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Taryn L. Bauerle and Michela Centinari

, 1987 ; Guo et al., 2011 ; Pierret et al., 2007 ) and in some cases on a tree’s root architectural or morphological factors in response to the soil environment ( Comas and Eissenstat, 2004 ; Pregitzer, 2002 ). Rightly so, root system morphology and

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J.G. Williamson and E.P. Miller

have a significant effect on nutrient availability and uptake and may influence grower-adopted fertilization practices. This is particularly true if a major portion of the root system is located in the pine bark layer rather than in the underlying soil

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D. M. Glenn and W. V. Welker

Carbon dioxide is produced by microbial and plant respiration and accumulates in the soil. In previous field studies, CO2 levels were higher under a killed sod soil management system, relative to cultivation and herbicide systems (1.8 vs 0.8 and 1.0%), respectively. Our objective in these studies was to measure the effect of elevated levels of root system CO2 on root and shoot growth and nutrient uptake. Using soil and hydroponic systems in greenhouse studies, we maintained root system CO2 levels between 1.5 and 2.5%. Control CO2 levels were less than 1%. Root length density and dry matter partitioning to the root system were increased by root CO2 in soil and hydroponic studies; shoot growth was unaffected. In hydroponic culture, root CO2 increased P uptake, solution pH, root volume and the number of lateral roots/cm root axis. Elevated levels of CO2 in the root system stimulated root growth in both the soil and hydroponic studies.

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Thomas E. Marler and Haluk M. Discekici

`Red Lady' papaya transplants were planted on a slope with a 30% to 35% grade and grown for 5 months. Excavation was used to determine root distribution on the uphill and downhill sides of the plants. Roots were separated into the taproot system and lateral roots on the uphill and downhill sides. The line intersect method was used to determine length of the lateral roots, and length of the taproot system was measured directly. All roots were dried at 70°C. The taproot system accounted for 2% of the total root length and 66% of the total root mass. Of the 130-m of lateral roots, 71% were located on the downhill side. Similarly, 69% of the dry mass of the lateral root system was located on the downhill side. Primary lateral roots on the uphill side of each plant developed horizontally, but some secondary lateral roots developed against gravity to maintain a portion of the root system close to the surface of the slope. Some of these lateral roots developed at angles of 55° to 60° above the horizontal.

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Sean B. Fort and Douglas V. Shaw

Seedling offspring of crosses among 10 selected strawberry genotypes (Fragari ×ananassa Duch.) from the University of California strawberry improvement program were established in annual hill culture. Soil treatments consisted of 1) preplant fumigation using a mixture of methyl bromide and chloropicrin or 2) no fumigation. Root systems of individual plants were sampled with a soil probe in January, April, and July 1994 to determine root mass (RM), secondary root mass (SRM), and a subjective root appearance score (RAS). For each trait, genetic analyses of partial diallels were performed to quantify sources of genetic, environmental, and interaction variance. Root trait values differed significantly between soil treatments only for the April sampling date, with all trait values greater in fumigated soils than in nonfumigated soils. For RM and SRM, variance due to general combining ability (GCA) was significant in April and July. Narrow-sense heritabilities (h2) for RM increased between January (0.14) and July (0.40); SRM showed a similar trend with a higher h2 on each sampling date. GCA variances were nonsignificant for RAS, however, significant fumigation × GCA interaction variance was detected for RAS in January. Specific combining ability (SCA) variances were nonsignificant for all traits. To further quantify the extent of interactions, correlations (rg) between genotypic expressions in fumigated soils and nonfumigated soils were calculated for each root trait. These rg values were at or near unity (> 0.85) for RM and SRM on all sampling dates, implying that genetic variability for these traits is conditioned by genes with identical effects within each soil environment. Conversely, rg between soil environments was 0.52, 0.62, and -0.18, for January, April, and July RAS, respectively. These findings suggest that genetic variability exists within this germplasm base for strawberry root mass characteristics. Genetic variation also exists for January root appearance score, but it is not conditioned identically across fumigation treatments.

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Bernadine C. Strik, Amanda J. Davis, David R. Bryla, and Scott T. Orr

the second year because the root systems were larger and the plants were able to access more of the N fertilizer than they could in the previous year ( Bryla and Strik, 2015 ). Alleyways between the rows were planted in Mar. 2017 with a blend of

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W.A. Erb, A.D. Draper, and H.J. Swartz

Interspecific blueberry (Vaccinium spp.) progenies were examined to determine combining abilities and genetic variability for seedling root system size and shoot vigor and to establish whether a large root system is correlated with good growth when plants are grown on a mineral soil and exposed to a moderate soil water deficit. General combining ability (GCA) variance components for root system size and shoot vigor and specific combining ability variance components for shoot vigor were significant. US226, a tetraploid hybrid of V. myrtilloides Michaux × V. atrococcum Heller, had the highest GCA effect for root system size and the lowest GCA effect for shoot vigor. US75 (V. darrowi Camp × V. corymbosum L.) had the highest GCA effect for shoot vigor and was second in GCA effect for root system size. Comparison of the crosses containing G111 (V. corymbosum) with those containing G362 (V. corymbosum) indicates that selecting for the best V. corymbosum clone to start a breeding program seems as important as selecting the mineral soil-adapted parent. Root system ratings were highly correlated with total dry weight of field-grown plants (r = 0.89). The method used in this study to evaluate seedlings for root system size and shoot vigor could be used to eliminate the less vigorous plants from a population before field planting and to evaluate mineral soil adaptability.

