Inflorescence and flower development of the `Hass' avocado (Persea americana Mill.) were investigated at the macro- and microscopic level with three objectives: 1) to determine the time of transition from vegetative to reproductive growth; 2) to develop a visual scale correlating external inflorescence and flower development with the time and pattern of organogenesis; and 3) to quantify the effect of high (“on”) and low (“off”) yields on the flowering process. Apical buds (or expanding inflorescences) borne on summer shoots were collected weekly from July to August during an “on” and “off” crop year. Collected samples were externally described and microscopically analyzed. The transition from vegetative to reproductive condition probably occurred from the end of July through August (end of shoot expansion). During this transition the primary axis meristem changed shape from convex to flat to convex. These events were followed by the initiation of additional bracts and their associated secondary axis inflorescence meristems. A period of dormancy was not a prerequisite for inflorescence development. Continued production of secondary axis inflorescence meristems was observed from August to October, followed by anthesis seven months later. In all, eleven visual stages of bud development were distinguished and correlated with organogenesis to create a scale that can be used to predict specific stages of inflorescence and flower development. Inflorescence development was correlated with minimum temperature ≤15 °C, whereas yield had little effect on the timing of developmental events of individual inflorescence buds. However, the high yield of the “on” year reduced inflorescence number and increased the number of vegetative shoots. No determinate inflorescences were produced during the “on” year. For the “off” year, 3% and 42% of shoots produced determinate and indeterminate inflorescences, respectively.
Pre-ripe `Booth 7' avocado (Persea americana Mill.) fruit, a cross of West Indian and Guatemalan strains, were treated with 0.9 μL·L-1 1-methylcyclopropene (1-MCP) for 12 hours at 20 °C. After storage for 18 days in air at 13 °C, at which time whole fruit firmness values averaged about 83 N, half of the 1-MCP-treated fruit were treated with 100 μL·L-1 ethylene for 12 hours and then transferred to 20 °C. 1-MCP delayed softening, and fruit treated with 1-MCP retained more green color than air-treated fruit when full ripe (firmness 10 to 15 N). 1-MCP affected the activities of pectinmethylesterase (EC 3.2.1.11), α-(EC 3.2.1.22) and β-galactosidases (EC 3.2.1.23), and endo-β-1,4-glucanase (EC 3.2.1.4). The appearance of polygalacturonase (EC 3.2.1.15) activity was completely suppressed in 1-MCP-treated fruit for up to 24 days, at which time the firmness of 1-MCP-treated fruit had declined nearly 80% compared with initial values. The effect of exogenous ethylene applied to partially ripened 1-MCP-treated fruit differed for different ripening parameters. Ethylene applied to mid-ripe avocado exerted no effect on the on-going rate or final extent of softening of 1-MCP-treated fruit, even though polygalacturonase and endo-1,4-β-glucanase activities increased in response to ethylene. β-galactosidase decreased in 1-MCP-treated fruit in response to ethylene treatment. 1-MCP delayed the increase in solubility and depolymerization of water- and CDTA (1,2-cyclohexylenedinitrilotetraacetic acid)-soluble polyuronides, likely due to reduced polygalacturonase activity. At the full-ripe stage, the levels of arabinose, galactose, glucose, mannose, rhamnose, and xylose associated with the CDTA-soluble polyuronide fraction were similar among all treatments. In contrast, the galactose levels of water-soluble polyuronides declined 40% and 17% in control and 1-MCP treated fruit, respectively. Hemicellulose neutral sugar composition was unaffected by 1-MCP or ethylene treatment. The data indicate that the capacity of avocado fruit to recover from 1-MCP-mediated suppression of ripening can be only partially amended through short-term ethylene application and differs significantly for different ripening parameters.
Abstract
A method to measure the severity of chilling injury (Cl) in stored avocados (Persea americana Mill.) is described that gives better results than visual appraisal. Colored metabolites are extracted from chilled mesocarp and measured in a colorimeter.
