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 ## Powdery...

# 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 ## Powdery Mildew of Cucurbits **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; Subdiv. - Ascomycotina)** **Host:** Most of the plants of Cucurbitaceae, specially _Lagenaria vulgaris_ (Bottle gourd, vern. Launki) # Plant Pathology ## Symptoms * 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. * Gradually 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 * **Figure 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 and are 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.