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Sanliang Gu, R. Scott Johnson, Carlos H. Christo, Robert C. Cochran and David Garner

Fruit from 8 `Hayward' kiwifruit vineyards in central California were harvested at 2 week intervals after soluble solids content (SSC) reached 6% and subjected to 4 and 6 months of storage at 0°C in an ethylene free environment. Macro-nutrients were analyzed from leaf and fruit tissues. Leaf petiole N and NO3 --N were 2 to 3 times higher for vines that had softer fruit after long-term storage. Where the correlations were significant, fruit firmness and SSC were correlated negatively with N, P, K, Cl, and N/Ca and positively with Ca and Mg of leaf and fruit tissues. The significance of the correlations depended on the harvest maturity and growing locations. Soil nitrogen application increased Mg and reduced Ca and Cl in lamina but did not influence macro-nutrients in fruit tissues.

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Don R. La Bonte, Christopher A. Clark, Tara P. Smith, Arthur Q. Villordon and C. Scott Stoddard

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J.W. Scott, J.B. Jones, G.C. Somodi and R.E. Stall

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.

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J.W. Scott, J.B. Jones, G.C. Somodi, D.O. Chellemi and S.M. Olson

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Timothy L. Grey, David C. Bridges, Paul Raymer, Don Day and D. Scott NeSmith

Field studies were conducted to determine the tolerance of 11 sweet corn (Zea mays L.) cultivars to the herbicides nicosulfuron and primisulfuron. The su cultivar `Merit' was intolerant of nicosulfuron and primisulfuron, as indicated by significant differences from the untreated check for all measured variables. Most other su cultivars exhibited stunting, but injury was ≤19% (0% = no injury; 100% = dead) with nicosulfuron and primisulfuron in 1992. The se cultivars Alpine and Harris Moran Silverado exhibited variable stunting to nicosulfuron (25% and 23% injury, respectively) and primisulfuron (43% and 50%, respectively) in 1992. The sh2 cultivar Supersweet Jubilee was injured less by nicosulfuron (16%) than by primisulfuron (33%) in 1992. All cultivars except Merit recovered from early-season herbicide injury in 1992 and 1993. Significant differences among the se, su, and sh2 cultivars were recorded for the remaining variables (stalk height, marketable ear number and yield, ear length and diameter), but no patterns with respect to a specific sugary genetic background developed in 1992 or 1993. Nicosulfuron and primisulfuron were safely applied to the cultivars Alpine, Harris Moran Silverado, Royal Gold, Seneca Chief, Calumet, Jubilee, and Supersweet Jubilee without reductions in fresh ear yield. Chemical names used: {2-[[[[(4,6-dimethoxy-2-pyrimidinyl)amino] carbonyl]amino]sulfonyl]-N,N-dimethyl-3-pyridinecarboxamide} (nicosulfuron); {methyl 2[[[[[4,6-bis(difluoromethoxy)-2-pyrimidinyl]amino]carbonyl]amino]sulfonyl]benzonate} (primisulfuron).

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Michael C. Shannon, Catherine M. Grieve, Scott M. Lesch and John H. Draper

Saline agricultural drainage water may be used as a resource to grow high value horticultural crops and reduce the volume of drainage for eventual disposal. To explore reuse options the effects of salinity and timing of application were tested on selected leafy vegetables grown in 24 sand culture plots in Riverside, Calif. The leafy winter vegetables included `Ruby Red Chard' Swiss chard [Beta vulgaris L. var. flavescens (Lam.) Lam.], `Space' spinach (Spinacia oleracea L.), `Vitamin Green' salad greens [Brassica rapa L. (Narinosa Group)], `Red Giant' mustard greens [Brassica juncea L. (Czerniak)], pac choi [Brassica rapa L. (Chinensis Group)], `Winterbor' kale [Brassica oleracea L. (Acephala Group)], tatsoi [Brassica rapa L. (Narinosa Group)], `Salad King' curly endive (Cichorium endivia L.), and `Red Preco No. 1' radicchio (Cichorium intybus L.). All vegetables were planted at the same time and irrigated initially with tap water and nutrients. At 3 and 7 weeks after seeding (application times), six salinity treatments were initiated by adding salts to the irrigation water to represent the chemical compositions of drainage waters found typically in the San Joaquin Valley, Calif. The six salinity treatments had electrical conductivities of 3 (control), 7, 11, 15, 19, or 23 dS·m-1. A randomized complete block design was used with (6 salinities × 2 application times × 2 replications). Within each plot a 1.5-m row of each of the nine vegetables was grown as split plots. Salinity reduced fresh weight (FW) yields of all species. Salt stress applied at 3 weeks after seeding reduced FWs for seven of the nine vegetables compared to salination at 7 weeks. Analyses of salt tolerance curves, maximum yields, and the point of 50% yield reduction (C50) were conducted. Greens produced the highest biomass at 874 g/plant, but was the most affected by application time. Swiss chard and radicchio were not significantly affected by timing of salinity application, and Swiss chard was the most salt tolerant overall. Greens, kale, pac choi, and to a lesser extent, tatsoi, have potential as winter-grown, leafy vegetables in drainage water reuse systems.

