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Christian Chervin, Janyce K. Truett and Jim Speirs

Regulation of alcohol dehydrogenase (ADH), activity of pyruvate decarboxylase (PDC) and accumulation of acetaldehyde and ethanol in `Packham's Triumph' pears (Pyrus communis, L.) subsequent to different storage regimes were investigated. Pears were stored for two months at -1 °C either in air (Air) or under hypoxia at 3 kPa O2 (Hyp) and subsequently warmed and allowed to ripen in air at 20 °C. One set of fruit stored in air at -1 °C was subjected to 3 days of hypoxia at -1 °C (Air+Hyp) before ripening in air. Acetaldehyde, ethanol and methanol levels increased in all fruit in a similar fashion during ripening and did not reflect differences in storage treatments. During ripening, ADH activities in posthypoxic samples were generally twice that of air samples. PDC activities increased for ≈6 days during ripening then declined slightly but did not differ significantly among treatments. Upon transfer to 20 °C in air, slightly higher levels of Adh mRNA were observed in samples treated with hypoxia than in air controls. Over the following 2 days at 20 °C, the Adh transcription was markedly induced in Air and Air+Hyp samples. Although all Adh mRNAs returned to control levels within 4 days, ADH activities remained higher in hypoxia-treated fruit than in controls for up to 18 days. These results suggest that, in ripening pears, ADH does not limit ethanol production, and that the expression of this enzyme comprises post-transcriptional regulations. GenBank accession numbers of the Adh cDNAs are AFO 31899 and AFO 31900.

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Christian Chervin, Peter Franz, Sarita Kulkarni, Steve Whitmore and Graeme McGregor

Insect feeding traces on fruit are a major concern to orchardists. Breeding fruit for insect resistance is becoming more important as available pesticides are limited by more stringent regulations, problems of insect resistance, and residue limits. We present a method to analyze fruit skin damage via treatment of video images. This aspect has not been well studied to date, but would allow a more rapid assessment of fruit resistance to insects in breeding programs. The method uses equipment available on the world video and computer markets. Over 24 hours, larvae of lightbrown apple moth [Epiphyas postvittana Walker (Lepidoptera: Tortricidae)] were permitted to chew restricted areas of skin on the pear cultivars Sensation Red Bartlett, Packham's Triumph, Doyenne du Comice, Beurre d'Anjou, and Corella (Pyrus communis L.); Twentieth Century (Pyrus pyrifolia Burm. Nak.); Ya Li (Pyrus ×bretschneideri Rehd.); and F1 hybrids of `Packham's Triumph' × `Twentieth Century'. Optimum experimental conditions and statistical analyses are described and sensitivity of the various cultivars is discussed. The method allowed us to identify some highly resistant and sensitive pear hybrids. The ability to rapidly screen F1 hybrids for insect resistance may encourage breeders to incorporate such a factor in breeding programs, and should hasten the release of resistant cultivars. The application of this technique in the orchard is discussed. The method also allows the analysis of various aspects of larval feeding, such as number and size of wounds, which may be responses to various fruit skin defense systems.