Effects of manure composts on soil biota and root-rot disease incidence of ginseng (Panax ginseng)

Some saprophytic fungi are pathogenic to ginseng, and input of organic materials may influence these pathogens. The objective of this study was to investigate the application effects of manure composts on soil-borne pathogenic fungi and the responses of soil organisms in relation to root rot disease. Manure composts from 3 different organisms, namely, chicken, cow, and pig, were applied at 20 Mg ha−1. We compared these effects between paddy-converted fields and upland fields. Despite the input of manure composts, the root yield did not increase because of root loss and growth disorder caused by root rot disease. We isolated Cylindrocarpon destructans and Fusarium solani from the diseased roots, which suggested that these 2 fungi were the main causal pathogens. Hyphal growth of the 2 fungi increased in soils of both fields treated with manure composts, but the promoting effect was high in paddy-converted fields. These findings suggest that the application of manure composts may accelerate root rot disease by promoting pathogenic fungi. Microflora was estimated by analysing phospholipid fatty acids, and non-metric multidimensional scaling analysis showed that the responses of microflora were different between the two fields. Aerobic bacterial PLFAs were greatly increased in the upland field, which indicated that influences of manure compost might differ according to soil type. Fungal PLFAs showed correlations with fungivorous nematodes but not with abundance of Collembola and Oribatida. It seemed that the suppressive effect of fungivorous fauna promoted by manure compost is minor and restricted to some organisms. Our study suggests that increased substrates in the soil might promote the growth of C. destructans and F. solani, and suppression of these pathogenic fungi is required in relation to the application of manure composts.