نقش علفهاي هرز و نباتات زراعي در پايدازي قارچ Phytophthora drechsleri عامل بوته ميري كدوييان دراستان فارس

ROLE OF ALTERNATE HOSTS ON SURVIVAL OF PHYTOPHTHORA DRECHSLERI THE CAUSE OF CUCURBIT ROOT AND CROWN ROT IN FARS PROVINCE

The role of alternate hosts in cucurbits fields in relation to the activity and survival of Phytophthora drechsleri was investigated in some regions of Fars province. Due to interference by Pythium spp., isolation of P. drechsleri from roots of various weeds on CMA supplemented with pimarcin (10 ppm) and ampicillin (500 ppm) (CMAPA) was not successful. Addition of hymexazol (50 ppm) to CMAPA resulted in exclusion of Pythium spp and isolation of P. drechsleri from the following prennial and annual weeds. Alhagi persarum. Chenopotlium album, C. amaranticolor. Glycyrrhiza glabra, Melilotus offlcinalis and Rhaphanus raphinstrum. Only M. officinalis had visual field symptoms of wilting and root rot. The pathogen was not detected in roots of Amaranthus retroflexus, Carthamus oxyacantha, Convolovolus arvensis, Cynodon dactylon, Euphorbia petiolata, Helintropium europeum, Lepidium draba, Malva rothundifolia, Physalis lanceifolia, Portulaca oleracea, Rumex acetosella, Solanum nigrum and Turgenia latifolia. The fungus could not be isolated also from roots of rotational crops such as barley, wheat, potato, alfalfa, corn and pepper. All isolates of P. drechsleri from weeds grew at 37c and were pathogenic on cantaloupes. Most of the weeds grown in autoclaved or non autoclaved virgin soils became infected after inoculation with zoospores of P. drechsleri. Propopis stephaniana, P. lanceifolia, L. draba, C.oxyanatha and M. rotundifolia were not infected by zoospores of the pathogen. Inoculation of zoospores to non cucurbit plants resulted in the appearance of disease symptoms within 2-3 weeks in Cicer arietinum, Lens esculenta, Lepidium sativum, Kfedica^o sativa and 3-4 weeks in Lathyrus odoraus and Phaseolus areus. No chlamydospores were observed in roots of inoculated plants . Oospores were formed in root of inoculated plaints if both mating types of the pathogen were present.