Soil fungal communities as indicators for replanting new peach orchards in intensively cultivated areas

Abstract

Italy and Spain are Europe's main peach-producing countries. Since the mid-90s, however, peach-growing areas have decreased in Italy thus causing its loss of European leadership. One of the reasons for the decline is the presence of replant disorders in peach orchards. As soil-borne pathogens are one of the biotic components of aetiology, a study was performed in an intensively cultivated area of southern Italy, to investigate the use of soil fungi as indicators of soil health when planting new peach orchards. Soil sampling was carried out in five replanted peach orchards and five horticultural sites in the “Piana del Sele”, a peach and vegetable-growing valley in the Campania region. Three different soil fungi communities were recorded: soil-inhabiting filamentous fungi; endophytic root fungi, based on cultural methods; and uncultured soil fungi, based on nucleotide sequences of internal transcribed spacers (ITS1 and ITS2) and rDNA gene fragments. Soil health was evaluated with a greenhouse bioassay, using young plants of peach rootstock GF677. Diversity and composition of fungal communities were compared using PAST, a software which includes several functions commonly used in paleoecology. Each peach tree orchard was characterized by a significantly higher diversity score than horticultural crops. The two cultivation systems differed widely for species composition suggesting that vegetative cover and cultivation practices strongly affected fungal community composition. The bioassay to evaluate soil health showed a significant growth reduction in horticultural sites compared to peach sites. This finding was supported by the high abundance of Cylindrocarpon destructans and Thielviopsis basicola, two aggressive root rot agents, within endophytic fungal communities in horticultural sites. In this survey, greatest fungal diversity corresponds to best plant growth. From a practical point of view, when deciding to replant a new fruit tree orchards in intensively cultivated areas, a greenhouse bioassay with the target crop, combined with a quantitative analysis of endophytic root fungal communities, may help in deciding the best soil use.