A procedure was developed to regenerate plants via tissue culture from embryonic axes of mature avocado seeds. Explants were cultured in Murashige and Skoog (MS) medium supplemented with benzyladenine (BA) and naphthalene-acetic acid (NAA) or thidiazuron (TDZ) and NAA. Culture were kept in the dark for 7-10 days to reduce browning resulting from phenolic oxidation. Multiple shoots (5-8) were formed after transfer to light. Further multiplication were achieved using different combination of BA and NAA or TDZ and NAA. Shoots were cultured in MS supplemented with 2mg/l indolebutyric acid (IBA) for 2 weeks then transferred to MS supplemented with lg/l activated charcoal for root induction. Complete plants were obtained in vitro.
Abstract
Fruit of avocado (Persea americana Mill.) were stored for up to 6 weeks in air or ethylene-enriched air at low temperatures. In one experiment, opposite ends of intact fruit were exposed individually to ethylene-enriched air. The severity of chilling injury of ripened fruit was significantly greater in fruit or fruit ends exposed to low ethylene concentrations.
Abstract
The response of fruits of avocado (Persea americana Mill.) to various temperatures was found to differ in the range 0° to 25°C. This temperature range was divided into 3 groups: 1) between 10° and 25°, the fruit softened at a rate which increases with increasing temperature; 2) between 5° and 8°C, fruit softening was inhibited and the fruit softened only after transfer to a higher temperature; and 3) between 0° and 4° storage life without the occurrence of chilling injury was limited.
Abstract
Leaves were collected in 1974 and 1975 from mature ‘Tonnage’, ‘Lula’, ‘Taylor’, and ‘Booth 8’ avocado trees (Persea americana Mill.) on sand, muck, and calcareous rock soils and analyzed for N, P, K, Ca, Mg, Mn, Cu, Zn, and Fe. Significant differences in levels of all 9 elements in ‘Tonnage’ leaves occurred among the 3 soil types. Crop size, fertilization, soil pH, soil Ca level, and exchange capacity of the soil appeared to be important factors in the variations. Differences in concentration of N and P were not significant among the 4 cultivars but were significant for the other elements.
Abstract
As leaves of ‘Tonnage’ avocado (Persea americana Mill.) increased in age, N, P, and K contents decreased, while Ca, Mg, Mn, Cu, Zn, and Fe contents were higher. A comparison of leaves from 1st and 2nd flushes showed similar trends reflected in leaf age. The basal leaf was lower in P but higher in Ca, Mg, and Cu when compared with the terminal leaf of the same twig. Only N and Cu contents were different when leaves from fruiting and nonfruiting twigs were compared. Practical application of the data in sampling avocado leaves is discussed.
Abstract
The effects of 2 rootstocks of avocado (Persea americana Mill.), 2 soil oxygen levels, and 2 soil moisture levels on nutrient uptake and translocation showed that seedling Duke and Topa Topa rootstocks produced little change in the growth of ‘Hass’ scion, nutrient concentrations in the leaves, stems, and roots or the total amount of nutrients absorbed per plant. Total amounts of 11 nutrients studied were significantly lower, irrespective of concentrations found in the various plant tissues, in plants grown in with 2% soil oxygen than in plants supplied with 21% soil oxygen. Low soil moisture reduced dry weights of leaves and stems, and total dry weight of plants. Total amounts of N, P, K, Ca, Mg, Zn, and Mn per plant, irrespective of nutrient concentrations in the leaves, stems, and roots, were significantly lower in plants grown under low soil moisture.
Abstract
The respiratory rate, ethylene production and softening of untreated and treated (propylene or ethylene) avocado fruit (Persea americana Mill, cv Hass) were determined during growth and maturation using fruit harvested monthly from August to July. Untreated immature fruit harvested in August exhibited a climacteric, produced ethylene and softened after 18, 21 and 18.5 days, respectively. Treatment of these immature fruit for 1 to 3 days beginning 1 day after harvest stimulated respiration during the treatment, but the respiratory rate decreased to the level of the untreated fruit within 1 day after the treatment was terminated and they subsequently paralleled the response of the untreated fruit. Ethylene production was not induced by the treatment in immature fruit, but was in mature fruit. The climacteric peak rate and the peak rate of ethylene production increased as the fruit matured. The days to the climacteric peak and days to soften decreased as the season progressed. The ethylene or propylene treated fruit had a progressively shorter time to the climacteric and to softening as they matured compared to the untreated fruit.