SUMMARY The seasonal trends of Ca in Fuerte and Hass avocado fruits from vigorous and non-vigorou... more SUMMARY The seasonal trends of Ca in Fuerte and Hass avocado fruits from vigorous and non-vigorous trees were studied. Non-vigorous trees, with moderate root infection by Phytophthora cinnamomi, produced fruit with significantly higher Ca concentration and Ca content than vigorous trees of the same cultivar. This appeared to be related to less competition from the spring vegetative growth flush. Fuerte fruits had significantly less Ca than Hass fruits throughout the growing season. Management implications are discussed with a view to increasing fruit Ca for better storage ability and reduced post-harvest problems.
The avocado breeding and germplasm preservation projects in California may ultimately provide the... more The avocado breeding and germplasm preservation projects in California may ultimately provide the industry with consistently heavier producing, high-quality avocado varieties, better pollinizer varieties, and improved rootstock hybrids. The program will rely on the continued evaluation of new material generated through traditional selection techniques and the introduction of new material from other countries, as well as refined genetic techniques used to increase the efficiency of crossing and selection. Selections from open pollinated progeny; the main approach of the breeding program for over 60 years, will probably not yield great progress without the help of modern genetic tools. Most modern plant breeding programs incorporate new molecular genetic methods. Methods that provide a systematic analytical approach to predictability will be essential to breeding progress in the future.
Tree form in Persea americana varies from tall and open to short and compact with varying composi... more Tree form in Persea americana varies from tall and open to short and compact with varying composites. Tree form is modified in the nursery by grafting, pinching, pruning and nursery spacing. Therefore, the resulting tree is not necessarily in the shape programmed by its genetic information, but has been modified by nursery conditions. The authors point out the problems with the present tree form, and offer an alternative form, the central-leader. Where the centralleader form is most appropriate and how it may enhance orchard productivity is discussed.
Development of a phenology model for avocados could greatly enhance a grower’s ability to plan ma... more Development of a phenology model for avocados could greatly enhance a grower’s ability to plan management practices in relation to the events occurring within the tree. Knowledge of the time of root and shoot growth, flowering and fruit set, and the relationships between these events will allow for application of irrigation, fertilization, and other cultural practices at optimum times. While a model has been proposed (Whiley et al., 1988; Whiley and Wolstenholme, 1990), it is based on Queensland, Australia and Natal, South Africa environmental conditions. The growing conditions in these humid semi-tropical areas are characterized by wet summers and relatively dry winters. This is the opposite of the Mediterranean climate of California which is characterized by wet winters and dry, hot summers. Furthermore, the model was developed using trees on seedling rootstocks. Clonal rootstocks are used in California orchards be- cause of their resistance to Phytophthora cinnamomi and may affec...
The effect of integrated applications of various rates of irrigation and fertilization on product... more The effect of integrated applications of various rates of irrigation and fertilization on productivity of the 'Hass' avocado (Persea americana Mill.) has been analyzed since 1987. The resulting data were used in a partial budgeting analysis to determine the optimum combination of irrigation and fertilization that maximize returns using various water cost scenarios. This is an ongoing project and to date the 100 percent ETc has been identified to be the optimal irrigation level. Neither the substitution of fertilizer for reduced water use nor the combination of high levels of fertilizer and water was found to be maximizing returns. Water costs to avocado growers have increased significantly in most Southern California production areas. Furthermore, the increasing urban demand for water has created concern about further water cost increases and reduced profit in agriculture. Some growers have been toying with the idea of minimizing costs through supplementation of fertilizer f...
J. L. Meyer, M. L. Arpaia, M. V. Yates, E. Takele, G. Bender, and G. Witney Department of Soil an... more J. L. Meyer, M. L. Arpaia, M. V. Yates, E. Takele, G. Bender, and G. Witney Department of Soil and Environmental Sciences, University of California, Riverside, CA 92521; Department of Botany and Plant Sciences, University of California, Riverside, CA 92521; Department of Soil and Environmental Sciences, University of California, Riverside, CA 92521; Cooperative Extension, Building 4, 5555 Overland Avenue, San Diego, CA 92123; and Cooperative Extension, 21150 Box Springs Road, Moreno Valley, CA 92387, respectively.
