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Shawn A. Mehlenbacher and David C Smith

The contorted hazel, Corylus avellana `Contorta', is an ornamental tree prized for its grotesquely twisted trunk and branches. `Contorta' was discovered in a hedgerow in England about 1863 and has been commercially propagated by layerage or graftage because it was thought to not breed true from seed. We investigated the inheritance of contorted growth habit in the course of our work breeding hazelnuts. Crosses between normal growth habit cultivars and `Contorta' produce all normal seedlings. Sib matings of compatible normal seedlings of `Contorta' produce offspring in the proportion of 3 normal: 1 contorted. The backcross of a normal `Contorta' seedling to `Contorta' gives progeny in the ratio of 1 normal: 1 contorted, indicating control of the trait by a single recessive gene.

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Roger G. Fuentes-Granados, Mark P. Widrlechner and Lester A. Wilson

The inheritance of five allozymes was studied in anise hyssop (Agastache foeniculum) by analyzing the progeny of controlled crosses. The loci studied [Cat-1, Got-2, Pgm-2, Tpi-1, and Tpi-2] were scored by using starch gel electrophoresis. Segregation analyses of families polymorphic at each of these loci support the following hypotheses: Cat-1 is controlled by a single gene with codominant alleles; Got-2 is controlled by a single gene with codominant alleles coding for dimeric protein products; Pgm-2 is controlled by a single gene with codominant alleles coding for monomeric proteins; and Tpi-1 and Tpi-2 are each controlled by a single gene with codominant alleles coding dimeric protein products. Distorted segregation ratios were observed in some families segregating for Got-2 and Pgm-2. No linkages were detected among any of the cosegregating loci.

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J.R. Baggett and D. Kean

Inheritance of a twisted pod characteristic, in which bean pods develop with a twist that sometimes exceeds 360°, was studied in crosses between round-podded green bean cultivars. In crosses between `Oregon 91G' (normal) or `Oregon 54' (normal) and OSU 5256-1 (twisted), the F1 was normal. Segregation in F2 populations, tested over a 4-year period and including 4,995 plants, clearly fit a 3 normal: 1 twisted ratio. All plants of backcrosses of the F, to the normal parent were normal and backcrosses of the F1 to the twisted parent segregated 1 normal: 1 twisted. The ratios observed indicated that twisted pods are conditioned by a single recessive gene for which the symbol tw is proposed.

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Maureen C. O'Leary and Thomas H. Boyle

Cultivars and seedlings of Rhipsalidopsis and Schlumbergera were subjected to isozyme analysis using seven enzyme systems [aspartate aminotransferase (AAT), aminopeptidase (AMP), glucose-6-phosphate isomerase (GPI), malate dehydrogenase (MDH), phosphoglucomutase (PGM), shikimate dehydrogenase (SKD), and triose phosphate isomerase (TPI)]. Isozymes were extracted from phylloclades and roots, and were separated by polyacrylamide gel electrophoresis (PAGE) using single percentage (5% to 10%) gels. Six enzymes exhibited polymorphism in Rhipsalidopsis, whereas all seven enzymes were polymorphic in Schlumbergera. Inheritance studies were performed on AAT, GPI, MDH, PGM, and TPI for Rhipsalidopsis and on AMP, PGM, and SKD for Schlumbergera. Significant segregation distortion was observed in some families. Polymorphic isozymes are potentially useful markers for cultivar identification and for genetic and breeding studies.

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Sang-Min Chung, Jack E. Staub and Gennaro Fazio

Chilling temperatures (≤12°C) can cause substantial economic damage to cucumber (Cucumis sativus L.) plants. Previous studies suggest chilling tolerance trait is controlled by nuclear gene(s). To investigate inheritance of chilling injury in cucumber, cucumber lines [susceptible GY14 (P1), tolerant `Chipper' (P2), and tolerant `Little John' (P3)], and their exact reciprocal F1 and F2 cross-progeny were evaluated to determine the inheritance of chilling injury at the first true-leaf stage when challenged at 4 °C for 5.5 hours. The mean chilling ratings [1(trace) to 9(dead)] of progeny comparisons were F1(P1 × P2) = 6.2 vs. F1(P2 × P1) = 1.6; F2(P1 × P2) = 6.4 vs. F2(P2 × P1) = 2.7; F1(P1 × P3) = 5.4 vs. F1(P3 × P1) = 1.7; and F2(P1 × P3) = 5.8 vs. F2(P3 × P1) = 2.2. These data suggest that chilling tolerance was maternally inherited as is the chloroplast genome in cucumber. Parents, reciprocal F1, and F2 progeny were evaluated for variation using random amplified polymorphism DNA (RAPD). Although no maternally inherited RAPD markers were detected, polymorphic and paternally inherited RAPD bands AD21249, AV8916, and AV8969 amplified by AD2 and AV8 primers were cloned and sequenced. A BLAST search of these sequences suggested that their origin is likely cucumber mitochondrial DNA. These results indicate that the mitochondria genome is not associated with the chilling tolerant trait because this genome is paternally inherited in progeny derived from this reciprocal mating. Therefore, the results of maternally inherited chilling tolerant trait and paternally transmitted mitochondria genome support that the chilling tolerant trait as identified is likely associated with the chloroplast genome which is maternally transmitted in cucumber.

