VIEW ARTICLE

Effect of Pentachloronitrobenzene on Colonization of Alfalfa Residues by Fungi and Streptomycetes in Soil. J. Katan, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823, Present address of senior author: the Hebrew University, Faculty of Agriculture, Rehovot, Israel; J. L. Lockwood, Department of Botany and Plant Pathology, Michigan State University, East Lansing 48823. Phytopathology 60:1578-1582. Accepted for publication 2 June 1970. DOI: 10.1094/Phyto-60-1578.

Pentachloronitrobenzene (PCNB) at a concentration of 10 µg/g soil produced quantitative and qualitative changes in fungal and streptomycete populations colonizing particles of alfalfa hay in natural soil. At incubation periods from 1 to 32 days, total numbers of fungi in alfalfa particles were reduced when the soil contained PCNB. The proportion of fungi which were tolerant to PCNB was greater in residues recovered from soil containing PCNB than from soil without PCNB. Populations of Pythium ultimum and Fusarium spp. colonizing alfalfa particles increased in the presence of PCNB in soil, while those of Rhizopus stolonifer and Penicillium oxalicum, and of streptomycetes, decreased. These changes were correlated with the sensitivity of these microorganisms to PCNB in agar. Alfalfa hay accumulated PCNB to levels 7- to 11-fold higher than the concentration in soil. In sterile soil infested with pairs of microorganisms differing in sensitivity to PCNB, populations of the more sensitive microbes colonizing alfalfa particles decreased and those of the more tolerant microbes increased.