Abstract
Seedlings of strawberry (Fragaria × ananassa Duch.) from 29 crosses were evaluated in a field trial over a 2½-year period for tolerance to a complex of viruses. The seedlings and plants of the parent clones were subjectively rated for tolerance on the basis of vigor, runnering, and appearance of virus symptoms. ‘Totem’ and ‘Aiko’ produced the highest percentage of tolerant-appearing seedlings, while ‘Olympus’, ‘Belrubi’, and ‘Hood’ produced the highest percentage of susceptible seedlings. At the end of the trial, when the symptoms were most severe, heritability for tolerance was 0.73. Specific combining ability variance was much smaller than general combining ability variance, indicating that a high proportion of genetic variance was additive. Therefore, rapid progress in breeding for tolerance can be expected from selecting parent clones on the basis of phenotypic performance.
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.
Three populations of navy bean (Phaseolus vulgaris L.), consisting of recombinant inbred lines, were grown at two locations for 2 years and were used to study canning quality. The traits measured included visual appeal (VIS), texture (TXT), and washed drained mass (WDM). Genotype mean squares were significant for all three traits across populations, although location and year mean squares were higher. We found a positive correlation (r = 0.19 to 0.66) between VIS and TXT and a negative correlation (r = -0.26 to -0.66) between VIS and WDM and between TXT and WDM (r = -0.53 to -0.83) in all three populations. Heritability estimates were calculated for VIS, TXT, and WDM, and these values were moderate to high (0.48 to 0.78). Random amplified polymorphic DNA markers associated with quantitative trait loci (QTL) for the same canning quality traits were identified and studied in each population. Marker-QTL associations were established using the general linear models procedure with significance set at P=0.05. Location and population specificity was common among the marker-QTL associations identified. Coefficient of determination (R2) values for groups of markers used in multiple regression analyses ranged from 0.2 to 0.52 for VIS, 0.11 to 0.38 for TXT, and 0.25 to 0.38 for WDM. Markers were identified that were associated with multiple traits and those associations supported correlations between phenotypic traits. MAS would offer no advantage over phenotypic selection for the improvement of negatively associated traits.
Genetic characterization of anthracnose resistance in tomato (Lycopersicon esculentum Mill.) caused by Colletotrichum coccodes (Wallr.) Hughes was accomplished using populations developed from crosses between the anthracnose susceptible cultivar US28 and three resistant breeding lines (115-4, 625-3, and 88B147) that varied in their degree of anthracnose resistance and relative stage of adaptation for commercial use. These lines were of common parental lineage with resistance derived from the small-fruited L. esculentum USDA PI 272636. Anthracnose lesion diameters and fruit weight were measured in puncture inoculated fruit of parental, F1, F2, and backcross generations within each cross. Correlation coefficients between fruit size and lesion diameter were low and generally nonsignificant. Estimates of broad and narrow sense heritabilities for resistance were moderate and declined as relative anthracnose susceptibility of the resistant parent increased coincident with increasing horticultural adaptation. A simple additive dominance model, m[d][h], was adequate to explain the genetic variance for anthracnose resistance in all crosses. Genetic variance for anthracnose resistance was primarily additive. The minimum number of effective factors or loci conditioning anthracnose resistance declined during attempts to transfer high levels of resistance from PI 272636 into adapted breeding lines.
The inheritance and heritability (H) of leaf and pods reactions and seed infection of common beans (Phaseolus vulgaris L.) to Xanthomonas campestris pv. phaseoli (Smith) Dye (Xcp) were studied in three crosses along with flower and stem color, and the association of reactions to Xcp in the plant organs. Recombinant inbred lines from the crosses `PC 50' × XAN 159, BAC 6 × HT 7719, and BelNeb 1 × A 55 were used. Quantitative inheritance patterns were observed for disease reactions in leaves, pods, and seeds. Stem and flower color were inherited qualitatively. Low to intermediate and intermediate H estimates were found for pod reactions when inoculated on the same time, allowing the infection to occur in a uniform environment. Intermediate to high H estimates were found for leaf and seed reactions to Xcp, respectively. Significant positive intermediate to moderately high correlations were found between the reactions to Xcp of the first trifoliolate with later-developed leaves and pods in all three populations. The moderately high genetic correlations between leaves and pods suggested that some common genes may control the reactions to Xcp in these plant organs. No association was detected between flower or stem color and reactions to Xcp.
