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Pilar Soengas, Pablo Velasco, Guillermo Padilla, Amando Ordás, and Maria Elena Cartea

Brassica napus includes economically important crops such as oilseed rape, rutabaga, and leaf rape. Other vegetable forms of Brassica napus, namely nabicol and couve-nabiça, are grown in northwestern Spain and north of Portugal, respectively, and their leaves are used for human consumption and fodder. The relationship of nabicol with other Brassica napus leafy crops was studied before, but its origin remained unclear. The aims of this work were to study the genetic relationships among nabicol landraces and other B. napus crops based on microsatellites and to relate the genotypic differences with the use of the crop. The relationship among 35 Brassica napus populations representing different crops was studied based on 16 microsatellite markers. An analysis of molecular variance was performed partitioning the total variance into three components. The source of variation resulting from groups was defined considering the main use of the crop and accounted for a smaller percentage of variation than other sources of variation, proving that this division is not real. Populations clustered into seven different clusters using a similarity coefficient of 0.82. No clear association was evident between clusters and the main use of populations, suggesting genetic differences among populations could reflect differences in their origin/breeding or domestication. Spanish nabicol could have originated from a sample of couve-nabiças, and couve-nabiças could be used to improve nabicol landraces, because they have a narrow genetic basis that limits their potential for breeding.

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S. Alan Walters, Todd C. Wehner, and Kenneth R. Barker

The inheritance of resistance to M. arenaria races 1 and 2 in Cucumis sativus var. hardwickii (R.) Alef. line LJ 90430 was studied in several crosses with cultivated cucumber (C. sativus L.). Initially, parents, F1, F2, and BC1 to both parents of `Sumter' x LJ 90430 tested in a split-root experiment showed that resistance was quantitative. In addition, it appeared that the same genes were controlling resistance to race 1 and race 2 of M. arenaria (genetic correlation of 0.97 and 0.99 for gall index and egg mass data, respectively). In later greenhouse experiments, two other families were evaluated (`Addis' x LJ 90403 and `Poinsett 87' x LJ 90430) for inheritance of resistance to M. arenaria race 1. In all crosses using gall index data, additive variance was the largest component of genetic variance, and estimates of narrow-sense heritability ranged from 0.50 to 0.85 (0.57 to 0.81 for broad-sense heritability). Estimates of the minimum number of genes (effective factors) using gall index data ranged from 1.1 to 2.7 (0.2 to 0.3 for egg mass data).

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Ann Marie Connor, M. Joseph Stephens, Harvey K. Hall, and Peter A. Alspach

Variance components and narrow-sense heritabilities were estimated for antioxidant activity (AA), total phenolic content (TPH), and fruit weight in red raspberry (Rubus idaeus L.) fruit from offspring of a factorial mating design. Forty-two full-sib families utilizing seven female and six male parents were evaluated in each of two years in Motueka, New Zealand. In a single year, values within individual half-sib families ranged as widely as 25.3-79.4 μg·g-1 fruit for AA, 205-597 mg/100 g fruit for TPH, and 1.06-7.69 g for fruit weight. Analyses of variance for these three variates demonstrated significant parental source variation in both individual and combined year analyses. For AA and TPH, female parental effects accounted for ≈7% to 19% of total variation, while male effects accounted for ≈6% to 8%. A partially pigment deficient R. parvifolius L. derivative female parent accounted for some of these differences. Female × male parent interaction was not significant for AA and TPH and was marginally significant for fruit weight in combined year analysis. Year had a significant effect on the overall mean AA and TPH, but contributed less than genetic effects to the overall variation in all three traits. Interactions of year with genetic effects were not statistically significant for AA or TPH, indicating that between-year rank or scale changes among families were negligible. The largest proportion of variation was found within rather than among full-sib families. However, variation among plots within full-sib families accounted for 12% to 19% of total variation, indicating environmental differences accounted for some of the observed within-family variation in AA and TPH. Antioxidant activity and TPH were highly phenotypically correlated (r = 0.93); their genetic correlation (r = 0.59) implies that substantial additive genetic factors underlie the phenotypic correlation, but that nonadditive genetic or environmental influences are also important. Both AA and TPH were weakly negatively phenotypically correlated with fruit weight (r = -0.34 and -0.33, respectively), but the corresponding genetic correlations were close to zero. Thus, selection for both high AA or TPH and high fruit weight is possible. Narrow-sense heritability estimates based on variance components from combined year data were h 2 = 0.54, 0.48, and 0.77 for AA, TPH, and fruit weight, respectively. These estimates imply a rapid response to selection is possible.

