Untersuchungen der genetischen Diversität von Maiszünsler-Populationen (Ostrinia nubilalis, Hbn.) und ihrer Suszeptibilität gegenüber dem Bacillus thuringiensis (Bt)-Toxin als Grundlage für ein Resistenzmanagement in Bt-Maiskulturen

摘要

Transgenic maize cultivars expressing Bacillus thuringiensis (Bt) toxin need management to avoid resistance development of the target pest species European corn borer (Ostrinia nubilalis Huebner), the most important insect pest in corn. The European Corn Borer can reduce yields up to 20%. Due to the continuous expression of the Bt toxin during the vegetation period, a selection of resistant genotypes of the Europen Corn Borer is expected to be more likely than from conventional Bt sprays. Sustainability of transgenic plants use requires a solid understanding of the insect population for maintaining susceptible individuals The aim of this work was to establish methods to be able to forecast a possible development of resistance in an early stage. For this reason the baseline susceptibility of different ECB populations in Germany was measured. Tests were performed by treating first instar larvae with different Bt-toxin concentrations incorporated into the nutrition medium or applied onto the medium (surface treatment). LC50 values of the different German populations ranged from 0,12-0,41 µg/g diet and 1,55-2,42 µg/g diet for truncated Cry1Ab depending on the production of the toxin. For untruncated Cry1Ab the LC50 was between 0,82-1,15 µg/g diet. The surface treatment was carried out as comparison to the incorporation method. LC50 values ranged from 16,50-35,14 ng/cm2. No significant differences were detected for populations from different regions of Germany with both methods. Additional effort was spent into the methodology on how to detect susceptibility change through regular monitoring, including harmonization of different approaches in various research groups of EU countries. The second part of the study identifed geographical distinct ECB populations by help of molecular fingerprinting techniques such as AFLP and RAPD-PCR. Knowledge about the population structure is helpful for gene flow estimation, which is an essential information for resitance management. Based on dendograms fingerprint analysis, very small genetic differences were detected between populations. Although genetic distances were small, separation into distinct populations was possible by use of the AFLP method. These data suggest little genetic differentiation among populations, both in terms of susceptibility to Bt toxin and of the genetic background. Future monitoring can sufficiently be performed concentrating on a single ECB population representative for south western Germany.