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Kevin J. McInnes and James C. Thomas

Chronic dry spots that occur on the upper reaches of slopes on golf putting greens lead to increased frequency of irrigation to maintain a healthy turfgrass surface. To limit one cause of dry spots, the downslope wicking of water, we investigated the use of subsurface barriers to interrupt the capillary connectivity of the bottom portion of the root zone on a 3.5-m long, laboratory-simulated section of a green having a 5% slope. We evaluated the effectiveness of the barriers on a green constructed with a sand root zone over gravel drainage and on a green constructed with a sand root zone over a geotextile atop a porous plastic grid for drainage. With sand over gravel, the barriers were effective at reducing downslope wicking and the consequential loss of stored water in the root zone on the slope. In the top 0.5 m of the slope, there was 24 mm more water stored in the root zone profile of the green constructed with barriers compared with that in the green constructed without barriers. With sand over geotextile atop a plastic grid, the barriers were effective at reducing wicking of water, but only when the downslope continuity of the geotextile was broken. In that case, there was 35 mm more water stored in the root zone profile at the top of the slope in the green constructed with barriers and a discontinuous geotextile compared with the greens constructed with barriers and continuous geotextile or with sand over gravel and no barriers.

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Yiran Yu, James Harding and Thomas Byrne

Genetic components of variance and heritability of flowering time were estimated for five generations of the Davis Populationof Gerbera hybrids, Composite, Estimates of narrow-sense heritability averaged 0.50 and broad-sense heritability averaged 0.77 using the NCII design. Narrow-sense heritability was also estimated with two models of parent-offspring regression, resulting in average heritability of 0.49 and 0.51. Estimates of components of variance indicated that the major genetic effect controlling flowering time is additive. However, the dominance component accounted for 28% of the total variance; the environmental component was only 23%. Flowering time is negatively correlated with cut-flower yield. The phenotypic coefficient was –0.34; genetic correlations were –0.47 when estimated from the NCII design, and –0.72 when estimated from the parent-off-spring method. A practical model was constructed to assess the efficiency of indirect selection for cut-flower yield using flowering time as a marker trait. The advantages of indirect selection accruing from increased population size and reduced generation time are discussed.

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Thomas L. Davenport and James T. O'Neal

Flowering and fruit set characteristics were examined in the popular commercial cultivar Magaoa in an effort to elucidate the reproductive phenology of mamey sapote, Calocarpum sapota (Jacq.) Merr. [syn. Pouteria sapota (Jacq.) H.E. Moore and Stearn]. Flowers opened during the night with anthesis beginning around sunset. The length of floral opening varied according to season, ranging from 6 days in winter to a single day in summer. Bursts of new flowers generally appeared in cycles of about 7 days in declining numbers of flowers per burst until all the floral buds of a particular floral bud flush had flowered. Floral buds flowered randomly along a branch with only a few flowers open at any one time. Flower position around the branch was a factor in fruit set. Flowers and small fruitlets encircled horizontal branches in great numbers, but immature fruit most often developed from flowers located on the upper branch quadrant. The lower quadrant contained the fewest immature fruit. As fruit matured, however, more upper quadrant fruit abscised until by harvest, most mature fruit were found on the lower quadrant. The observations provide new insights into the reproductive phenology of mamey sapote.

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Hongzhan Huang, James Harding and Thomas Bvrne

The effects of long-term genetic improvement are measured by selection response predicted from estimates of narrow-sense heritability. However, changes of population mean must be partitioned into genetic and environmental components-in order to accurately estimate selection response.

A long-term selection experiment for cut-flower yield in the Davis population of gerbera (Gerbera hybrida, Compositae) was conducted for sixteen generations. Breeding value was estimated for individual plants in the population using Best Linear Unbiased Prediction (BLUP). Genetic change was calculated from breeding values of individual plants in each generation. The results of this study indicate: the long-term selection experiment was successful and necessary for genetic improvement. Genetic change over sixteen generations was 33 flowers. Mean breeding values increased monotonously with an “S” shape pattern. Environmental effects fluctuated from generation to generation. Cut-flower yield in the Davis population of gerbera will continuously respond to selection.

