The mechanical properties and anatomy of fruit wall peels and their enzyme-isolated cuticular membranes (CM) are reported for three cherry tomato (Lycopersicon esculentum Mill.) cultivars that are crack-resistant, crack-intermediate, and crack-prone (i.e., Inbred 10, Sweet 100, and Sausalito Cocktail, respectively). The resistant and intermediate fruit peels strain-hardened when extended progressively; those of the crack-prone cultivar did so only modestly. The CM of all cultivars strain-hardened when extended with small forces; the CM of the intermediate and crack-prone cultivars strain-softened under tensile forces that did not strain-soften the crack-resistant cultivar. The peels and CM of the resistant cultivar were stiffer, stronger, and required more energy to break than crack-prone peels. The CM of crack-resistant peels developed deeper within the subepidermis than in the crack-prone or crack-intermediate peels. The CM in the outer epidermal periclinal walls of the crack-resistant and crack-intermediate cultivars was thicker than that of crack-prone peels. These data indicate that CM thickness can be used to gauge crack susceptibility among cherry tomato fruit, which can be useful in breeding programs and would facilitate QTL mapping of the underlying genetic factors.
Antonio J. Matas, Eward D. Cobb, Dominick J. Paolillo Jr., and Karl J. Niklas
Daniel J. Cantliffe
Transplants are grown and shipped locally or over long distances. Shipping conditions and time in transit depend on the distance travelled. Local growers may receive transplants in trays they were grown in while those shipped long distances are pulled and packed in boxes. Plant field performance is directly correlated with seedling vigor at the time of transplanting. Factors which can affect transplant vigor during growing and shipping include the plant hardening techniques employed, mechanical injury at any stage of plant growing, shipping and planting, length and conditions of transit, and storage prior to transplanting. Mechanical injury begins as soon as the plants are removed from the tray, while reduced watering and/or nutrition during hardening may have a long term effect on plant productivity. High temperature during shipping, packing plants too densely, and prolonged storage in the dark can reduce subsequent yields. Knowledge of proper conditions for transplant pre- and post-harvest handling and shipping are not clearly understood by many transplant producers and growers. Such knowledge can greatly improve transplant vigor and potentially give growers better yields.
Mosbah M. Kushad
Polyamines and the activities of their biosynthetic enzymes were evaluated during peach (Prunus persica L. `Biscoe') mesocarp (pulp) and seed growth starting at full bloom and until full fruit maturity at 14 weeks after full bloom (AFB). Mesocarp fresh mass exhibited a double-sigmoidal pattern characteristic of peaches. Seed fresh mass increased to a maximum of≈1 g at 4 weeks AFB then remained unchanged during the remaining weeks of sampling. Free putrescine, spermidine, and spermine levels were significantly higher in the flower bud, declined in the mesocarp tissue during the first 2 weeks AFB, then exhibited another increase between 2 and 6 weeks AFB. In contrast, conjugated spermidine and spermine levels were low in flower buds, then increased to their maximum level at 6 weeks AFB, then declined at full fruit development. Ornithine decarboxylase (ODC, EC 18.104.22.168) activity was high in flower buds (89.3 nmol·h-1·mg-1 protein) and in early stages of mesocarp development then declined to its lowest level (5.8 nmol·h-1·mg-1 protein) at full-fruit development. Arginine decarboxylase (ADC, 22.214.171.124) activity did not change during the first 6 weeks of mesocarp growth but declined later, reaching its lowest (1.95 nmol·h-1·mg-1 protein) at 14 weeks AFB. During the first 5 weeks AFB, ODC activity was 3.0- to 4.5-fold that of ADC activity; however, at full-fruit maturity (14 weeks AFB) the activities of both enzymes were similar. The slowdown in mesocarp growth during pit hardening between 6 and 9 weeks AFB did not change polyamines concentrations or their biosynthetic enzymes. Free spermidine and spermine levels declined during seed development; however, between 7 and 9 weeks AFB an increase in putrescine was observed. Similarly, conjugated putrescine increased substantially during seed growth reaching its highest level of 680 nmol·g-1 fresh mass at week 8 then declined at the later weeks, while conjugated spermidine and spermine peaked at week 10 to 1,169 and 2,148 nmol·g-1 fresh mass. ODC and ADC activities declined between 3 and 5 weeks AFB. However, a significant increase in ADC but not ODC activity in the seed tissue was observed during pit hardening between 6 and 10 weeks AFB. Based on the rapid increase in putrescine and ADC activity in the seed tissue, it appears that pit hardening may be a stress-related phenomenon. Data also suggest that polyamine levels in the mesocarp and seed tissue are independently regulated.
Randall H. Hagen and David A. Palzkill
The `Desert Museum' hybrid between the Blue, Foothills, and Mexican palo verdes has been well received by the public. However, it has remained unavailable due to difficulties in asexual propagation. Studies were conducted on effects of IBA cone. (0 to 10,000 ppm), cutting position along the stem, size of cutting, season, and temperature of the medium.
For `Desert Museum', basal cuttings of slightly hardened new stem growth rooted much better than apical cuttings. Best rooting for apical cuttings was 79% using IBA from 2,500-5,000 ppm. Basal cuttings averaged 95% rooting and showed no response to IBA. Rooting of cuttings taken in September declined to 10% for apical and 2170 for basal cuttings averaged over all IBA levels. Six other species or hybrids of Cercidium and Parkinsonia and five of Prosopis were also rooted.
