FUNGAL PATHOGENS AND PRATYLENCHUS PENETRANS ASSOCIATED WITH PRECEDINGCROPS OF CLOVERS, WINTER-WHEAT, AND ANNUAL RYEGRASS AND THEIR INFLUENCE ON SUCCEEDING POTATO CROPS ON PRINCE-EDWARD-ISLAND

The incidence of soilborne fungal pathogens of potatoes and root lesio n nematodes were determined in preceding crops of clovers, annual ryeg rass, and winter wheat, in the succeeding potato crops and soils and s everity of associated potato diseases recorded in two, 2-yr field tria ls. Differences were not evident in yearly recovery of Rhizoctonia sol ani, Verticillium dahliae, V. albo-atrum, and Colletotrichum coccodes from previous crops and soils. However, overall trends were present wi th a higher recovery of V. dahliae from wheat and a greater recovery o f R solani from clover than either wheat or ryegrass. A previous crop of ryegrass resulted in lower levels of R solani in succeeding potato soils in both trials and after clover in one trial at the pre-harvest sampling time. In trial 1 greater numbers of Pratylenchus penetrans we re recovered from clover soils than from soils of ryegrass or wheat. O ne instance of lower nematode recovery in potato soils following ryegr ass occurred but no differences in their recovery from potato roots we re observed. Potato wilt incidence was lowest after clovers. Stem rot severity was positively correlated with recovery of R. solani and V. d ahliae from potato stems and roots and negatively correlated with V. a lbo-atrum from potato stems only Nematode populations were not related to potato disease symptom severity ratings. Results reported herein i ndicate that only a portion of soilborne diseases of potatoes on Princ e Edward Island may be related to previous crops produced in the 3-yr rotation selected for this study.