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The midgut is a key tissue in insect science. Physiological roles include digestion and peritrophic membrane function, as well as being an important target for insecticides. We used an expressed sequence tag (EST) approach to identify candidate genes and gene families involved in these processes in the light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae). Two cDNA libraries were constructed from dissected midgut of third to fifth instar larvae. Clustering analysis of 6416 expressed sequence tags produced 1178 tentative unique genes comprising 725 tentative contigs and 453 singletons. The sequences show similar codon usage to sequences from other lepidopterans, a Kozak consensus sequence similar to Drosophila and single nucleotide polymorphisms (SNPs) were detected at a frequency of 1.35/kb. The identity of the most common Interpro families correlates well with major known functions of the midgut. Phylogenetic analysis was conducted on representative sequences from selected multigene families. Gene families include a broad range of digestive proteases, lipases and carbohydrases that appear to have degradative capacity against the major food components found in leaves, the diet of these larvae; and carboxylesterases, glutathione-S-transferases and cytochrome P450 monooxygenases, potentially involved in xenobiotic degradation. Two of the larger multigene families, serine proteases and lipases, expressed a high proportion of genes that are likely to be catalytically inactive.

Tubers of 23 potato cultivars and breeding lines were assessed for susceptibility to infection by Erwinia carotovora subsp. atroseptica (Eca) over five maincrop seasons between 1984 and 1989. Susceptibility to Eca-induced soft rot was determined by measuring the weight of rotted tissue in anaerobically incubated whole tubers 6 days after inoculation with Eca. Potato lines differed in susceptibility to soft rot. Lines ‘1463.1’, ‘Bison’, and ‘Rua’ were consistently very susceptible, and ‘Kaipara’, ‘064/18’, and ‘065/27’ were least susceptible to Eca-induced soft rot.

Cutins from fruit of Cucurbita maxima and Cucurbita moschata cultivars, apple and a C(16) alcohol (hexadecanol) were used to induce cutinolytic esterase activity during saprophytic growth of strains of the two cucurbit pathogens, Fusarium solani f. sp. cucurbitae, race 1 (Nectria haematococca mating population (MPI) and F. solani f. sp. cucurbitae, race 2 (MPV). Four strains of MPV and 11 strains of MPI were were included in the study. Although we were primarily interested in the two cucurbit pathogens (MPI and MPV), six strains of the pea pathogen F. solani f. sp. pisi (MPVI) were included to provide a comparison since most of the knowledge on cutinase activity in N. haematococca has come from a study of that group. Cutinolytic esterase was induced in all strains from both MPV and MPVI but was not detected in any of the 11 strains from MPI regardless of the induction conditions. The amount of cutinolytic esterase activity induced in the MPV strains differed according to the strain and both the source and the amount of cutin used in the induction medium. Information on the influence of cutin source and pH on the induction of cutinolytic esterase activity during saprophytic growth of strains from MPV demonstrates that the gene is regulated differently from that in MPVI.