Harveson R M, Rush C M
Department of Plant Pathology, University of Florida, P.O. Box 110680, Gainesville 32611.
Texas A & M University System, Texas Agricultural Experiment Station, P.O. Drawer 10, Bushland 79012.
Plant Dis. 1998 Sep;82(9):1039-1042. doi: 10.1094/PDIS.1998.82.9.1039.
Fusarium root rot, caused by Fusarium oxysporum f. sp. betae is one of several root diseases damaging to sugar beet production in Texas. As a primary symptom, most isolates produce a severe tip rot on the distal end of the taproot, in addition to discoloration of vascular elements and wilting. Tip rot distinguishes Fusarium root rot from another F. oxysporum f. sp. betae-incited disease, Fusarium yellows, which induces vascular discoloration and wilting but no root rot. This study was conducted to further characterize a selection of five Texas F. oxysporum f. sp. betae isolates representing different vegetative compatibility groupings, symptom types (tip rot, and non-tip rot), and hosts. Radial growth at six temperatures was measured for each isolate in culture on half-strength potato dextrose agar. Significant growth differences were detected, indicating a substantial amount of variation among the isolates. Virulence of isolates was evaluated by inoculating 6-week-old sugar beet plants with a microspore suspension and transplanting them into infested field soil. The plants were incubated at 20 and 30°C in controlled temperature boxes within the greenhouse and grown under two different irrigation schedules. After 6 weeks, plants were harvested and assigned a root disease rating, and root and foliar dry weights were determined. Disease ratings among isolates at 30°C resulted in three isolates (all tip rot isolates) being severe, one mild, and one intermediate. At 20°C, only one isolate caused appreciable root damage. Irrigation treatments had no effect on disease incidence or severity. Significant differences in colony diameter growth and virulence among isolates at the two temperatures provide further evidence of variation among Texas F. oxysporum f. sp. betae populations. Results also suggest that the tip rot phenotype may be induced by some genetic factor unique to tip rot isolates. Therefore, the form name F. oxysporum f. sp. radicis-betae is proposed for those isolates from Texas causing a tip rot.
由尖孢镰刀菌甜菜专化型（Fusarium oxysporum f. sp. betae）引起的镰刀菌根腐病是德克萨斯州危害甜菜生产的几种根病之一。作为主要症状，大多数分离株除了导致维管束变色和萎蔫外，还会在主根远端产生严重的根尖腐烂。根尖腐烂将镰刀菌根腐病与另一种由尖孢镰刀菌甜菜专化型引起的病害——镰刀菌黄化病区分开来，后者会导致维管束变色和萎蔫，但不会引起根腐。本研究旨在进一步表征从德克萨斯州选取的5株尖孢镰刀菌甜菜专化型分离株，这些分离株代表了不同的营养亲和群、症状类型（根尖腐烂和非根尖腐烂）以及寄主。在半强度马铃薯葡萄糖琼脂培养基上，测定了每个分离株在6个温度下的径向生长。检测到显著的生长差异，表明分离株之间存在大量变异。通过用小孢子悬浮液接种6周龄的甜菜植株并将其移植到受侵染的田间土壤中来评估分离株的毒力。将植株在温室中的控温箱中于20℃和30℃下培养，并在两种不同的灌溉方案下生长。6周后，收获植株并给予根病评级，同时测定根和叶的干重。在30℃下，分离株之间的病害评级结果为3个分离株（均为根尖腐烂分离株）病情严重，1个分离株病情轻微，1个分离株病情中等。在20℃下，只有1个分离株引起了明显的根部损伤。灌溉处理对发病率或病情严重程度没有影响。两个温度下分离株在菌落直径生长和毒力方面的显著差异进一步证明了德克萨斯州尖孢镰刀菌甜菜专化型种群之间的变异。结果还表明，根尖腐烂表型可能是由根尖腐烂分离株特有的某些遗传因素诱导的。因此，对于来自德克萨斯州导致根尖腐烂的那些分离株，建议使用新的专化型名称尖孢镰刀菌甜菜根专化型（F. oxysporum f. sp. radicis-betae）。
