The fungus Monosporascus cannonballus is an important melon root pathogen in the Northeast of Brazil, where it causes a disease called collapse. As information on population levels of M. cannonballus ascospores in Brazilian soils does not exist, this study aimed to compare ascospore density between soil samples of 15 non-cultivated areas of the Caatinga and 15 soil samples of melon producing areas in the States of Rio Grande do Norte and Ceará. Ascospores of M. cannonballus were detected in all soil samples analyzed. The density of the ascospores varied from 0.18 to 18.30 ascospores.g-1 of soil in non-cultivated Caatinga soil. Ascospore density in areas cultivated with melon varied from 0.50 to 26.04 ascospores.g-1 of soil. There was no significant statistical difference (P=0.05) in the ascospore average density between cultivated and non-cultivated soil. Among the cultivated areas, the ascospore average density was significantly higher in the areas with a history of collapse caused by M. cannonballus when compared with areas without a disease history. There is evidence that M. cannonballus was not introduced in Brazil by propagation material, but is possibly a natural inhabitant of non-cultivated soils of Caatinga.
Cucumis melo L.; melon collapse; ascospore extraction; inoculum
