Abstract
The population structure of Monosporascus cannonballus, which causes vine decline in melons, was assessed based on the determination of mycelial compatibility groups (MCGs) in a collection of 58 isolates obtained from seven melon fields in three municipalities of Northeastern Brazil. For comparison, an additional 11 isolates of M. cannonballus from Spain were included in the analysis. MCGs were determined through comparisons of paired isolates growing on PDA culture media in the dark at 30oC in various combinations. The Brazilian isolates were a ssigned into four MCGs: MCG-1 (n = 35 isolates), MCG-2 (n = 20), MCG-3 (n = 2), and MGC-4 (n = 1). MCG-1 and MCG-2 included isolates from all surveyed areas. The Spanish isolates were assigned into six different MCGs, and none of them were compatible with the Brazilian isolates. The genetic structure was determined using the frequencies of MCGs and genotypic diversity indices. The maximum genotypic diversity was 6.9 and 54.5% for the Brazilian and Spanish populations, respectively. The low level of genetic diversity in the M. cannonballus population from Northeastern Brazil suggests that breeding melons for disease resistance may be a promising strategy for the region.
Highlights
Monosporascus cannonballus Pollack and Uecker (Ascomycota: Sordariales) is a destructive root pathogen that causes vine decline in melons (Cucumis melo L.) and watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai) in arid, semi-arid and subtropical regions worldwide
Two areas were located in the municipalities of Icapuí and Quixeré in Ceará State (Table 1), and five areas were located in the municipality of Mossoró in Rio Grande do Norte State (Table 1)
After pairing the M. cannonballus isolates on PDA, two types of mycelial interactions were observed: intermingling mycelia, where the two colonies grew together with a uniform surface, which was typical of a vegetative compatibility reaction; and a barrage zone formed as a result of the interaction between the colonies, considered a vegetative incompatibility reaction (Figure 1)
Summary
Monosporascus cannonballus Pollack and Uecker (Ascomycota: Sordariales) is a destructive root pathogen that causes vine decline in melons (Cucumis melo L.) and watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai) in arid, semi-arid and subtropical regions worldwide Monosporascus cannonballus Pollack and Uecker (Ascomycota: Sordariales) is a destructive root pathogen that causes vine decline in melons (Cucumis melo L.) and watermelon (Citrullus lanatus (Thunb.) Matsum. 2011; COHEN et al, 2000; MARTYN; MILLER, 1996; PIVONIA et al, 2010). The disease symptoms include yellowing, the death of the crown leaves and a gradual decline of the vine as the plant approaches maturity. Monoporascus cannonballus produces perithecia with ascospores that are present on the affected roots by the end of the cropping season (MARTYN; MILLER, 1996). In 2002, M. cannonballus was first detected in Northeastern Brazil, causing root rot and vine decline in melon plants (SALES JÚNIOR et al, 2004). The disease is widespread in this region (SILVA et al, 2010), which accounts for 85% of Brazilian melon production and covers approximately 14,900 ha. The primary producing areas are located in Ceará State (CE), which covers 4,880 ha and produces 124,000 ton, and Rio Grande do Norte State (RN), which covers 6,806 ha and produces 192,100 ton. (IBGE, 2010)
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