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Suzanne S. Sanxter, Kate A. Nishijima, and Harvey T. Chan Jr.

Chilling injury symptoms were reduced when `Sharwil' avocados (Persea americana Mill.) were held at 37 to 38C for 17 to 18 hours and then air-cooled at 20C for 4 hours before storage at 1.1C for ≥14 days. In contrast, nonheated fruit developed severe surface discoloration and pitting. Chilling injury symptoms were reduced further when the heated fruit were stored in perforated polyethylene bags during 1.1C storage. No treatment equaled or surpassed the quality of fruit in nontreated controls.

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Uri Lavi, Emanuel Lahav, Chemda Degani, and Shmuel Gazit

Avocado (Persea americana Mill.) progeny that originated from 11 crosses (both self-pollinations and crosses between cultivars) were evaluated for the length of their juvenile period. Time to first flowering, “flowering age,” and time to first fruit production, “fruiting age,” were recorded for each progeny. The mean values for both ages, the sd, and the progeny distribution were calculated. Significant statistical differences in flowering age and fruiting age between various progeny populations were detected. No differences were detected between self-pollinated plants and crosses. The time until first flowering was found to be the limiting factor in evaluation of seedlings.

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B.K. Gabor, F.B. Guillemet, and M.D. Coffey

Twelve avocado (Persea americana Mill.) rootstock selections were tip-grafted with a commercial scion, cv. Hass, and evaluated for their field resistance to Phytophthora cinnamomi Rands. Percentage difference in trunk cross-sectional area of the inoculated compared to uninoculated rootstock, the overall growth in trunk cross-sectional area, and visual rating of disease severity of the commercial scion were used to evaluate rootstock over 79 weeks. Avocado trees on the rootstock selections Thomas, Martin Grande (G75Sa, b, and c), Barr Duke, and D9 demonstrated the highest level of resistance to P. cinnamomi, whereas those on Topa Topa, Borchard, and G6 had the lowest levels. Trees on Duke 7, G1033, and Toro Canyon rootstock were intermediate in their levels of resistance. Among uninoculated rootstock, trees on Thomas and G6 exhibited the greatest growth in trunk cross-sectional area. whereas those on D9 showed the least.

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Edna Pesis, Rosa Marinansky, Giora Zauberman, and Yoram Fuchs

Prestorage treatment of avocado fruit (Persea americana Mill. cv. Fuerte) with a low-O2 atmosphere (3% O2 + 97% N2) for 24 hours at 17C, significantly reduced chilling injury (CI) symptoms after storage at 2C for 3 weeks. Fruit softening was also delayed by this treatment. The treated fruit had lower respiration and ethylene production rates during storage at 2C and subsequently at 17C. Electrolyte leakage was significantly lower in peel disks from treated fruit. Reducing power, expressed as total sulfhydryl groups, was higher in the peel and pulp of low-O2-treated fruit. The amount of peel chlorophyll was inversely correlated with the severity of CI symptoms.

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Dror Sharon, Avital Adato, Samir Mhameed, Uri Lavi, Jossi Hillel, Maria Gomolka, Conny Epplen, and Jorg Thomas Epplen

Plant genomes contain polymorphic repetitive sequences that can be used as DNA markers. Minisatellites (16 to 64 bp per repeat) and simple-sequence repeats (2 to 6 bp per repeat) are the most polymorphic markers found in plant and animal genomes. In this study, the hybridizations between genomic DNA and variable number of tandem repeat probes were examined in Arabidopsis thaliana L. (Heynn), onion (Allium cepa L.), tomato (Lycopersicon esculentum L.), wheat (Triticum aestivum L.), avocado (Persea americana Mill.), litchi (Chinensis Sonn.), mango (Mangifera indica L.), and Carica species. Some of the probes detected polymorphic sequences in all the species, but others were useful only for one or two species. None of the probes gave clear band patterns in either onion or wheat. The in-gel hybridization method was similar to Southern blot hybridization using the simple-sequence repeat probes.

