Submitted to: American Phytopathological Society
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/1996
Publication Date: N/A
Technical Abstract: Phomopsis cucurbitae causes serious postharvest losses of cantaloupe grown in the Southwestern U. S., Mexico, Costa Rica, Guatemala and Japan. P. cucurbitae in shake cultures using autoclaved fruit tissue (mesocarp) or pectin as carbon source produced both polygalacturonase (PG) and pectate lyase (PL). Eight PG and 4 PL isozymes were detected on IEF-PAGE from the shake culture using fruit mesocarp as the carbon source. When pectin was used as a sole carbon source, P. cucurbitae produced at least 14 PG and 4 PL isozymes, respectively. However, when ripe fruit was inoculated with P. cucurbitae, only 8 PG isozymes and no PL isozymes were detected from decayed tissue. The most prominent PG isozyme (PI 4.2) was purified from the pathogen decayed fruit for further characterization. Induction of fungal pectolytic isozymes in vitro is very different as compared to in vivo production. Differential fungal PG expression occurred when pectin was used as the sole carbon source as compared to in vivo, suggesting that pectin may stimulate a family of PG genes. Evidence suggests that PG isozymes may play an important role in tissue maceration following activation of the latent infection after harvest.