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Thomas M. Davis and James E. Pollard

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Hongzhan Huang, James Harding and Thomas Byrne

Inbreeding depression is found in most flower crops. Limited population size can cause inbreeding even in outcrossed populations. The Davis population of Gerbera hybrida has been selected for increasing flower yield for 15 generations. The mean yield per plant of the population has been increased from 14.2 to 28.0 flowers per winter six-month period. In each generation 23 to 80 selected parents have been crossed at random. Inbreeding coefficients were estimated from the pedigrees of each of the 6199 plants in the 16 generations. The inbreeding level in this population was found to increase in each generation and currently is 16.5%. Mean yield and inbreeding per family have a statistically significant negative correlation in generations 13 to 16. The results indicate that inbreeding is increasing in this randomly outcrossed population because of its finite number of parents, and that yield is reduced by 3.9 flowers per six-month due to inbreeding.

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Thomas M. Kon and James R. Schupp

Trials were conducted in 2009 and 2010 to evaluate the use of a hand-thinning gauge [Equilifruit; Institut National de la Recherche Agronomique (INRA), Montpelier, France] on three cultivars of apple (Malus ×domestica) trees trained to tall spindle. Hand-thinning treatments were applied after June drop to trees with supra-optimal crop loads. Three hand-thinning treatments were applied using the hand-thinning gauge: 1) thinning to ≈6 fruit/cm2 branch cross-sectional area (BCSA) (F value), 2) subtracting the delta value [Δ (an adjustment factor to increase or decrease the number of fruit per BCSA] from the F value (F − Δ), and 3) F − 2Δ. These treatments were compared with a control and a traditional hand-thinning heuristic of spacing a solitary fruit every 7 to 8 inches of branch length. Use of the hand-thinning gauge generally improved fruit weight and maintained whole tree yields when compared with the control. Hand-thinning based upon traditional fruit-spacing heuristics reduced crop density and increased final fruit weight of apple, but significant reductions in yield were observed in two of four studies when compared with the control. We find the hand-thinning gauge a useful tool in adjusting final crop load of apple.

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Yiran Yu, James Harding and Thomas Famula

Additive genetic components of variance and narrow-sense heritabilities were estimated for flowering time and cut-flower yield for generations 8-13 of the Davis population of gerbera, using the least squares (LS) and restricted maximum likelihood (REML)

methods. Estimates of heritability for flowering time were 0.54 and 0.50 using REML and LS, respectively, indicating a close agreement between the two methods. However, estimates of heritability for cut-flower yield were 0.30 and 0.46 from REML and LS. This may result from the fact that cut-flower yield was selected in each generation; flowering time was not. Realized heritability for cut-flower yield was estimated to be 0.26 which agreeded more closely with the heritability estimated from REML. The advantages of REML, and its applications in the estimation of components of genetic variance and heritability of plant populations are discussed.

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R. Thomas Fernandez and James A. Flore

Fruit of sweet cherry (Prunus avium L.) crack during or after rain due, in part, to absorption of water through the fruit surface driven by the water potential gradient. In 1972, J. Vittrup-Christensen suggested that overhead misting of calcium salts during precipitation may be an effective way to prevent cherry cracking by reducing the water potential gradient. We tested this hypothesis by designing a computer-controlled irrigation system to intermittently spray a 10% CaCl2 solution on trees during rain events. Spray emitters were placed in the middle and at the top of the canopy. The program turned the system on for 90 s at each 0.3 mm of rain and monitored daily rainfall and accumulated mist times. Two `Emperor Francis' and two `Ulster' were treated with equal number of controls. Intact and cracked cherries were counted on four branches per tree at three times when cherries were susceptible to cracking. Overall, cracking was reduced from 33% to 11% by the CaCl2 spray at the end of the experiment. Treated `Ulster' had 9% cracked fruit, while control had 43% cracked fruit. Differences for `Emperor Francis' were not significant. Phytotoxicity was estimated at about 15 % of leaf area. This system will be reevaluated in 1995 with the added objective of quantifying and reducing phytotoxicity.

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Yiran Yu, James Harding and Thomas Byrne

Genetic components of variance and heritability of flowering time were estimated for five generations of the Davis Populationof Gerbera hybrids, Composite, Estimates of narrow-sense heritability averaged 0.50 and broad-sense heritability averaged 0.77 using the NCII design. Narrow-sense heritability was also estimated with two models of parent-offspring regression, resulting in average heritability of 0.49 and 0.51. Estimates of components of variance indicated that the major genetic effect controlling flowering time is additive. However, the dominance component accounted for 28% of the total variance; the environmental component was only 23%. Flowering time is negatively correlated with cut-flower yield. The phenotypic coefficient was –0.34; genetic correlations were –0.47 when estimated from the NCII design, and –0.72 when estimated from the parent-off-spring method. A practical model was constructed to assess the efficiency of indirect selection for cut-flower yield using flowering time as a marker trait. The advantages of indirect selection accruing from increased population size and reduced generation time are discussed.