About 5 to 10% of avocado trees planted in the late 1970's in the Temecula/Rancho California ... more About 5 to 10% of avocado trees planted in the late 1970's in the Temecula/Rancho California area of California are suffering a decline of unknown origin. The apparent random distribution of the trees within groves and their strong rootstock-scion discontinuities suggest that the rootstock genotype plays a role in the decline. This hypothesis is reinforced by the fact that rootstock material of the late 1970's was obtained from a variety of sources. Therefore, we used allozyme analysis to ask whether avocado performance varied with rootstock racial origin. We sampled and analyzed rootstock bark from adjacent pairs of healthy and declining trees in a Rancho California 'Hass' grove. We obtained the racial identity of 90% of the rootstocks: 50% were seedlings of the Mexican race; 25%, Mexican x West Indian hybrids; the rest, West Indian seedlings. We did not find any systematic genetic differences between healthy and declining trees. If genotype plays a role in the perf...
An integrated approach to determine the relationship between the amount of low-volume irrigation ... more An integrated approach to determine the relationship between the amount of low-volume irrigation water applied, fertility, yield, and root distribution was used in this study. Four years of yield data have shown no significant increase in total crop yield with water use above 100 percent ETc. Evapotranspiration has averaged 70 cm depth of water. Fruit size at early harvest and root distribution are significantly related to the amount of applied water. California is in the fifth year of critical water shortages. Research on the actual water use for maximum yield of mature avocados has not been effectively conducted in the past in California, nor has the interrelationship of yield, fruit quality and fruit size, relative to water and fertility been investigated. The rapidly escalating cost of water in California has narrowed grower margins of profitability over the past decade. This project used an integrated approach to evaluating amounts of water use, fertility, yield, fruit size, an...
Mature 'Hass' avocado (Persea americana Mill.) trees on four rootstocks (Thomas, Topa T... more Mature 'Hass' avocado (Persea americana Mill.) trees on four rootstocks (Thomas, Topa Topa, Duke 7, or D9) were monitored from 1992 to 1996 to determine the relative timing of shoot and root growth, bloom, and carbohydrate levels, as well as the relationships between ...
A project evaluating the performance of cv. Hass on eight clonal avocado rootstocks—G755A, G755B,... more 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 frui...
Development of a phenology model for avocados could greatly enhance a grower's ability to pla... more Development of a phenology model for avocados could greatly enhance a grower's ability to plan management practices in relation to the events occurring within the tree. Knowledge of the time of root and shoot growth, flowering and fruit set, and the relationships between these events will allow for application of irrigation, fertilization, and other cultural practices at optimum times. While a model has been proposed (Whiley et al., 1988; Whiley and Wolstenholme, 1990), it is based on Queensland, Australia and South African environmental conditions. The growing conditions in these humid semi-tropical areas are characterized by wet summers and relatively dry winters. This is the opposite of the Mediterranean climate of California which is characterized by wet winters and dry hot summers. Furthermore, the model was developed using trees on seedling rootstocks. Clonal rootstocks are used in California orchards because of their resistance to Phytophthora cinnamomi and may affect the...
A project designed to evaluate the performance of 'Hass' on ten avocado rootstocks in the... more A project designed to evaluate the performance of 'Hass' on ten avocado rootstocks in the absence of Phytophthora cinnamomi has been established at the University of California South Coast Research and Extension Center in southern California. In March, 1991, the fourth year of yield data were collected from the trial. Total yield from years 2 through 5 show the highest cumulative yields from 'Hass' planted on Duke 7 (103.5 kg/tree), and the lowest on G755B (19.5 kg/tree). There were no statistical differences in average fruit size in years 2 to 4. Average fruit weight per tree for these years was 260 g. In the fifth year, average fruit size was smaller (151 g) than in previous years with G755A producing the largest fruit (171 g) and Toro Canyon the smallest (121 g). Using canopy volume data, the yield efficiencies of 'Hass' on the various rootstocks were calculated. In 1990, Duke 7 and Thomas produced significantly more fruit per cubic meter of canopy than al...
The influence of three irrigation treatments on flowering, yield, tree growth, root distribution,... more The influence of three irrigation treatments on flowering, yield, tree growth, root distribution, and leaf analysis of mature `Hass' avocado (Persea americana Mill.) was investigated over a six year period (1987-1992). Three irrigation treatments; 60, 80, and 100% of evapotranspiration (ETc) were applied using low-volume spray emitters. The differential irrigation treatments were maintained year round. Irrigation treatments did not affect the timing or intensity of bloom. Yield data from years 2-6 show a significant irrigation effect on cumulative weight and total number of fruit per tree. Trees receiving 100% ETc had higher yield/tree. This increased yield was due both to increased fruit numbers and individual fruit weight per tree. Tree growth was also significantly impacted by the irrigation treatments. Trees receiving 100% ETc exhibited the greatest amount of vegetative growth over the study. Yield efficiency (Kg fruit/m3 canopy) was not influenced by irrigation treatment. I...
