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Kathleen G. Haynes

Although potato (Solanum tuberosum L.) tuber yellow flesh per se is known to be controlled by a single gene, the intensity of yellow flesh varies widely in Solanum L. species. Many diploid species have very intense yellow flesh, as compared to the commercial tetraploid yellow-flesh cultivar `Yukon Gold'. Inheritance of yellow-flesh intensity at the diploid level was investigated in a hybrid population of S. phureja ssp. phureja (Juz. & Buk.)-S. stenotomum ssp. stenotomum (Juz. & Buk.) (PHU-STN). Six randomly chosen male parents were crossed to five randomly chosen female parents in a Design II mating scheme. In 1993, ≈12 progeny (clones) from each of the 30 families were planted in a randomized complete block design with two replications in Presque Isle, Maine, and evaluated for tuber yellow-flesh intensity as measured by a reflectance colorimeter. Twenty-five tubers from each plot were scored using the YI E-313 yellow intensity scale. An average YI E-313 score was obtained for each plot. Narrow-sense heritability on a plot mean basis was estimated as 0.99 with a SE of 0.65 to 0.72. There were significant differences among clones within a family. Results suggest that rapid progress can be made in breeding for intense yellow flesh in this diploid population. Clones from this population that produce 2n gametes represent an important source of germplasm for enhancing the intensity of the yellow-flesh trait in tetraploid potatoes.

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John R. Stommel and Kathleen G. Haynes

Inheritance of resistance to tomato anthracnose caused by Colletotrichum coccodes (Wallr.) S.J. Hughes was evaluated in parental, F1, F2, and backcross populations developed from crosses between adapted resistant (88B147) and susceptible (90L24) tomato (Lycopersicon esculentum Mill.) breeding lines. Resistance was evaluated via measurement of lesion diameters in fruit collected from field-grown plants and puncture inoculated in a shaded greenhouse. Backcross and F2 populations exhibited continuous distributions suggesting multigenic control of anthracnose resistance. Anthracnose resistance was partially dominant to susceptibility. Using generation means analysis, gene action in these populations was best explained by an additive-dominance model with additive × additive epistatic effects. A broad-sense heritability (H) of 0.42 and narrow-sense heritability (h2) of 0.004 was estimated for resistance to C. coccodes. One gene or linkage group was estimated to control segregation for anthracnose resistance in the cross of 90L24 × 88B147.

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John R. Stommel and Kathleen G. Haynes

Anthracnose, caused by Colletotrichum coccodes, is a serious ripe tomato fruit rot disease. Genetic resistance to anthracnose is not available in commercial tomato cultivars, but has been reported in small-fruited Plant Introductions (P.I.), and with lesser intensity in a number of breeding lines. Transfer of high levels of resistance from these breeding lines or P.I.s to elite materials has proven difficult. Inheritance of resistance has been described as complex with at least six loci influencing resistance reactions. Segregating populations originating from a cross between a susceptible tomato breeding line and a large-fruited breeding line (88B147) with resistance derived from Lycopersicon esculentum var. cerasiforme P.I. 272636, were evaluated for anthracnose resistance. Analysis of anthracnose resistance in puncture-inoculated fruit indicated small, but significant, additive genetic effects for resistance. Additional populations were developed from crosses of a susceptible inbred processing tomato cultivar with: 1) the resistant P.I. 272636, 2) an unadapted small-fruited resistant line developed from P.I. 272636, and 3) the large-fruited breeding line 88B147, also with resistance derived from P.I. 272636. Small additive effects identified in large-fruited material, in comparison to the resistant P.I., suggests that resistance loci have been lost during germplasm development. This is consistent with the relatively larger lesions observed in large-fruited lines derived from P.I. 272636. Positive correlations were noted between small fruit size and high levels of anthracnose resistance. Identification of molecular markers linked to resistance genes in the respective populations will be discussed.

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John R. Stommel and Kathleen G. Haynes

Fruit of the cultivated tomato (Lycopersicon esculentum Mill.) store predominantly glucose and fructose whereas fruit of the wild species L. hirsutum Humb. & Bonpl. characteristically accumulate sucrose. Reducing sugar and sucrose concentrations were measured in mature fruit of parental, F1, F2, and backcross (BC1) populations derived from an initial cross of L. esculentum `Floradade' × L. hirsutum PI 390514. Generational means analysis demonstrated that additive effects were equal to dominance effects for percentage of reducing sugar. It was determined that a single major gene, dominant for a high percentage of reducing sugar, regulates the percentage of reducing sugar in tomatoes. We propose that this gene be designated sucr. Only additive effects were demonstrated to be important for glucose: fructose ratios. Using L. hirsutum as a donor parent for increasing total soluble solids concentration in the cultivated tomato is discussed.

