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Though little published data have been collected, it is commonly accepted that damage caused by soil-borne pathogens, such as FON and plant parasitic nematodes ( Meloidogyne spp.), has increased since the phase-out of methyl bromide. The ban on

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Resistance to root-knot nematodes (Meloidogyne spp.) in tomato (Lycopersicon esculentum Mill.) plants has been reported to break down at soil temperatures >28C. We evaluated in vitro root explants of tomato heterozygous (Mimi), homozygous (MiMi) at the Mi locus, or lacking the Mi-1 gene for resistance to Meloidogyne incognita (Kofoid & White) Chitwood and Meloidogyne arenaria (Neal) Chitwood at 28, 31, 34, and 37C. Genotypes Ace-55 UF and Rutgers, lacking the dominant allele, were susceptible to M. incognita and M. arenaria at all temperatures. Genotypes possessing the dominant allele (heterozygous or homozygous) were equally resistant to both nematode species. The resistance level in these genotypes was maintained fully at 31C, partially maintained at 34C, and lost at 37C. Resistance in the heat-tolerant Mi-heterozygous accession CLN 475-BC1F2-265-4-19 was not different from that of the heat-sensitive genotypes. As temperature increased, the genotypes differed in their sensitivity to resistance conferred by the Mi-1 locus.

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Heritabilities for resistance to root knot nematodes (Meloidogyne javanica and Meloidogyne incognita races 1, 2, 3, and 4) were studied in a population of 226 sweetpotato clones of diverse origin. For each nematode isolate tested, 128-cell speedling trays were filled with previously inoculated substrate (30000 eggs/1000 mL substrate). Sweetpotato clones suitably tagged and identified were randomly planted in the cells (one plant/cell), with a total of four plants per clone per isolate. Ninety days after inoculation, sweetpotato plants had their roots washed for substrate removal, and treated with 150 mg·L–1 Phloxine B to stain nematode egg masses. The number of egg masses per root was recorded, and plants were accordingly assigned scores from 0 (highly resistant) to 5 (highly susceptible). Broad-sense heritability estimates were 0.87, 0.91, 0.81, 0.95, and 0.93 respectively for resistance to M. javanica and races 1, 2, 3, and 4 of M. incognita. The frequencies of resistant genotypes were higher for M. javanica and lower for M. incognita race 2. Genotypic correlations (rG) among the resistances to the various Meloidogyne isolates utilized were weak, ranging from 0.11 to 0.57, suggesting independent genetic controls. Clones could be selected, however, with high levels of resistance to all nematode isolates tested. (This work was supported by CNPq, CAPES, FAPEMIG, and FAEPE/UFLA.)

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( Meloidogyne spp.) cause extensive damage to watermelon throughout the southern United States ( Sumner and Johnson, 1973 ; Thies, 1996 ; Thomason and McKinney, 1959 ; Winstead and Riggs, 1959 ) and increase the severity of Fusarium wilt in watermelon

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. Literature Cited Atamian, H.S. Roberts, P.A. Kaloshian, I. 2012 High and low throughput screens with root-knot nematodes Meloidogyne spp J. Vis. Exp. 61 E3629 Box, G.E. Cox, D.R. 1964 An analysis of transformations Journal of the Royal Statistical Society

Open Access

), increased soil salinity ( Rudisill et al. 2015 ), and lack of crop rotation and sanitation ( Bruce et al. 2019 ). One of those challenges includes RKN ( Meloidogyne spp.). RKNs are one of the most destructive plant-parasitic nematodes worldwide with a

Open Access

by a number of soilborne pests, including pathogens such as Pythium spp. and Verticillium dahlia ; nematodes such as lesion nematode ( Pratylenchus spp.), root-knot nematode, and dagger nematode ( Xiphinema spp.); and competition from a wide

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Plant-parasitic root-knot nematodes (RKNs; Meloidogyne spp.) can cause severe damage to their hosts, leading to reductions in crop yield and quality ( Taylor and Sasser, 1978 ). These pathogens become problematic, especially in warmer weather in

Open Access

often limited options for prevention and management—can favor the development of many soil-related issues, including soilborne diseases and root-knot nematodes (RKN; Meloidogyne spp.). There are limited options to manage many of these issues once they

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Abstract

Significant differences in relative field resistance to root-knot nematode (Meloidogyne spp.) were found among 21 muskmelon (Cucumis melo L.) cultivars and breeding lines.

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