Degree

Doctor of Philosophy (PhD)

Department

Department of Plant Pathology and Crop Physiology

Document Type

Dissertation

Abstract

Root-knot nematodes (RKN), Meloidogyne spp., are significant agricultural pests that cause severe economic losses on a wide range of agricultural crops worldwide, including sweetpotato. The economic viability of the sweetpotato industry in the United States is threatened by Meloidogyne enterolobii, which reproduces on sweetpotato cultivars resistant to other RKN species. To address this issue, 69 sweetpotato genotypes were evaluated to identify sources of resistance to M. enterolobii (Me) and M. incognita (Mi). Results showed that twenty-six genotypes were highly resistant to Me and eleven were resistant to Mi, with three genotypes showing resistance to both nematode species. The second objective was to evaluate the penetration, development, and reproduction of Me and Mi in sweetpotato. In resistant genotypes, such as ‘Jewel’, ‘LA14-31’, and ‘LA19-65’, Me remained as J2-stage, with halted development linked to necrotic reaction in response to root penetration by Me. For Mi, the defense response resulted in nematodes dying, maturing as males, or experiencing delayed development into adult females, with a marked reduction in egg production. The third objective involved follow-up histological observations that revealed hypersensitive cells reacting to nematode penetration in resistant genotypes. These findings provide evidence that the resistance mechanism in sweetpotato against Me is mediated by a hypersensitive reaction (HR) response that prevents the feeding site establishment and inhibits nematode development. The fourth objective was to evaluate the root system architectural (RSA) response of sweetpotato genotypes to varying inoculation levels of Me and Mi. Results showed that the genotype ‘LA18-100’ (released as ‘Avoyelles’) had greater RSA attributes compared to other genotypes evaluated. The RSA response to nematode infection was genotype-specific, and not linked to nematode resistance. However, incorporating RSA attributes into the breeding programs holds potential for identifying genotypes with favorable rooting and possible yield traits. Overall, these findings suggest that resistance to both nematode species is available in the sweetpotato genotypes developed at the LSU AgCenter. Resistance to Me appears to be qualitative and involves an HR response that prevents migration and feeding site establishment, whereas resistance to Mi appears to be quantitative, involving delayed nematode development and reductions in egg production in resistant genotypes.

Date

10-25-2024

Committee Chair

Watson, Tristan

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