Abstract
The powdery mildew caused by Oidium spp. is an important disease for several crops of the Cucurbitaceae family. Although the teleomorphs, Podosphaera xanthii and Golovinomyces cichoracearum, currently have already been described as the causal agents of powdery mildew in Brazil, only P. xanthii is considered the main causal agent of powdery mildew field epidemics. The objective of this work was to identify and determine the prevalence of the species causing powdery mildew in cucumber (Cucumis sativus) and melon (Cucumis melo var. reticulatus) grown in greenhouses in the State of Paraná in Brazil. The morphological traits of the conidial stages, such as the presence of fibrosin bodies and a germinative tube, were used to identify the species. Leaves exhibiting high severity of powdery mildew were collected from plants of 13 plastic greenhouses during different seasons in 2003/2004 and in different regions of Paraná State. In all environments, a significant prevalence of P. xanthii (80-100%) was observed affecting parthenocarpic or ordinary cucumber and melon. Golovinomyces cichoracearum was observed in six greenhouses, with up to 20% of conidia of this species on the samples.
Highlights
Powdery mildew is a common disease of both domesticated and wild species of cucurbits; it is one of the most destructive leaf diseases, affecting mainly melon (Cucumis melo L.) and cucumber (Cucumis sativus L.) among the several cucurbits
According to Reifschneider et al (1985), six different fungal species have been reported to be associated with powdery mildew of cucurbits
Material and methods Leaf samples were collected from melon (Cucumis melo var. reticulatus, hybrid Bonus II), ungrafted parthenocarpic cucumber (Cucumis sativus, hybrids Hokushin, Natsubayashi and Samurai), grafted parthenocarpic cucumber and ordinary cucumber (C. sativus, hybrid Safira) plants grown in plastic greenhouses in the State of Paraná, Brazil
Summary
Powdery mildew is a common disease of both domesticated and wild species of cucurbits; it is one of the most destructive leaf diseases, affecting mainly melon (Cucumis melo L.) and cucumber (Cucumis sativus L.) among the several cucurbits. According to Reifschneider et al (1985), six different fungal species have been reported to be associated with powdery mildew of cucurbits. Sphaerotheca fuliginea (Schlecht) Pollacci and Erysiphe cichoracearum DC. Ex Mérat, currently named Podosphaera xanthii and Golovinomyces cichoracearum, respectively (KUZUYA et al, 2006), are the most common and damaging species. P. xanthii can be represented by more than one strain and causes powdery mildew predominantly in tropical and subtropical climates
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