Intraspecific molecular variation among Trichoderma harzianum isolates colonizing mushroom compost in the British Isles

Department of Applied lant Science, The Queen's University of Belfast, 1 and lant Pathology Research Division Department of Agriculture for Northern ieland, 2 Newforge Lane, belfast, BT9 5PX, UK ABSTRACT The genetic diversity in Trichoderma harzianum isolates from mushroom compost was assessed using various molecular techniques. Restriction fragment length polymorphism (RFLP) analysis of ribosomal DNA (rDNA) and mitochondrial DNA (mtDNA) divided the 81 isolates into three major groups, 1, 2 and 3. There was no variation within a group in rDNA, while a low degree of polymorphism was detected in mtDNA. Random amplified polymorphic DNA (RAPD) analysis of 30 randomly chosen isolates, with six primers, in general confirmed the RFLP groups. Nucleotide sequence determination of rDNA internal transcribed spacer (ITS) 1 revealed three distinct ITS types, 1, 2 and 3, possessed by isolates from the respective groups 1, 2 and 3. Based on these molecular data, group 2 isolates, which are aggressive colonizers of mushroom compost, could be clearly distinguished from the isolates belonging to the other two groups. 1 Author for correspondence: P. R. Mills. Tel: +44 903 716123 ext. 2368. Fax: +44 903 726780. Keywords: Trichoderma harzianum , mushroom compost, molecular variation, systematics Present address: Horticulture Research International, Wellesbourne, Warwick CV35 9EF, UK.