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Kevin E. McPhee, Robert S. Zemetra, Jack Brown, and James R. Myers

Common bean (Phaseolus vulgaris L.) is a nutritionally complete food, but contains antinutritional compounds that reduce digestibility. One group of compounds includes the raffinose family oligosaccharides (RFOs) (raffinose, stachyose, and verbascose), which are partly responsible for flatulence after beans are eaten. RFOs stabilize cell membranes during seed desiccation and when the seed rehydrates during germination. While low levels of RFOs are desirable nutritionally, high levels may enhance germination and emergence, particularly in cold, wet soils. Eight landraces selected for high and low sucrose, raffinose, and stachyose content, were crossed in a diallel mating design to investigate genetic control of the RFOs. Derivatized soluble sugars were measured using gas-liquid chromatography. Fructose, sucrose, raffinose, and stachyose were detected. In the F1, fructose varied from 0.1 to 2.5 mg·g-1 dry weight (DW), sucrose from 17.2 to 56.5 mg·g-1 DW, raffinose from 0.1 to 4.1 mg·g-1 DW, and stachyose ranged from 7.6 to 43.7 mg·g-1 DW. Griffing's analysis estimates of general combining ability were on average, 16.5 times larger than specific combining ability for all the RFOs, indicating that additive genetic variance was most important. Significant reciprocal differences were detected in the F1 and F2, but not in the F3. RFO accumulation was partially dominant as indicated by Hayman's analysis. Narrow sense heritability averaged over F2 and F3 generations for sucrose, raffinose, stachyose, total sugar, and total oligosaccharides were 0.22, 0.54, 0.44, 0.17, and 0.27, respectively. Moderate heritabilities indicate that manipulation of RFO accumulation in this set of bean lines would probably need to be done on a progeny row basis with replication.

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Valdomiro A.B. de Souza, David H. Byrne, and Jeremy F. Taylor

Seedlings of 108 families from crosses among 42 peach [Prunus persica (L.) Batsch] cultivars and selections were evaluated for six plant characteristics in 1993, 1994, and 1995. The data were analyzed by using a mixed linear model, with years treated as fixed and additive genotypes as random factors. Best linear unbiased prediction (BLUP) was used to estimate fixed effects. Restricted maximum likelihood (REML) was used to estimate variance components, and a multiple trait model was used to estimate genetic and phenotypic covariances among traits. The narrow-sense heritability estimates were 0.41, 0.29, 0.48, 0.47, 0.43, and 0.23 for flower density, flowers per node, node density, fruit density, fruit set, and blind node propensity, respectively. Most genetic correlations among pairs of traits were ≥0.30 and were, in general, much higher than the corresponding phenotypic correlations. Flower density and flowers per node (ra = 0.95), fruit density and fruit set (ra = 0.84) and flower density and fruit density (ra = 0.71) were the combinations of traits that had the highest genetic correlation estimates. Direct selection practiced solely for flower density (either direction) is expected to have a greater effect on fruit density than direct selection for fruit density.

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E. Arnaud-Santana, D.P. Coyne, J.R. Steadman, A.K. Vidaver, K.M. Eskridge, and J.S. Beaver

Heritabilities (H) of seed transmission and leaf and pod reactions to common bacterial blight (CBB) Xanthomonas campestris pv. phaseoli (Xcp) and to web blight (WB) Thanatephorus cucumeris (Tc) were studied. The reaction to CBB was quantitatively inherited. H values of .36, .46, and .34 for leaf reaction, .14, .12, and .27 for pod reaction, .53, .26, and .36 for seed transmission were estimated based on variation of F6 lines derived from bean crosses 'PC-50' × XAN-159, 'PC-50'× BAC-6, and 'Venezuela 44' × BAC-6 (greenhouse, NE). No significant correlations were detected between leaf and pod reactions or between pod reaction and seed transmission. Quantitative inheritance patterns were observed for leaf reactions to Xcp, Tc, and architecture (AR) in F6lines from the cross BAC-6 × HT 7719 (field, Dominican Republic). H values of .23 (CBB), .14 (WB), and .30 (AR) were obtained. No significant correlations were detected between CBB with WB or AR. A low correlation (+.22) was found between WB and AR.

