One hundred-eighty six strawberry genotypes from the Univ. of California strawberry (Fragaria ×ananassa Duch.) breeding program were evaluated for resistance to Phytophthora cactorum Schroet. in trials conducted over 6 years; 60 of these genotypes were tested in 2 years or more. Mother plants of each genotype were grown in a propagation nursery beginning in June, and runner plants were set into soil infested with inoculum from a mix of four P. cactorum isolates in August or September of the same year. Runner plants of each genotype were harvested from the inoculated nursery, transferred to a fruiting field location, and evaluated for disease symptoms during the winter and spring following inoculation using a disease severity score. Significant variation for the disease severity score was detected due to years, genotypes, and their interaction. Differences among genotypes were responsible for 60.6% of the phenotypic variance, whereas years and year × genotype interactions contributed relatively little to this variance, 8.2% and 9.3%, respectively. A separate analysis conducted using a balanced subset of six cultivars that were present in all trial years detected variance components due to years and year × genotype interaction slightly smaller than those estimated for the complete trial, 5.0% and 3.9%, respectively. These results highlight the utility of the screening system and suggest that stable resistance to P. cactorum is obtainable in California strawberry breeding populations and production systems.
Parental potential, or breeding value, was evaluated for strawberry (Fragaria × ananassa Duch.) genotypes selected for high, intermediate, or low phenotypic expression of soluble solids content (SSC) and titratable acid content (TA). Progeny means and genetic variance parameters were estimated using seedlings from 40 crosses among these selections, conducted in two factorial sets. Selection response for breeding value was detected for SSC in the upward direction and for TA in both upward and downward directions. Populations created by divergent selection of parents followed by intermating expressed additive genetic variances 2.3 and 9.3 times larger than those estimated for appropriate controls for SSC and TA, respectively. For TA, the response to selection for breeding value was consistent with results for genotypic selection reported earlier. The significant selection response in breeding value obtained for SSC differed from the results of previous clonal tests that had detected no significant genotypic selection response. These results, together with previous assessments, suggest that cumulative genetic gain can be obtained for both SSC and TA. However, gain for SSC will be contingent on selection under conditions that approximate commercial treatment; this will not be necessary for TA, as expression for this trait is stable across test location and cultural treatments.
Three individuals in progeny from each of 39 crosses and their parents in Japanese persimmon (Diospyros kaki Thunb.) were evaluated for fruit ripening time. Analysis of variance for the progeny, which estimated between- and within-cross variance, and the regression of the mean value in a full-sib family on the mid-parental value (MP) revealed that the genetic differences among crosses could be explained solely by MP. Genotypic values of individuals in progeny from a cross were assumed to be normally distributed around the regression line with within-cross genetic variance. Based on the parental mean performance of 3.5 fruit on a single tree for three years, the coefficient of regression of mean values in a full-sib family on MP was 0.99 ± 0.10, and the proportion of individuals in progeny having genotypic values ripening earlier than early October was estimated as 52%, 24%, and 7% for three sets of mid-parents differing in their ripening time, i.e., early, middle, and late October, respectively. On the basis of the parental mean performance in 10 fruit on a single tree without yearly repetition, the regression coefficient was estimated as 0.91 and the proportion was estimated as 44%, 20%, and 6% for the three sets of mid-parents, respectively.
The expected proportion of individuals in progeny having genotypic values for fruit weight over a given selection criterion to the total individuals derived from a cross was estimated by multiple-regression analysis in which inbreeding coefficient (F) and midparental (MP) value were independent variables and progeny mean was the dependent variable in Japanese persimmon (Diospyros kaki Thunb.). A total of 117 seedlings from 39 crosses was used. Genetic differences of progenies among crosses could be explained solely by F and MP, the effect of the former being greater than the latter. The expected proportion of progenies with large fruit decreased as MP decreased and severely decreased as F increased. Based on the parental mean of 35 fruit on a single tree for 3 years, the proportion of individuals in progeny with fruit weight >200 g was estimated as 34%, 21%, and 12% for 0, 0.125, and 0.25 F values, respectively, in individual from a cross with MP = 200 g.
Absence or long delay of budbreak, also known as prolonged dormancy, is the most important symptom during incomplete dormancy. Budbreak number was evaluated to quantify seedling response to chilling and selection on excised and intact 1-year-old apple (Malus ×domestica Borkh.) seedlings under controlled and natural environmental conditions. Indices based on: 1) the number and distribution of budbreak (prolonged dormancy grade = PDG); 2) the number of buds breaking, including shoot length with increased budbreak as part of the calculation (prolonged dormancy index = PDI); and 3) budbreak number per 100-cm shoot (NB) were tested in association with budbreak time (TB). The indices expressed the effects of cold treatments that induce earlier and higher numbers of budbreak. PDI and NB, but not PDG, identified families with increased budbreak. Seedlings with high PDG and NB were also associated with families in which high chill requiring parents were used, indicating that TB as pre-selection criterion may fail to identify seedlings with increased budbreak. Response to pre-selection for increased budbreak using PDG could be verified with the PDS and NB indices in seedlings and seedling clones. The NB of intact 1-year-old shoots under natural conditions is recommended as a pre-selection criterion against prolonged dormancy in suboptimal winter conditions.
