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Mark K. Ehlenfeldt

Inbreeding coefficients were calculated for highbush blueberry (Vaccinium corymbosum L.) cultivars based on a tetrasomic inheritance model. This model yielded lower inbreeding coefficients than previous calculations based on a disomic tetraploid inheritance model. Recent trends in breeding have resulted in significant use of V. darrowi Camp as a source of low-chilling germplasm for use in the southern United States. There is also a trend toward increased inbreeding in several crosses from which recently released cultivars have been derived. Increased inbreeding coefficients do not represent a detrimental situation in blueberry per se.

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Shiow Y. Wang and Miklos Faust

Polyamine, putrescine, spermidine, and spermine contents were determined during endodormancy in the buds of low-chilling-requiring `Anna' apples (Malus domestics Borkh.). Putrescine, spermidine, and spermine contents increased greatly in buds when their chilling requirement was satisfied. Polyamine biosynthetic inhibitors α -difluoromethylarginine (DFMA) or α -difluoromethylornithine (DFMO) reduced bud break and bud growth in concert with decreased polyamine titers. DFMO or DFMA did not inhibit bud break when it was applied to buds after they received the full chilling requirement. DFMO was more inhibitory than DFMA. The polyamine requirement was much higher for bud growth and bud development than during differentiation and bud break.

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Joseph K. Njuguna*, Leonard S. Wamocho, and Teddy E. Morelock

Temperate zone fruit crops undergo bud dormancy which can be described as a mechanism for avoiding the exposure of tender flowers and leaves to low winter temperatures. In Kenya, apple growing is mostly hampered by inadequate chilling that causes the plants to have prolonged dormancy leading to poor flowering and consequently low yield. Although the chilling requirements are obligatory, under subtropical and especially tropical conditions avoidance is possible. To achieve this, it is necessary to select cultivars with low chilling requirements. This has proven effective in Zimbabwe with cultivar Matsu which is grown without a need for artificial breaking of dormancy. In Kenya like Zimbabwe, low chilling requiring cultivars such as Anna have been grown successfully. However, for cultivars with high chilling requirements, there is need to apply artificial techniques/methods to enhance bud break. Some of the cultural techniques used are: defoliation after harvesting and bending of the shoots holizontally. Defoliation after harvesting has particularly been used successfully in the island of Java in Indonesia and it enables two crops to be grown per year. Root chilling of rootstock has also been found to enhance bud break of the shoot. In addition, chemicals like KNO3, mineral oil and thiourea (TU) have been found to be effective in breaking bud dormancy in Kenya. This paper is reviewing the challenges encountered in growing apples in the tropics and Kenya in particular and the progress that has made in addressing them.

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Marvin Pritts

Primocane-fruiting raspberries (Rubus idaeus L.) have the capacity to fruit in the fall and again the next summer. Because of their low chilling requirement, this type is used to produce a double crop in warmer regions of the world. However, many growers prune canes to the ground after the fall crop, sacrificing the summer crop for a single, large fall crop. This practice is less labor-intensive than the selective cane removal required for double-cropping and crop quality is often higher. Primocane-fruiting raspberries also are easily manipulated to extend the season. Early- and late-fruiting cultivars, cultural manipulations, rowcovers, high tunnels, and greenhouses are all used commercially to extend the season of primocane raspberries year-round. This is beneficial for consumers because high-quality fruit is now available for a much longer period than was possible in the past.

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Raul L. Grijalva-Contreras, Arturo Lopez-Carvajal, Manuel J. Valenzuela-Ruiz, Rogelio A. Juarez-Gonzalez, and Fabian Robles-Contreras

The total shell almond production in northwestern area in Mexico is ≈80 tons per year; therefore, almond fruit tree would be a potential fruit crop in this agricultural area. Also, this crop offers some advantages with lower costs than other fruit crop, and the water requirement needs for almond trees is low in support to the limited water availability. Our objective was to test new five almond cultivars of low chilling requirement. Almond cultivars were grafted on Nemaguard rootstock and planted during 1990. The data were collected from the almond orchard using the inshell kernel. The average yield during 1993 and 1994 were 970, 602, 552, 419, and 388 kg·ha–1 for `R-633', `Cavaliera', `Constantini', `Um El Fahm', and `Rane', respectively. `Cavaliera' and `Um El Fahm' showed good inshell percent and kernel weight. `Cavaliera' was harvested early in last week of June compared to the other cultivars that were harvested in mid-July.

