The Relationship between Insect Resistance and Tree Age of Transgenic Triploid Populus tomentosa Plants

Yachao Ren, Jun Zhang, Guiying Wang, Xiaojie Liu, Li Li, Jinmao Wang, Minsheng Yang

To explore the stability of insect resistance during the development of transgenic insect-resistant trees, this study investigated how insect resistance changes as transgenic trees age. We selected 19 transgenic insect-resistant triploidPopulus tomentosalines as plant material. The presence of exogenous genes and Cry1Ac protein expression were verified using polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) analyses. The toxicity forClostera anachoretaandLymantria disparwas evaluated by feeding fresh leaves to first instar larvae after the trees were planted in the field for 2 years and after the sixth year. Results of PCR showed that the exogenous genes had a long-term presence in the poplar genome. ELISA analyses showed significant differences existed on the 6-year-old transgenic lines. The insect-feeding experiment demonstrated significant differences in the mortality rates ofC. anachoretaandL. disparamong different transgenic lines. The average corrected mortality rates ofC. anachoretaandL. disparranged from 5.6-98.7% to 35.4-7.2% respectively. The larval mortality rates differed significantly between the lines at different ages. Up to 52.6% of 1-year-old transgenic lines and 42.1% of 2-year-old transgenic lines causedC. anachoretalarval mortality rates to exceed 80%, whereas only 26.3% of the 6-year-old transgenic lines. The mortality rates ofL. disparexhibited the same trend: 89.5% of 1-year-old transgenic lines and 84.2% of 2-year-old transgenic lines causedL. disparlarval mortality rates to exceed 80%; this number decreased to 63.2% for the 6-year-old plants. The proportion of 6-year-old trees with over 80% larval mortality rates was clearly lower than that of the younger trees. The death distribution ofC. anachoretain different developmental stages also showed the larvae that fed on the leaves of 1-year-old trees were killed mostly during L1and L2stages, whereas the proportion of larvae that died in L3and L4stages was significantly increased when fed on leaves of 6-year-old trees. Results of correlation analysis showed there was a significant correlation between the larvae mortality rates of trees at different ages, as well as between Cry1Ac protein contents and larvae mortality rates of 6-year-old trees.