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N. Georgelis, J.W. Scott, and E.A. Baldwin

Small-fruited cherry tomato accession PI 270248 [Lycopersicon esculentum Mill. var. cerasiforme (Dunal) A. Gray] with high fruit sugars was crossed to large-fruited inbred line Fla.7833-1-1-1 (7833) (L. esculentum) that had normal (low) fruit sugars. The F1 was crossed to PI 270248 and 7833 to obtain BCP1 and BCP2, respectively, and self-pollinated to obtain F2 seed. The resulting population was used to study the inheritance of high sugars from PI 270248. Continuous sugar level frequency distributions of BCP1, BCP2, and F2 suggest that the trait is under polygenic control. Additive variation was significant, but dominance variation was not. There was a heterozygote × heterozygote type of epistasis present that likely caused the F1 sugar level to skew nearly to the level of the high sugar parent. The F2 mean sugar level was lower than the midparent level. Broad-sense heritability was 0.86. There was a significant line × season (fall, spring) interaction where lines with higher sugars were affected more by seasons than lines with lower sugars. Sugar level, in general, was higher in spring. Higher solar radiation in spring than in fall may explain the sugar level difference between the seasons.

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M.R. Foolad and G.Y. Lin

The genetic relationship between cold tolerance (CT) during seed germination and vegetative growth in tomato (Lycopersicon esculentum Mill.) was determined. An F2 population of a cross between accession PI120256 (cold tolerant during both seed germination and vegetative growth) and UCT5 (cold sensitive during both stages) was evaluated for germination under cold stress and the most cold tolerant progeny (the first 5% germinated) were selected. Selected progeny were grown to maturity and self-fertilized to produce F3 families (referred to as the selected F3 population). The selected F3 population was evaluated for CT separately during seed germination and vegetative growth and its performance was compared with that of a nonselected F3 population of the same cross. Results indicated that selection for CT during seed germination significantly improved CT of the progeny during germination; a realized heritability of 0.75 was obtained for CT during seed germination. However, selection for CT during germination did not affect plant CT during vegetative growth; there was no significant difference between the selected and nonselected F3 populations in either absolute CT [defined as shoot fresh weight (FW) under cold stress] or relative CT (defined as shoot FW under cold as a percentage of control). Results indicated that, in PI120256, CT during seed germination was genetically independent of CT during vegetative growth. Thus, to develop tomato cultivars with improved CT during different developmental stages, selection protocols that include all critical stages are necessary.

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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.

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Roger L. Vallejo, Wanda W. Collins, and Rocco D. Schiavone

Preliminary data on the genetics of glandular trichomes and the feasibility of incorporating A and B glandular trichomes and polyphenol oxidase (PPO) activity from Solanum berthaultii Hawkes (Ber) into an advanced S. phureja Juz. et Buk.-S. stenotomum Juz. (Phu-Stn) diploid potato population are presented. A random sample of four Phu-Stn clones was intercrossed with a sample of three Ber progenies (pollen bulk per progeny) segregating for high density of A and B glandular trichomes. Nine F1 families [(Phu-Stn) × Ber] were evaluated over two experiments in the greenhouse for A and B trichome density (5 mm2 of abaxial surface) and PPO activity 45 days after planting. A completely randomized design in an experimental hierarchical classification arrangement was used to quantify the genetic variability and to estimate broad-sense heritabilities (defined on an individual basis) for the attributes under study. To characterize the inheritance of these attributes further and to estimate narrow-sense heritabilities, fifteen backcross (BC) families were evaluated in a randomized complete-block design with three replications and analyzed by half-sib family analysis. Phenotypic and genotypic correlations between these attributes were also estimated. In the F1 families, broad-sense heritabilities were 0.59 and 0.41 for density of A and B trichomes, respectively. In the BC population, narrow-sense heritabilities were 0.15 and 0.08 for A trichome density and PPO activity, respectively; expression of B trichomes was almost absent in this generation. Genotype × environment interaction was significant for density of A trichomes and highly significant for density of B trichomes in F1 families. There was some level of positive association between density of A and B trichomes and PPO activity. Additive genetic variance of these attributes was very low in this study; therefore, selection schemes based on family selection and progeny testing would be an appropriate breeding strategy for improving these traits.

