David Obenland

Expansin protein levels decline with the development of mealiness in peaches

Expansin mRNA and protein expression in peaches was examined to investigate the possibility that expansins may be involved in the development of mealy flesh texture. Immunoblot analysis, using an expansin antibody, detected a 27kDa protein corresponding to the predicted molecular mass of expansins in the later stages of ripening but not in fullsize green fruit and indicated that expansin is associated with the progression of ripening in peaches. Peach cultivars ‘O’Henry’ and ‘Summer Lady’ were stored at 5 8C to induce the development of mealiness and individual fruit samples collected periodically to measure mealiness (free water) and provide samples for expansin quantification. Initially, stored fruit were juicy (50/60% free water), but as storage progressed they became visibly mealy at free water percentages of 30% for ‘O’Henry’ and 46% for ‘Summer Lady’. In both cultivars expansin protein abundance decreased as the fruit became mealy. Development of mealiness within individual fruit was often not uniform and lead to the existence of distinct juicy and mealy regions. Immunoblot analysis indicated that mealy regions contained substantially less expansin than juicy regions. Analysis of expansin mRNA abundance using a ripening-related expansin cDNA probe from peach indicated that expansin mRNA expression was also markedly reduced in mealy tissues. The relationship observed in this study between expansin expression and mealiness suggests a possible role for expansin in the development of the disorder. Published by Elsevier Science B.V.

Sodium chloride reduces damage to nectarines caused by hot water treatments

Abstract The tolerance of six nectarine ( Prunus persica L. Batch var. (Ait.) Maxim.) cultivars to hot water treatment was evaluated and the effect of addition of NaCl to the treatment solution tested as a means of reducing treatment damage. Hot water immersion was extremely damaging to all cultivars tested, although differences in tolerance existed. Treatment at 50°C for 25 min, a treatment for fruit fly disinfestation, rendered the fruit of all cultivars unmarketable. Sodium chloride at a concentration of 200 mM reduced the mean injury rating averaged over all six cultivars from 3.9 (severe damage) to 1.9 (slight damage), although the latter was still too severe for the fruit to be marketable. At the less injurious temperature of 46°C, the slight amount of injury caused by hot water treatment was eliminated in the presence of NaCl. Flesh firmness was not altered by NaCl in the treatment solution, but firmness was slightly greater in fruit treated at 50°C as compared with 46°C. Sodium chloride reduced damage by effectively reducing the amount of water entering the fruit during treatment and may be useful in reducing the damage from hot water immersion treatments used for surface disinfestation.

Postharvest Treatment of Fresh Fruit from California with Methyl Bromide for Control of Light Brown Apple Moth (Lepidoptera: Tortricidae)

ABSTRACT Methyl bromide (MB) chamber fumigations were evaluated for postharvest control of light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae), in fresh fruit destined for export from California. To simulate external feeding, larvae were contained in gas-permeable cages and distributed throughout loads of peaches, plums, nectarines (all Prunus spp.), apples (Malus spp.), raspberries (Rubus spp.), or grapes (Vitis spp.). Varying the applied MB dose and the differential sorption of MB by the loads resulted in a range of exposures, expressed as concentration x; time cross products (CTs) that were verified by gas-chromatographic quantification of MB in chamber headspace over the course of each fumigation. CTs ≥60 and ≥72 mg liter-1 h at 10.0 ± 0.5 and 15.6 ± 0.5°C ( ± s, average ±SD), respectively, yielded complete mortality of ≈ 6,200 larvae at each temperature. These confirmatory fumigations corroborate E. postvittana mortality data for the first time in relation to measured MB exposures and collectively comprise the largest number of larval specimens tested to date. In addition, a kinetic model of MB sorption was developed for the quarantine fumigation of fresh fruit based on the measurement of exposures and how they varied across the fumigation trials. The model describes how to manipulate the applied MB dose, the load factor, and the load geometry for different types of packaged fresh fruit so that the resultant exposure is adequate for insect control.