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Unaroj Boonprakob and D.H. Byrne

Blind nodes in peach, the condition in which a node has no obvious vegetative or reproductive buds, is a problem in peach production in low and medium chill regions. Observations were made at 3 locations in Texas on peach cultivars which range in chilling requirement from 150 to 850 chill units. Four types of growing shoots (terminal or lateral shoot and east or west side) from peripheral canopy about 150-200 cm were sampled twice a month to determine the phonological development. Blind bud development was most frequent during the period of highest daily temperature and did not correspond with the position of the sample on a tree. High chilling cultivars showed greater susceptibility to the symptoms than low chilling cultivars. The anatomical differences between normal and blind nodes are described.

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Gregory A. Lang and Robert G. Danka

Southern highbush (“low chill tetraploid”) blueberries are an earlier-ripening, self pollen-compatible alternative to rabbiteye blueberries. `Sharpblue', the first southern highbush cultivar planted on a commercial scale, has been shown to require cross-pollination for optimal fruit size and earliness of ripening. `Gulfcoast', a recently released cultivar for Gulf states growers of about latitude 30 to 32 N, differs in heritage from `Sharpblue', incorporating about 50% more self-compatible northern highbush germplasm. `Gulfcoast' fruit development after honey bee-mediated self- or cross-pollination with `Sharpblue' was similar in terms of set (85.5 vs. 82.2%), weight (1.26 vs. 1.18g), and seed number (32.8 vs. 33.6), respectively. Cross-pollination did not result in significantly earlier ripening. Thus, `Gulfcoast' appears to be more self-fertile than `Sharpblue'. Other closely-related cultivars are being examined to determine the genetic influence on potential for self-fruitfulness.

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Hsin-Shan Lin and Chien Yi Wang

Off-season production of several tropical and subtropical fruits has been successfully practiced commercially in Taiwan. By combining pruning, removal of leaves, and application of growth regulators, it is possible to have two to three crops of grapes per year. By grafting the chilled scions of temperate Asian pear onto the water shoots of low-chilling native pear varieties, it is possible to produce high-quality Asian pears (temperate-origin) in a subtropical environment. By using techniques such as root-pruning, flooding, and application of growth inhibitors, it is possible to induce flower bud formation and hasten the production of wax apples. The production periods of other fruit crops such as jujubes and sugar apples, can also be modified by pruning and other techniques.

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Dan E. Parfitt, Craig E. Kallsen, and Joe Maranto

`Randy' is an early flowering male pistachio that will be used as a pollenizer for `West Hills' and `Lost Hills'. It has excellent flowering synchrony with `West Hills' and `Lost Hills' and can be used to cover the earlier part of the `Kerman' flowering period during seasons in which `Kerman' flowering is extended. This generally occurs during seasons of low chill, which are expected to become more frequent in the future due to continued global warming. `Peters', the standard male used to pollenize `Kerman', often flowers too late to cover the earlier part of the `Kerman' bloom period under these conditions or to serve as an effective pollenizer for the new female cultivars. `Randy' was selected for high pollen viability, pollen durability, and a high level of pollen production (based on visual evaluation). `Randy' flowers 1–3 weeks earlier than `Peters', the standard pollenizer for `Kerman'.

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Dehua Liu, Helen A. Norman, Gary W. Stutte, and Miklos Faust

Lipase activity was studied during endodormancy in low-chilling-requiring `Anna' and high-chilling-requiring `Northern Spy' apples (Malus domestica Borkh.). Lipase activity greatly increased in bud axes when the chilling requirement of buds was almost satisfied regardless of the absolute chilling needed. Lipase activity greatly increased in `Anna' after 400 chill units (CU) and in `Northern Spy' after 2600 CU. This corresponded with an increase in budbreak at 22 to 24C. The increase in lipase activity also coincided with the release of water in buds from the bound to the free form. We propose that lipase(s) activity is an integral part of breaking dormancy and that lipase participates in causing changes in membrane lipid composition that coincides with releasing water into the free form.