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William L. Holdsworth, Carly F. Summers, Michael Glos, Christine D. Smart and Michael Mazourek

2009–10, these plants were advanced to the BC 1 F 2 and F 3 generations, respectively. Additionally, selected BC 1 F 1 individuals were backcrossed to the high-quality downy mildew-susceptible parent to regain multiple disease resistances and flavor

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Loong S. Chang, Amy Iezzoni and Gerald Adams

Heritability and the genetic and environmental variance components of resistance to the canker-causing pathogen Leucostoma persoorrii were estimated in a population of diverse peach (Prunus persica L.)-genotypes. Disease resistance was measured as the length of necrotic tissue, i.e., canker length, following artificial inoculation in the field. Genetic and environmental variations were partitioned as variance components of the linear statistical model. Heritability was estimated by regressing average performance of seedlings on performance of their maternal parent. The genetic variance was highly significant, and the heritability for canker necrotic length was relatively high (0.72), suggesting that it should be possible to select L. persoonii -resistant individuals within the population.

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Wenjing Guan, Xin Zhao, Danielle D. Treadwell, Michael R. Alligood, Donald J. Huber and Nicholas S. Dufault

uptake of melon plants ( Zitter et al., 1996 ). Therefore, specialty melon cultivars with disease resistance or tolerance would be valued by producers and create novel markets. Breeding for disease resistance is one of the major goals in developing new

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Xiaohe Song and Zhanao Deng

levels of similarity to the plant nucleotide binding-site leucine-rich repeat (NB-LRR) class of disease resistance genes ( Song et al., 2012 ). The SSR markers were developed from gerbera expressed sequence tags (ESTs) in the GenBank ( Gong and Deng, 2010

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James D. Kell

55 COLLOQUIUM 2 (Abstr. 995-999) Classical and Molecular Approaches to Breeding Horticultural Plants for Disease Resistance

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Yun-Chan Huh, Du-Hyun Kim, Sang-Gyu Lee, Kyoung-Sub Park, Dong-Kum Park, Young-Hoe Woo and Jung-Myung Lee

Growth response of `Sambok Honey' watermelon grafted onto different rootstocks, including four Citrullus rootstocks and three other cucurbitaceous rootstocks, was evaluated at low and normal temperature regimes. Marked reduction in plant growth rate was observed in plants grown at low temperatures as compared to those grown at normal or optimal temperatures. Relative growth reduction rates were 40% to 48% for vine length, 39% to 51% for total leaf area, 37% to 60% for shoot fresh weight, and 50% to 79% for shoot dry weight, respectively. Watermelon rootstock PI 482322 showed comparable plant growth as the most popular rootstock (Shintozwa pumpkin) even at low temperatures. `Sambok Honey' watermelon grafted onto watermelon hybrids `PI 271969 × PI 296341' and `PI 271769 × Calhoun Gray', showed comparable plant growth as FR Dantos bottle gourd rootstock. Index of growth ability at low temperature (IGALT), which was calculated on the basis of reduced rate of vine length, dry weight, and leaf area, was comparatively high in C. martinezii, Shintozwa, PI 482322, and `PI 271769 × PI 296341' rootstocks (50% or higher) and lowest in own-rooted `Sambok Honey' or in watermelon plants on `Knight' rootstock. Watermelon hybrids `PI 271969 × PI 296341' and `PI 271769 × Calhoun Gray' exhibited better or at least comparable growth at low temperatures as compared to `FR Dantos', thus confirming the feasibility of using watermelon rootstocks even in winter greenhouse conditions.

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B.T. Scully, J.L. Brewbaker, J.K. Pataky, W.F. Tracy and M.E. Smith

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Annick Moing, Jean-Luc Poëssel, Laurence Svanella-Dumas, Michèle Loonis and Jocelyne Kervella

Prunus davidiana (Carr.), a wild species with poor fruit quality that is related to peach [Prunus persica (L.) Batsch], is used as a source of resistance to pests and diseases in peach breeding programs. Two genotypes of P. davidiana were studied for fruit biochemical composition and compared to three genotypes of P. persica (`Summergrand', `Bailey' and `Pamirskij'), and two P. persica × P. davidiana hybrids. Fruit of P. davidiana clones had higher malic acid, neochlorogenic and cryptochlorogenic acid and lower sucrose concentrations than fruit of all P. persica genotypes, even poor-quality Bailey. Differences in biochemical composition could be related to sensory evaluation. P. persica × P. davidiana hybrids had intermediate values between their parents for neochlorogenic acid concentration. They were similar to the P. persica parent for total soluble sugar, malic and citric acid, amino acid and catechin concentrations, indicating possible rapid progress for fruit quality in a breeding program.

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D.P. Coyne, J.R. Steadman, D.T. Lindgren, David Nuland, Durward Smith, J.R. Stavely, J. Reiser and L. Sutton

Common bacterial blight (CBB), rust (RU), and white mold (WM) are serious diseases of great northern (GN) and pinto (P) beans in Nebraska and Colorado. The bacterial diseases halo blight (HB) and brown spot (BS) are sporadic. Severe Fe-induced leaf chlorosis (Fe ILC) occurs on calcareous sites. Separate inoculated disease nurseries are used to screen for resistance to the pathogens causing the above diseases. Yields and seed quality of lines are also determined in non-disease trials. Sources of exotic resistance to the above pathogens and to Fe ILD have been identified and their inheritance determined. A non-structured recurrent selection scheme has mainly been used, occasionally with a backcross program, to combine high levels of the desired traits. Selection for highly heritable traits such as seed size, shape and color, maturity, plant architecture, and RU resistance occurs in early generations while traits of low heritability, such as CBB resistance, WM avoidance, yield, seed coat cracking resistance, and canning quality, are evaluated in separate replicated tests over several years and finally for yield in on-farm-trials. A number of multiple disease resistant, high-yielding, well-adapted GN and P lines are or will be released; P `Chase' (on about 30,000 acres in 1996) and GN WM 3-94-9 (for possible release).