Engineering Tolerance to the Diaprepes Root Weevil (Diaprepes abbreviates L.) through Expression of the Snowdrop Lectin (Galanthus nivalis agglutinin; GNA) in Citrus

Diaprepes abbreviatus is a major pest of citrus in Florida. This weevil has a wide host range and in addition to citrus can feed on many ornamental plants and other economically important crops such as corn, sweet potato and sugarcane.  In citrus, the larvae feed on the roots, girdling the structural roots and preventing the uptake of water and nutrients. This damage can result in plant mortality, especially in younger trees. Root damage due to Diaprepes can also increase root rot caused by Phytophthora  Carrizo citrange rootstock engineered to constitutively express Snowdrop lectin (GNA) demonstrated superior tolerance to the Diaprepes weevil after feeding experiments. Larval mortality rate was higher in several transgenic lines expressing GNA. In addition, larval fresh weight was reduced.  A few transgenic lines had minimal root damage compared to the control trees, most of which had no roots at the end of the study. The copy number varied from 1 to 3 in most Diaprepes tolerant lines, while most of the susceptible lines had more copies of the transgene stably incorporated into the genome. Gene expression profiling using qPCR demonstrated a wide variation among the various lines. Our results indicate that the GNA protein can be useful for improvement of Diaprepes tolerance in citrus. GNA can also potentially be used for Diaprepes protection in other economically important crops.