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J.W. Scott, D.M. Francis, S.A. Miller, G.C. Somodi and J.B. Jones

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.

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Robert K. Prange, John M. DeLong, Peter A. Harrison, Jerry C. Leyte and Scott D. McLean

A new chlorophyll fluorescence (F) sensor system called FIRM (fluorescence interactive response monitor) was developed that measures F at low irradiance. This system can produce a theoretical estimate of Fo at zero irradiance for which we have coined a new fluorescence term, Fα. The ability of Fα to detect fruit and vegetable low-O2 stress was tested in short-term (4-day) studies on chlorophyll-containing fruit [apple (Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.), pear (Pyrus communis L.), banana (Musa ×paradisiaca L.), kiwifruit (Actinidia deliciosa C.S. Liang & A.R. Ferguson), mango (Mangifera indica L.), and avocado (Persea americana Mill.)] and vegetables (cabbage (Brassica oleracea L. Capitata Group), green pepper (Capsicum annuum L. Grossum Group), iceberg and romaine lettuce (Lactuca sativa L.)). In all of these fruit and vegetables, Fα was able to indicate the presence of low-O2 stress. As the O2 concentration dropped below threshold values of 0 to 1.4 kPa, depending on the product, the Fα value immediately and dramatically increased. At the end of the short-term study, O2 was increased above the threshold level, whereupon Fα returned to approximately prestressed values. A 9-month study was undertaken with `Summerland McIntosh' apple fruit to determine if storing the fruit at 0.9 kPa O2, the estimated low O2 threshold value determined from Fα, would benefit or damage fruit quality, compared with threshold + 0.3 kPa (1.2 kPa O2) and the lowest recommended CA (1.5 kPa O2). After 9 months, the threshold treatment (0.9 kPa) had the highest firmness, lowest concentration of fermentation volatiles (ethanol, acetaldehyde, ethyl acetate) and lowest total disorders. Sensory rating for off-flavor, flavor and preference indicated no discernible differences among the three treatments.

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D.O. Chellemi, H.A. Dankers, S.M. Olson, N.C. Hodge and J.W. Scott

Several procedures for evaluating the resistance of tomato (Lycopersicon esculentum Mill.) to bacterial wilt were used to account for diversity in strains of Pseudomonas solanacearum Smith and to approximate resistance under field conditions. Five strains of P. solanacearum from Florida and one from North Carolina were inoculated onto 19 tomato genotypes and one tomatillo (Physalis ixocarpa Brot.) genotype using a stem-puncture technique. Genotypes were also transplanted as seedlings into naturally infested soil. Resistance was evaluated by comparing the response of each genotype to the susceptible cultivars Bonny Best and Sunny. With the stem-puncture technique, the mean incidence of disease ranged from 30% with the strain from North Carolina to 94% with a strain from northern Florida. Significant differences in the resistance of genotypes and pathogenicity of strains were observed. However, no interaction between strain and genotype was observed. Using naturally infested soil, the mean incidence of disease was 51% and significant differences in the resistance of genotypes were also observed. Hawaii 7997, Hawaii 7998, and CRA 66 had the lowest incidence of disease, regardless of inoculation method. The results indicate that assessing pathogen diversity and using a combination of resistance screening techniques can facilitate the evaluation of many genotypes, account for potential regional variability in the pathogen, and differentiate levels of field resistance to tomato bacterial wilt.

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Don R. La Bonte, Christopher A. Clark, Tara P. Smith, Arthur Q. Villordon and C. Scott Stoddard