Powdery Mildew of Cucurbits PDF

## Powdery Mildew of Cucurbits (8) POWDERY MILDEW OF CUCURBITS The disease is worldwide in distribution. It occurs throughout India almost every year. Causal organism: *Sphaerotheca fuliginea* (Sc.) Poll. or *Sphaerotheca humuli var. fuliginea* (Schl.) Poll. ### Plant Diseases #### Figure 12...

## Powdery Mildew of Cucurbits (8) POWDERY MILDEW OF CUCURBITS The disease is worldwide in distribution. It occurs throughout India almost every year. Causal organism: *Sphaerotheca fuliginea* (Sc.) Poll. or *Sphaerotheca humuli var. fuliginea* (Schl.) Poll. ### Plant Diseases #### Figure 12.11. Powdery mildew of cucurbits caused by *Sphaerotheca fuliginea*. - A symptoms. - B-D Asexual stage. - E-I Cleistothecium and is germination. (fam. Erysiphaceae; Class, Plectomycetes; Subviv. As-comycotina). Host: Most of the plants of Cucurbitaceae, specially *Lagenaria vulgaris* (Bottle gourd, vern. Launki). ### Plant Pathology #### Symptoms (Fig. 12.11A): First visible symptoms of the disease appear on leaves and stem in the form of small white superficial spots which become powdery as they enlarge. The powdery mass covers the entire host surface. In the later stage of the disease, small, black, pin-head like structures called cleistothecia appear on the white powdery mass. The infected leaves fall off and the fruits remain undersized. #### Host-parasite Relationship (Fig. 12.11 B-I): The fungus is obligate parasite and ectoparasite. The mycelium grows superficially over the surface of host and sends intracellular haustoria in epidermal cells. The haustoria are pear shaped with lobed margins and absorb nourishment from the host. The fungus reproduces by producing chain of white unicellular conidia on special conidiophores. The conidia spread and dispersed by wind to cause secondary infection. The sexual reproduction results in the formation of spherical fruiting body, called cleistothecium. Each cleistothecium contains single ascus with eight ascospores. #### Environmental Relationship The powdery mildews are generally favoured by dry conditions. The spores of these fungi contain a very high proportion of moisture. It's not dependent on external water for germination. However, the primary infection requires presence of moisture. The optimum temperature needed for the development of powdery mildews ranges between 11°C to 28°C. #### Disease Cycle The fungus has a wide range of host and survives throughout the year on collateral hosts. Thus, the primary infection occurs by the germination of conidia on host surface which come from collateral hosts. The cleistothecia are rarely formed and, therefore, not effective in disease recurrence. #### Control 1. Dusting with colloidal sulphur and thiram are effective in controlling the disease. 2. Foliar spray of Benomyl is effective in controlling the disease in bottle gourd.