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Samuel Salazar-García, Elizabeth M. Lord, and Carol J. Lovatt

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.

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Jiwon Jeong and Donald J. Huber

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, α-(EC and β-galactosidases (EC, and endo-β-1,4-glucanase (EC The appearance of polygalacturonase (EC 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.

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Yaseen Mohamed-Yaseen, Raymond J. Schnell, Robert J. Knight, and T.L. Davenport

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.

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S. L. Ontai, M. L. Arpaia, and J. S. Reints Jr.

In southern California, avocados are often left in the field for up to 12 hours after harvest. Fruit in the bin may reach up to 40C during the summer months and may take up to 24 hours to cool to the recommended storage temperature. A study was conducted using `Hass' avocados over two growing season during the months of July and August to determine the effect of delayed cooling on fruit quality. Fruit were held at 20, 30 or 40 C for 0, 6, 12 or 24 hours before storage at 5C for 0, 2, 4, or 6 weeks. Fruit quality was determined by flesh firmness, time to ripe, vascular and flesh discoloration and the presence or absence of decay. The level of damage seen in storage varied with the harvest. Overall, after 4 or 6 weeks in storage, there was a considerable increase in either vascular or flesh discoloration and decay especially when fruit had been held at 30 or 40C prior to storage. The results indicate that harvested avocados should be kept as cool as possible in the field and that fruit should be processed within 12 hours for storage periods greater than 2 weeks.

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Vincent Ianaro and Robert J. McNeil

The Fuerte avocado cultivar is known to be an alternate and inconsistent producer of avocados in cool coastal areas and hot interior areas of California because of its sensitivity to such extremes of climate during its bloom and fruit setting periods. This study attempted to increase fruit set and yield of this cultivar in a cool central coast area by applying a three-eighths inch wide girdle to one large limb, equivalent to one-third of the tree, on each of five 43-year-old trees. A double bladed girdling knife was used to remove the bark all around each limb. Another equal sized limb on each tree was used as the control. Girdling was completed on December 15. Girdled limbs had means of 42.6 more pounds which was 186.8% more fruit yield as compared to control limbs. Girdled limbs also had means of 89 more fruit which was 222.5% more fruit by count than control limbs. Fruit on girdled limbs was smaller in size (8.1 oz. average) than that on control limbs (9.1 oz. average) but was still of an acceptable size to bring good prices.

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Emanuel Lahav, Eli Tomer, Shmuel Gazit, and Uri Lavi

Most fruit-tree breeding projects are based on selection of seedlings in regard to their performance. The selected seedlings are vegetatively propagated, usually by grafting. It is highly important for the breeder to know whether the performance of the grafted tree will resemble the performance of the original seedling. In this study the performance of avocado and mango seedlings was compared with that of their grafted duplicates. Significant differences were found in only 8 out of 36 avocado traits and 2 out of 10 mango traits. Significant seedling x graft interaction was detected in 10 other avocado traits. These differences were considered of no practical significance, since their magnitude was of minor importance for the breeder. The conclusion for avocado and mango breeders is that for most traits selection could be carried out on ungrafted seedlings.

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Allan B. Woolf and Michael Lay-Yee

`Hass' avocados [Persea americana Mill.] were pretreated in water (38 °C for up to 120 min) immediately before 50 °C hot water treatments of up to 10 min. Fruit were stored for 1 week at 6 °C and ripened at 20 °C. External browning was evaluated immediately upon removal from cold storage, and fruit quality evaluated when fruit were ripe. Pretreatments at 38 °C tended to reduce the levels of external browning, skin hardening, and internal disorders, such as tissue breakdown and body rots, that were associated, and increased, with longer hot water treatments. A pretreatment of 60 min was the most effective for eliminating external browning, and reducing hardening of the skin when fruit were ripe following hot water treatment. Examination of heat shock protein (hsp) gene expression in avocado skin tissue, showed that levels of hspl7 and hsp70 homologous mRNA increased with increasing pretreatment duration. The results demonstrate that 38 °C pretreatments increase the tolerance of avocado fruit to subsequent hot water treatments.

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Bruce Schaffer, Frederick S. Davies, and Jonathan H. Crane

The effects of flooding calcareous soil on physiology and growth have been studied for several subtropical and tropical fruit crops including avocado (Persea americana Mill.), mango (Mangifera indica L.), carambola (Averrhoa carambola L.), and several Annona species. In calcareous soils that have a high pH, short-term flooding can actually be beneficial to subtropical and tropical fruit crops by increasing the solubility of particle-bound nutrient elements such as Fe, Mn and Mg due to flooding-induced decreases in soil pH. Additionally, flooding reduces the redox potential in the soil, resulting in Fe being reduced from Fe3+ to Fe2+, which is the cation metabolized by plants. As with other woody perennial crops, one of the early physiological responses of subtropical and tropical fruit trees to flooding is a decrease in stomatal conductance and net CO2 assimilation. If the flooding period is prolonged, lack of O2 (anoxia) in the soil results in a reduction of root and shoot growth, wilting, decreased nutrient uptake and eventual death. The flooding duration required to cause tree mortality varies among species, among cultivars within species, and with environmental conditions, particularly temperature. Several tropical and subtropical fruit crops have anatomical or morphological adaptations to tolerate prolonged flooding, such as development of hypertrophied stem lenticels, adventitious rooting or formation of porous aerenchyma tissue. For grafted trees, flooding-tolerance is conferred by the rootstock and not the scion. Therefore there is a possibility to increase flood tolerance of subtropical and tropical fruit crops by identifying or developing flood-tolerant rootstocks.

Open access

Enrique I. Sánchez-González, Adriana Gutiérrez-Díez, and Netzahualcóyotl Mayek-Pérez

outcrossing rate (t s ), and full siblings rate (t m – t s ) per Mexican race avocado family. Table 4. Analysis of molecular variance for 10 families of Persea americana var. drymifolia based on simple sequence repeat and intersimple sequence repeat

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Pablo Rodriguez, Juan Camilo Henao, Guillermo Correa, and Ana Aristizabal

regions. Units Literature cited Alcaraz, M.L. Thorp, T.G. Hormaza, J.I. 2013 Phenological growth stages of avocado ( Persea americana ) according to the BBCH scale Scientia Hort. 164 434 439 American Organization of Analytical Chemists 1998 Official method