Tomato fruit firmness is a key quality component of tomatoes produced for processing applications. Fruit firmness is generally considered a quantitatively inherited trait. Pericarp firmness of modern tomato cultivars is believed to be derived from a fairly narrow genetic background and is the result of the cumulative effort of numerous breeders over many years. Despite inferior phenotypes, wild species contain loci that can substantially increase tomato fruit quality. In the current study, inheritance of fruit firmness in firm and ultra-firm processing tomato germplasm developed from transgressive segregants of interspecific Lycopersicon esculentum × L. hirsutum and intraspecific L. esculentum crosses was characterized. Large-fruited breeding lines that varied in fruit firmness from soft to firm were identified for genetic analyses. A six-parent diallel of these advanced breeding lines was developed for field trials over multiple locations. Fruit firmness in the resulting 36 lines was determined by measuring fruit elastic properties during fruit puncture and compression. Following loading for compression, stress relaxation was recorded for 15 s. A three-parameter model was used to fit the relaxation curves. There was little correlation between firmness (maximum force) and the three relaxation parameters, i.e., firmness measured the elastic component and the relaxation parameters measured the viscous portions of the texture. General and specific combining ability for firmness derived from the respective genetic backgrounds was determined. Genetic variance components for fruit firmness were estimated using a diallel analysis and narrow sense heritability was measured using parent-offspring regression.
Tomato mottle virus (ToMoV) is a silverleaf whitefly (Bemisia argentifolii Bellows and Perring n. sp.) transmitted, bipartite geminivirus that infects tomatoes (Lycopersicon esculentum Mill.). Inbred lines resistant to ToMoV were derived from Lycopersicon chilense Dunal accession LA 1932. Inheritance was studied using a family developed from the crossing of a resistant inbred with a susceptible tomato inbred over two seasons. The F1 had resistance intermediate to the parents and generation means analysis of F1 and F2, backcross and parental populations suggested that the action of at least two additive genes with high heritability (h2 n.s. = 0.87) controlled ToMoV resistance. When data from the two seasons were combined, an acceptable fit to an additive-dominance genetic model was obtained. Single plant comparisons, bulk comparisons, and tailends of F2 populations segregating for ToMoV resistance derived from LA 1932 identified randomly amplified polymorphic DNA (RAPD) markers using eight hundred 10-mer oligonucleotide primers. The F2 populations used for inheritance studies were screened for polymorphic markers, and 12 RAPD markers associated with the ToMoV resistant line were linked to the morphological markers self-pruning (sp) and potato leaf (c) on chromosome 6. RAPD markers that were associated with ToMoV resistance segregated into two linked regions flanking either side of the sp and c loci. The molecular studies suggested that the action of at least two additive regions controlled ToMoV resistance which supported the inheritance analysis.
between seedling and grafted plants, after removal of a general average propagation effect. Narrow-sense heritability and individual broad-sense heritability were estimated for each trait at the t th trial by p th density as: h t p 2 = v A s p v A s p
Twenty-six clones of pepino (Solanum muricatum Aiton) were evaluated for yield, fruit weight, fruit shape (length to width ratio), soluble solids concentration (SSC), titratable acidity (TA), and ascorbic acid concentration (AAC) over two growing seasons: autumn-winter (AW) and spring-summer (SS). Significant differences were found for the effects of clone, season, and clon× season interaction for all traits, except in the case of season for fruit shape. Mean values for yield, SSC, and AAC were higher in the AW than in the SS season, while mean fruit weight and TA were lower. Many clones (13 in AW and six in SS) had a yield higher than 30 t·ha-1. Substantial genotypic variation was found for all traits studied except for SSC. Clones stable for all traits were detected over both seasons, except for SSC, where the differences between seasons were very high. The significant clone × season interaction for all traits indicates that selection of genotypes adapted specifically to either AW or SS seasons would maximize the response to selection. Broad sense heritabilities were highest for fruit shape and yield (>0.70), while SSC had the lowest values (0.39 in AW, 0.17 in SS, and almost 0 when considering both seasons combined). For the AW season, significant fruit weight-SSC and fruit weight-AAC genotypic correlations were detected; for the SS season the significant genotypic correlations were yield-SSC, fruit weight-TA, fruit shape-TA, and SSC-TA. Results suggest there are ample opportunities for improving several traits in this crop using intraspecific variation for adaptation to specific environments.
A study of leaf chlorosis in rabbiteye blueberries (Vaccinium ashei Reade) grown in soil containing 300 to 400 ppm diethylenetriaminepentaacetic acid (DTPA)-extracted Mn revealed no relationship between leaf Mn content and chlorosis. A second study was conducted to estimate heritability of the content of Mn, Fe, and certain other mineral elements that have been associated with leaf chlorosis and to determine the genetic relationships among shoot dry weight, visual rating, and the mineral elements in rabbiteye blueberry. Heritability estimates were high for all variables except Fe, suggesting that changes in Mn, Zn, Ca, Mg, or K contents could be expected from phenotypic recurrent selection. However, manipulation of mineral content probably would not ameliorate the Fe chlorosis. The high heritability of shoot dry weight and visual rating and the high genetic correlation between these variables suggest that plants resistant to mineral effects on Fe metabolism can be selected on the basis of visual rating.