Field Performance of Bt Eggplants (Solanum melongena L.) in the Philippines: Cry1Ac Expression and Control of the Eggplant Fruit and Shoot Borer (Leucinodes orbonalis Guenée)

Abstract

Plants expressing Cry proteins from the bacterium, Bacillus thuringiensis (Bt), have become a major tactic for controlling insect pests in maize and cotton globally. However, there are few Bt vegetable crops. Eggplant (Solanum melongena) is a popular vegetable grown throughout Asia that is heavily treated with insecticides to control the eggplant fruit and shoot borer, Leucinodes orbonalis (EFSB). Herein we provide the first publicly available data on field performance in Asia of eggplant engineered to produce the Cry1Ac protein. Replicated field trials with five Bt eggplant open-pollinated (OP) lines from transformation event EE-1 and their non-Bt comparators were conducted over three cropping seasons in the Philippines from 2010–2012. Field trials documented levels of Cry1Ac protein expressed in plants and evaluated their efficacy against the primary target pest, EFSB. Cry1Ac concentrations ranged from 0.75–24.7 ppm dry weight with the highest in the terminal leaves (or shoots) and the lowest in the roots. Cry1Ac levels significantly increased from the vegetative to the reproductive stage. Bt eggplant lines demonstrated excellent control of EFSB. Pairwise analysis of means detected highly significant differences between Bt eggplant lines and their non-Bt comparators for all field efficacy parameters tested. Bt eggplant lines demonstrated high levels of control of EFSB shoot damage (98.6–100%) and fruit damage (98.1–99.7%) and reduced EFSB larval infestation (95.8–99.3%) under the most severe pest pressure during trial 2. Moths that emerged from larvae collected from Bt plants in the field and reared in their Bt eggplant hosts did not produce viable eggs or offspring. These results demonstrate that Bt eggplant lines containing Cry1Ac event EE-1 provide outstanding control of EFSB and can dramatically reduce the need for conventional insecticides.

Assessing Potential Impact of Bt Eggplants on Non-Target Arthropods in the Philippines

“…We reported previously that Bt eggplant demonstrated nearly 100% control of its major pest, EFSB, without the use of supplemental sprays [39]. Ex-ante studies for Bt eggplant in the Philippines [12, 13] indicated that producers and consumers would be benefited by Bt eggplant technology adoption.…”

“…[39]. The experimental materials used in the series of three Confined Field Trial (CFT) experiments are listed in Table 1.…”

“…The Bt eggplant lines (D2, D3, M1, M4, M8 used as test entries) in the field trials are advanced breeding lines (BC 3 F 4 to BC 3 F 6 ) derived from initial crosses of Mara selection x Mahyco EE-1 and DLP selection x Mahyco EE-1. The Cry1Ac protein levels expressed in the terminal leaves (shoots) of Bt eggplant lines ranged from 10.58–24.87 ppm dry weight, and with < 1% EFSB shoot damage compared with up to 46.6% shoot damage in non-Bt comparators [39]. …”

Assessment of Pigeonpea (Cajanus cajan L.) transgenics expressing Bt ICPs, Cry2Aa and Cry1AcF under nethouse containment implicated an effective control against herbivory by Helicoverpa armigera (Hübner)

“…While both the wild types TTB-7 and Pusa 992 showed maximum leaf damage above 45% (Fig. 2), transgenic events of cry2Aa (1, 4, 9, 10, 11, 13, 14,) and cry1AcF (19,22,25,26) showed leaf damage below 20%. However, one of the transgenics, event 7 of cry2Aa, showed about 22% leaf damage and the remaining events 5, 6, 8, 21, 23 and 24 showed leaf damage below 30%.…”

“…Several studies have demonstrated successful field trials of transgenics developed for various traits, including insect resistance, through Bt ICPs. [20][21][22][23][24][25][26][27] However, there are no reports of evaluation of the reported pigeonpea transgenics outside laboratory conditions and under confined and contained soil conditions.…”