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John R. Stommel, Robert W. Goth and Kathleen G. Haynes

Bacterial soft rot of bell pepper (Capsicum annuum L.), caused by Erwinia spp., is a destructive postharvest market disease of this crop. Control is presently limited to chemical treatments. Methods of inoculating pepper fruit were evaluated to develop a reliable technique for soft rot resistance screening. Erwinia carotovora subsp. atroseptica (Eca) was isolated from partially decayed field grown pepper fruit at Beltsville, MD. Fruit were inoculated with suspensions of Eca via: (a) abrasion with Carborundum, (b) hypodermic puncture, or (c) non-wounded tissue. Inoculated fruit were held under high humidity at 21-23C for two to three days prior to scoring. Degree of soft rot decay was determined via fruit weight loss from two replicates of the experiment over the course of the growing season. Significant differences were not evident among varieties or experiment dates for weight loss due to tissue decay. Hypodermic puncture inoculation was superior to other methods for inducing fruit rot.

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Robert W. Goth, Ernest W. Goins and Kathleen G. Haynes

Potato leafroll virus (PLRV) is a serious aphid transmitted virus disease of potato (Solanum tuberosum L.). Field observations suggest that the cv. BelRus is tolerant to PLRV. Greenhouse grown BelRus and PLRV susceptible potato cvs. Green Mountain and Katahdin were tested for PLRV with enzyme linked immunosorbant assay (ELISA) and subsequently infested with PLRV infected green peach aphids (Myzus persicae). ELISA was used to test leaves from the top, middle and bottom portion of the plants at 7 day intervals beginning 7 days after aphid infestation. PLRV was detected in all tested locations of the Green Mountain and Katahdin plants 21 days after inoculation. In BelRus, throughout the 11 week test, PLRV was detected predominantly in the top portion of the plants and at low titres. These results suggest that tolerance to PLRV infection in the cv. BelRus may be due to suppression of virus replication.

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Kathleen G. Haynes, Lincoln Zotarelli, Christian T. Christensen and Stephanie Walker

Consumer demand for specialty market potatoes has been growing. Cultivated South American diploid potatoes possess great variation for skin and flesh colors, shape, and taste. A long-day adapted population of Solanum tuberosum groups Phureja and Stenotomum (phu-stn) was evaluated for characteristics associated with the type known as papa criolla or papa amarilla in South America. Tubers have intense yellow flesh and may be fried or roasted and eaten whole. A U.S. northern location (Maine), representative of a seed growing region, and two southern locations (Florida and New Mexico), representative of potato growing regions near large Hispanic populations, evaluated yellow-fleshed clones selected within a phu-stn population. Agreement between selectors at two locations was greater than 50%. Tuber skin color and shape were highly correlated between locations; flesh color and tuber dormancy moderately so; eye depth had low correlation between locations; and appearance and skin texture had low or no correlation between locations. Tuber dormancy was generally short, but a few longer dormant clones were identified. There were significant differences among clones for yields, with the highest yields occurring in Maine. More intense evaluations are planned for a subset of these clones before possible release as new varieties. Future breeding efforts will be undertaken to lengthen tuber dormancy in this population.

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Kathleen G. Haynes, Beverly A. Clevidence, David Rao and Bryan T. Vinyard

Carotenoids have a wide range of human health benefits. Yellow-fleshed tetraploid potato (Solanum tuberosum) cultivars have more than twice the concentration of carotenoids as white-fleshed cultivars. However, carotenoid concentrations in some diploid potatoes have been reported to be up to 13 times higher than in ‘Yukon Gold’, the most popular yellow-fleshed potato cultivar grown in the United States, and up to 22 times higher than in white-fleshed potatoes. The purpose of this study was to determine the feasibility of using these high-carotenoid diploids to develop high-carotenoid tetraploid germplasm. Three diploid clones with high (dark yellow-flesh), moderate (moderate yellow-flesh), and low (white–cream-flesh) carotenoid levels that produced 2n pollen were crossed with a light yellow-fleshed tetraploid advanced breeding selection to determine the inheritance of carotenoid content. Twenty-six to 43 progeny from these three 4x-2x families were grown in a replicated field experiment in Presque Isle, ME, for 2 years. After harvest, carotenoids were extracted and quantified by high-performance liquid chromatography in 13 to 14 randomly selected clones from each family; however, flesh color was scored as white or yellow in all progeny. A continuous distribution of carotenoid concentration with high- and low-carotenoid segregants was observed in all three families. There were no significant differences among these three families for individual or total carotenoid concentrations; however, there were significant differences among clones within families. Broad-sense heritability estimates were high for total carotenoid (0.81), lutein (0.77), zeaxanthin (0.73), and the lycopene beta-cyclase pathway carotenoids (0.73); moderate for neoxanthin (0.42); and low for violaxanthin (0.21) and antheraxanthin (0.13). Based on flesh color segregation, the two yellow-fleshed diploid parents were heterozygous for the Chy2 allele governing yellow-flesh and produced 2n gametes by a second division restitution mechanism. It appears that selection for high-carotenoid tetraploid germplasm can be made from within any family with at least one yellow-fleshed parent. Selections will have to be made on an individual clonal basis rather than on a family basis.

