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Vesicular-arbuscular mycorrhizae and apples (Malus domestica Borkh.) in the nursery and in apple replant desease Gamiet, Sharmin


The purpose of this study was to determine if different clonal rootstock from apple (Malus domestica Borkh.) formed different vesicular arbuscular mycorrhizal (VAM) associations. Different fertilizers and VAM fungi were tested to determine their effects on apple seedling growth in apple replant diseased (ARD) soils. VAM associations in apple stoolbed nursery were low. Over 80% of all samples had less than 10% mycorrhizal colonization. This reduction in VAM colonization amongst various rootstock clones is a result of detrimental management practices in the stoolbed nursery. Apples grown in a budded nursery had high mycorrhizal colonization, the lowest colonization rate was 30%. Different rootstocks from the budded nursery do not show any significant differences in VAM colonization, whereas clonal rootstocks from the stoolbed nursery do. From the stoolbed nursery, Mailing (M) 2 consistantly showed higher VAM colonization rates, compared to M 4, M7, M9, M 26, Mailing Merton (MM) 106, MM 111, Alnarp 2 and Ottawa 3. Apple replant disease (ARD) is identified as the reason for poor growth of apple seddlings in 5 soils from the Okanagan Valley of British Columbia. Sterilization by autoclaving, pasteurization and formalin increased test seedling height. Air-drying test soil does not affect ARD pot bioassays. However, air-drying the soil and pasteurizing or adding formalin increased plant height significantly more than these treatments in nonair-dried soils. The fertilizer monoammonium phosphate (11-55-0) increased plant height more than ammonium nitrate (34-0-0) while triple superphosphate (0-45-0) did not increase plant height. Root growth was increased by 0-45-0 only. VAM fungi were drastically reduced or eliminated by sterilization and 11-55-0, but not by the other fertilizers. VAM fungi in 2 ARD soils do not overcome ARD. Test seedlings grown in sterilized ARD soils inoculated with 4 species of VAM fungi do not show as great an increase in shoot height compared to the addition of 11-55-0 fertilizer. Root growth shows the inverse response. Glomus intraradices Schenck and Smith, was the best colonizer but inoculation with G. versiforme (Karsten) Berch resulted in the greatest shoot and root growth. Glomus clarum Nicholson and Schenck, and G. monosporum Gerdemann and Trappe, did not result in increases in plant growth in ARD soils. In sterilized ARD soils, VAM fungi do not increase shoot growth as expected, but do increase root growth, suggesting the initial growth of inoculated apple seedlings is root mass. Seedlings given 11-55-0 fertilizers show the reverse pattern of growth. In nonsterilized ARD soils, the growth of seedlings appears to be inversely proportional to VAM colonization.

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