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R.E. Gough

In 1999, `Sweet Banana' pepper [Capsicum annuum L. (Grossum Group)] plants were grown under clean cultivation or with red, silver, or black polyethylene selective reflecting (SMR) mulches over the soil surface. Plants in each of three replications per treatment were field-set on 15 June. On 22 Sept., the plants were excavated and their root systems examined using a trench profile method and a succession of trench wall slices. The total numbers of roots of each plant at depths of 5, 10, 15, 20, and 25 cm and 10, 20, 30, 40, 50, and 60 cm from the plant stem were recorded. Distribution and architecture of the root systems were also examined. Plants grown under clean cultivation developed 50 to 60 adventitious roots each, while those grown under red mulch developed ≈20 and those under black and silver mulch about nine adventitious roots each. In all treatments, the adventitious roots radiated downward from the stem at an angle of 35° from the horizontal. No plants had vertical roots. Root system architecture was similar among treatments, with 40% of the roots in the upper 5 cm of soil and 70% in the upper 10 cm. Thirty percent of the roots were within 10 cm, 50% within 20 cm, and nearly 100% within 40 cm of the stem. Root numbers decreased with increasing depth and distance from the stem. The greatest number of lateral roots were produced under silver mulch, intermediate numbers under clean cultivation and black mulch, and the fewest roots under red mulch. Colored mulches influenced the total number of adventitious and lateral roots but not the root system architecture of pepper plants.

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Sean B. Fort and Douglas V. Shaw

Genotypic and phenotypic relationships among root system and above-ground traits of strawberry (Fragaria ×ananassa Duch.) were evaluated for seedlings grown in annual hill culture, with soil treatments consisting of 1) preplant fumigation with methyl bromide and chloropicrin or 2) nonfumigation. Seedlings were from crosses among 10 genotypes within the University of California strawberry improvement program that had been selected previously for yield and other production traits. Root mass had positive genotypic correlations with plant diameter 5 months after planting in both fumigated (r = 0.58) and nonfumigated (r = 0.69) soils. Genotypic correlations between root mass and two production traits, yield and fruit size, were nonsignificant. However, plant diameter had positive genotypic correlations with yield (r = 0.36 to 0.51) and negative genotypic correlations with fruit size (r = -0.47 to -0.60). In general, root appearance scores were uncorrelated with production traits, but their genotypic correlations with vegetative traits were occasionally strong. Genotypic path coefficient analyses conducted separately for fumigated soils and nonfumigated soils both indicated that plant diameter had positive direct effects on yield that were twice the magnitude of that for any other trait. Root mass had a small negative direct effect on yield in each fumigation environment, while root appearance scores had small to moderate direct effects on yield that were more positive for samples obtained after fruiting (in April) versus before fruiting. Pleiotropic relationships appear to exist between root traits and plant diameter, but plant diameter is the best single predictor of genotypic variation for yield in both soil fumigation environments.

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James H. Aldrich and Jeffrey G. Norcini

The response of the root system of `Barbara Karst' bougainvillea [Bougainvillea buttiana (Bougainvillea glabra Choicy × Bougainvillea peruviana Humb. & Bonpl.) `Barbara Karst'] cuttings to 100 g Cu(OH)2·liter-1 in a white latex paint applied to the interior surface of square 66 ml, 120 ml, or 280 ml plastic pots was determined. Cuttings (10 cm long; 3-5 nodes; 2 leaves) were scored on opposite sides and dipped in 6000 mg·liter-1 KIBA for 3 sec. The cuttings were placed in treated or untreated pots that contained a medium of 1 Canadian sphagnum peat: 1 coarse perlite (v/v). The pots were completely randomized in a 3×2 factorial design. The cuttings were rooted under intermittent mist 9 sec·min-1 for 12 hr·day-1 in a greenhouse (20% shade). The number of primary roots, fresh and dry weights, and root quality were determined 15 June. The Cu(OH)2-treated pots resulted in a more compact, well-branched root system and eliminated root circling. However, root fresh weight was reduced by Cu(OH)2 treatment. Pot size influenced the number of primary roots and fresh and dry weights.