T. Niino and A. Sakai
In-vitro-grown shoot tips of apple (Malus domestia Borkh cv. Fuji) were successfully cryopreserved by dehydration of alginate-coated shoot tip. Cold-hardened shoot tips (at 5°C for 3 weeks) were precultured on a medium containing increasing concentrations of sucrose. The shoot tips were trapped into alginate coated beads containing 0.5M sucrose followed by preculture in a medium supplemented with 1.0M sucrose. Beads containing 1 shoot tip were dehydrated up to about 32% on sterile dry silica gel at 25°C followed by a plunge in LN. After rapid warming, approximately 80% shoot formation was achieved. This encapsulation-dehydration technique may permit strage of shoot tips at higher temperatures than that of LN.
William Randle, Orville Lindstrom, and Daniel Warnock
The onion crop in Georgia is often damaged by suboptimal winter temperatures. Proper acclimation of seedlings is a way of limiting freeze damage. Because photoperiod is among the factors involved in plant acclimation, the effects of photoperiod on the acclimation of short-day Allium cepa seedlings was investigated. A single short-day cultivar, 'Granex 33', was greenhouse grown under an eleven hour photoperiod. After ten weeks of growth, four photoperiod treatments (8, 11, 14, and 24 hrs.) were administered during a two week hardening period at 3* C. Plants were then frozen in an ethylene glycol bath. Degree of acclimation was determined based on regrowth and visual observation. Acclimation of seedlings was completely inhibited by the 24 hour photoperiod. Varying degrees of acclimation were achieved with the other photoperiod treatments.
Mosbah M. Kushad
Seasonal variation in polyamines were evaluate during growth of fruit and seed of peach (Prunus persica L. cvs. Loring and Biscoe) starting at fruit set. In both cultivars, putrescine and spermidine increase significantly while spermine increase only slightly during the early stages of development then declined at the later stages. During pit hardening, polyamines in the flesh remained unchanged but their level in the seed continued to decrease. In both cultivars, polyamine levels corresponded to changes in fruit and seed sizes. when polyamines were vacuum infiltrated into commercially mature Biscoe fruits, flesh firmness, ethylene biosynthesis, and flesh color were significantly different from untreated tissue. The relationship between polyamines, seed development, and fruit development and ripening will be examined.
Masayuki Oda, Kunihiko Okada, Hidekazu Sasaki, Shigeki Akazawa, and Masahiro Sei
Eggplant (Solanum melongena L.) at the two-leaf stage were grafted on scarlet eggplant (Solanum integrifolium Poir.) by hand or a newly developed robot. The scion and rootstock were fixed with an elastic tube for hand grafting or with an adhesive and a hardener for robotic grafting. After acclimatization, the grafted plants were planted at the three- or 11-leaf stage in a glasshouse. Plants grafted by the robot showed a higher percentage of survival, and attained the three- and 11-leaf stages 8 days earlier on average than those grafted by hand. Stems were longer, and shoot fresh mass and fruit yield of plants were higher for the three-leaf-than for the 11-leaf-stage planting, irrespective of the grafting method. Such vigorous growth and high yield by robotic grafting were absent for the 11-leaf-stage planting but obvious for the three-leaf-stage planting.
Karen E. Burr, Stephen J. Wanner, and Richard W. Tinus
It is not known when changes in primary direct heat stress tolerance of conifer seedlings occur in relation to other seasonally changing physiological parameters. This information should be incorporated into nursery practices and the matching of genotypes to landscape sites. Greenhouse-cultured, container-grown Douglas-fir, Engelmann spruce, and ponderosa pine. were cold acclimated and reacclimated in growth chambers over 19 weeks. Direct heat stress tolerance of needles, cold hardiness, and bud dormancy were measured weekly. Douglas-fir and Engelmann spruce heat stress tolerance increased with the development of new growth through one complete growth cycle, i.e., bud break, maturation, cold hardening, dehardening, and bud break the following growing season. Ponderosa pine differed in that new needles had intermediate tolerance, and fully cold hardy needles were the most intolerant. In none of the species did the timing of changes in heat stress tolerance coincide consistently with changes in cold hardiness or bud dormancy.
J.J. Le Roux and J. Van Staden
Two cold-tolerant species (Eucalyptus macarthurii Deane et Maiden and E. smithii R.T. Baker), a cold-tolerant hybrid (E. macarthurii×E. grandis Hill ex Maiden), and E. saligna Sm. were propagated in vitro from nodal explants collected from field-grown seedlings and from clonal hedges. Shoot growth was initiated on modified Murashige and Skoog (MS) medium containing BA at 0.1 mg·liter-1. Modified MS medium with BA (0.2 mg·liter-1) and NAA (0.01 mg·liter-1) was most effective in promoting shoot proliferation. Root initiation was achieved on half-strength modified MS medium with 2 mg IBA/liter. Rooted plants were hardened and established in the field. Chemical names used: N-(phenylmethyl)-1EZ-purin-6-amine (BA); 2-(1-naphthyl)acetic acid (NAA); 1H-indole-3-butyric acid (IBA).