Effect Of Soil Pasteurization And Rotation On Apple Replant Problem

The experiment was conducted from 2002 to 2004 in Root Research Lab,College of Horticulture, Shandong Agricultural University. Using pot-plantedseedlings of M.hupehensis Rehd. as plant material, effects of soilpasteurization, short-term crop rotations and dominant microorganism inreplant soils on apple replant disease (ARD) were observed. Soil nutrition, soilenzyme activity, microbial quantity and species, fruit quality were alsodetermined for crop rotated, no-rotated replant apple orchards in Qixia country.The main results obtained were summarized as follows: 1. Soil pasteurization at 50℃, 70℃ and 90℃ improved plant growth ofM.hupehensis Rehd. seedlings. Leaf area, plant biomass, root surface area,root length, root tip number, root respiration rate were all increased. Treatmentof 70℃, 90min reached the best result. Biotic element could play a veryimportant role in apple replant disease. 2. Cultivation of soybean, maize and sorghum in replant soil enhancedplant growth, improved root morphology and decreased plant mortality rate,compared to untreated soils. Soils with crop rotation had lower fungipopulation and higher soil enzyme activity than untreated soil. Among threerotated plants, sorghum was the best. 3. Six apple orchards in Qixia country were investigated, includingre-planted, rotated with 2-year's peanut, new orchard; rotated with 1 year maize,old orchard and maize field. Soil nutrition content and soil enzyme activities 2山东农业大学硕士学位论文were decreased in replant orchards. There were more fungi and less bacteria inreplant soil than no-replant orchards' soil. Fruit quality of rotated peanutorchard was much improved, but still smaller than that of new orchard. Croprotation is an effective measure to overcome apple replant disease, but moreexperiments should be done to find the best crop and limited rotation period. 4. Three kinds of fungi, one kind of actinomycetes and fourteen kinds ofbacteria were isolated from rhizosphere soil in replant apple orchard. Then putthese soil microorganisms in pot plant soil. Actinomycetes significantlydecreased plant fresh weight, height, leaf area, root surface area, root tipnumber and root density. Fungi greatly reduced seedling growth too. Amongthree kinds of fungi, F1 reduced more growth than F2 and F3. F1 is asmall-spored Alternaria spp.. Most bacteria isolated from replant apple orcharddo not obviously affect the growth of M.hupehensis Rehd. seedlings. In allbacteria treatments, X63, X41, X7 slightly reduced seedling growth but X32,X21 promoted the growth. The results above suggested that fungi andactinomycetes might be implicated as potential causal agents of apple replantdisease but not bacteria.