Biological Control of Damping-Off Caused byPythium ultimumandRhizoctonia solaniwithGliocladium virensin Soilless Mix

Abstract

Gliocladium virens controlled damping-off of zinnia, cotton, and cabbage caused by Phthium ultimum or Rhizoctonia solani in nonsterile soilness mix. This antagonist most effective controlled disease among 50 isolates of bacteria and fungi, including species of Pseudiomonas, Bacillus, Trichoderma, and Penicillium. Twenty isolates of G. viren varied in their efficacy in controlling P. ultimum and R. solani. Some isolates contolled P ultimum but not R. solani, and vice versa. This range of activity suggest a complex mehanism of action that might apply to one pathogen but not the other. Inoculant of G. virens routinely was preincubated in the soilless mix before cotamination of the mix with pathogen inoculum. Control of P. ultimum was effective when sporangial inoculum of the pathogen was introduced at the time of planting the host seed; however, control R. saloni required prior contact of G. virens with inoculum of R. solani. Disease control efficacy last for at least 2 mo when G. virens was introduced with the pathogen inoculum and the mix was planted with zinnia seeds at intevals. The number of colony-forming units of G. virens remained high during the testing period, but the number of pathogen colony-forming units of G. virens. Sodium alginate formulations of isolate G20 of G. virens, selected for control both pathogens, maintained a high population density in a dry formulation when stored 2 mo at 4 and 20 C, but not at 30 C. Storage of an alginate formulation at these same temperatures in air-dried soilness mix was not successful. Alginate formulations of G. virens added to soilless mix before planting seed show primise as a control damping-control for damping-off in the greenhouse production of bedding plants.