Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/1998
Publication Date: N/A
Interpretive Summary: The cucurbit family is extremely diverse and comprises important horticultural crops grown from the tropics to semi-arid desert where supplemental irrigation is available. Within the cucurbits, the major cultivated species are cucumber, muskmelon, pumpkin, squash, and watermelon. Cucurbit diseases caused by Fusarium spp. are responsible for the greatest losses in yield due to fruit rot and can cause severe postharvest losses as well. Little is known about the fruit rots caused by Fusarium spp. One of the more important fungal species involved in fruit rot of cucurbits is Fusarium solani. We established that the polygalacturonase enzymes play a role in the decay of fruit by this fungus. The enzyme was purified, characterized, and assayed for its ability to macerate fruit tissue. In addition, the enzyme was sequenced using molecular techniques which may ultimately allow the introduction of genes into cucurbit plants that would interfere or block the polygalacturonase enzymes. This could provide a control method greatly reducing the need for pesticides and enhancing the margin of food safety.
Technical Abstract: Fusarium solani is one of the most important fungal pathogens involved in pre- and post-harvest decay of muskmelon fruit. Production of polygalacturonase (PG), a cell wall-degrading enzyme, by F. solani was studied in vitro and in vivo. The fungus produced at least 13 PG isozymes with pIs of 4.5 to 9.7 in shake culture using pectin as the carbon source. In contrast, only one PG isozyme (pI 9.7) was detected in extracts from inoculated fruit tissue. The PG isozyme was purified to homogeneity by protein extraction, ultrafiltration, gel filtration, and cation exchange chromatography. The molecular weight of the isozyme was estimated at 38 kDa based on SDS-PAGE with a pI of 9.7 according to IEF-PAGE. According to TLC plate assay, the enzyme demonstrated only endo-PG activity. The optimum pH for activity was 5, with an activity range between 3 and 11. The Km and Vmax of the enzyme using polygalacturonic acid as the substrate were 1.34 mg/ml and 0.30 units/ug protein, respectively. The purified PG effectively macerated fruit tissue which suggests that it may play an important role in decay of muskmelon fruit caused by F. solani.