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Abstract

Two hundred eight-four Lycopersicon spp. genotypes reported to have some resistance to bacterial pathogens of tomato (L. esculentum Mill.) were inoculated in the field with Xanthomonas campestris pv. vesicatoria (XCV), the incitant of bacterial spot, and rated for disease severity in summer 1982 and/or summer 1983. One line tested in 1983, Hawaii 7998, had no definite XCV lesions and later was determined to be resistant to XCV in the laboratory. Genotypes with the highest levels of resistance during 2 years of testing were: Ohio 4013-3, Ohio 4014-4, Heinz 1568-F3, [(Subarctic Delite × MH1) × H603] F5, L556, ‘Campbell-28’, PI 127813, Heinz 603-F11, PI 224573, ‘Monense’, ‘Heinz 2990’, and PI 324708. Genotypes with highest levels of resistance in one year of testing were PI 379032 and ‘Burgess Crack Proof. In 1982, PI 270248- ‘Sugar’ had a high level of resistance to XCV on fruit, but foliage was susceptible.

Open Access
Authors: and

Abstract

Hawaii 7998 (foliage resistant to bacterial spot) was crossed with ‘Walter’ (susceptible) and F1, backcross, and F2 generations were derived. These genotypes were grown in the field at Bradenton, Fla. in the summers of 1984 and 1985 and inoculated with Xanthomonas campestris pv. vesicatoria, the incitant of bacterial spot. Disease severity for respective genotypes was similar both years, although somewhat greater in 1985. Disease severity in the F1 was intermediate to the parents, but slightly skewed toward resistance both years. The percentage of F2 plants with resistance comparable to Hawaii 7988 was 9.6% in 1984 and 4.6% in 1985. There was no evidence of cytoplasmic inheritance from three sets of reciprocal crosses tested in 1985. The data fit an additive-dominance genetic model, but dominance variance was negative both years, which indicates a small or negligible dominance effect. The negative dominance variance resulted in biased estimates of additive variance, narrow-sense heritability, and the number of effective factors. Nevertheless, narrow-sense heritability was moderate to high. When incorporating this resistance into new genetic backgrounds, we suggest that a modified backcrossing scheme with rigorous disease screening be used to obtain plants from homozygous resistant BCF3 lines before crossing.

Open Access

Resistance of tomato (Solanum lycopersicum) to bacterial spot race T4 (Xanthomonas perforans) was characterized by generation means analysis (GMA) in three advanced breeding lines: Fla. 8326, Fla. 8233, and Fla. 8517. GMA of Fla. 8326 for two of three seasons (Fall 2006 and Summer 2007) indicated that resistance is mostly dominant with significant additive and epistatic effects. GMA of Fla. 8233 in Spring 2007 and of Fla. 8517 in Summer 2007 also showed dominance to be the main effect in addition to additive and epistatic effects. Duplicate dominance or recessive suppressor type epistasis was indicated in each breeding line. Transgressive segregation was not clearly observed in F2 populations of crosses between resistant parents, suggesting that these lines have quantitative trait loci in common.

Free access
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Hawaii 7981 tomato (Lycopersicon esculentum Mill.), resistant to race T3 of the bacterial spot pathogen [Xanthomonas campestris pv. vesicatoria (Doidge) Dye], was crossed to the susceptible tomato inbred, Fla. 7060, and subsequently F2 and backcross seed were obtained. These generations were planted in the field, inoculated with the race T3 pathogen and evaluated for disease severity over two summer seasons. Data were tested for goodness-of-fit to a model based on control by the incompletely dominant gene Xv3 that confers hypersensitivity. The F1 was intermediate in disease severity to the parents for both seasons. When data were combined over both seasons, the backcrosses fit the expected 1:1 ratios although each deviated from the expected ratio in one of the 2 years tested. The F2 did not fit the expected 1:2:1 ratio in either year or when data from the two years were combined due to a deficiency of resistant plants. Thirty-three F2 plants representing an array of disease severities and hypersensitivity reactions were selected in the second season and their F3 progeny were inoculated and evaluated for disease severity. Hawaii 7981 was significantly more resistant than the 12 most resistant F3 selections even though all expressed hypersensitivity. A hypersensitive F3 with intermediate field resistance was crossed to Hawaii 7981 and subsequently, F2 and backcross generations were obtained. These generations were field inoculated with the race T3 pathogen and evaluated for disease severity. Hawaii 7981 was significantly more resistant than the F3 parent as in the previous year. The data did not fit an additive-dominance model and epistatic interactions were significant. Thus, it appears that field resistance to race T3 of bacterial spot found in Hawaii 7981 is conferred quantitatively by Xv3 and other resistance genes. Breeding implications are discussed.

