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G.S. Sibbett, G. McGranahan, V. Polito, P. Catlin, L. Hendricks, K. Kelley, W. Coates, and J. Grant

Preliminary studies with controlled pollinations have shown that pistillate flower abscission (PFA) in walnut (Juglands spp.) is associated with heavy pollen loads on the flowers. This study measured percent pistillate flower abscission (PFA), pollen grains per flower, yield and yield efficiency on Serr walnut from trees adjoining pollinizing cvs and at sequential intervals up to 197m away in twelve orchard locations. A highly significant, negative correlation in PFA existed as distance from the foreign pollen source increased. Pollen grains per flower were highly correlated with percentage PFA. Yield and yield efficiency, measured in two of the test orchards, were positively correlated with distance from the pollen source.

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Usman Siswanto and Frank B. Matta

This study was established to determine the influence of scion/stock combination on leaf area, yield efficiency, and fruit quality attributes in effort to identify the most suitable scion/stock combination for Mississippi. Twenty-nine scion/stock combinations were grown at the Pontotoc Ridge-Flatwoods Research and Extension Center, North Mississippi. The treatments were arranged in a completely randomized design (CRD) with six single tree replications. `Jon-A-Red' on Mark produced the smallest leaf area, while the largest leaf area was produced by the combination of `Royal Gala' on MM106 and `Blushing Golden' on M7A. Scion/stock combinations significantly affected yield efficiency, fruit yellow pigment dvelopment, firmness and fruit mineral composition. Scion cultivars on Mark resulted in the highest yield efficiency, except `Empire'. `Ultra Gold' and `Braeburn' on Mark and `Blushing Golden' on MM111 led to yellow pigmentation in the highest category. Meanwhile, `Braeburn' on Mark was among the scion/stock combinations that produced the firmest fruit. And fruit from trees on Mark consistently had high calcium (Ca) levels. After 7 years, `Royal Gala' on Mark produced the highest yield efficiency. `Braeburn' on Mark resulted in both the firmest fruit and the highest fruit Ca concentration.

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Mosbah M. Kushad

Yield performance and postharvest quality of `Gala' apple on Mac.39, P.1, Mark M.26E, M.9E, B.9, and M.27E were evaluated. Trees on B.9 and Mark had the highest yield efficiency, while trees on P.1 and M.9E had the lowest yield efficiency. Trees on P.1 were most vigorous, while trees on B.9 and M.27E were least vigorous. Trees and fruit buds survived a –32C during Jan. 1994. Fruit firmness, soluble solids, starch, and ethylene production rate were similar in fruits from all seven rootstocks at harvest. However, after 3 months in storage, fruits from trees on M.27E, P.1, and Mark rootstocks were less firm than fruits from trees on the other four rootstocks. Glucose, fructose, sucrose, and sorbitol levels at harvest and after storage were similar in fruits from all rootstocks.

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C.G. Embree, K.B. McRae, E.N. Estabrooks, and C. Pratt

Vegetative and fruiting characteristics were measured for a spur mutant of `McIntosh' apple (Malus × domestics Borkh.). Nine-year-old `MacSpur' trees in an orchard in New Brunswick, Canada, were grouped according to three degrees of spurriness. Reduced terminal growth, fewer limbs per tree, more flowering spurs per unit length of 2- and 3-year-old wood, less yield, and lower yield efficiency were associated with the highest degree of spurriness. The variability suggests that `MacSpur' may be an unstable periclinal chimera.

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Rachel Byard and Ian A. Merwin

We planted grafted and seedling chestnuts of six cultivars in Lansing, N.Y., in April 1995 to evaluate performance of the different cultivars in our region and to compare grafted and seedling trees. We used the following cultivars: the Chinese chestnut cultivar Mossbarger (Castanea mollissima) and five interspecific hybrid cultivars [Douglas 1A (C. mollissima × C. dentata), Eaton [C. mollissima × (C. crenata × C. dentata)[, Skioka (C. mollissima × C. sativa), Layeroka (open-pollinated daughter of `Skioka'), and Grimo 142Q (an open pollinated daughter of `Layeroka')]. Growth was not significantly different between cultivars. There were no notable correlations between trunk cross-sectional area at planting and any measurement after the first year. Significant differences between cultivars were found for mortality, yield, and yield efficiency. `Eaton' had the lowest mortality rate (2%) of all cultivars. `Grimo 142Q' and `Layeroka' had the highest dry weight yields and the greatest yield efficiencies, although `Grimo 142Q' had significantly larger nuts than `Layeroka'. In 1998, the largest nuts (5.2 g) were harvested from `Mossbarger' and `Eaton trees'. `Skioka' had the highest mortality (48%), lowest yield, lowest yield efficiency, and smallest nut size. In the first 2 years, most grafted trees showed significantly higher yields and greater yield efficiency than seedling trees. By the third year, differences in yield between grafted and seedling trees were no longer significant for most cultivars. Over the 3 years most grafted trees revealed higher mortality and slower growth than seedlings of the same cultivar. Seedlings did not show more variability in measurements than grafted trees of the same cultivar.

