 1.1-2.0: moderately resistant; 2.1-3.0: susceptible; 3.1-4.0: highly susceptible (Sales Júnior et al, 2019). The RI DM was calculated by the following expression: RI DM = (DMc - DMi) / (DMc), where DMc: dry matter of access without inoculation (control) and DMi: matter access inoculated with one of the species.…”

“…Several works reported melon genotypes with moderate to high resistance to M. cannonballus (Salari et al 2012; Park et al 2013; Sales Júnior et al 2019). Some of them surveyed potential genotypes for melon breeding programs, for selection of melon genotypes (Park et al 2013) and pumpkin genotypes for root stocks (Ben Salem et al 2015a) and selection of resistant melon cultivars (Salari et al 2012; Sales Júnior et al 2019). These researches demonstrate the MRRVD genetic control is one of the best alternative solutions for controlling Monosporascus species.…”

Resistance in melon toMonosporascus cannonballusandM. eutypoides: Fungal pathogens associated with Monosporascus root rot and vine decline

“…Screening assays aimed at the identification of tolerance or resistance to collapse caused by M. cannonballus have been carried out in different conditions (Crosby, 2000a;Crosby, Wolff, & Miller, 2000;Esteva & Nuez, 1994;Sales Júnior, Senhor, Michereff, & Negreiros, 2019;Wolff, 1995;Wolff & Miller, 1998). However, very few resistance sources have been identified so far.…”

“…However, very few resistance sources have been identified so far. A recent screening of commercial melon cultivars under natural M. cannonballus-infested soils in Brazil has attributed the difficulty in identifying resistant sources to the aggressiveness of the pathogen (Sales Júnior, Senhor, Michereff, & Negreiros, 2019). The influence of the environmental factors in the expression of symptoms has also been reported as hindering the identification of resistance sources (Cohen et al, 2000;Fita, Picó, Monforte, & Nuez, 2008).…”