Background and Aims:

The formation of chasmothecia (sexual phase) in Podosphaera xanthii, the fungus that causes powdery mildew in cucurbits, is unusual. Absence of one of the mating or compatibility types (CT) MAT1-1 or MAT1-2, or an unequal ratio, is the most likely explanation. In this work, the CT present in P. xanthii populations infecting cucurbits were identified and quantified in various localities from Veracruz, Mexico.

Methods:

Samples of P. xanthii were collected in squash, chilacayote, and cucumber crops in 28 localities from 2018 to 2021 during the four seasons. Microscopic preparations were made to corroborate the presence of chasmothecia. DNA was extracted from 114 samples to identify the CT with multiplex PCR using specific oligonucleotides for genes MAT1-1-1 and MAT1-2-1 from P. xanthii. Amplification was verified by electrophoresis. Compatibility type frequencies by crop field, season, collection year, and host were analyzed using χ2.

Key results:

None of the specimens examined had chasmothecia. Sixty-four amplified both genes, 34 only MAT1-2-1, and 16 just MAT1-1-1. There were no differences in the ratio of CT by crop field, season, or collection year. In contrast, proportion per host presented differences (χ2=16.856, p=0.009). This relationship was only significant in Cucurbita moschata with a higher proportion of MAT1-1-1 (p=0.002) and in C. okeechobeensis subsp. martinezii with a higher proportion of MAT1-2-1 (p=0.01).

Conclusions:

Both CT required for P. xanthii’s sexual reproduction were found in a ratio close to 1:1 in most populations from Veracruz. Therefore, the lack of chasmothecia is not apparently related to the absence of one of them but to different factors that need to be evaluated.

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