Root-Knot Nematode Resistance in Sweetpotato and Development of Sweetpotato Differential Host Genotypes for Meloidogyne spp.

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Title: Root-Knot Nematode Resistance in Sweetpotato and Development of Sweetpotato Differential Host Genotypes for Meloidogyne spp.
Author: Cervantes-Flores, Jim Carlos
Advisors: G. Craig Yencho, Co-Chair
Eric L. Davis, Co-Chair and Minor representative, Member
William H. Swallow, Minor representative, Member
Rebeca C. Rufty, Member
Abstract: Root-knot nematodesrepresent a significant problem in sweetpotato, Ipomoea batatas (L.) Lam., causing reduction in yield and quality of the storageroots. The following experiments were conducted to: (1) test the use of an alternative screening method for root-knotnematode resistance; (2) assess the effect of different root-knot nematode spp. on sweetpotato cultivars; and (3) develop a setof sweetpotato differential host genotypes for Meloidogyne species. In the first study, five sweetpotato cultivars were selectedand evaluated for resistance to Meloidogyne incognita race 3, M. arenaria race 2, and M. javanica. Screening was conductedin 400-cm3 square pots and 150-cm3 Conetainers. Nematode infection was measured as the percentage of root systemgalled, percentage of root system necrosis, and the number of nematode eggs per gram of root tissue. Means of dependentvariables were not significantly different between the two container types. Conetainers were the more efficient pot type,because they required less space and permitted an easier assessment of nematode infection. Resistance responses differeddepending on the nematode species and sweetpotato cultivar. All cultivars were resistant to M. arenaria race 2, while 'Hernandez', 'Excel' and 'Jewel' were also resistant to M. incognita race 3 and M. javanica. In the second study, twenty-sevensweetpotato genotypes were evaluated for their resistance to North Carolina root-knot nematode populations: M. arenaria(races 1 and 2), M. incognita (races 1, 2, 3, and 4), and M. javanica. Sweetpotato plants were evaluated in 150-cm3Conetainers. Nematode infection was assessed as the number of egg masses per root system. Different sweetpotatogenotypes were hosts for different Meloidogyne populations. Five out of the 27 genotypes ('Beauregard', L86-33, PDM P6,'Porto Rico', and 'Pelican Processor') were selected as sweetpotato differential hosts because of their resistance reaction to theMeloidogyne spp. These genotypes were tested against twelve M. incognita populations belonging to the four standardizedhost races collected from different geographical locations worldwide. Virulence of the M. incognita populations varieddepending on the sweetpotato genotype and did not always correspond to host race as classified by the North CarolinaDifferential Host Test. 'Beauregard', L86-33, and PDM P6 were hosts for the 12 nematode populations, but differences in theaggressiveness of the populations were observed among the three sweetpotato genotypes. 'Porto Rico' and 'Pelican Processor'had differential host status to the M. incognita populations irrespective of their host race. These results suggest that: 1) multiplefactors might be responsible for conferring virulence in the nematodes; 2) multiple genes could be involved in the resistance toroot-knot nematodes in sweetpotato; and 3) the final outcome of root-knot nematode resistance in sweetpotato would dependon the specific interaction of these two factors. Further, these results suggest that Meloidogyne populations should be testedagainst sweetpotato differential hosts in order to determine the pathotypes affecting sweetpotato. This would help tostandardize the evaluation of resistance to root-knot nematodes in sweetpotato breeding programs, and possibly identifyreliable sources of resistance to numerous pathotypes of Meloidogyne spp.
Date: 2001-01-12
Degree: MS
Discipline: Horticultural Science

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