SURFACTANT-INDUCED PHYTOTOXICITY - EVIDENCE FOR INTERACTION WITH EPICUTICULAR WAX FINE-STRUCTURE

Phytotoxicity of two homologous series of non-ionic surfactants [octylphenoxy polyethoxyethanol (OP), alpha-[4-(1,1,3,3-tetramethylbutyl) phenyl]-omega-hydroxypoly-(oxy-1,2-ethanediyl) and nonylphenoxy polyethoxyethanol (NP), alpha-(nonylphenol)-omega-hydroxypoly-(oxy-1,2-ethanediyl)], of varying oxyethylene (EO) chain length was studied in Brassica oleracea var. gongylodes (L.). Surfactant toxicity following foliar application was determined by visual rating of leaf damage and measurement of ethylene production. Surfactants of medium EO chain length (9.5 and 10 EO) were most phytotoxic; phytotoxicity decreased with decrease to 5 EO or increase to 30 EO. No difference in phytotoxicity was found between OP and NP surfactants. Ethylene production 12 h after application increased with increasing surfactant concentration (0.01-1% w/v) and was greater for droplets of 1.0-mu-l than for those of 0.5-mu-l. Regardless of droplet size and surfactant concentration, application of OP + 9.5EO enhanced ethylene production more than OP + 5EO. After disruption of epicuticular wax fine structure or removal of epicuticular wax, ethylene production following OP + 5EO application was significantly greater than that with OP + 9.5EO. In Hordeum vulgare (L.), Triticum aestivum (L.) and Vicia faba (L.), OP + 5EO induced highest ethylene production, whereas in Brassica napus var. napus (L.) and Brassica oleracea var. gemmifera (DC.) OP + 9.5EO was most phytotoxic. Surfactant phytotoxicity is discussed in relation to wetting characteristics of microrough leaf surfaces of Brassica species.