Krasnow Charles S, Hammerschmidt Raymond, Hausbeck Mary K
Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing 48824.
Plant Dis. 2017 May;101(5):659-665. doi: 10.1094/PDIS-06-16-0867-RE. Epub 2017 Mar 14.
Root and crown rot incited by Phytophthora capsici causes considerable annual losses in squash-producing regions in the United States. 'Spineless Perfection' zucchini and 'Cougar' straightneck squash (Cucurbita pepo L.), partially resistant and susceptible to root and crown rot, respectively, were investigated for differences in root and crown physical factors and the histology of crown infection by P. capsici. The pH and titratable acidity of healthy root and crown tissue from tissue extracts were not significantly different between cultivars (P = 0.05). Crude fiber content (%) of blended and oven-dried root and crown tissue from healthy plants was similar between cultivars. However, dry matter (%) was highest for Cougar (P = 0.05). Colonies of P. capsici grown from mycelial plugs in root exudates collected from each cultivar were similar in diameter. Whole mounts and histological sections of healthy and infected crown tissue revealed that vascular bundles and metaxylem vessels were more abundant in crowns of Spineless Perfection than Cougar. Twelve to 48 h post inoculation (hpi), mycelia in the crown of each cultivar was limited to the cortex and hypodermal tissue. By 72 hpi, hyphae were observed in the cortex and endodermal tissue of Cougar and were concentrated in the phloem and parenchyma cells surrounding vascular bundles. Mycelia were limited to the outer cortex in Spineless Perfection. Mycelia and occluding material were present in the majority of metaxylem vessels of Cougar but not Spineless Perfection at 92 hpi; dissolution of parenchyma cells surrounding vascular bundles was apparent in Cougar. The vascular occlusions observed in Cougar may be responsible for plant wilting, a common disease symptom. Additional straightneck, crookneck, scallop, and acorn squash (C. pepo ssp. ovifera), and zucchini, marrow, and pumpkin (C. pepo ssp. pepo) cultivars were evaluated in a greenhouse study for resistance to root and crown rot. Cucurbita pepo ssp. ovifera cultivars were significantly more susceptible than C. pepo ssp. pepo to root and crown rot (P < 0.0001). Growing C. pepo ssp. pepo cultivars may be beneficial in an integrated Phytophthora management program.
由辣椒疫霉引起的根腐病和冠腐病在美国南瓜种植区每年造成相当大的损失。分别对部分抗根腐病和冠腐病的“无刺完美”西葫芦以及感病的“美洲狮”直颈南瓜（西葫芦种）进行了研究，分析其根和冠部物理因素以及辣椒疫霉对冠部感染的组织学差异。各品种间来自组织提取物的健康根和冠组织的pH值和可滴定酸度无显著差异（P = 0.05）。各品种间健康植株经混合和烘干的根与冠组织的粗纤维含量（%）相似。然而，“美洲狮”的干物质含量（%）最高（P = 0.05）。从各品种收集的根分泌物中菌丝块长出的辣椒疫霉菌落直径相似。健康和受感染冠组织的整装片和组织切片显示，“无刺完美”冠部的维管束和后生木质部导管比“美洲狮”更多。接种后12至48小时（hpi），各品种冠部的菌丝体局限于皮层和皮下组织。到72 hpi时，在“美洲狮”的皮层和内皮层组织中观察到菌丝，且集中在维管束周围的韧皮部和薄壁细胞中。“无刺完美”的菌丝体局限于外层皮层。在92 hpi时，“美洲狮”的大多数后生木质部导管中有菌丝体和堵塞物质，而“无刺完美”中没有；“美洲狮”中维管束周围薄壁细胞的溶解明显。在“美洲狮”中观察到的维管束堵塞可能是植物萎蔫这一常见病害症状的原因。在温室研究中还对其他直颈南瓜、弯颈南瓜、扇贝南瓜、橡子南瓜（西葫芦亚种）以及西葫芦、笋瓜和南瓜（西葫芦亚种）品种进行了根腐病和冠腐病抗性评估。西葫芦亚种品种比西葫芦亚种品种对根腐病和冠腐病更易感（P < 0.0001）。种植西葫芦亚种品种可能有利于综合疫霉病管理计划。
