Apple replant disease: the influence of soil phosphorus and other factors on the growth responses of apple seedlings to soil fumigation with chloropicrin

Abstract

The effects of fumigating field soils before replanting apple are frequently predicted from bioassays where apple seedlings are grown in pots, some containing untreated soil and the others containing chloropicrin-fumigated soil. The results from 418 such bioassays made during eight years are discussed with reference to the effects of certain physical and chemical soil features.Soil phosphorus (P) content and pH had large effects on growth in fumigated (but not untreated) soils; they therefore had large effects on the growth response to soil fumigation. There were no indications of important effects due to soil content of potassium or magnesium or to soil texture.In fumigated soils, the height of seedlings was generally greater, the greater the soil P content, but in untreated soils it was mostly independent of P (range 1 -156 mg P litre-' soil). The differing effects of native P on growth in untreated or fumigated soils were attributed respectively to the presence and absence of vesicular-arbuscular mycorrhizas : their absence in fumigated soils was considered (for apple) to be an artefact in the seedling bioassay. The results for untreated soils indicated that the apple mycorrhizal system was very efficient in retrieving P when there was little available.Growth responses to soil fumigation were usually greater in acidic than in alkaline soils for any given level of P. When soils were P-amended before testing, the effects of native P and pH virtually disappeared and the proportion of orchard soils with economically significant growth responses increased from 39% to 67%.

Apple Replant Disease: Causes and Mitigation Strategies

“…These may include, for instance, the use of selected micronutrients such as zinc while possibly excluding or at least very carefully operating with others like boron (Tukey et al, 1984). Adding mineral fertilizer, e.g., with P, (Sewell et al, 1988), as well as managing ground cover by adding compost or even biochar, may induce increased biocontrol properties of soils including a reduction of nematodes causing root lesions. Fertilization may thus affect ARD severity in nutrient-limited soils (van Schoor et al, 2009), but frequently failed to replace fumigation for replanting in temperate climates (St. Laurent et al, 2008;Mazzola and Manici, 2012;Glisczynski et al, 2016;Peruzzi et al, 2017).…”

Apple Rootstock Response to Vesicular-arbuscular Mycorrhizal Fungi in a High Phosphorus Soil

“…As far as we know, mycorrhizae-induced growth depression of apple tree has never been reported. Sewell et al (1988) conducted bioassays in which apple seedlings were grown in pots to predict the need of fumigation against apple replant disease. The results indicated that seedling height was generally greater when soil P availability was high in fumigated soils, but that in untreated soils it was mostly independent of P. This observation seems to suggest that, as mycorrhizal colonization is affected by soil P availability, mycorrhizal colonization with its potentially associated C drain is not involved in replant disease.…”

Apple replant disease: the assessment and results of seedling bio‐assays of growth responses to soil fumigation with chloropicrin

“…The original apple seedling bio-assay was based on methods recommended by Hoestra (1968) and the ADAS procedures were described in detail by Sewell et al (1988). Briefly, samples of soils to be replanted were divided into two parts; one was untreated and the other was partially sterilised by fumigation with chloropicrin.…”

“…This artefact of the seedling bio-assay, associated with the absence of vesicular-arbuscular (VA) mycorrhizal fungi after soil fumigation, was largely corrected by amending all soils with P before the tests. With P-amendment, the proportion of soils with economically significant growth responses increased from 39% (299 tests, 1976-81) to 67% (119 tests, 1982-84) (Sewell, Preece & Elsey, 1988). This paper considers further results from bio-assays made during 1985-88, additional effects of improvement in the assessment of plant growth, actual rather than proportional growth increases following soil fumigation, and effects of soil fumigation in relation to soil PH.…”