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Janine K. Hasey, Dave Ramos, Warren Micke, and Jim Yeager

In a comparison of six walnut rootstocks either nursery-grafted or field-grafted to `Chandler' (Juglans regia), the highest-yielding trees after 9 years are on either seedling or clonal Paradox rootstocks. Trees growing on both Paradox rootstocks had higher yield efficiency than trees on the black rootstocks in both 1995 and 1996. Since 1993, relative tree size based on trunk circumference has not changed: southern California black (J. californica), seedling Paradox and northern California black (J. Hindsii) have remained significantly larger than clonal Paradox, Texas (J. microcarpa) or Arizona (J. major) black rootstocks. The smaller size of clonal as compared with seedling Paradox trees might be explained by a delay in field grafting success. Although both northern and southern California black rootstock trees were significantly larger than clonal Paradox trees, they did not differ significantly in yield and had significantly lower yield efficiency in 1996. Clonal Paradox trees have significantly smaller nut size than northern California black rootstock trees that can be explained by its higher yield efficiency. An adjacent trial planted in 1991 compares micropropagated `Chandler' on its own root vs. `Chandler' on seedling Paradox rootstock. In 1995 and 1996, own-rooted `Chandler' had significantly greater trunk circumference, yield, and yield efficiency than did `Chandler' on Paradox rootstock. Many of the trees on Paradox rootstock are growing very poorly compared to the own rooted trees. This could be due to diversity within the Paradox seed source. If own-rooted `Chandler' trees become commercially available, they may have potential in areas where other rootstocks are undesirable because of hypersensitivity to cherry leafroll virus.

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Dwight Wolfe and Gerald Brown

The maturity indices of percent fruit drop, percent soluble solids, and flesh firmness of apples from trees with `Starkspur Supreme' scions on nine rootstocks were compared over the five-year period 1985-1989. The nine rootstocks included EMLA 7, EMLA 9, EMLA 26, EMLA 27, Mark, MAC 24, Ottawa 3, OAR 1, and M9.

The five-year averages of each of the maturity indices varied significantly among the nine stions. The average percent fruit drop was more strongly correlated with trunk cross-sectional area (r=0.572) than it was with cumulative yield efficiency (r=0.346). Flesh firmness was significantly correlated with cumulative yield efficiency (r=0.398) but not with either trunk cross-sectional area or cumulative yield. The average percent soluble solids was more significantly correlated with trunk cross-sectional area (r=0.770) than it was with either cumulative yield efficiency (r=0.383) or cumulative yield (r=0.637). It is suggested that tree size may be used as an indicator for predicting maturity in cases where little or no information is available on the effects of that particular rootstock on maturity.

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Fenton E. Larsen and Stewart S. Higgins

Tree size, cumulative yield, yield efficiency and anchorage of 6 micropropagated (MP) apple (Malus domestica Borkh.) cultivars were determined in 1991 after 5 years of production, as compared with trees on seedling (sdlg) or M 7a roots. Trees were planted in 1984, with crops harvested from 1987 through 1991. Trees were generally smallest (trunk cross-sectional area) on M 7a and were largest with 4 cultivars (`Delicious', `Jonathan', `Rome', `Spartan') when micropropagated. `Golden Delicious' (GD) was largest on sdlg. Cumulative yield was affected by a scion × rootstock interaction, with few trends in scion or rootstock effects. Mean cumulative yield was 84 kg tree-1, 71 and 58 for M 7a, MP and sdlg, respectively. Yield efficiency was also affected by a scion × rootstock interaction. In 1991, mean yield efficiency was 0.5 kg cm-2 for sdlg and MP trees, but was 1.05 for M 7a. Efficiency on M 7a was superior to other rootstocks with all scions except `GD', while sdlg and MP trees were statistically similar with all scions. All trees leaned in response to prevailing westerly winds, with trees on sdlg tending to be more upright than MP or M 7a trees.

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M.L. Arpaia, G.S. Bender, and G.W. Witney

A project evaluating the performance of cv. Hass on eight clonal avocado rootstocks—G755A, G755B, G755C, Duke 7 (D7), Borchard (BR), D9, Toro Canyon, and Topa Topa was established in southern California in 1986. Two additional rootstocks, Thomas and G1033, were added in 1987. Of the trees planted in 1986, the BR and D7 rootstocks have consistently had the highest total yields for all rootstocks, whereas the three G755 selections have had the lowest productivity. No differences in productivity between the two rootstocks planted in 1987 have been detected. The influence of rootstock on the magnitude of alternate bearing will be discussed, although the oscillation in yield is greater for the higher-yielding rootstocks. Tree size has been measured throughout the study. The BR selection has consistently produced a larger tree, even though it has continued to have high productivity. There are no consistent differences between the other rootstocks. Yield efficiency, measured as the kg fruit/m3 of canopy volume has been calculated. In selections that are prone to severe alternate bearing, the swing in yield efficiency is also the greatest. The data thus far suggests that a yield efficiency of ≈2.5 kg fruit/m3 canopy volume is the maximum yield possible for California `Hass' avocado.

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Richard P. Marini and Donald Sowers

Abbreviations: CD, crop density; FI, flowering index; FS, fruit set; FSD, flowering spur density; FW, fruit weight; PD, pygmy density; SLW, specific leaf weight; VSD, vegetative spur density; YE, yield efficiency. 1 Associate Professor. 2 Research