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Naofumi Hiehata, Shinji Fukuda, Yoshihiko Sato, Yukiko Tominaga, Osamu Terai and Masahiko Yamada

al. (2012) elucidated the inheritance of the resistance to Group C derived from ‘Shiromogi’. ‘Shiromogi’ originated as a seedling derived from an open-pollinated ‘Mogi’ seed irradiated with gamma rays ( Ichinose et al., 1982 ). The resistance to

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James W. Olmstead, Gregory A. Lang and Gary G. Grove

Most sweet cherry (Prunus avium L.) cultivars grown commercially in the Pacific Northwestern states of the United States are susceptible to powdery mildew, caused by the fungus Podosphaera clandestina (Wall.:Fr.) Lev. The disease is prevalent in the irrigated arid region east of the Cascade Mountains in Washington State. Little is known about genetic resistance to powdery mildew in sweet cherry, although a selection (PMR-1) was identified at Washington State Univ.'s Irrigated Agriculture Research and Extension Center that exhibits apparent foliar immunity to the disease. The objective of this research was to determine the inheritance of powdery mildew resistance from PMR-1. Reciprocal crosses were made between PMR-1 and three high-quality, widely-grown susceptible cultivars (`Bing', `Rainier', and `Van'). Resultant progenies were screened for reaction to powdery mildew colonization using a laboratory leaf disk assay. Assay results were verified by natural spread of powdery mildew among the progeny in a greenhouse and later by placing them among infected trees in a cherry orchard. Segregation within the progenies for powdery mildew reaction fit a 1 resistant: 1 susceptible segregation ratio (P ≤ 0.05), indicating that resistance to powdery mildew derived from PMR-1 was conferred by a single gene.

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Richard L. Fery and Howard F. Harrison Jr.

Experiments were developed to study the inheritance of the high level of tolerance to the herbicide bentazon exhibited by the pepper (Capsicum annuum L.) cultivar Santaka. Parental, F1, F2, and backcross populations of the cross `Santaka' × `Keystone Resistant Giant' were evaluated for injury in a greenhouse test using bentazon at a rate of 4.5 kg·ha-1 (1.1 kg×ha-1 is the rate recommended for most applications). Additionally, parental and F1 populations were evaluated for injury under field conditions using sequential bentazon applications of 4.5, 4.5, 6.75, and 9.0 kg·ha-1. A single, dominant gene determined tolerance. F1 hybrid plants (heterozygous at the locus conditioning tolerance) exhibited a high level of tolerance under field conditions. Results of the greenhouse test suggested a possible cytoplasmic involvement in the expression of the tolerance gene, but the results of the field test provided strong evidence that cytoplasm does not play a significant role. We propose that this gene be designated Bentazon tolerance and symbolized Bzt. Chemical name used: 3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide (bentazon).

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Urszula Klosinska, Elzbieta U. Kozik and Todd C. Wehner

A new trait, twin fused fruit, was discovered in gynoecious cucumber (Cucumis sativus L.) line B 5263. Plants with the twin fused fruit trait had two fruit fused into a single unit. In addition to having the twin fused fruit trait, line B 5263 had fruit with necks, large tubercles (warts), and dark green skin. The inheritance of twin fused fruit was studied in populations resulting from crosses between gynoecious line B 5263 (twin fused fruit) and monoecious line B 5404 (single fruit). Research was done in 1999 to 2001 in the greenhouses of the Research Institute of Vegetable Crops, Skierniewice, Poland. The F1 progeny developed single fruit in all cases. The observed distribution of plant phenotypes in the F2 fitted the expected ratio of 3 with single fruit: 1 with twin fused fruit. The observed distribution of plant phenotypes in the BC1A fitted the expected ratio of 1 with single fruit: 1 with twin fused fruit. Twin fused fruit occurred only in gynoecious plants, and never in monoecious plants of the cross. In the F2 progeny, the ratio of twin fused fruit within gynoecious plants fitted the expected ratio but the gene was not expressed in monoecious plants. In the F2 generation, the observed distribution of plant phenotypes fitted the expected ratio of 9 gynoecious single: 4 monoecious single: 3 gynoecious twin fused: 0 monoecious twin fused, indicating that there was epistasis, with twin fused fruit hypostatic to monoecious. The new gene will be named tf (twin fused fruit).

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Maurus V. Brown, James N. Moore, Ronald W. McNew and Patrick Fenn

A study was conducted to determine how resistance to downy mildew [Plasmopara viticola (Bert. & Curt.) Berl. & de Toni] is inherited in germplasm (Vitis vinifera L., V. labrusca L., V. rupestris Scheele, and V. riparia Michx.) used for breeding table grapes. Crosses, including reciprocals, among parents possessing different levels of downy mildew resistance were evaluated in 1994 and 1995. The proportion of foliar tissue with sporulation, chlorosis, or necrosis was used to measure resistance. All genotypes were rated for these characters on two separate dates in 1994 and 1995. Hypersensitive flecking was also evaluated in the 1995 seedlings to determine its relationship with downy mildew resistance. Crosses with at least one resistant parent had a larger number of resistant offspring than crosses between two susceptible parents. General combining ability (GCA) effects were highly significant for 1994 and 1995. Specific combining ability effects were significant, but were relatively small compared to GCA, suggesting additive gene action was a primary influence on downy mildew resistance. Heritability estimates for sporulation, chlorosis, and necrosis were the highest at the second rating in 1994 (0.88, 0.74, and 0.57, respectively) and 1995 (0.50, 0.60, and 0.60, respectively). Reciprocal crosses indicated that maternal inheritance did not influence downy mildew resistance. A small percentage of progeny with hypersensitive flecking were identified from the germplasm. Seedlings with the flecking characteristic tended to have lower sporulation, chlorosis, and necrosis ratings earlier in the growing season.