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  • Author or Editor: Robert Bernatzky x
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Early blight disease on tomato, Lycopersicon esculentum, is caused by Alternaria solani, a fungus that primarily affects plants experiencing stress due to adverse growing conditions and heavy fruit loads. A. solani spreads rapidly under conditions of heavy dew and humid, damp weather which frequently occur during Massachusetts summers. Early blight appears as spots and cankers on tomato fruit, stems, and foliage. Host plant resistance to A. solani is exhibited by several lines of wild tomato relatives, including Lycopersicon hirsutum. Breeding efforts at North Carolina State Univ. to incorporate this resistance by making crosses to the wild tomatoes and then making backcrosses to L. esculentum have resulted in advanced breeding lines. These initial lines showed some resistance but have later maturity and lower yields than current commercial cultivars. Field evaluations of yield and early blight resistance were completed for 22 cultivars and advanced breeding lines in 1992 and 20 cultivars, advanced breeding lines, and new crosses in 1993. The new crosses in the 1993 trial were made between high yielding, susceptible lines and lower yielding, resistant lines as evaluated in 1992. Two of these crosses, NC-EBR1 × JETSTAR and 88B231 × SUNRISE, were selected to be used in single seed descent and bulk breeding programs. David L. Holm phone (413) 545-2917, e-mail dholm@hamp.hampshire.edu; Robert Bernatzky phone (413) 545-5222, e-mail rb@pssci.umass.edu

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A first backcross population of walnuts {[Juglans hindsii (Jeps.) Jeps. × Juglans regia L.] × J. regia} was used to evaluate the correlation between morphological (statistical) and genetic distance during introgression. Five traits based on leaf morphology were identified to quantitate the morphology of the parental species, their F1 hybrids, and the backcrosses to each parent. These traits were used to evaluate the morphological similarity of first backcrosses to J. regia using Mahalanobis' distance. The amount of genomic introgression of each backcross was estimated using 59 randomly amplified polymorphic DNA (RAPD) and 41 restriction fragment-length polymorphism (RFLP) genetic markers that identify polymorphisms between J. regia and J. hindsii. A smaller scaffold set of markers was also identified using published linkage data. The correlation between the measures of morphological and genomic introgression for the first backcrosses was low (0.23) but significant. The results suggest that selection based on morphology during backcrossing will not be an effective way to recover recurrent parent genome.

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We characterized a population of hybrids between English walnut and Northern California black walnut (Juglans regia X J. hindsii) and their backcrosses (BC) using both genomic markers and morphological traits. ANOVA and regression methods were used on three years' data to identify a subset of five variables that describe the morphological variability among backcross populations and their parents (R2 = 0.89). Genomic markers were identified using randomly amplified polymorphic DNA (RAPD). A subset of 60 markers specific to the donor species (J. hindsii) were scored in 50 backcrosses to estimate the percent recipient genome in each evaluated BC. The backcrosses were ranked using each method of evaluation; correlation between the ranks was 0.423 and highly significant. Each evaluation method has advantages but neither was able to reliably identify elite progeny.

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Twenty-five random decamer primers were used to evaluate the level of polymorphism between Persian walnut and the Northern California black walnut. Sixty-six randomly amplified polymorphic DNA (RAPD) markers were identified using an interspecific walnut backcross population [(Juglans hindsii × J. regia) × J. regia]. Segregation data from these polymorphisms were joined to a previously published set of restriction fragment-length polymorphism (RFLP) marker data to expand the genetic map of walnut to 107 markers in 15 linkage groups.

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Nonflowering-sized Dutch iris bulbs 'Telstar' were treated at 20 °C in a flow-through system with ethylene-free air or air containing 10 μL.L-1 of ethylene (C2H4) for 1 or 24 hours. Following the treatment, bulbs were placed in a 10 °C cooler for 5 weeks before planting and subsequently forced in a 20 °C day/18 °C night glasshouse. Results demonstrated that a 24-hour C2H4 treatment induced earlier flowering as well as percent flowering. Flowering responses of bulbs treated with C2H4 for 1 hour were the same as those treated with air. The 24-hour ethylene treatment did not affect the combined fresh weight of the daughter bulb and bulblets but reduced the number of bulblets produced by each. The effects of ethylene on the protein changes in the apex were examined at two time periods: immediately after the treatment and after the cold treatment. Each sample consisted of proteins extracted from three apices. There are significant changes in one-dimensional SDS PAGE protein patterns of bulbs apices after treatment with ethylene. However, the differences are apparent after only 1 hour of ethylene treatment. The cold treatment resulted in minimal further changes in protein patterns.

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Self-incompatibility (SI) is the inability of otherwise fertile gametes to produce viable zygotes upon self-fertilization. The S locus of chromosome 1 in Lycopersicon is thought to be the main controlling factor in SI. However, the significance of other chromosome segments in the control of SI or the effect of a foreign genetic background on the S locus has not been thoroughly explored. In addition, the relationship between SI and wider interspecific crossing barriers remains unclear. Using DNA and protein markers for chromosome 1, we have created a series of backcross lines that contain either 1) the SI locus and flanking chromosome region from a SI species in a SC species background or 2) the same chromosome region from a SC species in a SI species background. The reproductive behavior of these plants will be discussed.

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