Helicoverpa zea, commonly referred to as corn earworm, has been a major pest of corn and cotton, along with many major crops grown in United States. Migration of this pest plays a major role in its distribution and successful survival. Part of the current resistance management strategy for transgenic crops, using non-Bt crops as refuges, is totally based on the movement of the adult populations between the Bt and non-Bt fields, and successful exchange of genetic material between the rare resistant and susceptible populations. To study the movement and migration patterns, and their implications in resistance management, suitable molecular genetic markers were comparatively selected, followed by a study of temporal variations in populations from north Mississippi. The dominant marker system Inter Simple Sequence Repeats (ISSR) was selected for the study based on higher polymorphism (5.0) and PIC (0.34) values compared to Simple Sequence Repeats (SSR) and Sequence Related Amplification Polymorphism (SRAP) marker systems. 53 ISSR loci were used in understanding the temporal variations in H. zea. Percent polymorphism and heterozygosity levels showed variation among the twelve collections tested. Early spring putative migrants were distinct from the rest of the generations. Population differentiation was higher in the beginning of the season and then declined by end of the season (pairwise FST = 0.341, early in March and 0.025, late in August). Average heterozygosity levels recorded were 0.11, coinciding with 1993 and 2002 data. The result of this study supports the existence of spring migration of adults and their contribution to the local gene pool. The extent of genetic exchange between the putative migrants and the local populations varied among three years. There is variation in population densities from migrants and local emergence in one of the three years. The results of this study indicate a need for continuous monitoring for genetic changes and their possible implications for resistance management in transgenic crops in Mississippi.
| Identifer | oai:union.ndltd.org:MSSTATE/oai:scholarsjunction.msstate.edu:td-4565 |
| Date | 02 May 2009 |
| Creators | Vemula, Satya Ravikanth |
| Publisher | Scholars Junction |
| Source Sets | Mississippi State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
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