Zhou X G, Everts K L
University of Maryland, Lower Eastern Shore Research and Education Center, 27664 Nanticoke Road, Salisbury, 21801.
University of Maryland, Lower Eastern Shore Research and Education Center, 27664 Nanticoke Road, Salisbury, 21801 and University of Delaware, 16684 County Seat Highway, Georgetown, 19947.
Plant Dis. 2003 Jun;87(6):692-698. doi: 10.1094/PDIS.2003.87.6.692.
A survey was conducted to determine races and inoculum density of Fusarium oxysporum f. sp. niveum, the causal agent of Fusarium wilt of watermelon in Maryland and Delaware. Virulence on six differential cultivars was tested for each of 63 isolates of F. oxysporum f. sp. niveum, obtained from 25 commercial watermelon fields. Thirteen isolates (21%) were identified as race 0, 36 isolates (57%) as race 1, and 14 isolates (22%) as race 2. Races 0 and 1 were present in 12 (48%) and 10 (40%) of the fields, respectively. The highly aggressive race 2 was identified from five fields in two counties in Maryland and from one field in Delaware, representing 24% of the fields. Race 2 was copresent with one or two other races. Race 2 (19 isolates) predominated among the 25 isolates obtained from a research field in Maryland. Nineteen commercial fields had inoculum densities of F. oxysporum f. sp. niveum ranging from 100 to 1,200 CFU/g of soil at harvest. Within this range of inoculum densities, >20% incidence of wilt was observed when the susceptible watermelon cv. Sugar Baby was planted in samples of soil collected from these fields. The relationship (P < 0.0001) between inoculum density of F. oxysporum f. sp. niveum (X) and incidence of Fusarium wilt (Y) on Sugar Baby was best described using the monomolecular equation, Y = 1 - exp. The ratio of pathogenic to total population of F. oxysporum in the fields linearly increased with increasing inoculum density of F. oxysporum f. sp. niveum (R = 0.4; P < 0.0009).
开展了一项调查，以确定尖孢镰刀菌西瓜专化型（Fusarium oxysporum f. sp. niveum）的小种及接种体密度，该病菌是马里兰州和特拉华州西瓜枯萎病的致病因子。对从25个商业西瓜田采集的63株尖孢镰刀菌西瓜专化型菌株，检测了其对6个鉴别品种的毒力。13株菌株（21%）被鉴定为0号小种，36株菌株（57%）为1号小种，14株菌株（22%）为2号小种。0号和1号小种分别存在于12个（48%）和10个（40%）田块中。高侵袭性的2号小种从马里兰州两个县的5个田块以及特拉华州的1个田块中鉴定出来，占田块总数的24%。2号小种与一或两个其他小种共存。在从马里兰州一个研究田块获得的25株菌株中，以2号小种（19株）为主。19个商业田块在收获时尖孢镰刀菌西瓜专化型的接种体密度为每克土壤100至1200 CFU。在此接种体密度范围内，当在从这些田块采集的土壤样本中种植易感西瓜品种“甜心宝贝”（Sugar Baby）时，观察到枯萎病发病率>20%。尖孢镰刀菌西瓜专化型的接种体密度（X）与“甜心宝贝”上枯萎病发病率（Y）之间的关系（P < 0.0001）用单分子方程Y = 1 - exp能得到最佳描述。田间尖孢镰刀菌致病型与总菌量的比例随尖孢镰刀菌西瓜专化型接种体密度的增加呈线性增加（R = 0.4；P < 0.0009）。
