Powdery mildew is one of the main diseases of cantaloupe in México and in the Comarca Lagunera, since it can cause losses in yield up to 50%.
The objectives of the present work were: the identification of the fungus which causes powdery mildew in cantaloupe and to determine if this fungus has physiological races in the Comarca Lagunera.
Inoculum collection was done by direct sampling in the field, in the main cantaloupe production areas of the Comarca Lagunera. The inoculum was kept in plants of the cantaloupe variety Top Mark, which is susceptible to this disease. In the identification of the causal agent, three morphological characteristics of the asexual phase of the fungus were taken into account: the production or not of conida in chains, presence or absence of fibrosin bodies in the conidium and the germination of the conidium (simple or bifurcate).
Some simple conidiophores not branched were observed, they were hyaline, erect, relatively short with several conida in chains. The number of conidia varied from 7 to 11 with an average of 8 conidia by conidiophore. The conidia were hyaline, elliptical and all of them presented cylindric fiber bodies, which were straight or curved. The germination of the conidia was relatively low, since only 72 conidia germinated out of 1,163. Out of these 72 germinated conidia on 1 y 2 had a bifurcated germination. The above observed characteristics are typically of Sphaerotheca fuliginea, therefore it is concluded that the causal agent of powdery mildew in the Comarca Lagunera is Sphaerotheca fuliginea. Since Top Mark and PMR‑45 were susceptible and PMR‑6 and Edisto 47 were resistant to the inocolum collected in the field, it is possible to conclude that race 2 is present in the area. Since there is not a genotype resistant to race 2 and susceptible to race 1, it is not possible to assure that race 1 is not present in the area. Race 2 is present in all the sampled cantaloupe fields of the Comarca Lagunera.