Effects of Pythium species on the growth of apple and their possible causal role in apple replant disease

Abstract

SUMMARY Several lines of circumstantial evidence collectively indicated that poor early growth of apple (‘replant disease’) might be associated with the effects of soil‐borne pythiaceous fungi. This hypothesis was supported by pathogenicity tests. All isolates tested of P. sylvaticum and certain isolates of seven other Pythium spp. significantly reduced the growth of apple seedlings. The growth reductions caused by certain Pythium isolates were of comparable magnitude to the growth increases occurring after chloropicrin‐fumigation of apple orchard soils. The Pythium isolates most virulent to apple were of low virulence to a clonal cherry rootstock. Reappraisal of the nature of the disease as a non‐specific soil malaise is consistent with established features of the pathology of Pythium spp. The disease, however, is an ill‐defined ‘poor growth phenomenon’ with no diagnostic symptoms and conclusive evidence that Pythium spp. are widely causal is likely to be elusive.

Effects of nematodes, fungi and bacteria on the growth of young apple trees grown in apple replant disease soil

“…In various parts of the world, fungi such as Cylindrocarpon lucidum and Pythium species (Jaffee et al, 1982;Sewell, 1981), soil bacteria and actinomycetes have been implicated in ARD (Hoestra, 1968;Savory, 1981;Westcott et al, 1986). The combination of fungi and bacteria in soil did not affect the growth of apple seedlings (Table 3).…”

“…(Jaffee et al, 1982;Mai and Abawi, 1981;Slykhuis and Li, 1985). Sewell (1981) suggested pythiaceous fungi as the primary cause of ARD in England. Soil bacteria and actinomycetes have also been implicated in ARD (Hoestra, 1968;Savory, 1966;Westcott et al, 1986).…”

Characterization of fungi (Fusarium and Rhizoctonia) and oomycetes (Phytophthora and Pythium) associated with apple orchards in South Africa

“…Some of these pathogens contribute to a phenomenon known as apple replant disease, which refers to the poor growth of apple trees on soil previously cultivated to apple or closely related species. The primary fungal and oomycete genera reported as containing species that are pathogenic toward apple, include the fungal genera Cylindrocarpon, Fusarium and Rhizoctonia, and the oomycete genera Phytophthora and Pythium (Sewell 1981;Dullahide et al 1994;Mazzola 1998;Manici et al 2003).…”

The Effects of Chemical Fumigants, Nitrogen, Plastic Mulch and Metalaxyl on the Establishment of Young Apple Trees in Apple Replant Disease Soil

“…Plant (Jan' 1988) clear, Pythium spp. (Sewell 1981 (Mathur et al 1980) which has been used as an ARD control in Great Britain (Savory 1966), Nova Scotia (Ross et al 1983), anct the Northeastern U.S.A. (Mai and Abawi 1981). The use of fungicides to control ARD has been limited and results have been conflicting (Sewell 1978;Jaffee et al 1982 (Sewell and Fleck 1979).…”