Effect of temperature on disease severity of charcoal rot of melons caused by Macrophomina phaseolina: implications for selection of resistance sources

Abstract

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.

Melon Genetic Resources Characterization for Rind Volatile Profile

“…The presence in this wild accession of high levels of monoterpenoids in contrast to the remaining accessions may be an interesting starting point for future studies about possible resistant/repellent responses against pests. This accession has been reported as resistant to soil pathogens [55,56], although to date no studies have focused on its behavior in relation to insects. Surprisingly, this wild PI 185111, with no good scent, also presented one of the highest levels for some acetates (6-nonenyl acetate) and ethyl esters (ethyl propanoate) in the collection (LSD test, p < 0.05, Supplementary Table S3), showing that non-cultivated types present more variability than expected and can have also high levels of some esters.…”

Grafting Snake Melon [Cucumis melo L. subsp. melo Var. flexuosus (L.) Naudin] in Organic Farming: Effects on Agronomic Performance; Resistance to Pathogens; Sugar, Acid, and VOC Profiles; and Consumer Acceptance

“…Regarding the incidence of fungi, global warming is favoring the increasing incidence of highly damaging fungi to melon (Cohen et al, 2012;de Sousa Linhares et al, 2020;Timmusk et al, 2020). M. phaseolina and N. falciformis were identified as major pathogens in snake melon NG plants.…”

“…Our inoculation studies confirm the worse response of snake melon, compared to Piel de Sapo sweet melon, to both pathogens, being highly susceptible to M. phaseolina and MR to N. falciformis. The former has been described as a main pathogen of melon worldwide, with recently available resistant sources (Ambrósio et al, 2015;Cohen et al, 2016;de Sousa Linhares et al, 2020) and the determination of the genetic control under study. The latter has been very recently reported for the first time as a melon pathogen in Spain (González et al, 2020b,c).…”

“…Symptoms started at 7 DAI and were severe at 15 DAI (Figure 2A). Average damage score was higher in snake melons than in the control sweet melon Piel de Sapo that has also proven to be susceptible to this disease (de Sousa Linhares et al, 2020). All the snake melon plants were dead after 30 DAI, while the mortality of the susceptible control Piel de Sapo was 20%.…”

“…The degree of susceptibility/tolerance of the snake melon cultivar against four of the most frequently isolated soilborne pathogens, the fungi Neocosmospora keratoplastica and Neocosmospora falciformis, recently detected causing Fusarium wilt in melon in Spain for the first time (González et al, 2020b,c), and M. cannonballus and Macrophomina phaseolina, previously reported to cause severe vine decline and charcoal root rot in melons (Castro et al, 2020;de Sousa Linhares et al, 2020), was evaluated. Isolates from Carrizales were used for Neocosmospora spp.…”