The regulation capacity of four humic substance (HS) samples, a soil humic acid (HA) and two HAs and one fulvic acid (FA) isolated
from a composting substrate, was evaluated at two concentrations on the growth in vitro of one plant pathogenic, Sclerotinia
sclerotiorum, and two antagonistic, Trichoderma viride and T. harzianum, soil-borne fungi. The presence of any HS sample in the growing
medium, especially those from the composting substrate, caused a relevant inhibition of the mycelial growth of S. sclerotiorum and a
marked stimulation of sclerotial formation that was exhibited as early appearance and numerical increase. On the contrary, the same HS
treatments generally did not inhibit the growth of the two Trichoderma species. In particular, T. viride was significantly stimulated by any
HS sample at any concentration, with the only exception of HA from fresh-composting substrate, whereas T. harzianum appeared to be
stimulated only slightly or not significantly influenced. Only S. sclerotiorum showed evident high correlations of both the extent of the
inhibitory action on mycelial growth and the final number of sclerotia with some chemical and functional properties of HS, such as total
acidity, COOH group content, and elemental composition.
The regulation capacity of four humic substance (HS) samples, a soil humic acid (HA) and two HAs and one fulvic acid (FA) isolatedfrom a composting substrate, was evaluated at two concentrations on the growth in vitro of one plant pathogenic, Sclerotiniasclerotiorum, and two antagonistic, Trichoderma viride and T. harzianum, soil-borne fungi. The presence of any HS sample in the growingmedium, especially those from the composting substrate, caused a relevant inhibition of the mycelial growth of S. sclerotiorum and amarked stimulation of sclerotial formation that was exhibited as early appearance and numerical increase. On the contrary, the same HStreatments generally did not inhibit the growth of the two Trichoderma species. In particular, T. viride was significantly stimulated by anyHS sample at any concentration, with the only exception of HA from fresh-composting substrate, whereas T. harzianum appeared to bestimulated only slightly or not significantly influenced. Only S. sclerotiorum showed evident high correlations of both the extent of theinhibitory action on mycelial growth and the final number of sclerotia with some chemical and functional properties of HS, such as totalacidity, COOH group content, and elemental composition.
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