Date of Award

12-2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Plant and Environmental Science

Advisor

Agudelo, Paula

Committee Member

Knap , Halina

Committee Member

Lawton-Rauh , Amy

Committee Member

Mueller , John

Committee Member

Shipe , Emerson

Abstract

Rotylenchulus reniformis, reniform nematode, is a highly variable species and an economically important pest in many cotton fields across the southeast. Rotation to resistant or poor host crops is a prescribed method for management of reniform nematode. An increase in the incidence and prevalence of the nematode in the United States has been reported over the last two decades. However it is not clear whether the observed increase is related to the emergence of novel populations that are more aggressive or have a higher fitness or shifts in host availability or susceptibility. The objectives of this research were to determine the variability of the species by studying the effect of crop rotations on the genotype of reniform nematode populations, the effect of temperature on the embryonic development of reniform nematode populations from the southeastern United States, and to determine the genetic diversity of R. reniformis populations representing cotton-growing areas in the United States. We used AFLPs (Amplified Fragment Length Polymorphisms) to determine changes in population structure due to rotations. Six rotation schemes were used that included susceptible cotton and soybean, resistant soybean, and non-host corn during four planting cycles. Distinct changes in genotype were observed following rotations with resistant soybean or corn. Rotations involving reniform nematode resistant and susceptible soybean cultivars had the most distinct effect on population structure. To determine variability of populations in the absence of a host, embryogenesis was compared among three geographic reniform nematode populations at 20, 25, 30, and 35ºC. The greatest differences among populations occurred at 20 and 35ºC. Results at the intermediate temperatures (25 and 30oC) were similar for the three populations. Reniform nematode may have the ability to increase its distribution range through variants able to reproduce in a wider temperature range, but genetic variability of isolates needs to be determined. To determine the genetic variability of individual reniform nematodes we developed and optimized 10 polymorphic microsatellite loci and tested loci on 160 individual reniform nematodes to determine informative genetic variation of isolates from the Southeastern United States, Colombia, and Japan and R. parvus isolated from a field in Arizona. Most isolates exhibited significant genotypic differentiation and moderate to very high genetic differentiation based on FST analysis. The most consistently differentiated isolates were found reproducing parthenogenetically in Japan. Understanding the adaptive potential of this species is crucial for the development of durable management strategies, and our results indicate a need for an standardized method to genetically characterize R. reniformis variants and monitor variation.

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