Charles L. Wilson

Postharvest biological control of stone fruit brown rot by bacillus subtilis

A method for treating postharvest stone fruit to prevent or inhibit brown rot of stone fruit with effective amounts of any of the following active ingredients in a carrier is disclosed: Bacillus subtilis B-3; Bacillus subtilis B-3 in combination with 2,6-dichloro-4-nitroaniline; Bacillus subtilis B-3 in combination with water based wax; and, Bacillus subtilis B-3 in combination with paraffin and mineral oil base.

Alternative disease control agents induce resistance to blue mold in harvested 'red delicious' apple fruit.

ABSTRACT Alternative control agents, including UV-type C (254 nm) irradiation, yeasts antagonistic to fungal growth, chitosan and harpin, were evaluated for their ability to induce resistance in cv. Red Delicious apple fruit against postharvest blue mold caused by Penicillium expansum. Freshly harvested and controlled atmosphere (CA)-stored fruit were treated with these agents at different doses and concentrations or with paired combinations of the agents. Treated fruit were inoculated with P. expansum 24, 48, or 96 h following treatment, and stored at 24 degrees C in the dark. The fruit were evaluated for development of disease every 2 days for 14 days by measuring the diameter of lesions that formed. The area under the disease progress curve (AUDPC) was calculated and analyzed statistically. All treatments were effective in reducing the AUDPC; UV-C was most effective, followed by harpin, chitosan, and the yeasts, respectively. Regardless of treatment, fresh fruit were more responsive to treatments than CA-stored fruit. There was a clear time-dependent response of the fruit to the treatments, in which treatments applied 96 h before inoculation provided the best results. In a few situations, the combinations of agents did provide an additive effect, but no synergistic effects were detected. Moreover, disease severity in fruit treated by any combination was markedly better than that in the controls. Although the combinations of treatments was overall less effective than the single treatments, they did provide significant reductions of the progress of disease in comparison with the controls. Because the fungus did not come into contact with any of the control agents, this study showed conclusively that the agents studied were able to induce resistance in the fruit rather than merely inhibit the pathogen directly. It also showed, for the first time, that harpin is able to induce resistance in harvested apple fruit. The use of these control agents may minimize the costs of control strategies and reduce the risks associated with the excessive use of fungicides in harvested apple fruit.

Pre- and Post-harvest Harpin Treatments of Apples Induce Resistance to Blue Mold

Harpin was studied for its ability to induce resistance in apple fruit to blue mold caused by Penicillium expansum after harvest. Red Delicious fruit were harvested and sprayed with harpin at 0, 40, 80, and 160 mg/liter applied as a commercial formulation. At 48, 96, and 144 h after treatment, fruit were wound inoculated with spore suspensions of P. expansum at 103, 5 × 103, or 104 spores/ml. The diameters of the resulting lesions were directly proportional to the inoculum concentration. Fewer fruit treated with harpin became infected relative to the controls, and disease progress was considerably reduced. In a second experiment, apple trees of the cultivars McIntosh, Empire, and Red Delicious were sprayed with different concentrations of harpin 8 or 4 days before harvest. Fruit were harvested, wounded, inoculated with the fungus, and stored in a commercial cold room. Fewer fruit treated with harpin became infected compared with the controls. Greater control resulted from the higher concentrations of harpin, but no difference in control occurred as a function of interval between the spray time and harvest. Spraying apple trees with harpin a few days before harvest is a promising strategy for reducing blue mold decay in storage.

Some cellular correlates of harpin-induced resistance to blue mold of apples

Harpin is a protein produced by Erwinia amylovora that is involved in its pathogenesis of apple. We studied cellular correlates of harpin-induced resistance in apple fruit to blue mold caused by Penicillium expansum using Light (LM), scanning (SEM) and transmission (TEM) electron microscopy. SEM study of wound surfaces showed the fungus colonizing the wounds within 48 h, and profuse colonization of the wound and penetration of the tissue occurred within 72 h after inoculation of control samples. In harpin-treated samples, spore germination and wound colonization were not evident until 96 h. LM showed that intramural mycelial growth appeared as early as 72 h, and intense tissue colonization occurred by 96 h after inoculation in the control samples. In the harpin-treated fruit, spore germination and wound colonization occurred only by 144 h in the treated specimens. Numerous putative tannin vacuoles and appositions were observed in the epidermal and hypodermal cells of inoculated harpin-treated samples, but only a few appeared in control samples. TEM showed that intramural growth of the fungus occurred frequently in the controls. In harpin-treated specimens, wall depositions and appositions occurred very frequently. The results suggest that harpin may trigger or intensify cellular responses in harpin-treated apples.