Screening Larch in Vitro for Resistance to Mycosphaerella laricina. M. E. Ostry, Principal Plant Pathologist, USDA Forest Service, North Central Forest Experiment Station, St. Paul, MN 55108. P. M. Pijut, and D. D. Skilling. Research Plant Physiologist, and Principal Plant Pathologist, USDA Forest Service, North Central Forest Experiment Station, St. Paul, MN 55108. Plant Dis. 75:1222-1224. Accepted for publication 31 May 1991. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1991. DOI: 10.1094/PD-75-1222.

Needle blight of larch caused by Mycosphaerella laricina seriously limits the productivity of susceptible trees in the north central and northeastern United States. Adventitious shoots, derived from cotyledon tissue culture, of selected European larch (Larix decidua) and a hybrid larch were inoculated in vitro with three isolates of M. laricina. Inoculation with any of the three isolates resulted in disease severity ratings similar to resistance rankings of seedlings in field trials. Tissue-cultured shoots showed evidence of infection within 3 wk after in vitro inoculation. Thus, in vitro screening offers a reliable system for determining the resistance of larch from various seed lots to infection by M. laricina within a few weeks rather than the years required in the field.