Free access

Abstract

Tomato (Lycopersicon esculentum Mill.) accession PI 270248 (‘Sugar’) had high levels of resistance to bacterial spot [incited by Xanthomonas campestris pv. vesicatoria (Doidge) Dye] on fruit, but foliage was susceptible. Hawaii 7998 (H7998) was highly resistant to foliar infection, but was intermediate in resistance to fruit infection. Fruit spot on hybrids between ‘Sugar’ and H7998 was usually intermediate to the parents. Occasionally, disease incidence of hybrids was not statistically different from one or both parents, but tended to resemble ‘Sugar’ more closely than H7998. There were no significant differences between reciprocal hybrids, indicating a lack of cytoplasmic inheritance. Under low disease incidence, hybrids between ‘Sugar’ and ‘Walter’ (susceptible to bacterial spot on fruit and foliage) had fruit spot incidence similar to ‘Sugar’ and significantly less than ‘Walter’. Thus, there was a high level of dominance for resistance to bacterial spot on fruit.

Open Access

A `spray-inoculation seedling screening procedure was developed for detecting resistance to Xanthomonas campestris pv. vesicatoria (Doidge) Dye, causal agent of bacterial spot of tomato (Lycopersicon esculentum Mill.). Two-week-old transplants were preconditioned under 95% humidity for 16 hours before spray inoculation and then rated for bacterial spot 2 weeks later. Resistant plants could also be distinguished from susceptible genotypes using a modified bacterial speck [Pseudomonas syringae pv. tomato (Okabe) Young, Dye, and Wilkie] screening procedure (cotyledon-dip technique). When results of both screening methods were compared to field ratings from three previous seasons, significant correlations were more frequently observed for the spray-inoculation method. In Summer 1991, individual plants were evaluated by the spray-inoculation technique and then were placed in the field to determine susceptibility under field conditions. Correlations (r = 0.28 to 0.34) between spray-inoculation seedling screening ratings and field ratings, although low, were significant (P ≤ 0.0001). More than 90% of susceptible plants could be eliminated, saving labor, space, and time.

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Available water for urban landscape irrigation is likely to become more limited because of inadequate precipitation and the ever-increasing water demand of a growing population. Recent droughts in the western United States have also increased the demand for low-water-use landscapes in urban areas. Penstemon species (beardtongues) are ornamental perennials commonly grown in low-water-use landscapes, but their drought tolerance has not been widely investigated. The objectives of this study were to determine the effects of water availability on the morphology, physiology, and canopy temperature of Penstemon barbatus (Cav.) Roth ‘Novapenblu’ (Rock Candy Blue® penstemon), P. digitalis Nutt. ex Sims ‘TNPENDB’ (Dakota™ Burgundy beardtongue), P. ×mexicali Mitch. ‘P007S’ (Pikes Peak Purple® penstemon), and P. strictus Benth. (Rocky Mountain penstemon). Twenty-four plants of each penstemon species were randomly assigned to blocks in an automated irrigation system, and the substrate volumetric water content was maintained at 0.15 or 0.35 m3⋅m−3 for 50 days. The decreased substrate volumetric water content resulted in a decreased aesthetic appearance of the four penstemon species because of the increased numbers of visibly wilted leaves and chlorosis. Plant growth index [(height + (width 1 + width 2)/2)/2], shoot number, shoot dry weight, leaf size, and total leaf area also decreased as the substrate volumetric water content decreased, but the root-to-shoot ratio and leaf thickness increased. Photosynthesis decreased, stomatal resistance increased, and warmer canopy temperatures were observed when plants were dehydrated. Additionally, as substrate volumetric water content decreased, the leaf reflectance of P. barbatus and P. strictus increased. Penstemon digitalis, which had the highest canopy–air temperature difference, was sensitive to drought stress, exhibiting a large proportion of visibly wilted leaves. Penstemon ×mexicali, which had the lowest root-to-shoot ratio, had the lowest shoot water content of the species studied and more than 65% of leaves visibly wilted when experiencing drought stress. Penstemon barbatus and P. strictus, native to arid regions, exhibited lower canopy–air temperature differences and better aesthetic quality than the other two species. Under the conditions of this study, Penstemon barbatus and P. strictus exhibited better drought tolerance than P. digitalis and P. ×mexicali.

