Although BCPD can provide levels of control that are commercially acceptable, the performance margin of biocontrol is generally lower than for fungicides. For example, higher concentrations of the antagonist must be used to achieve the same control of decay as fruit mature. To increase the performance margin of biocontrol, attempts have been made to integrate biocontrol with other alternatives to synthetic fungicide methods that were developed mainly during the past two decades (Conway and Sams 1983; Falik et al. 1995; Smilanick et al. 1995; 1997; 1999; Smoot and Melvin 1965; Spotts 1984; Spotts and Chen 1987; Tukey 1993). These methods alone did not provide commercially acceptable control of fruit decay, but in combination with biocontrol increased its performance margin.
Infiltration of apples with calcium chloride alone reduced blue mold decay by approximately half (Conway and Sams 1983), but in combination with the antagonist, P. syringae, resulted in greater reduction of fruit decay than either treatment alone (Janisiewicz et al. 1998). The effects of calcium treatment were greatest on more mature fruit, inoculated after 3 or 6 months in storage, when the effectiveness of biocontrol declines (Conway et al. 1999). Combining biocontrol with a calcium treatment complements each other to overcome the shortcomings of each, and may allow for reduced amounts of both products to be used without compromising decay control. In addition, applying lower calcium concentrations would reduce potential calcium injury, while maintaining other benefits, including alleviating storage maladies, such as bitter pit. The addition of calcium chloride to the yeast antagonist Candida sp. also improved control of blue mold and gray mold on apples (McLaughlin et al. 1990; Wisniewski et al. 1995).
Treating apples with hot air (4d at 38°C) may virtually eliminate blue mold of apple but it has no residual effect, and any inoculation with pathogens following heat treatment results in decay (Falik et al. 1995; Lurie et al. 1998). Combining antagonistic yeasts or bacteria with heat treatment improved control of blue mold on apples (Conway et al. 1999). The heat treatment eradicated P. expansum infections up to 12 h after inoculation, and yeast and bacterial antagonists provided the residual effect. The heat treatment complemented the lack of eradicative activity of the antagonists, the major shortcoming of BCPD. It may have additional benefits of eradicating pathogens from fruit bins and storage rooms (Douglas 1998).
Substances generally regarded as safe (GRAS), such as sodium carbonate, sodium bicarbonate, ethanol, acetic acid, hydrogen peroxide, chitosan, or some edible coatings can reduce pathogen germination and growth. They are acceptable to the consumers, and in contrast to synthetic fungicides, do not have the prospect of a lengthy and costly approval process from regulatory agencies. For example, sodium carbonate has been used to treat lemons in commercial packinghouses (Smilanick et al. 1999). Combining 3% sodium carbonate with the antagonist P. syringae ESC-10 was superior to the individual treatments in controlling green mold on citrus (Smilanick et al. 1999). This compound also improved control of blue mold and gray mold of oranges in combination with antagonist P. agglomerans (CPA-2) (Teixido et al. 2001). Sodium carbonate has up to 24 h of eradicative activity, but little residual activity, which, like heat treatment, complements biocontrol. Treatment of lemons with 10% ethanol reduced green mold to less than 5% (Smilanick et al. 1995). The addition of 10% ethanol to suspensions of S. cerevisiae strains 1440 and 1749, which had little biocontrol activity, reduced gray mold decay of apple from more than 90% to close to 0% (Mari and Carati 1998). Chitosan and its derivatives can reduce fungal growth and induce resistance responses in harvested fruits and vegetables (Allan and Hadwiger 1979; El-Ghaouth 1998). The addition of 0.2% glycolchitosan to a suspension of the antagonist C. saitoana increased control of green mold of oranges and lemons, and gray and blue mold of apples over that of the antagonist alone (El-Ghaouth et al. 2000a, b).
There are many more possibilities for combining biocontrol agents with GRAS substances or other nonfungi-cidal treatments. The above examples of improving biocontrol and integrating biocontrol with other nonfungici-dal treatments demonstrate that biocontrol is amenable to manipulation and can be easily integrated with various decay control measures resulting in additive or synergistic effects. Strategies must be developed for the integration of various treatments in order to maximize decay control (Conway et al. 1999). Various control measures may be applied in succession and these applications may be customized to fit different postharvest practices.
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