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The Response of the Mycobiome to the Biofumigation of Replanted Soil in a Fruit Tree Nursery
In a long-term monoculture with fruit trees and tree nurseries, it is necessary to regenerate the soil due to the risk of apple replant disease (ARD). The occurrence of ARD is manifested in the structure of the mycobiome. The assumption of our experiment was that the use of oil radish (Raphanus sativus var. oleifera), white mustard (Sinapis alba), and marigold (Tagetes patula L.) as phytosanitary plants for biofumigation would provide crops with nutrients, improve soil physicochemical properties, and influence the diversity of microbiota, including fungal networks, towards a beneficial mycobiome. Metagenomic analysis of fungal populations based on the hypervariable ITS1 region was used for assessing changes in the soil mycobiome. It showed that biofumigation, mainly with a forecrop of marigold (Tagetes patula L.) (R3), caused an improvement in soil physicochemical properties (bulk density and humus) and the highest increase in the abundance of operational taxonomic units (OTUs) of the Fungi kingdom, which was similar to that of agriculturally undegraded soils, and amounted to 54.37%. In this variant of the experiment, the most OTUs were identified at the phylum level, for Ascomycota (39.82%) and Mortierellomycota beneficial fungi (7.73%). There were no such dependencies in the soils replanted with forecrops of oilseed radish (Raphanus sativus var. oleifera) and white mustard (Sinapis alba). Biofumigation with marigold and oil radish contributed to a reduction in the genus Fusarium, which contains several significant plant-pathogenic species. The percentages of operational taxonomic units (OTUs) of Fusarium spp. decreased from 1.57% to 0.17% and 0.47%, respectively.
Biofumigation Treatment Using Tagetes patula, Sinapis alba and Raphanus sativus Changes the Biological Properties of Replanted Soil in a Fruit Tree Nursery
Apple replant disease (ARD) may cause significant losses both in commercial orchards and in fruit tree nurseries. The negative effects of ARD may be limited by using biofumigation. The aim of the study was to assess the influence of this treatment on the biological properties of replanted soil in a tree nursery. In two-year experiment, apple trees of the ‘Golden Delicious’ cultivar were used. The trees were planted into soil from two sites. The soil from one site had not been used in a nursery before (crop rotation soil). The other soil had been used for the production of apple trees (replanted soil). Three species of plants were used in the replanted soil as a forecrop: French marigold (Tagetes patula), white mustard (Sinapis alba), and oilseed radish (Raphanus sativus var. oleifera). The following parameters were assessed in the experiment: the enzyme and respiratory activity of the soil, the total count of bacteria, fungi, oomycetes and actinobacteria in the soil, as well as the count and species composition of soil nematodes. The vegetative growth parameters of the apple trees were also assessed. The biological properties of the replanted soil were worse than those of the crop rotation soil. In the replanted soil, the organic matter content, enzyme and respiratory activity as well as the count of soil microorganisms were lower. The biofumigants, used as a forecrop on the replanted soil, significantly increased its enzyme activity and respiratory activity. Dehydrogenase activity increased more than twofold. Growth parameters of the trees were significantly improved. The height of the trees increased by more than 50%, and the leaf area, weight and total length of side shoots were higher as well. The density of nematodes in the replanted soil after biofumigation was significantly reduced, with a larger reduction in the marigold fumigated soil. Eight of the eleven nematode species were completely reduced in the first year after biofumigation treatment.