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Kathleen G. Haynes, Beverly A. Clevidence, David Rao, Bryan T. Vinyard and J. Marion White

Consumption of carotenoid-containing foods can promote human health. Although yellow-fleshed potatoes (Solanum tuberosum) have a higher carotenoid content than white-fleshed potatoes, little is known about how growing environments may affect individual and total carotenoid content in different potato clones. The purposes of this study were to estimate the amount of genetic variability in potato for five xanthophyll carotenoids, their concentration, and to determine the stability of these carotenoids across environments. Nine white- or yellow-fleshed tetraploid clones were grown in Maine and Florida for 2 years. Carotenoids were extracted in acetone and analyzed by high-performance liquid chromatography. There were significant differences among clones for zeaxanthin, antheraxanthin, lutein, and total carotenoid content. There were significant clone × environment interactions for zeaxanthin, antheraxanthin, violaxanthin, neoxanthin, lutein, and total carotenoid. Broad-sense heritabilities (and their 95% confidence intervals) were 0.89 (0.79–0.98) for zeaxanthin, 0.93 (0.87–0.99) for antheraxanthin, 0.68 (0.14–0.92) for violaxanthin, 0.51 (0.00–0.88) for neoxanthin, 0.85 (0.70–0.97) for lutein, and 0.96 (0.89–0.99) for total carotenoid. Clonal mean total carotenoid content ranged from 101 to 511 μg/100 g fresh weight. A higher proportion of carotenoids were produced by the lycopene epsilon cyclase branch of the carotenoid biosynthetic pathway in white-fleshed than yellow-fleshed clones. Total carotenoid content in B2333-5 was significantly greater than in ‘Yukon Gold’. With genetic variation for individual and total carotenoid content in potatoes, improving the levels of carotenoids has been and should continue to be feasible; however, concentrations are likely to vary in different environments.

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Aref A. Abdul-Baki, John R. Teasdale, Robert W. Goth and Kathleen G. Haynes

The use of mulches in vegetable production is undergoing a radical change away from high-input, nonrenewable resources, such as plastic, to the use of high-residue organic mulches from cover crops. The purpose of this study was to compare the marketable yield of various fresh-market tomato genotypes when grown under plastic and hairy vetch mulches. In 1996 and 1997, 12 fresh-market tomato genotypes were evaluated for yield on the North Farm of the Beltsville Agricultural Research Center (BARC), MD in a randomized split-plot design. Tomatoes were grown in conventional tillage plastic mulch (PM) and no-till hairy vetch mulch (HVM). Early blight, caused by Alternaria solani Sor., developed naturally in the plots both years and was recorded over time. All 12 genotypes were susceptible to early blight. Area under the disease progress curve (AUDPC) was calculated for each plot. AUDPC was similar both years. However, the year × mulch and year × mulch × genotype interactions were significant for AUDPC. Adjusting yields for AUDPC had a minimal effect on the data. Overall, yields were similar in PM and HVM both before and after adjusting for AUDPC. However, the mulch × genotype interaction was significant. The yield of eight of the genotypes was significantly higher in the HVM than in the PM system both years, ranging from 12% to 57% higher in 1996 and 10% to 48% higher in 1997. There was no yield difference for one genotype in HVM as compared to PM. The yield in the remaining three genotypes was either higher under HVM than PM or there was no difference. As yields from the HVM system are greater than or equal to yields in the PM system, soil compaction is reduced and nitrogen inputs are lower. The no-till HVM system is at least as good, and often better, than the conventional tillage PM system.