LAUSR

Phytophthora capsici is a destructive pathogen of cucurbits causing root, crown, and fruit rot. Winter squash (Cucurbita sp.) production is limited by this pathogen in Michigan and other U.S. growing regions. Age-related resistance (ARR) to P. capsici occurs in Cucurbita moschata fruit but is negated by wounding. The objective of this research was to determine if structural barriers to infection exist in the intact exocarp of maturing fruit exhibiting ARR. Five C. moschata cultivars were evaluated for resistance to P. capsici 10, 14, 16, 18, and 21 days post pollination (dpp). Scanning electron microscopy (SEM) imaging of 'Chieftain' butternut fruit exocarp at susceptible 7 dpp and resistant 14 dpp and 21 dpp revealed significant increases in the cuticle and epidermal thicknesses as fruit age. P. capsici hyphae penetrated susceptible fruit 7 dpp directly from the surface or through wounds before 6-hour post inoculation (hpi) and completely degraded the fruit cell wall within 48 hpi. Resistant fruit, 14 dpp, and 21 dpp remained unaffected. The high correlation between the formation of a thickened cuticle and epidermis in maturing winter squash fruit and resistance to P. capsici indicates the presence of a structural barrier to P. capsici as the fruit matures.