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M.T. Vidal, C. Azcón-Aguilar, J.M. Barea, and F. Pliego-Alfaro

Micropropagated plantlets of avocado (Persea americana Mill.) exhibit a very slow rate of growth during the acclimatization phase, possibly because mycorrhizae are absent. Inoculation of plantlets with the vesicular-arbuscular mycorrhizal fungus Glomus fasciculatum (Thaxter sensu Gerd) Gerd and Trappe improved formation of a well-developed root system that was converted into a mycorrhizal system. Introduction of the mycorrhizal fungus at the time plantlets were transferred from axenic conditions to ex vitro conditions improved shoot and root growth; enhanced the shoot: root ratio; increased the concentration and/or content of N, P, and K in plant tissues; and helped plants to tolerate environmental stress at transplanting. Inclusion of soil as a component of the potting medium appeared to favor mycorrhiza formation and effectiveness. Thus, mycorrhiza formation seems to be the key factor for subsequent growth and development of micropropagated plants of avocado.

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Allan B. Woolf

`Hass' avocado (Persea americana Mill.) fruit were heat treated in water at 38 °C for 0 to 120 minutes, and stored at 0.5 °C for up to 28 days. After storage, fruit were ripened at 20 °C and their quality evaluated. External chilling injury (CI) developed during storage in nonheated fruit. Skin (exocarp) sectioning showed that browning developed from the base of the exocarp, and with longer storage, this browning moved outwards toward the epidermis. Longer durations of hot water treatment (HWT) progressively reduced CI; 60 minutes was the optimal duration that eliminated external CI, while best maintaining fruit quality. Concomitantly, electrolyte leakage of heated skin tissue increased ≈70% during storage, whereas electrolyte leakage of nonheated skin tissue increased ≈480% over the same period. Thus, significant protection was conferred by HWTs against low temperature damage to avocados and these effects are reflected in the morphology and physiology of the skin tissue.

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Dana F. Faubion, Mary Lu Arpaia, F. Gordon Mitchell, and Gene Mayer

Optimum controlled atmosphere (CA) storage conditions were evaluated over a two year period for California-grown `Hass' avocado (Persea americana). Fruit harvests corresponded to early, middle and late season commercial harvests. Various temperatures and CA conditions were tested. The results indicate that the storage life of `Hass' can be extended from 3 to 4 weeks in 5C air, to 9 weeks in 5C CA if they are held in 2% oxygen and 2 to 5% carbon dioxide. Loss of quality as determined by chilling injury expression and flesh softening was greatly reduced in these conditions. Fruit maturity influenced the response to CA storage. Late season fruit had greater loss of quality in storage than earlier fruit. In 2% oxygen and 2.5% carbon dioxide, continuous exposure to ethylene levels as low as 0.1 ppm significantly increased quality loss. Delays in cooling and CA atmosphere establishment of up to three days after harvest did not effect quality.

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Jim Downer, Ben Faber, and John Menge

Mulches can exert positive (disease controlling) or negative (disease enhancing) potential when applied to young avocado (Persea americana) trees. Regulation of root disease in avocado is a complicated process that is affected by host resistance, inoculum density, temperature, soil salinity and soil water potential. There are short-term immediate effects from mulching and subtle long-term effects that regulate disease caused by the root rot pathogen Phytophthora cinnamomi. Short-term effects include increased soil moisture and soil temperature moderation. Long-term effects include increases of: soil mineral nutrients, soil aggregation and drainage; microbial activity; and cellulase enzyme activities. Biological control of Phytophthora in mulched soil is partially regulated by cellulase enzyme activities. This soil enzyme concept of biological control is discussed in regard to the classical Ashburner method of biological control.

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Jeffrey G. Williamson and Jonathan H. Crane

A wide variety of temperate, subtropical, and tropical fruit crops are grown commercially in Florida. Farm size ranges from large commercial operations exceeding 100 acres to small 1- or 2-acre “estate” farms. Irrigation and fertilization practices vary widely with crop, soil type, and management philosophy. However, many growers are adopting practices such as microirrigation, fertigation, and other technologies, which, if properly used, should reduce water and fertilizer inputs and minimize leaching and runoff of fertilizers and pesticides. Although fertilizer and irrigation recommendations exist for major crops such as avocado (Persea americana), mango (Mangifera indica), and blueberry (Vaccinium spp.), there is little research-based information specific to Florida for many minor crops, including muscadine (Vitis rodundifolia), blackberry (Rubus spp.), sapodilla (Manilkara zapota), guava (Psidium guajava), papaya (Carica papaya), and others. Even where recommendations exist, refinement of irrigation and fertilization practices is needed because of changes in technology.