Biological control of brown rot of postharvest peaches with Bacillus subtilis.
Hazen, Beth Eva.
Thesis of Ph.D., Cornell University, 1989, 76 pages
1989
บทคัดย่อ
Various parameters of the biological control system involving the antagonist Bacillus subtilis against the pathogen Monilinia fructicola on harvested peach fruit were defined. The developmental fate of the fungus, its association with the bacteria and the timing of cytological interactions between B. subtilis and M. fructicola, both in vivo and in vitro, were monitored. Fruit were pretreated with bacteria either in their nutrient medium or resuspended in water, then challenged with an aqueous suspension of conidia. Sections were excised between 0 and 48 h after inoculation for light microscopy and scanning electron microscopy. Pretreating harvested, wounded peach fruit with about 108 colony forming units bacteria ml(-1) culture medium completely inhibited brown rot decay by 105 to 107 conidia ml(-1) water. Bacteria and benomyl pretreatments of nonwounded fruit inhibited all decay from conidia but only partially suppressed decay from mycelium. All peaches decayed when inoculated with coni
dia more than 3 h in advance of the bacteria. Populations of bacteria initially applied at about 109 cfu ml(-1) on wounded fruit stored at 24 C increased ten-fold in 24 h. Populations continued to increase over the 4-d period, in both the presence and absence of the fungus. These fruit decayed, even when the fungus was not present. Bacterial populations applied to intact surfaces, however, decreased over time without causing rot. When fruit were held at 4 C, populations decreased ten-fold within the first 24 h, then stabilized at this population for 4 d, regardless of the presence of wounds or fungus. Microscopy showed that conidial germination was inhibited by bacteria in either medium or water. The fungus did colonize the wounds, but only fruit treated with bacteria in water had lesions. Hyphal elongation was reduced, and some hyphae were lysed by bacteria. In vitro germination was totally inhibited, and many conidia were lysed by 107-10(10) cfu bacteria ml(-1) of culture medium. Germination was
only partially inhibited and hyphal elongation was retarded by bacteria at 106 cfu ml(-1) of medium and by culture filtrate from 107 cfu ml(-1). When applied at appropriate levels, B. subtilis controlled postharvest rot that was initiated from conidia by inhibiting germination and hyphal elongation, but did not control rot that was initiated from mycelium.