The county farm advisors in California are responsible to develop and distribute county newletter... more The county farm advisors in California are responsible to develop and distribute county newletters to subtropical fruit farmers. The purpose of these newsletters is to appraise growers of emerging research developments and discuss topics of current importance. There is often repitition of information and duplication of mailing lists resulting in costly and innefficient use of the University's limited resources. A cooperative effort between the California Avocado Society, the Citrus Research Board, and University of California farm advisors involved with subtropical fruit production has resulted in Subtropical Fruit News. This newsletter greatly improves Cooperative Extension's outreach education programs, makes better use of limited resources, yet retains the identity of each advisor and the county or region they serve. This newsletter should serve as a model for other extension programs looking toward maximizing efficiency.
Monthly samples were taken from 9-year-old `Hass' avocado trees on Duke 7 rootstock grown at ... more Monthly samples were taken from 9-year-old `Hass' avocado trees on Duke 7 rootstock grown at the UC Southcoast Research and Extension Center in Irvine, Calif. Changes in starch and total soluble sugars were monitored from fine and coarse roots, trunk (above the bud union), small diameter stems, leaves, and fruit. When possible, seasonal carbohydrate changes were compared to root and shoot flushing patterns. In all of the vegetative plant organs monitored, total soluble sugars accounted for most of the carbohydrate. Starch accounted for ≈10% of the sample dry weight, whereas the total soluble sugars accounted for ≈18%. D-mannoheptulose and perseitol, both C7 sugars, were the predominant soluble sugars throughout the year. Fructose, glucose, and sucrose accounted for <5% of the total soluble sugars. During fruit development, soluble sugar content of the exo- and mesocarp tissues >25% of the dry weight. The significance of these findings will be discussed in relationship to t...
SUMMARY The seasonal trends of Ca in Fuerte and Hass avocado fruits from vigorous and non-vigorou... more SUMMARY The seasonal trends of Ca in Fuerte and Hass avocado fruits from vigorous and non-vigorous trees were studied. Non-vigorous trees, with moderate root infection by Phytophthora cinnamomi, produced fruit with significantly higher Ca concentration and Ca content than vigorous trees of the same cultivar. This appeared to be related to less competition from the spring vegetative growth flush. Fuerte fruits had significantly less Ca than Hass fruits throughout the growing season. Management implications are discussed with a view to increasing fruit Ca for better storage ability and reduced post-harvest problems.
The avocado breeding and germplasm preservation projects in California may ultimately provide the... more The avocado breeding and germplasm preservation projects in California may ultimately provide the industry with consistently heavier producing, high-quality avocado varieties, better pollinizer varieties, and improved rootstock hybrids. The program will rely on the continued evaluation of new material generated through traditional selection techniques and the introduction of new material from other countries, as well as refined genetic techniques used to increase the efficiency of crossing and selection. Selections from open pollinated progeny; the main approach of the breeding program for over 60 years, will probably not yield great progress without the help of modern genetic tools. Most modern plant breeding programs incorporate new molecular genetic methods. Methods that provide a systematic analytical approach to predictability will be essential to breeding progress in the future.
Tree form in Persea americana varies from tall and open to short and compact with varying composi... more Tree form in Persea americana varies from tall and open to short and compact with varying composites. Tree form is modified in the nursery by grafting, pinching, pruning and nursery spacing. Therefore, the resulting tree is not necessarily in the shape programmed by its genetic information, but has been modified by nursery conditions. The authors point out the problems with the present tree form, and offer an alternative form, the central-leader. Where the centralleader form is most appropriate and how it may enhance orchard productivity is discussed.
