EXPRESSION OF A BACILLUS-THURINGIENSIS CRYIA(C) GENE IN TRANSGENIC PEANUT PLANTS AND ITS EFFICACY AGAINST LESSER CORNSTALK BORER

The invasion of peanut (Arachis hypogaea L.) pods and seeds by aflatox in-forming species of Aspergillus is linked to injury by the lesser co rnstalk borer and frequently causes a severe reduction in crop quality . The lesser cornstalk borer is susceptible to the lepidopteran-active Bacillus thuringiensis insecticidal crystal protein. We have introduc ed a codon-modified Bacillus thuringiensis crIA(c) gene into peanut us ing microprojectile bombardment. The toxin-coding region of a Bt cryIA (c) gene was reconstructed for expression in plants and the resulting 3.4 kb gene cassette (promoter: 1.8 kb coding: 3') was directly cloned into the BglII site of plant transformation vectors. The vectors cont ained the hph gene, conferring resistance to the antibiotic hygromycin . Somatic embryos initiated from immature peanut cotyledons of two cul tivars were used as the target for bombardment. DNA from hygromycin-re sistant embryogenic cell lines, regenerated plants, and a progeny plan t showed the presence and integration of hph and Bt genes by PCR and/o r Southern blot analyses. ELISA immunoassay of the CryIA(c) protein fr om the hygromycin-selected plants showed the expression of CryIA(c) pr otein up to 0.18% of total soluble protein, Insect feeding bioassay of transformed plants indicated various levels of resistance to the less er cornstalk borer, from complete larval mortality to a 66% reduction in larval weight. A negative correlation between percent survival or l arval weight and the amount of Bt CryIA(c) protein was recorded indica ting in general that the higher the protein level the lower the surviv al or larval weight of the insect. Based on leaf bioassay, transformat ion of peanut with vectors containing the Bt cryIA(c) gene may be effe ctive in protecting the peanut plants from damage by lepidopteran inse ct larvae of lesser cornstalk borer.