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T.E. Thompson and L.J. Grauke

The U.S. Dept. of Agriculture, Agricultural Research Service conducts the largest and oldest pecan [Carya illinoinensis (Wangenh.) K. Koch] breeding program in the world. This program evaluates thousands of nut and kernel samples each year using a standard nut and kernel evaluation system developed and refined for more than 70 years. This report relates the effectiveness of these evaluations to commercial shelling efficiency by direct comparison of these data to commercially shelled samples from the same clone performance test. Visual ratings of shelled kernel samples (1-5, with 1 = best) were correlated with time required to hand clean kernel samples (r = 0.55). As percent kernel increased, visual ratings of shelled kernels improved (decreased) (r = -0.73). More intact halves were recovered from shelled samples with the best (lowest) visual ratings (r = -0.67). Conversely, fewer pieces of any size were present in samples with the best visual ratings. Visual ratings improved as nut density decreased (r = 0.33). Samples with the lightest kernel color also had the best visual ratings (r = 0.38). These data show that the standard U.S. Dept. of Agriculture pecan nut and kernel evaluation system needs to be refined by modifying selection pressure placed on various standard evaluation traits.

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Mark A. Mikel

To determine the genealogy of cultivated lettuce in the United States, a survey was conducted on the pedigree of proprietary and publicly developed lettuce cultivars registered from 1970 through 2004. This was facilitated through information furnished by the U.S. Plant Variety Protection Act, U.S. patent, and journal publication of registered cultivars. In total, there were 328 registered cultivars of which 90.5% (297 cultivars) were from proprietary and 9.5% (31) from public breeding programs. The lettuce cultivars of this era are 61.6% crisphead, 19.5% loose leaf, 13.7% cos/romaine, 4.9% butterhead, and 0.3% latin lettuce types. To facilitate an understanding of current U.S. lettuce germplasm, the most recombined and putatively elite cultivars in the development of new cultivars were identified. The 10 most recombined cultivars were ‘Salinas’ (parent of 28 new cultivars), ‘Calmar’ (27), ‘Vanguard’ (22), ‘Vanguard 75’ (13), ‘Vanmax’ (13), ‘Prize Head’ (12), ‘Parris Island Cos’ (12), ‘Empire’ (11), ‘Great Lakes 659’ (11), and ‘Red Coach 74’ (10). The types of breeding populations used for new cultivar development during this era were two-parent (52% of new cultivars), within cultivar selection (31%), three-parent (7%), backcross two or greater (5%), backcross one (2%), four or more parents (2%), and interspecific cross (1%).

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Robert D. Marquard

Six phosphoglucomutase phenotypes were observed in pecan [Carya illinoensis (Wangenh.) K. Koch] progeny after controlled pollinations. At least one locus (Pgm-1) is present that controls polymorphism of phosphoglucomutase (PGM) isozymes in pecan. The inheritance appears simple with three observed alleles. However, progeny produced from two crosses resulted in significant deviation from the expected segregation ratios. Out of 65 named cultivars, 61 were of a single phenotype, and two of six possible phenotypes were not observed. Only one region of PGM activity was consistently expressed by gel electrophoresis from pecan tissue.

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Y. Aron, S. Gazit, H. Czosnek, and C. Degani

The segregation pattern of individuals originating from selfing of several monoembryonic cultivars and one polyembryonic line indicated that polyembryony in mango was of genetic nature. All the plants originating from monoembryonic cultivars bore monoembryonic fruits. A one-monoembryonic to three-polyembryonic segregation pattern was observed among individuals originated from the polyembryonic line, indicating that polyembryony in mango is under the control of a single dominant gene.

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Richard L. Fery and Howard F. Harrison Jr.

