The basis for rootstock resilient to capnodis species: Screening for genes encoding δ-endotoxins from Bacillus thuringiensis

BACKGROUND: Conventional methods often fail to control the flatheaded borers Capnodis spp., major pests of stone fruit trees; the larvae are protected from insecticides and predation because they feed deep in the roots. A potential solution is transgenic trees producing in their roots toxic compounds such as Cry proteins of Bacillus thuringiensis (Bt). RESULTS: Toxicities against Capnodis larvae were demonstrated by exploiting a recently designed artificial larval diet and an available collection of field isolated Bt. An isolate of Bt tenebrionis (Btt) from commercial bioinsecticide (Novodor) displayed LC₅₀ and LC₉₅ values of 3.2 and 164mg g^-1, respectively, against neonates of Capnodis tenebrionis, whereas values of the most toxic field isolate K-7 were 1.9 and 25.6mg g^-1 respectively. Weights of surviving larvae after 1month on diets containing low concentrations of K-7 (0.1-1.0mg g^-1) were lower than on Btt or untreated larvae. K-7 was also toxic against larvae of C. cariosa and C. miliaris and found to harbour genes encoding Cry9Ea-like and Cry23Aa/Cry37Aa binary toxins. CONCLUSION: Larvae of Capnodis spp. are susceptible to Bt Cry toxins. Expressing cry genes active against these pests thus seems a feasible solution towards production of transgenic rootstock trees resilient to the pest.