Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Abstract Only
Publication Acceptance Date: January 7, 2000
Publication Date: N/A
Technical Abstract: A comparison of parents and mutants of P strains of Trichoderma virens with respect to gliovirin production, induction of terpenoid synthesis in cotton, enzymatic digestion of pathogen hyphae, germination and growth from the air dried carrier, and biocontrol efficacy indicates that some are important mechanisms in biocontrol. Mutants of T. virens that have lost efficacy as biocontrol agents of P. ultimum-induced cotton seedling disease still induce terpenoid synthesis in cotton roots equal to that of parent strains. Mutants, however, that are deficient for production of the antibiotic gliovirin uniformly show reduced biocontrol efficacy. This reduction is variable, with some mutant strains being much more adversely affected than others. Some mutant strains that are totally ineffective as biocontrol agents have lost both gliolvirin production and the ability to degrade pathogen hyphae. This indicates that enzymatic degradation may also be important in biocontrol. Another interesting phenomenon was the occurrence of a mutant that retains gliovirin production, induction of terpenoid synthesis, and enzymatic degradation, but that has lost biocontrol efficacy. This strain shows slow germination and development from the air dried biocontrol preparation. Since P. ultimum is a fast acting pathogen that can initiate pathogenesis within hours after planting, time is apparently of the essence when it comes to germination and metabolic activity by the biocontrol agent. These mutational studies indicate that fully successful biocontrol of P. ultimum-induced cotton seedling disease by T. virens requires antibiotic production, degradation of pathogen hyphae, and timely germination and growth of the biocontrol agent from the air-dried preparation coated on the seed.