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The effects of seed-storage lipid emulsion sprays on the interactions between plants and their fungal pathogens Young, Roderick James


Emulsions of the seed-storage lipids jojoba wax and canola oil were tested for phytoprotective activity against two powdery mildews and two rot-causing fungi, and for phytotoxicity on two host plants, grape ( Vitis vinifera) and cucumber (Cucumis sativus). Against the powdery mildews tested (Erysiphe cichoracearum and Uncinula necato,), greenhouse cucumber plants and field grape plants treated with jojoba wax emulsions showed 75-100% reductions in powdery mildew disease severity, as compared to water sprayed plants. The canola oil emulsion reduced cucumber powdery mildew disease severity by 63-69%. Scanning electron microscope analyses of E. cichoracearum conidia on cucumber leaves sprayed with the seed-storage lipid emulsions showed normal germination structures with inhibited appressorium formation. The jojoba wax emulsions did have slight phytotoxic effects observable on both the cucumber and grape plants, especially during periods of higher temperature. However, these effects were not observed to reduce the yield or survival of the grape plants sprayed in field trials. Jojoba wax and canola oil emulsions did not seem to have an effect against the infection processes of rot-causing fungi (Botrytis cinerea and Didymelia bryoniae). Instead, the lack of differences between the growth of B. cinerea colonies on potato dextrose agar (PDA) treated with the seed-storage lipid emulsions or the emulsifying surfactant Triton X-100 alone indicated that the presence of the surfactant was correlated with reduced colony growth. Colony growth on Triton X-1 00-treated PDA was reduced by 87-92% as compared to the water control-treated PDA. In addition, field grape plants treated with emulsions containing Triton X-1 00 showed a 68-87% reduction in B. cinerea-caused disease incidence. While similar reductions in D. bryoniae growth were observed in vitro for PDA treated with emulsions containing Triton X-100, the surtactant or the lipid emulsions did not reduce D. bryoniae-caused disease incidence in the in vivo trials on greenhouse cucumbers plants. Applied treatments may have been washed away by exuding sap.

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