Greenhouse and field studies were conducted to determine the genetic relationship between bentazon tolerance exhibited by the pepper (Capsicum annuum L.) cultivars Bohemian Chili and Santaka, and to evaluate the importance of cytoplasmic factors in expression of the tolerance in `Bohemian Chili.' Greenhouse evaluation of parental and F2 populations of the cross `Santaka' × `Bohemian Chili' indicated that the major dominant gene conditioning bentazon tolerance in `Bohemian Chili' is probably the Bzt gene that conditions bentazon tolerance in `Santaka' or a gene closely linked to the Bzt locus. Field evaluation of F1 and F2 progeny populations of the cross `Bohemian Chili' × `Sweet Banana' in both `Bohemian Chili' and `Sweet Banana' cytoplasms demonstrated that cytoplasmic factors do not affect the expression of the bentazon tolerance gene in `Bohemian Chili.' We conclude that `Santaka' and `Bohemian Chili' are equally satisfactory sources of a bentazon tolerance gene for use in pepper breeding programs. Chemical name used: 3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide (bentazon).

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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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Robert D. Marquard, Larry J. Grauke, Tommy E. Thompson, and Ruth S. Janos

More than 170 pecan [Carya illinoensis (Wangenh.) K. Koch] cultivars were evaluated formalate dehydrogenase, phosphoglucose isomerase, phosphoglucomutase, leucine aminopeptidase (LAP), and diaphorase (DIA). Isozymes of LAP were observed in two regions after starch gel electrophoresis. The faster region of activity (Lap-1) was polymorphic and consistently expressed in leaves, wood, and roots. Controlled crosses suggest that Lap-1 is simply inherited and controlled by at least two alleles. DIA was well resolved and storable only from leaf material and produced a complex banding pattern. The ability to differentiate among cultivars by isozymes was good. The 177 cultivars sorted into 72 classes. Forty of the cultivars (23%) possessed a unique series of isozyme patterns. Most cultivars (124 of 177) shared common banding patterns with less than four other cultivars. From the inheritance models of four isozymes, some historical pedigrees can be questioned. Most notably,' Western Schley' could not have been parented by `San Saba' based on the inheritance of Mdh-1 and Lap-1.

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T.E. Thompson and J.F. Baker

Heritability estimates for pecan [Carya illinoinensis (Wangenh.) K. Koch] nut weight, nut buoyancy, nut volume, nut density, kernel weight, and percentage kernel were determined from 8748 nut samples representing 152 families collected during 25 years in the U.S. Dept. of Agriculture (USDA) pecan breeding program at Brownwood, Texas. Measurements were corrected for year-to-year environmental variability using least-squares constants of individual year effects. Adjusted values were then regressed on midparent means. Generally, heritability (h2) estimates were low to moderate: nut weight 0.35, nut buoyancy 0.18, nut volume 0.35, nut density 0.03, kernel weight 0.38, and percentage kernel 0.32. The low values are probably due to the extreme alternate bearing tendency of this species, since crop load affects pecan nut characteristics so directly. Phenotypic correlations among these traits showed that larger or heavier nuts had significantly higher kernel weight, buoyancy, and percentage kernel. Nut density increased with higher nut and kernel weight, but decreased with nut volume.

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T. Casey Garvey and John D. Hewitt

An interspecific hybrid was made between an accession of Lycopersicon cheesmanii f. minor Riley (LA 1508) from the Galapagos Islands, Ecuador, and L. pennellii (Corr.) D'Arcy (LA 716). LA 1508 was used because of its high soluble solids content (SSC). It was crossed with LA 716 to test for linkage between isozymes and morphological markers and loci conditioning high SSC. For both accessions, chromosome numbers are equal and there are large differences between SSC and no barriers to crossing. Modified BC1 populations derived from the hybridization were assayed for isozyme markers using starch gel electrophoresis. Associations between marker loci and quantitative-trait loci (QTL) conditioning high SSC were determined using analysis of variance. Six isozymes located on five chromosomes and one morphological marker had significant associations with SSC, indicating linkage to QTL. Digenic epistatic interactions between pairs of independent markers did not appear to play an important role in the interactions between QTL that condition SSC.