Phytopathology. 1998 May;88(5):389-95. doi: 10.1094/PHYTO.1998.88.5.389.
ABSTRACT Phytophthora nicotianae and P. palmivora infect and cause rot of fibrous roots of susceptible and tolerant citrus rootstocks in Florida orchards. The infection and colonization by the two Phytophthora spp. of a susceptible citrus host, sour orange (Citrus aurantium), and a tolerant host, trifoliate orange (Poncirus trifoliata), were compared using light and electron microscopy. Penetration by both Phytophthora spp. occurred within 1 h after inoculation, regardless of the host species. No differences were observed in mode of penetration of the hypodermis or the hosts' response to infection. After 24 h, P. palmivora had a significantly higher colonization of cortical cells in susceptible sour orange than in tolerant trifoliate orange. Intracellular hyphae of both Phytophthora spp. were observed in the cortex of sour orange, and cortical cells adjacent to intercellular hyphae of P. palmivora were disrupted. In contrast, the cortical cells of sour orange and trifoliate orange adjacent to P. nicotianae hyphae and the cortical cells of trifoliate orange adjacent to P. palmivora were still intact. After 48 h, the cortical cells of both hosts adjacent to either Phytophthora spp. were disrupted. After 48 and 72 h, P. palmivora hyphae colonized the cortex of sour orange more extensively than the cortex of trifoliate orange; P. palmivora also colonized both hosts more extensively than P. nicotianae. A higher rate of electrolyte leakage among host-pathogen combinations reflected the combined effects of greater cell disruption by P. palmivora than by P. nicotianae, and the higher concentration of electrolytes in healthy roots of trifoliate orange than of sour orange. Although cellular responses unique to the tolerant host were not observed, reduced hyphal colonization by both pathogens in the cortex of trifoliate orange compared with sour orange is evidence for a putative resistance factor(s) in the trifoliate orange roots that inhibits the growth of Phytophthora spp.
疫霉菌和棕榈疫霉菌会感染和导致佛罗里达果园中敏感和耐受柑橘砧木的纤维根腐烂。使用光镜和电子显微镜比较了两种疫霉菌对敏感柑橘宿主酸橙（Citrus aurantium）和耐受宿主三叶橙（Poncirus trifoliata）的感染和定殖。无论宿主种类如何，两种疫霉菌在接种后 1 小时内均发生穿透。在穿透下皮层或宿主对感染的反应方面，没有观察到差异。24 小时后，棕榈疫霉菌在敏感酸橙的皮层细胞中的定植率明显高于耐受三叶橙。在酸橙的皮层中观察到两种疫霉菌的细胞内菌丝，而与棕榈疫霉菌胞间菌丝相邻的皮层细胞被破坏。相比之下，酸橙和三叶橙的皮层细胞与疫霉菌菌丝相邻的细胞和与棕榈疫霉菌相邻的三叶橙的皮层细胞仍然完整。48 小时后，两种宿主相邻的皮层细胞均被破坏。48 和 72 小时后，棕榈疫霉菌在酸橙皮层中的定殖范围比三叶橙更广；棕榈疫霉菌在酸橙和三叶橙中的定殖范围也比疫霉菌更广。较高的电解质泄漏率反映了疫霉菌比疫霉菌造成的细胞破坏更大，以及三叶橙健康根系中电解质浓度比酸橙更高的综合影响。尽管没有观察到耐受宿主特有的细胞反应，但与酸橙相比，两种病原体在三叶橙皮层中的定殖率降低，这表明三叶橙根系中存在抑制疫霉菌生长的潜在抗性因子。