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Beiquan Mou and Yong-Biao Liu

Leafminer (Liriomyza langei Frick) is a major insect pest of many important agricultural crops including lettuce (Lactuca sativa L.). The goals of this study were to evaluate lettuce genotypes for resistance to leafminer and to estimate heritabilities of three leafminer-resistant traits. Forty-six lettuce genotypes were evaluated in two tests in insect cages. Wild species (Lactuca serriola L., Lactuca saligna L., and Lactuca virosa L.) had significantly fewer leafminer stings than cultivated lettuce (L. sativa) in both tests. PI 509525 (L. saligna) had few leafminer stings and no flies emerged. Leaf (leaf and romaine) lettuce also showed significantly less stings than head (crisphead and butterhead) types, while differences between leaf and romaine lettuces, and between crisphead and butterhead types were nonsignificant. Broad-sense heritability for number of stings per unit leaf area was relatively high, averaging 65% over the two tests. Heritabilities for egg-hatching period and flies per plant were 10% and 15%, respectively. Stings per unit leaf area from the two tests were highly correlated (r = 0.828), suggesting that resistance was stable over different plant ages and against different pressures of leafminer. These results suggest that genetic improvement of cultivated lettuce for leafminer resistance is feasible.

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Creighton L. Gupton and Barbara J. Smith

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Roger L. Vallejo, Wanda W. Collins, and Robert H. Moll

Glandular trichomes from some Solanum species have suppressed infestation by insects including green peach aphid, which is a main vector of potato virus Y (PVY) and potato leaf roll virus (PLRV), both of which contribute to a serious loss in potato production. Eight Solanum phureja Juz. et Buk.-S. stenotomum Juz. (Phu-Stn), three S. berthaultii Hawkes (Ber), nine F1 [(Phu-Stn) × Ber], fifteen backcross (BC) [(Phu-Stn) × F1], and seventeen reciprocal BC (BCR) [F1 × (Phu-Stn)] families were evaluated to determine the genetic variability and heritability of A and B glandular trichome density and polyphenol oxidase (PPO) activity. Experiments were carried out in completely randomized and randomized complete-block designs in the greenhouse. Genetic analysis was done using half-sib family and parent-offspring regression analysis. Phu-Stn showed a higher density of A trichomes than Ber and F1, while the BC and BCR had densities of A trichomes similar to Phu-Stn. B trichomes were not observed in Phu-Stn. Ber showed a high B trichome density, which was transmitted to the F1. In the BC, B trichomes were almost absent, but, in the BCR, the density of B trichomes was higher than that of BC. Ber and F1 had similar or higher PPO activity than Phu-Stn. PPO activity decreased in the BC, but, in the BCR, it was high and similar to Ber and F1. Broad-sense heritability estimates for A and B trichome density and PPO activity were from medium to high (0.48 to 0.77) in Phu-Stn, Ber, and F1. Narrow-sense heritability estimates for A and B trichome density and PPO activity were very low (0.04 to 0.24) in BC and BCR. In the BC families, additive genetic variance was very low for A and B trichome density and PPO activity. Half-sib family selection based on progeny testing and combined with BCs to Phu-Stn in subsequent generations would be a suggested breeding procedure to improve these traits. Phenotypic correlations between A and B trichome densities were 0.26 (F1) and 0.44 (BCR), between A trichome density and PPO activity 0.20 (F1) and 0.31 (BCR), and between B trichome density and PPO activity 0.04 (F1) and 0.27(BCR. Positive associations found between traits might facilitate simultaneous improvement for high levels of A and B trichome density and PPO activity.