Open Access

Crosses were made between tomato (Lycopersicon esculentum Mill.) inbreds susceptible to races T2 and T3 of bacterial spot (Xanthomonas vesicatoria and Xanthomonas campestris pv. vesicatoria, respectively) and accession PI 114490 with resistance to races T1, T2, and T3. Resistance to race T2 was analyzed using the parents, F1, and F2 generations from one of the crosses. The F1 was intermediate between the parents for disease severity suggesting additive gene action. The segregation of F2 progeny fit a two-locus model (χ2 = 0.96, P = 0.9-0.5) where four resistance alleles are required for a high resistance level, two or three resistance alleles provide intermediate resistance, and zero or one resistance allele results in susceptibility. The narrow sense heritability of resistance to T2 strains was estimated to be 0.37 ± 0.1 based on F2 to F3 parent-offspring regression. A second cross was developed into an inbred backcross (IBC) population to facilitate multilocation replicated testing with multiple races. Segregation for T2 resistance in the inbred backcross population also suggested control was by two loci, lending support to the two-locus model hypothesized based on the F2 segregation. To determine if the same loci conferred resistance to the other races, selections for race T2 resistance were made in the F2 and F3 generations and for race T3 resistance in the F2 through F4 generations. Six T3 selections (F5), 13 T2 selections (F4's that diverged from seven F2 selections), and control lines were then evaluated for disease severity to races T1, T2, and T3 over two seasons. Linear correlations were used to estimate the efficiency of selecting for resistance to multiple races based on a disease nursery inoculated with a single race. Race T1 and race T2 disease severities were correlated (r ≥ 0.80, P< 0.001) within and between years while neither was correlated to race T3 either year. These results suggest that selecting for race T2 resistance in progeny derived from crosses to PI 114490 would be an effective strategy to obtain resistance to both race T1 and T2 in the populations tested. In contrast, selection for race T3 or T2 will be less likely to result in lines with resistance to the other race. PI 114490 had less resistance to T3 than to T2 or T1. Independent segregation of T2 and T3 resistance from the IBC population derived from PI 114490 suggests that T3 resistance is not controlled by the same genes as T2 resistance, supporting the linear correlation data.

Free access

Tomato (Lycopersicon esculentum Mill.) accessions were tested for hypersensitivity and rated for resistance following field inoculation with tomato race 3 (T3) of the bacterial spot pathogen Xanthomonas campestris pv. vesicatoria (Doidge) Dye (Xcv) in 1992 and 1993. Hawaii 7981, PI 126932, PI 128216, and selections of the latter two expressed hypersensitivity. Hawaii 7981, only tested in the field in 1993, was nearly symptomless and developed significantly less disease than any other accession. PI 128216 had a level of disease similar to susceptible `Solar Set' when tested in 1993. However, a selection from it (PI 126218-S) was significantly more resistant than `Solar Set' in both years. Although PI 126932 had a level of disease similar to `Solar Set' in both years, a selection from it (PI 126932-1-2) was significantly more resistant than `Solar Set' in 1993. Other accessions without hypersensitive responses but more resistant than `Solar Set' for two seasons were PI 114490, PI 126428, PI 340905-S, and PI 155372. Hawaii 7975 was significantly more resistant than `Solar Set' in the one season it was tested.

Free access