|Bors Robert H,|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 22, 1995
Publication Date: N/A
Interpretive Summary: Synthetic fungicides for control of fruit molds after harvest have limitations. Many molds are resistant to fungicides, and the public has demanded reduction in the use of pesticides because of their potential hazard to humans and environment. A promising alternative to synthetic fungicides is biological control with beneficial microorganisms (bacteria and yeasts) that occur naturally on fruit trees. As the commercial potential of some of these beneficial microorganisms is being explored by private industry, the cost of production will become the major factor in future implementation of this method. We found that a mixture of beneficial bacterium and yeast was superior in controlling apple mold, as compared to applications of these organisms individually. These organisms have different abilities to utilize nutrients and cooperate well in exploiting available nutrients in apple wounds, the place of mold infection. Higher effectiveness of the mixture allows a reduced application rate of the beneficial organism without diminishing control and increases the economics of this method.
Technical Abstract: Two antagonists, bacterium Pseudomonas syringae and pink yeast Sporobolomyces roseus, effective against blue mold (caused by Penicillium expansum) on apple, controlled this disease more effectively when combined at approximately equal biomass (50/50 % of the same turbidity). The addition of L-asparagine enhanced biocontrol effectiveness of P. syringae, but decreased that of S. roseus and had not significant effect when antagonists were combined. Populations of both antagonists increased in apple wounds and were further stimulated by the addition of L-asparagine. The carrying capacity of wounds for P. syringae were not effected by S. roseus. Populations of P. syringae in wounds inoculated individually or in a mixture (50/50 %) with S. roseus reached the same level after three days at 22 C. However, populations of S. roseus from mixture applications were consistently lower than from individual applications. Thirty-six carbon and 35 nitrogen compounds were tested for utilization by both antagonists. Fourteen nitrogenous compounds were utilized by both P. syringae and S. roseus, and an additional 9 compounds were utilized by P. syringae. S. roseus utilized 17 and P. syringae 13 carbon sources, nine of which were common to both antagonists. Populations of these antagonists in apple wounds appear to form a relatively stable community dominated by P. syringae. This domination is probably due to greater ability to utilize nitrogen sources which is the limiting growth factor in carbon rich apple wounds.