Development of a phenology model for avocados could greatly enhance a grower’s ability to plan ma... more Development of a phenology model for avocados could greatly enhance a grower’s ability to plan management practices in relation to the events occurring within the tree. Knowledge of the time of root and shoot growth, flowering and fruit set, and the relationships between these events will allow for application of irrigation, fertilization, and other cultural practices at optimum times. While a model has been proposed (Whiley et al., 1988; Whiley and Wolstenholme, 1990), it is based on Queensland, Australia and Natal, South Africa environmental conditions. The growing conditions in these humid semi-tropical areas are characterized by wet summers and relatively dry winters. This is the opposite of the Mediterranean climate of California which is characterized by wet winters and dry, hot summers. Furthermore, the model was developed using trees on seedling rootstocks. Clonal rootstocks are used in California orchards be- cause of their resistance to Phytophthora cinnamomi and may affec...
The effect of integrated applications of various rates of irrigation and fertilization on product... more The effect of integrated applications of various rates of irrigation and fertilization on productivity of the 'Hass' avocado (Persea americana Mill.) has been analyzed since 1987. The resulting data were used in a partial budgeting analysis to determine the optimum combination of irrigation and fertilization that maximize returns using various water cost scenarios. This is an ongoing project and to date the 100 percent ETc has been identified to be the optimal irrigation level. Neither the substitution of fertilizer for reduced water use nor the combination of high levels of fertilizer and water was found to be maximizing returns. Water costs to avocado growers have increased significantly in most Southern California production areas. Furthermore, the increasing urban demand for water has created concern about further water cost increases and reduced profit in agriculture. Some growers have been toying with the idea of minimizing costs through supplementation of fertilizer f...
J. L. Meyer, M. L. Arpaia, M. V. Yates, E. Takele, G. Bender, and G. Witney Department of Soil an... more J. L. Meyer, M. L. Arpaia, M. V. Yates, E. Takele, G. Bender, and G. Witney Department of Soil and Environmental Sciences, University of California, Riverside, CA 92521; Department of Botany and Plant Sciences, University of California, Riverside, CA 92521; Department of Soil and Environmental Sciences, University of California, Riverside, CA 92521; Cooperative Extension, Building 4, 5555 Overland Avenue, San Diego, CA 92123; and Cooperative Extension, 21150 Box Springs Road, Moreno Valley, CA 92387, respectively.
About 5 to 10% of avocado trees planted in the late 1970's in the Temecula/Rancho California ... more About 5 to 10% of avocado trees planted in the late 1970's in the Temecula/Rancho California area of California are suffering a decline of unknown origin. The apparent random distribution of the trees within groves and their strong rootstock-scion discontinuities suggest that the rootstock genotype plays a role in the decline. This hypothesis is reinforced by the fact that rootstock material of the late 1970's was obtained from a variety of sources. Therefore, we used allozyme analysis to ask whether avocado performance varied with rootstock racial origin. We sampled and analyzed rootstock bark from adjacent pairs of healthy and declining trees in a Rancho California 'Hass' grove. We obtained the racial identity of 90% of the rootstocks: 50% were seedlings of the Mexican race; 25%, Mexican x West Indian hybrids; the rest, West Indian seedlings. We did not find any systematic genetic differences between healthy and declining trees. If genotype plays a role in the perf...
An integrated approach to determine the relationship between the amount of low-volume irrigation ... more An integrated approach to determine the relationship between the amount of low-volume irrigation water applied, fertility, yield, and root distribution was used in this study. Four years of yield data have shown no significant increase in total crop yield with water use above 100 percent ETc. Evapotranspiration has averaged 70 cm depth of water. Fruit size at early harvest and root distribution are significantly related to the amount of applied water. California is in the fifth year of critical water shortages. Research on the actual water use for maximum yield of mature avocados has not been effectively conducted in the past in California, nor has the interrelationship of yield, fruit quality and fruit size, relative to water and fertility been investigated. The rapidly escalating cost of water in California has narrowed grower margins of profitability over the past decade. This project used an integrated approach to evaluating amounts of water use, fertility, yield, fruit size, an...
Mature 'Hass' avocado (Persea americana Mill.) trees on four rootstocks (Thomas, Topa T... more Mature 'Hass' avocado (Persea americana Mill.) trees on four rootstocks (Thomas, Topa Topa, Duke 7, or D9) were monitored from 1992 to 1996 to determine the relative timing of shoot and root growth, bloom, and carbohydrate levels, as well as the relationships between ...
A project evaluating the performance of cv. Hass on eight clonal avocado rootstocks—G755A, G755B,... more 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 frui...
