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- Author or Editor: Douglas V. Shaw x
- HortScience x
The extended production season of strawberries raised in mediterranean environments depends on plant development that occurs during the winter months. Seedling genotypes from 20 bi-parental crosses and their nine parent genotypes were fully vernalized and grown at 11, 14, and 17C, to test for adaptation to growth at minimal temperatures. Genetic variance parameters were estimated and tests for genetic x temperature interactions were conducted for five vegetative growth traits. Highly significant (P < 0.01) genetic effects were detected for all traits, and broad-sense heritability estimates ranged from 0.09 to 0.41. None of the genetic x temperature interactions were significant for seedling genotypes, and interactions were significant only for leaf dry weights for parental genotypes. These results indicate a genetic basis for variable vegetative growth rates, but provide no evidence for specific adaptation to growth at low temperatures.
Yield for annual California strawberry (Fragaria ×ananassa Duch.) production systems in soils treated with combinations of methyl bromide–chloropicrin (MB:CP) were compared with four alternative soil treatment systems using meta-analysis. Studies represent 11 production seasons, and were conducted at three distinct locations in California. Fumigation with mixtures of methyl bromide (MB) and chloropicrin (CP) increased yield significantly compared with any and all alternatives lacking MB. In a combined analysis of 45 studies, fumigation with MB:CP compounds increased yield an average of 94.4% (d+ = 2.874 ± 0.098) compared with yields for plants in nonfumigated (NF) soils. Further, the effect of MB:CP fumigation increased over the first three strawberry cultivation cycles: MB:CP–fumigated soils provided a 59.2% (d+ = 2.166 ± 0.146) yield advantage when one cycle of fumigation was omitted, a 100.2% (d+ = 3.000 ± 0.143) advantage when two cycles were omitted, and a 148.4% (d+ = 6.201 ± 0.348) yield advantage when three or more cycles of MB:CP were omitted. In a combined analysis that included 34 studies, soil fumigation with MB:CP conferred a 9.6% (d+ = 0.751 ± 0.087) yield advantage over fumigation with CP alone. Soils treated with MB:CP yielded 6.8% (d+ = 0.437 ± 0.114) more fruit than those treated with very high rates of CP (336–396 kg·ha–1), and 15.4% (d+ = 1.190 ± 0.134) more than soils treated with commercially realistic rates (168–224 kg·ha–1). Similar to the comparison using NF soils, the efficacy of very high rates of CP appeared to diminish over cycles of strawberry cultivation; MB:CP increased yield 2.2% (d+ = 0.043 ± 0.162) in the first CP production cycle, 10.6% (d+ = 0.588 ± 0.174) and 13.7% (d+ = 2.054 ± 0.401) in the following two cycles. Combinations of dichloropropene (DP) and CP were no more effective than were lower rates of CP alone, and MB:CP conferred a 14.4% (d+ = 0.962 ± 0.162) yield advantage over mixtures of DP:CP. Mixtures of MB:CP increased yield 29.8% (d+ = 3.199 ± 0.287) compared with metam sodium (MS). The standardized effect was similar when comparing MB:CP combinations with either MS or NF soils, suggesting little effect of MS on the yield response. Chemical names used: trichloronitromethane (chloropicrin); 1,3-dichloropropene (dichloropropene); sodium N-methyldithiocarbamate (metam sodium).
Strawberry (Fragaria ×ananassa Duch.) genotypes retained for resistance to Verticillium wilt (Verticillium dahliae Kleb.) after two cycles of a two-stage (TS) selection procedure consisting of full-sib family selection followed by within-family selection of individuals, and genotypes retained for resistance using genotypic mass (GM) selection were crossed to a common set of moderately susceptible genotypes. The relative resistance of the seedlings from these progenies was compared using a resistance score and the percentage of stunted plants. Although the two sets of resistant parents had performed similarly in genotypic comparisons, those genotypes selected using the TS procedure yielded test cross offspring with significantly higher resistance scores (X̄ = 3.84 ± 0.09 vs. X̄ = 3.46 ± 0.09, t = 3.11**) and significantly lower rates of plant stunting (X̄ = 38.1% ± 3.1 vs. X̄ = 50.2% ± 2.9, t = 2.87**) than the parents chosen using GM selection. Further resolution using analysis of variance and general combining ability (GCA) estimates showed that these between-set differences resulted from higher resistance breeding values for parents selected using the TS procedure. The five genotypes with largest GCA for resistance score and four of the five genotypes with minimum GCA for percentage stunting were obtained by TS selection.