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

Heritability estimates are useful to predict genetic progress among offspring when the parents are selected on their performance, but they also provide information about major changes in the amount and nature of genetic variability through generations. Genetic and phenotypic correlations, on the other hand, are useful for better planning of selection programs. In this research, seedlings of 39 families resulting from crosses among 27 peach [Prunus persica (L.) Batsch] cultivars and selections were evaluated for date of full bloom (DFB), date of ripening (DR), fruit period development (FDP), flower density (FD), node density (ND), fruit density (FRD), fruit weight (WT), soluble solids content (SS), apical protuberance (TIP), red skin color (BLUSH), and shape (SH) in 1993 and 1994. The data were analyzed using the mixed linear model. The best linear unbiased prediction (BLUP) was used to estimate fixed effects and predict breeding values (BV). Restricted maximum likelihood (REML) was used to estimate variance components, and a multiple-trait model to estimate genetic and phenotypic covariances between traits. The data indicates high heritability for DFB, DR, FDP, and BLUSH, intermediate heritability for WT, TIP, and SH, and low heritability for FD, ND, FRD, and SS. They also indicate year effect as a major environmental component affecting seedling performance. High correlation estimates were found between some traits, but further analysis is needed to determine their significance.

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John C. Alleyne, Teddy E. Morelock, and Clay H. Sneller

Genotype by environment (G × E) effects in Regional Cooperative Southernpea trials for the southeastern United States were investigated to characterize the extent, pattern, and potential impact of G × E on seed yield of southernpea [Vigna unguiculata (L.) Walp] genotypes. The structure of G × E effects was investigated using the Additive Main Effect and Multiplicative Interaction (AMMI) method. AMMI analyses revealed a highly significant genotype × environment interaction, most of which was partitioned into a genotype × location component of variance. AMMI first principal component axis scores stratified environments into two groups that minimized variation within groups. Biological interpretation of groupings and visual assessment of the AMMI biplot, revealed high-yielding genotypes interacting positively with one group of environments and conversely, low-yielding genotypes interacting positively with the other group. There were some significant rank changes of genotypes as yield potential varied across environments. Some environments showed similar main effects and interaction patterns indicating that most of the G × E effects could be captured with fewer testing sites, and consequently redundancy of some testing environments over years.

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Graham H. Barry, William S. Castle, Frederick S. Davies, and Ramon C. Littell

Sources of variation in juice quality of `Valencia'sweet orange [Citrus sinensis(L.) Osb.] were quantified and their relative contributions to variability in juice quality were determined, from which sample sizes were estimated. Commercial orchards of `Valencia' sweet orange trees on Carrizo citrange [C. sinensis × Poncirus trifoliata (L.) Raf.] rootstock were selected at four geographic locations representing the major citrus-producing regions in Florida. Within- and between-tree variation in soluble solids concentration (SSC) and titratable acidity (TA) were estimated in two experiments over two or three seasons, respectively. Variance components for all treatment effects were estimated to partition total variation into all possible component sources of variation. Seasonal variation in SSC and TA was relatively small, but larger for TA than SSC. Variation in SSC among blocks within a location was intermediate to low, and was less than variation among locations. In contrast, tree-to-tree variation in SSC and TA was large, in spite of sampling from trees of similar vigor and crop load, and variation in SSC and TA among fruit was relatively large. Based on results of this study, samples consisting of 35 fruit are required to detect differences (P ≤ 0.05) of 0.3% SSC and 0.06% TA, whereas 20-fruit samples can be used to detect differences of 0.4% SSC and 0.08% TA. Seven replications are required to detect differences of 0.5% SSC and 0.1% TA, with small gains in precision when tree numbers exceed 10.

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Ann Marie Connor, Chad E. Finn, and Peter A. Alspach

Antioxidant compounds absorbed from our diet are thought to have a role in preventing chronic diseases that result from oxidative damage. Berry fruit have high levels of antioxidants, and further increases in antioxidant activity (AA) might be possible through breeding. We determined the AA, total phenolic content (TPH), and fruit weight in 16 blackberry and hybridberry (Rubus L.) cultivars harvested in New Zealand and Oregon in 2002 and 2003, to assess genetic and environmental variation. Both AA and TPH varied significantly between years within location, but not among cultivars or between locations per se. However, cultivar interactions with both location and year within location contributed to variation in both variates. In contrast, both cultivar and location contributed to variation in fruit weight, but years within location did not. However, the cultivar × year within location interaction was significant for this trait. Variance component distributions confirmed that cultivar and location effects together contributed little (<20%) to the total variation in either AA or TPH, while cultivar × environment interactions accounted for >50% of total variation in these traits. Cultivar and location effects together contributed ≈70% of the total variation observed in fruit weight. Phenotypic correlations were significant between AA and fruit weight (r = -0.44), and between TPH and fruit weight (r = -0.51). When adjusted for fruit weight, analyses for AA and TPH demonstrated that cultivar effects approached significance (P = 0.06) and accounted for ≈25% of total variance, while location effects accounted for none. Although the cultivars in this study had diverse interspecific backgrounds, utilization of various Rubus species in blackberry and hybridberry breeding is not uncommon, and our results demonstrating significant cultivar × environment interaction for AA and TPH should be applicable to breeding for high AA genotypes.

