Submitted to: Industrial Crops and Products
Publication Type: Abstract Only
Publication Acceptance Date: 8/1/1997
Publication Date: N/A
Technical Abstract: Phomopsis cucurbitae is a latent infecting pathogen that infects unripe muskmelon fruit but causes decay after harvest. This fungus causes severe losses during muskmelon fruit storage and marketing in the U. S., Japan and some Central American countries. Previous studies showed that the fungus produced the cell wall degrading enzyme polygalacturonase (PG) in both culture and muskmelon fruit tissue. The role of P. cucurbitae PG in the fruit decay process and its relating to latent infection is not well understood. A prominent PG isozyme produced by the fungus in decayed fruit was purified to homogeneity by a sequence of extraction, ultrafiltration, preparative isoelectric focusing, anion exchange, and gel filtration chromatography. This isozyme exhibited endo-activity, a molecular weight of 54 kD according to SDS-PAGE, and a pI of 4.2 based on IEF-PAGE. Isozyme activity was optimal at 40-45 deg C and pH 5.0. It had a Km of 44.7 ug/ml and a Vmax of 0.313. The purified isozyme also effectively macerated mature muskmelon fruit tissues. This isozyme was the most prominent of the PG isozymes produced by P. cucurbitae in decaying fruit, and may play an important role in postharvest decay of cantaloupe fruit.