LABORATORY EVALUATION OF INDIGENOUS NORTH-AMERICAN FUNGI FOR BIOLOGICAL-CONTROL OF PURPLE LOOSESTRIFE

Fifteen fungi were tested for pathogenicity to 6-week-old purple loose strife plants (Lythrum salicaria) grown from seed in growth chambers. Virulence, based on percentage of plant surface displaying symptoms, w as rated from 0 = no symptoms to 5 = dead plant. A fungus was consider ed virulent and a potential biological control agent when it caused a disease rating of 2.50 and above. On this basis, 6 of the 15 fungi wer e virulent, with Septoria lythrina being the most virulent followed by Alternaria alternata, Botrytis cinerea, Colletotrichum truncatum, Pho ma sorghina, and Coniothyrium olivaceum. Inoculation of purple loosest rife seedlings was most effective when spores were applied in a carrie r (referred to as DIGS) composed of 0.1% dextrose; 1.5% Intac (a blend of polymers and copolymers); 0.05% gelatin (Know, unflavored); and 0. 15% Silwet L-77 (a silicone-polyether copolymer). The virulence of B. cinerea was reduced when stored cultures (0-16 months at 5 degrees C) were used, but was regained when the fungus was reisolated from leaf s pots. There was a difference in virulence among A. alternata and B. ci nerea isolates from different locations,The mean disease ratings of A. alternata when inoculated on 4- or B-week-old plants were the same; h owever, disease ratings with B. cinerea were greater on 6- than on 4-w eek-old plants, Thus, based on these laboratory studies, A. alternata, B. cinerea, and P. sorghina applied in DIGS as a carrier may have pot ential for biological control of purple loosestrife. (C) 1997 Academic Press