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  • Author or Editor: S. Roy x
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Conventional scanning electron microscope (SEM) have greatly expanded our knowledge about the ultrastructure of plant tissues; however, the fixation, dehydration and drying procedures required for SEM preparation of specimens, are slow, extract soluble materials and cause shrinkage. Recent improvements in a technique referred to as low temperature (LT) SEM now allow samples to be observed in a frozen hydrated state, thereby avoiding the artifacts associated with conventional specimen preparation. To evaluate this technique, healthy and Botrytis cinerea infected `Golden Delicious' apple fruit were collected, frozen in liquid nitrogen, examined and photographed in a Hitachi S-4100 SEM equipped with and Oxford CT 1500 Cryotrans System. Results indicated that LT SEM (1) retained soluble materials such as platelets of the epicuticular wax; (2) preserved tissues in varying degrees of hydration and (3) maintained loosely associated structures such as spores and hyphae. These results suggest that LT SEM has potential applications to many horticultural problems.

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MN55 is an apple (Malus ×domestica Borkh.) cultivar recently released by the University of Minnesota apple breeding program, with fruit marketed in the U.S. as Rave®. When stored for 4 months at 0 to 4 °C, MN55 fruit can develop several storage disorders, including skin dimpling. Skin dimpling incidence was greater for fruit harvested 1 week later than those harvested earlier. Dimpling was not alleviated by prestorage treatments of 1-methylcyclopropene or diphenylamine or by holding fruit at room temperature for 1 day before long-term cold storage. However, dimpling incidence was very low when fruit were stored at 6 to 7 °C. Because viruses have been implicated in other fruit dimpling disorders, the presence of viruses in MN55 leaves and fruit was studied. Apple stem pitting virus (ASPV) was detected by microscopy, reverse transcriptase polymerase chain reaction (RT-PCR) methodology, and high throughput sequencing (HTS) in peel of fruit from MN55 trees that exhibited skin dimpling after 4 months of storage at 0 to 1 °C. ASPV was also detected in supermarket-purchased fruit of other cultivars with noticeable skin dimpling. Although ASPV was not conclusively demonstrated to cause skin dimpling in our work, its prevalence indicates that further investigations are warranted to determine the relationship between viruses and skin deformities in stored apples.

Open Access

Strawberries (Fragaria ×ananassa) are one of the major high-value crops in North America. There is increasing interest in commercial strawberry production for local markets in Virginia and surrounding states, but information on the performance of newer cultivars is extremely limited. We tested 10 commercially available June-bearing cultivars [Benicia, Camarosa, Camino Real, Chandler, Strawberry Festival, Flavorfest, FL Radiance, Treasure, Sweet Charlie, and Winterstar™ (FL 05-107)] and two day-neutral cultivars (Albion and San Andreas) for their spring and summer fruiting capacity in Virginia production systems in a randomized, replicated study, at three on-farm locations. Data were collected on vegetative growth, yield performance, fruit quality, sweetness, and fruit diameter. Cultivars with the highest total yields averaged across all three locations were Benicia, Camino Real, Chandler, and Camarosa. ‘Camino Real’ had the highest marketable yield at all three locations, not significantly different from ‘Chandler’, and ‘Benicia’ and ‘Camarosa’ had the highest marketable yield at two of the three locations. ‘Flavorfest’ and ‘Sweet Charlie’ had the highest total soluble solids concentration for the harvest season. Overall, for all locations, ‘Benicia’ and ‘Camino Real’ had the largest fruit diameter, and ‘Strawberry Festival’ had the smallest fruit diameter.

Open Access

Prestorage heat treatment of apples has been shown to have a positive effect on fruit quality in storage. Postharvest treatment of apples with CaCl2 also beneficially affected fruit during storage. However, calcium uptake seems limited in heat-treated apples which indicates that the surface of the fruit may have been affected by the heat treatment. This study examined the effect of heat treatment on the subsequent uptake of CaCl2 solutions and related this process to the ultrastructure of the epicuticular wax surface of the fruit. Apples were pressure infiltrated with a 4% CaCl2 solution either without heat treatment or following 4 days at 38°C. Examination of the apple surfaces with low temperature scanning electron microscopy revealed that heat treatment changed the pattern of epicuticular wax. The epicuticular wax of non heated fruit exhibited numerous deep surface cracks. The epicotictdar wax of heated fruit did not exhibit similar cracks. This apparent obstruction or elimination of deep cracks may limit the CaCl2, solutions from entering the fruit. The heated fruit contained significantly less calcium compared to the fruit that were pressure infiltrated with the CaCl2 solution but not heated. These results indicate that cracks on the fruit surface may be a” important pathway for the penetration of CaCl2 solutions.

Free access

Structural changes in the cuticle could be partially responsible for the differences in uptake of infiltrated Ca in apple fruit. We examined the relationship between the surface structure of epicuticular wax of `Golden Delicious' apple and Ca uptake by the fruit. Apples were nontreated or pressure infiltrated with distilled water, or with 0.14 or 0.27 mol·L-1 CaCl2 solutions 2 weeks before optimum harvest time, at optimum harvest, or after 2, 4, or 6 months of storage at 0 °C. Examination of the fruit surface with low-temperature scanning electron microscopy revealed that cracks in the epicuticular wax became wider and deeper as storage duration increased. After 6 months of storage, the cracks extended through the cuticle. Uptake of Ca by the infiltrated fruit was greater after 6 months of storage than after shorter storage intervals. These data indicate that as storage duration increased, epicuticular wax cracks became deeper and Ca uptake by the fruit increased.

Free access

`Golden Delicious' apples (Malus domestica Borkh) were pressure-infiltrated at harvest with a 4% CaCl2 solution either without prior heat treatment or following 4 days at 38C. Examination of the apple surfaces from both treatments by low-temperature scanning electron microscopy revealed that heat treatment changed the pattern of epicuticular wax. The epicuticular wax of nonheated fruit exhibited numerous deep surface cracks that formed an interconnected network on the fruit surface. The epicuticular wax of heat-treated fruit did not exhibit a similar network of deep cracks. This apparent obstruction or elimination of deep cracks may limit the CaCl2 solutions from entering the fruit. The heated fruit contained significantly less Ca than the fruit that were pressure-infiltrated with CaCl2 solutions but not heated. These results indicate that cracks on the fruit surface may be an important pathway for the penetration of CaCl2 solutions.

Free access

`Golden Delicious' apples (Malus domestica Borkh) were dipped in either distilled water, methylene chloride, or one of the following surfactants: Brij 30, Tween 20, Tween 80, Tergitol 15-S-9, and Triton X-100. The fruit then were pressure-infiltrated with a 2% solution of CaCl2. Following 4 months storage at 0 °C, fruit were removed and flesh Ca concentration analyzed. The fruit surface was observed using low-temperature scanning electron microscopy, and fruit were rated for surface injury. Brij 30 altered the epicuticular wax the least and resulted in the smallest increase in flesh Ca concentration and the softest fruit. Triton X-100 altered the epicuticular wax the most and resulted in the highest fruit flesh Ca concentration and firmest of the surfactant-pretreated fruit. Methylene chloride removed some of the epicuticular wax, and fruit pretreated with this solvent had the highest flesh Ca concentration and greatest firmness. However, all of the fruit treated with methylene chloride were severely injured.

Free access