Development of a phenology model for avocados could greatly enhance a grower's ability to pla... more Development of a phenology model for avocados could greatly enhance a grower's ability to plan management practices in relation to the events occurring within the tree. Knowledge of the time of root and shoot growth, flowering and fruit set, and the relationships between these events will allow for application of irrigation, fertilization, and other cultural practices at optimum times. While a model has been proposed (Whiley et al., 1988; Whiley and Wolstenholme, 1990), it is based on Queensland, Australia and South African environmental conditions. The growing conditions in these humid semi-tropical areas are characterized by wet summers and relatively dry winters. This is the opposite of the Mediterranean climate of California which is characterized by wet winters and dry hot summers. Furthermore, the model was developed using trees on seedling rootstocks. Clonal rootstocks are used in California orchards because of their resistance to Phytophthora cinnamomi and may affect the...
A project designed to evaluate the performance of 'Hass' on ten avocado rootstocks in the... more A project designed to evaluate the performance of 'Hass' on ten avocado rootstocks in the absence of Phytophthora cinnamomi has been established at the University of California South Coast Research and Extension Center in southern California. In March, 1991, the fourth year of yield data were collected from the trial. Total yield from years 2 through 5 show the highest cumulative yields from 'Hass' planted on Duke 7 (103.5 kg/tree), and the lowest on G755B (19.5 kg/tree). There were no statistical differences in average fruit size in years 2 to 4. Average fruit weight per tree for these years was 260 g. In the fifth year, average fruit size was smaller (151 g) than in previous years with G755A producing the largest fruit (171 g) and Toro Canyon the smallest (121 g). Using canopy volume data, the yield efficiencies of 'Hass' on the various rootstocks were calculated. In 1990, Duke 7 and Thomas produced significantly more fruit per cubic meter of canopy than al...
The influence of three irrigation treatments on flowering, yield, tree growth, root distribution,... more The influence of three irrigation treatments on flowering, yield, tree growth, root distribution, and leaf analysis of mature `Hass' avocado (Persea americana Mill.) was investigated over a six year period (1987-1992). Three irrigation treatments; 60, 80, and 100% of evapotranspiration (ETc) were applied using low-volume spray emitters. The differential irrigation treatments were maintained year round. Irrigation treatments did not affect the timing or intensity of bloom. Yield data from years 2-6 show a significant irrigation effect on cumulative weight and total number of fruit per tree. Trees receiving 100% ETc had higher yield/tree. This increased yield was due both to increased fruit numbers and individual fruit weight per tree. Tree growth was also significantly impacted by the irrigation treatments. Trees receiving 100% ETc exhibited the greatest amount of vegetative growth over the study. Yield efficiency (Kg fruit/m3 canopy) was not influenced by irrigation treatment. I...
The county farm advisors in California are responsible to develop and distribute county newletter... more The county farm advisors in California are responsible to develop and distribute county newletters to subtropical fruit farmers. The purpose of these newsletters is to appraise growers of emerging research developments and discuss topics of current importance. There is often repitition of information and duplication of mailing lists resulting in costly and innefficient use of the University's limited resources. A cooperative effort between the California Avocado Society, the Citrus Research Board, and University of California farm advisors involved with subtropical fruit production has resulted in Subtropical Fruit News. This newsletter greatly improves Cooperative Extension's outreach education programs, makes better use of limited resources, yet retains the identity of each advisor and the county or region they serve. This newsletter should serve as a model for other extension programs looking toward maximizing efficiency.
Monthly samples were taken from 9-year-old `Hass' avocado trees on Duke 7 rootstock grown at ... more Monthly samples were taken from 9-year-old `Hass' avocado trees on Duke 7 rootstock grown at the UC Southcoast Research and Extension Center in Irvine, Calif. Changes in starch and total soluble sugars were monitored from fine and coarse roots, trunk (above the bud union), small diameter stems, leaves, and fruit. When possible, seasonal carbohydrate changes were compared to root and shoot flushing patterns. In all of the vegetative plant organs monitored, total soluble sugars accounted for most of the carbohydrate. Starch accounted for ≈10% of the sample dry weight, whereas the total soluble sugars accounted for ≈18%. D-mannoheptulose and perseitol, both C7 sugars, were the predominant soluble sugars throughout the year. Fructose, glucose, and sucrose accounted for <5% of the total soluble sugars. During fruit development, soluble sugar content of the exo- and mesocarp tissues >25% of the dry weight. The significance of these findings will be discussed in relationship to t...
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