Effects of different soil improvement methods on soil nematode community in old peach orchard

Abstract: 【Objective】Peach replanting diseases inhibit the growth and development of peach trees, reduce fruit yield and quality, and even cause plant death, therefore restricting the development of the peach industry. The factors which cause the peach replanting diseases are multiple including soil pathogenic nematodes, harmful pathogens and allelotoxic substances. Previous studies have found that pathogenic nematodes are the common pests in replanting orchards. Tylenchorhynchus maxbnus, Helicotylenchus dihystera, Meloidogyne incognita, Aphelenchoides cyrtus and Criconemella sphaerocephala have been proved to be the pathogenic nematodes in peach. Soil disinfection can kill pathogenic nematodes, other harmful pathogens and weeds in the soil and effectively alleviate the replanting diseases.The present study analyzed the effect of different kinds of disinfection methods and microbial agents on the soil nematode community, to provide reference for alleviating the peach replanting diseases.【Methods】This study was carried out in Huzhou city, Zhejiang province, using peach replanted soil and oneyear-old Akatuki peach saplings as the material. In this study, sixteen treatments were set including dazomet(M), dazomet plus mushroom residue(MJ), mushroom residue(J), no disinfectant(CK) and the microbial agents including Trichoderma harzianum microbial inoculant(H), T. harzianum plus Bacillus microbial inoculant(HY), Bacillus microbial inoculant(Y), and no inoculation(O). The experimental treatments were implemented to explore the prevention effect for pathogenic nematodes, the influence for soil nematode community and mitigation effect for peach replanting diseases. The number of nematodes in different treatments was analyzed using microscope, and the pathogenic nematode types were identified by morphological and molecular biology methods. The primer pairs AB28/TW81were used to amplify the internal transcribed spacer region of the nuclear ribosomal RNA operon(ITS)sequence of pathogenic nematodes, which were identified by morphological methods. The number and species of nematodes between different treatments were compared.【Results】Results showed that, regardless of before and after reformation, the free-living nematodes at 25 cm from trunk in horizontal distance were significantly higher than those at the distance of 50 cm. Therefore, soil nematode community were mainly distributed around the rhizosphere of peach trees within 25 cm of the horizontal distance from the trunk. But the number of pathogenic nematodes was almost similar at two horizontal distances.The number of free-living nematodes and pathogenic nematodes at a vertical depth of 10-<30 cm was significantly larger than that of 30-40 cm. There were 89.67 free-living nematodes and 20.67 pathogenic nematodes in the 10-<30 cm depth soil layer in the old peach orchard, while only 13.00 and 3.50were distributed in the soil layer of 30-40 cm. However, there was no obvious distribution pattern in the newly planted peach orchard. At same time, the proportion of soil pathogenic nematodes in old peach orchards was higher than new orchards in most soil layers, especially at 25 cm of the horizontal distance from the trunk, the pathogenic nematodes in old peach orchards were 10% higher in soil nematode community than in newly planted peach orchards. However, at the distance of 50 cm of the horizontal distance from the trunk, the proportion of pathogenic nematodes in the two orchards was not significantly different. Tylenchus, Helicotylenchus, Tylenchida, Pratylenchidae, and Criconemella were the main pathogenic nematodes in Huzhou peach orchard identified by the morphological methods, among which Tylenchus and Helicotylenchus were the major types occupying more than 90% and have been reported as common plant parasitic nematodes. At the molecular level, there were 100% overlap between target sequence and the ITS sequence of H. dihystera, so H. dihystera was the main pathogenic nematode in this orchard. Except MH and MY treatments, all the soil reformation treatments could improve the free-living nematodes compared the control treatment in the same group. From this point of view,soil improvement can promote soil nematode community reconstruction. Compared with the control group, the disinfection methods of M and MJ and the microbial agent treatments of H, HY and Y significantly reduced the number of Tylenchus and Helicotylenchus. In these treatments, the M and HY showed the highest inhibition rate(77.97%-98.39% and 81.46%-97.10%, respectively), but J improved the number of Tylenchus.【Conclusion】In summary, the soil nematode community was mainly distributed in the 10-<30 cm shallow soil around the rhizosphere in peach orchard in Huzhou. The free-living nematodes make up the majority of soil nematode community, and the main pathogenic nematodes were Tylenchus and Helicotylenchus, and Helicotylenchus dihystera was the dominant species. Soil improvement can promote the reconstruction of soil nematode community and increase the number of free-living nematodes in the soil. Fumigating with dozamet and then applying of Trichoderma harzianum plus Bacillus microbial inoculant after planting can effectively control soil pathogenic nematodes and enhance soil free-living nematodes. But the mushroom residue treatment increased the number of Tylenchus. this may be due to the fact that the mushroom residue is not decomposed and Tylenchus moves the host from the mycelium to peach. Therefore, it is recommended to use the dozamet and Trichoderma harzianum plus Bacillus microbial inoculant to treat the peach soil in production.