Continued pursuit of sanitiser products for potential use in the apple and pear industry

Limited fruit sanitation products are registered and currently available to the South African pome fruit industry. Alternatives to chlorine (Cl) are needed. This study aims to identify alternative sanitisers or sanitiser combinations that can substitute or reduce the use of Cl in flume tanks

In vitro and in vivo tests were used to test the efficacy of nine alternative sanitiser products against Penicillium expansum, Botrytis cinerea and Alternaria alternata. The efficacy of the products was evaluated using different product concentrations, contact periods and spore concentrations. The most promising sanitisers and sanitiser combinations were selected for in vivo efficacy trials on Golden Delicious apples and Packham’s Triumph pears.

San (all doses), O₃ (> 2h exposure), IW (850 mV) and Cl (100 ppm) was the most effective against P. expansum, B. cinerea and A. alternata, with IA (4X), Pur (4X) and PCF (all doses) only effective against B. cinerea. The longer the exposure of the pathogen spores to the products, the higher the efficacy. San (4X) was the most effective at 1 min followed by Cl (125 ppm). Higher spore loads were more difficult to control. San (all doses), O₃ (> 2h exposure) and Cl (125 ppm) were the most effective against high spore loads. All treatments combined with San (1X) was 100% effective, most likely due to good efficacy demonstrated by San applied on its own. Combining Cl (50 ppm) with AI (2X), PCF (2X) and HD (2X), and combining HD (2X) with PCF (2X) and AI (2X) improved efficacy depending on the pathogen. San (1X) and Cl (100 ppm) were the most effective against B. cinerea on apples and pears. Most treatments expressed high efficacy against A. alternata on apples and pears but efficacy of the combination PCF (2X) + Cl (50 ppm) was the lowest. Phytotoxic effects were observed with PCF (2X) + Cl (50 ppm) on apples and pears. Generally, decay was higher on pears than apples, implying host susceptibility influences product efficacy.

Cl, San and O₃ were the most effective against P. expansum, B. cinerea and A. alternata. There are more sanitiser options available to control B. cinerea. Further in vivo research is recommended. Research should focus on San and O₃ gas, and ways in which they can be implemented along the supply chain. The stability of sanitisers in flume tanks over time (days) should be investigated.

San is a safer and potentially more effective sanitiser than Cl currently used in pome fruit packhouses. Further tests and large scale (in vivo) trials are however recommended prior to commercial use.