Heritability estimates for fruit firmness of strawberry (Fragaria × ananassa Duch.) based on the regression of mean offspring performance on average parent performance varied from 0.49 to 0.67 over a 4 year period. Analysis of variance of progeny data showed that general combining ability variance (additive) was much greater than specific combining ability variance. Of 29 parent clones studied ‘Holiday’, ‘Linn’, ‘WSU 1522’ and ‘MD-US 3184’ had the firmest fruit and on the basis of progeny analysis had the highest general combining ability parental values. Low parental values were obtained for ‘Tamella’, ‘Benton’, ‘Puget Beauty’, ‘WSU 1019’, ‘OR-US 3291’ and ‘OR-US 3522’.
Pungency, caused by the presence of capsaicinoids, is a major quality-determining factor in chile (CapsicumL. sp.) The inheritance of nordihydrocapsaicin, capsaicin, dihydrocapsaicin, isomer of dihydrocapsaicin, and homodihydrocapsaicin has not yet been determined. Generations mean analysis revealed that additive, dominance, and interaction effects were significant for capsaicin, dihydrocapsaicin, and isomer of dihydrocapsaicin in an interspecific hybridization of C. annuum L. × C. chinense Jacq. A simple additive-dominance model was sufficient to explain the genetic variation for nordihydrocapsaicin and homodihydrocapsaicin. Except dihydrocapsaicin and isomer of dihydrocapsaicin in the BCP1 family, the values of backcross families shift toward the recurrent parents. Because of the significant additive gene effect and the tendency of the values of the capsaicinoids at backcross families to shift toward the recurrent parents, repeated backcrossing and selection will increase and decrease (depending on the recurrent parent) the capsaicinoid content. Positive genetic correlations were observed between the capsaicinoids and the values ranged from 0.4 to 0.8. The estimated number of effective factors were 0.4 for nordihydrocapsaicin, 0.6 for homodihydrocapsaicin, 0.9 for isomer of dihydrocapsaicin, 1.1 for dihydrocapsaicin, 2.8 for total capsaicinoids, and 6.2 for capsaicin. Different gene actions and a different number of effective factors involved in the capsaicinoids inheritance imply that different genes are controlling the synthesis of each capsaicinoid.
Development of two-way onion (Allium cepa L.) hybrids is difficult due to poor seed yields on inbred female parents. Seed yield of onion is affected by inbreeding depression and the seed-production environment. A standard diallel was used to estimate combining abilities for seed yield among seven inbred onion lines. Males and hybrids differed significantly (P < 0.05) for seed yields. Combinations of relatively high-by-high seed-yielding inbred parents were not always the best combinations; combinations of medium-by-medium or medium-by-high seed yielders also produced good F1 seed yielders. For the seven inbred lines, significant correlations (P < 0.05) were observed between mean seed yield per bulb and scape height. Parent-offspring regressions revealed no significant relationship between seed yields of randomly selected, open-pollinated bulbs and their S1 families. Results indicate that relative seed yields of individual bulbs after self-pollination cannot be used to predict seed yields of progeny families. However, the seed yield of inbred lines of onion may reflect the potential seed yield of F1 male-sterile lines.
Nineteen interspecific hybrid breeding lines were tested for resistance to a TSWV isolate using enzyme-linked immunosorbent assay (ELISA) to check for presence of the virus after inoculation. These lines were all BC1F6 lines derived from L. esculentum crosses with seven L. chilense accessions. All of these lines had been selected for high tolerance/resistance to tomato mottle virus (ToMoV), a geminivirus [Scott et al., Bemisia 1995: Taxonomy, Biology, Damage Control and Management 30: 357–367 (1996)]. The initial TSWV screening indicated that eight of the 19 original lines had “possible” TSWV resistance. Seed from these selected eight lines were then planted and inoculated with TSWV ≈3 weeks after emergence. Three weeks later, ELISA results indicated that all plants from all lines were infected with TSWV. However, none of the plants from Y118 (derived from the LA 1938 cross) showed visual TSWV symptoms. The Y118-derived plants were allowed to grow for several months, and at no time developed significant visual symptoms of the virus. The consistent lack of TSWV symptoms prompted a second ELISA test on the Y118 plants, and the results indicated the plants were completely free of TSWV. Further tests were then initiated with F2 (L. esculentum × Y118) seed, and results indicate a single dominant gene is responsible for TSWV resistance. Data from this segregating population, including a molecular marker study which screened 800 randomly amplified polymorphic DNA (RAPD) primers, will be presented. Approximately two to five RAPD primers are possibly linked to TSWV resistance.