Strawberry (Fragaria ×ananassa L.) runner plant production during a 4-year period was compared on nursery soils treated with methyl bromide (MB) and chloropicrin (CP) mixtures (MB:CP) and three alternative soil treatments: CP, mixtures of 1,3-dichloropropene (Telone®) and CP (DP:CP), and no fumigation (NF). The effect of soil treatment on runner plant production for a single nursery propagation cycle was determined in all 4 years. In 2 years, runner production in a final propagation cycle was also determined as a function of soil treatment in previous cycles. A single propagation cycle in NF soil decreased runner production relative to all other treatments. Treatments with CP at rates of 140 to 191 kg·ha–1 generally decreased runner production significantly (P ≤ 0.05) in comparison with treatment with MB:CP; use of CP at rates ≥303 kg·ha–1 resulted in statistically equivalent runner production. In one trial, use of two DP:CP formulations (516 kg·ha–1 of a 7:3 DP:CP mixture, and 448 kg·ha–1 of a 3:7 DP:CP mixture) significantly reduced and did not affect runner production, respectively, relative to the use of MB:CP. Use of MB:CP in the previous propagation cycle also increased runner productivity in comparison with NF. Runner productivity of planting stock produced with 314 kg·ha–1 of CP did not differ statistically from that of stock produced with MB:CP, but productivity of planting stock on soil treated with 157 kg·ha–1 of CP was intermediate between that on NF and MB:CP-treated soil. Planting stock grown on nontreated soil in two previous propagation cycles produced 25% fewer runner plants than did similar stock grown on MB:CP-treated soil. Productivity of planting stock produced with CP at rates of 280 to 314 kg·ha–1 in two previous propagation cycles did not differ statistically from that of stock produced with MB:CP. Results of meta-analyses indicated that fumigation with MB:CP was more effective in increasing runner production than was CP or NF, regardless of the propagation cycle or rate of application. For mixtures of 1,3-dichloropropene and CP, nursery productivity was maximized by using at least 280 kg·ha–1 of CP.
Strawberry seedlings (Fragaria ×ananassa Duch.) from the Univ. of California strawberry improvement program were assigned randomly to soils prepared either with or without preplant fumigation with a mixture of 2 methyl bromide: 1 chloropicrin (by mass; 392 kg·ha-1) in order to evaluate sampling methods for root characters. After 5 months in annual hill culture, individual plant root systems were sampled with a single 1.9-cm-diameter × 24-cm-long soil core probe to determine root mass (RM), secondary rootlet mass (SRM), and a subjective root appearance score (RAS) based on root color and morphology. Whole plants were subsequently extracted and used to measure these root characters and total above-ground (shoot) mass. Soil core samples captured <1 % of total RM on average but explained 45% to 74% of the variability for whole-plant RM and SRM in both soil environments. Plants grown in fumigated soils had greater shoot mass, plant diameter, RM, SRM, and RAS than those grown in nonfumigated soils, regardless of sampling method. Phenotypic correlations between traits were fairly consistent across fumigation treatments, differing by more than ±0.20 only for associations involving RAS as a variable. Highly significant (P < 0.01) phenotypic correlations were detected among shoot mass, plant size, and root core and whole-plant RM and SRM in both fumigation environments; correlations between whole-plant RM and shoot mass were r =0.84 and 0.96 in fumigated and nonfumigated soils, respectively. Conversely, nearly all correlations between pairs of traits involving either soil core or whole-plant RAS were nonsignificant. Together, these results indicate that a strong correspondence exists between above- and below-ground vegetative growth and that most correlations between traits are consistent across fumigation treatments. Further, the strong relationship between soil core RM and whole-plant RM indicates that soil cores provide an accurate description of root growth relationships at the whole-plant level and can be substituted effectively for whole-plant (destructive) samples. Chemical name used: trichloronitromethane (chloropicrin).
Breeders of horticultural food crops are usually concerned with multiple traits related to yield and quality as well as other traits such as biotic and abiotic stresses. Yield in these crops is not solely tonnage of biomass produced in the field. Rather, it is the proportion of the crop that can be harvested and brought to market in a condition and at a price acceptable to the consumer. Quality may include flavor, color, shape, size, degree of damage, nutrient levels, and traits that permit greater perceived food safety or environmental sustainability. Some traits may exhibit phenotypic associations. Traits with unfavorable associations will be of concern to the breeder if the cause is unfavorably correlated genetic effects, especially those resulting from pleiotropy. Several multiple trait selection schemes have been developed, including independent culling levels, tandem selection, and index selection. These schemes can result in improvement even for traits with unfavorable associations. However, the breeder must have a strong rationale for each trait addressed in a breeding program because each additional trait necessitates larger breeding populations and more resources. Thus, the breeder's first challenge for each crop is to determine which traits are most important and which issues are most amenable to a breeding solution.