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M.R. Foolad

Breeding for salt tolerance in tomato (Lycopersicon esculentum Mill.) has been restricted by insufficient knowledge of the genetic control of tolerance. The genetic basis of salt tolerance during vegetative growth was investigated by growing a salt tolerant (PI174263) and a salt sensitive tomato cultivar (UCT5) and their F1, F2, and backcross progeny in saline solutions with electrical conductivity of 0.5 (control) and 20 dS·m–1 (salt-stress). The relative salt tolerance of each generation was determined as the percentage of growth (i.e., dry matter production) under salt-stress relative to growth under control conditions. In all generations, shoot growth was significantly reduced by salt-stress. The reduction was largest in UCT5 (56.1%) and smallest in the F1 (27.4%) followed by PI174263 (32.3%). Analysis of the absolute and relative growth under salt-stress indicated that genes contributing to vigor might be different from genes conferring tolerance. Generation means analyses of the absolute and relative growth indicated that the majority of the genetic variation among generations were due to simple (additive and dominance) genetic effects; nonallelic interactions, although significant, were far less important. Partitioning of the total genetic variance by weighted least square regression analysis and variance component analysis indicated that 88% or more of the variation were due to additive genetic effects. A moderate estimate of narrow sense heritability (0.49 ± 0.09) was obtained for shoot dry weight under salt-stress treatment. The results indicate that tomato salt tolerance during vegetative growth can be improved by breeding and selection.

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Douglas V. Shaw, W.D. Gubler, Kirk D. Larson, and John Hansen

Resistance to wilt caused by Verticillium dahliae Kreb. was evaluated for 41 strawberry genotypes from the Univ. of California breeding program and 1000 offspring from crosses among 23 of these genotypes. Runner plants from these genotypes and seedlings were inoculated with a conidial suspension containing a mixture of five isolates of V. dahliae from strawberry. Symptoms were scored as the number of dead or seriously stunted plants per plot, or based on a subjective phenotypic resistance score assigned to each plot on five dates during the spring after planting. Most of the California germplasm is highly susceptible to V. dahliae, with an average resistance score of 2.1 (±0.10) and 84.1% (±2.1) plants stunted or dead compared with a score of 3.2 (±0.24) and 57.4% (±4.9) of plants stunted or dead for a control set of six non-California genotypes identified previously as resistant. However, a broad range of intermediate resistance was detected, and 4 of the 41 California genotypes evaluated had resistance scores superior to the mean score for the non-California resistant checks. Plot-mean heritabilities for resistance and stunting scores estimated using genotypic, full-sib family, and offspring-parent analyses ranged from 0.44 to 0.88. Comparison of different estimates of variance components suggests that half or more of the genotypic variance for resistance traits detected is due to the additive effects of genes. There appears to be sufficient variation within the California population to proceed with an effective selection program, despite the absence of directional selection for resistance during the past 3 decades. However, developing cultivars with adequate resistance will ultimately depend on the recovery of transgressive segregants from superior parents, as even the most resistant genotypes from all sources showed some disease symptoms.

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Ann Marie Connor, Tony K. McGhie, M. Joseph Stephens, Harvey K. Hall, and Peter A. Alspach

We determined variance components and narrow-sense heritability estimates for total and individual anthocyanin (ACY) content and antioxidant activity (AA) in fruit from 411 genotypes in a red raspberry (Rubus idaeus L.) factorial mating design based on 42 full-sib families derived from seven female and six male parents, harvested in 2002 and 2003. Within half-sib family total ACY content ranged from ≈1-60+ mg/100 g fruit in both seasons. The four major ACYs quantified by high-performance liquid chromatography also showed wide ranges each year. Female and male parent contributions to variation in total and individual ACYs were significant (P ≤ 0.001) in combined year analysis, and together accounted for 29% to 48% of the total variation. A substantial proportion of the female contribution was attributed to the use of a pigment-deficient R. parvifolius L. × R. idaeus hybrid derivative as a female parent. Female × male interaction was nonsignificant and contributed negligibly to total variance. Year effects accounted for <2.5% of variation in ACYs and were only marginally significant. Year interactions were negligible. Within family variation (among plots and within plot) accounted for ≈50% of the variation in total ACY and 62% to 69% of the variation in individual ACYs. Combined year narrow-sense heritability estimates were high (h 2 = 0.54-0.90 for individual ACYs, 1.00 for total ACY) among all factorial genotypes, but moderate when the progeny of the R. parvifolius derivative were excluded (h 2 = 0.45-0.78 for individual ACYs, 0.74 for total ACY). The latter estimates are applicable to breeding programs in which pigment-deficient genotypes are rarely or never used in breeding. Parental main effects were significant for AA, together accounting for 19% of total variance; female × male interaction was nonsignificant. Year effects were marginally significant and year interactions nonsignificant; together these sources of variation contributed <2% of total variation in AA. The majority of AA variation was found within- and among-plots within family. The phenotypic correlation between AA and total ACY was r = 0.53, and ranged from r = 0.21-0.46 between AA and individual ACYs; genetic correlations between AA and the ACYs were similar to the phenotypic correlations, suggesting predominantly additive genetic effects accounted for the phenotypic correlations. Linear modelling for AA based on individual ACYs and their interactions explained ≈0.53 of AA variation, substantially less than that explained by total phenolic content (R 2 = 0.88). Our results show substantial variation and moderate to high narrow-sense heritability estimates for red raspberry ACYs, but ACY content and profile information are ineffective proxies and predictors for AA in red raspberry fruit.