Mechanisms inhibiting damping-off pathogens of slash pine seedlings with a formulated soil amendment

• Published in: Phytopathology 1991, Vol.81 (2), p.171-177
• Main Authors: Huang, J.W, Kuhlman, E.G
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; biological control; Control; cultural control; damping off; disease control; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; Hypocrea lixii; microbial activity; Other methods; Penicillium oxalicum; Phytopathology. Animal pests. Plant and forest protection; Pinus elliottii; plant diseases and disorders; Pythium aphanidermatum; seedlings; soil amendments; soil fungi; Thanatephorus cucumeris
• ISSN: 0031-949X; 1943-7684
• DOI: 10.1094/Phyto-81-171

Suppressiveness of soil amended with SF-21 mixture to Rhizoctonia solani and Pythium aphanidermatum was tested with a modified pine stem-segment colonization method and germ tube growth, respectively. Soil amended with 1% (w/w) SF-21 did not immediately inhibit hyphal growth and stem-segment colonization by R. solani, but 7 days after amendment it significantly inhibited the fungus. The population of other fungi increased significantly 4 days or more after application of SF-21. The density of this population was correlated with suppression of stem-segment colonization by R. solani in amended soil. Stem-segment colonization by R. solani increased 30-40% after amended soil was autoclaved, but the inhibitory effect returned 7 days after infestation with Trichoderma harzianum or Penicillium oxalicum or both. Infestations with T. harzianum also restored suppressiveness to autoclaved nonamended soil, whereas infestations of autoclaved nonamended soil with P. oxalicum did not. Increasing the population of T. harzianum or P. oxalicum or both in amended soil at day 0 to about the same level as that in amended soil at day 7 immediately rendered it suppressive to stem colonization by R. solani. In addition, amended soil at day 0 directly inhibited and lysed germ tubes of P. aphanidermatum, and at day 7 after amendment was even more effective. Autoclaved amended soil with or without added T. harzianum or P. oxalicum or both suppressed germ tube elongation by P. aphanidermatum. However, inhibition of germ tube elongation was partially nullified in amended soil mixed with benomyl at 50 micrograms/g soil after 7 days. Soil amended with SF-21 and incubated for 7 days produced inhibitory substances that diffused into a synthetic medium and inhibited hyphal growth of R. solani and P. aphanidermatum by 22 and 28%, respectively, compared with diffusates from nonamended soil. When the pH of amended soil was adjusted from 4.3 to 5.8, the suppressive effect on colonization by R. solani was completely nullified, but the soil remained partially inhibitory to germ tube elongation by P. aphanidermatum. Population density of Trichoderma spp. and Penicillium spp. in amended soils was negatively correlated (r = -0.91), with pH values from 4 to 6. The capacity of Al2(SO4)3 to inhibit growth of R. solani and P. aphanidermatum in water agar was much greater at pH 4 than at pH 6. P. aphanidermatum was more sensitive to Al2(SO4)3 at pH 4 than was R. solani. Sporangial formation by P. aphani