امراض نبات1 Plasmodiophora brassicae

disease
Clubroot of cabbage




SYMPTOMS
Above ground symptoms include wilted and yellowish leaves and stunted plants. Lower leaves may drop off. Affected plants do not grow acceptable produce. The distinctive symptom is abnormal enlargement (clubs) of roots, including fine roots, secondary roots, or the taproot, or even on the underground stem. The clubs usually are thickest at the center and tapered toward the ends. Clubs may be isolated and cover only part of some roots or they may coalesce and cover the entire root system of the plant. Some affected plants may not exhibit above ground symptoms until they are pulled and the tiny clubs are noticed on the roots (Sherf and MacNab, 1986; Agrios, 1978).
Identification: The most characteristic symptom of P. brassicae within a host, is the clubbing of host roots. A wide variety of root pathogens, however, produce similar symptoms, including root knot nematode and gall inducing fungi and bacteria. Presence of P. brassicae within a host is verified through dissection of clubbed roots. Clusters of enlarged host cells containing plasmodium and amoebae can then be observed with proper staining..