Changes in Winter Squash Fruit Exocarp Structure Associated with Age-Related Resistance to Phytophthora capsici

Abstract

Phytophthora capsici is a destructive pathogen of cucurbits that causes root, crown, and fruit rot. Winter squash (Cucurbita spp.) production is limited by this pathogen in Michigan and other U.S. growing regions. Age-related resistance (ARR) to P. capsici occurs in C. moschata fruit but is negated by wounding. This study aimed to determine whether 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 postpollination (dpp). Scanning electron microscopy imaging of Chieftain butternut fruit exocarp of susceptible fruit at 7 dpp and resistant fruit at 14 and 21 dpp revealed significant increases in cuticle and epidermal thicknesses as fruit aged. P. capsici hyphae penetrated susceptible fruit at 7 dpp directly from the surface or through wounds before 6 h postinoculation (hpi) and completely degraded the fruit cell wall within 48 hpi. Resistant fruit remained unaffected at 14 and 21 dpp. 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.

Developmentally regulated activation of defense allows for rapid inhibition of infection in age-related resistance to Phytophthora capsici in cucumber fruit

“…Furthermore, methanolic extracts from resistant-aged peels had inhibitory effects on pathogen growth and cucumber peels of resistant-aged fruit vs. susceptible age are enriched for genes associated with defense against biotic and abiotic stresses [14]. ARR to P. capsici also has been observed in whole pepper plants [4], chile pepper fruit [23], and several cucurbit fruits [6,10]. Similar to cucumber, wounding overcame the resistance in chili pepper fruit and squash.…”

“…Similar to cucumber, wounding overcame the resistance in chili pepper fruit and squash. The ARR in pepper and squash was suggested to result from structural changes in fruit surface properties such as cuticle thickness or cell wall lignification [10,23].…”

“…Evidence from various systems suggests possible physical, chemical, or physiological changes that may result from age-dependent, non-pathogen specific investment in defense such as cell wall modifications, production of anti-microbial phytoanticipins, or altered hormone balance [ 2 , 9 , 10 ]. There are also some examples where ARR may result from developmentally regulated expression of a pathogen receptor.…”

Developmentally regulated activation of defense allows for rapid inhibition of infection in age-related resistance toPhytophthora capsiciin cucumber fruit

“…Evidence from various systems suggests possible physical, chemical, or physiological changes that may result from age-dependent, non-pathogen specific investment in defense such as cell wall modifications, production of anti-microbial phytoanticipins, or altered hormone balance [2, 9, 10]. There are also some examples where ARR may result from developmentally regulated expression of a pathogen receptor.…”

“…Furthermore, methanolic extracts from resistant-aged peels had inhibitory effects on pathogen growth and cucumber peels of resistant-aged fruit vs. susceptible age are enriched for genes associated with defense against biotic and abiotic stresses [14]. ARR to P. capsici also has been observed in whole pepper plants [4], chile pepper fruit [23], and several cucurbit fruits [6, 10]. Similar to cucumber, wounding overcame the resistance in chili pepper fruit and squash.…”