PROTECTION OF STORED LEGUME SEEDS AGAINST ATTACK BY STORAGE FUNGI AND WEEVILS - MECHANISM OF ACTION OF LIPOIDAL AND OIL SEED TREATMENTS

Some lipids applied as seed treatments were effective in preventing adult development of the Mexican bean weevil, Zabrotes subfasicatus (Boheman), and others decreased seed infection by the storage fungus, Aspergillus ruber (Konig, Spieckermann and Bremer) Thom and Church. The mechanisms of three lipids, a mineral oil and two soybean lipids, differing in degree of saturation were studied. Treating seeds with lipids labelled with a fluorescent dye (Nile red) revealed that lipids differed in their ability to penetrate dry beans, Phaseolus vulgaris L., and indicated that different amounts of these lipids remained on the seed surface. Residual lipid from Nile red-labelled lipids was observed on and around the weevil egg laid on treated seeds. The incorporation of fluorescent microspheres into test oil or lipids demonstrated the migration of the highly saturated lipids over the egg surface. Scanning electron micrographs revealed a variation in the accumulation of residual lipid on the egg surface. After 80 h in storage all of the highly saturated soybean lipid applied to the seed surface could still be extracted. The highly unsaturated soybean lipid significantly reduced radial growth of A. ruber when tested 6 weeks after treatment, but not when tested on freshly prepared medium.