Bell Alois A, Wheeler Michael H, Liu Jinggao, Stipanovic Robert D, Puckhaber Lorraine S, Orta Heather
USDA-ARS-SPARC, 2765 F&B Road, College Station, TX 77845, USA.
Pest Manag Sci. 2003 Jun-Jul;59(6-7):736-47. doi: 10.1002/ps.713.
A group of 133 isolates of the cotton wilt pathogen Fusarium oxysporum Schlecht f sp vasinfectum (Atk) Sny & Hans, representing five races and 20 vegetative compatibility groups within race 1 were used to determine the identity, biosynthetic regulation and taxonomic distribution of polyketide toxins produced by this pathogen. All isolates of F oxysporum f sp vasinfectum produced and secreted the nonaketide naphthazarin quinones, bikaverin and norbikaverin. Most isolates of race 1 (previously denoted as races 1, 2 and 6; and also called race A) also synthesized the heptaketide naphthoquinones, nectriafurone, anhydrofusarubin lactol and 5-O-methyljavanicin. Nine avirulent isolates of F oxysporum from Upland cotton roots, three isolates of race 3 of F oxysporum f sp vasinfectum, and four isolates of F oxysporum f sp vasinfectum from Australia, all of which previously failed to cause disease of Upland cotton (Gossypium hirsutum L) in stem-puncture assays, also failed to synthesize or secrete more than trace amounts of the heptaketide compounds. These results indicate that the heptaketides may have a unique role in the virulence of race 1 to Upland cotton. The synthesis of all polyketide toxins by ATCC isolate 24908 of F oxysporum f sp vasinfectum was regulated by pH, carbon/nitrogen ratios, and availability of calcium in media. Synthesis was greatest below pH 7.0 and increased progressively as carbon/nitrogen ratios were increased by decreasing the amounts of nitrogen added to media. The nonaketides were the major polyketides accumulated in synthetic media at pH 4.5 and below, whereas the heptaketides were predominant at pH 5.0 and above. The heptaketides were the major polyketides formed when 10 F oxysporum f sp vasinfectum race 1 isolates were grown on sterilized stems of Fusarium wilt-susceptible cotton cultivars, but these compounds were not produced on sorghum grain cultures. Both groups of polyketide toxins were apparently secreted by F oxysporum f sp vasinfectum, since half of the toxin in 2-day-old shake culture was present in the supernatant. Secretion was enhanced by calcium. Glutamine and glutamic acid inhibited both nonaketide and heptaketide syntheses, even at low nitrogen
选用了133株棉花枯萎病病原菌尖孢镰刀菌（Fusarium oxysporum Schlecht f sp vasinfectum (Atk) Sny & Hans）分离株，它们代表5个生理小种以及生理小种1内的20个营养体亲和群，用于确定该病原菌产生的聚酮类毒素的特性、生物合成调控及分类分布。所有尖孢镰刀菌棉花专化型分离株均产生并分泌九酮萘并萘醌、比卡韦林和去甲比卡韦林。生理小种1的大多数分离株（以前称为生理小种1、2和6；也称为生理小种A）还合成七酮萘醌、镰孢菌素、脱水镰孢红素内酯和5-O-甲基爪哇菌素。来自陆地棉根的9株尖孢镰刀菌无毒分离株、3株尖孢镰刀菌棉花专化型生理小种3分离株以及4株来自澳大利亚的尖孢镰刀菌棉花专化型分离株，在茎穿刺试验中均未能引起陆地棉（Gossypium hirsutum L）发病，它们也未能合成或分泌超过痕量的七酮类化合物。这些结果表明，七酮类化合物可能在生理小种1对陆地棉的致病性中具有独特作用。尖孢镰刀菌棉花专化型ATCC分离株24908产生的所有聚酮类毒素的合成受pH值、碳/氮比以及培养基中钙的可用性调控。在pH值低于7.0时合成量最大，并且随着通过减少培养基中添加的氮量来提高碳/氮比，合成量逐渐增加。在pH值为4.5及以下时，九酮类化合物是合成培养基中积累的主要聚酮类化合物，而在pH值为5.0及以上时，七酮类化合物占主导。当10株尖孢镰刀菌棉花专化型生理小种1分离株在对枯萎病敏感的棉花品种的无菌茎上生长时形成的主要聚酮类化合物是七酮类化合物，但在高粱籽粒培养基上不产生这些化合物。两组聚酮类毒素显然都是由尖孢镰刀菌棉花专化型分泌的，因为在2日龄振荡培养物中，一半的毒素存在于上清液中。钙可增强分泌。谷氨酰胺和谷氨酸即使在低氮水平下也能抑制九酮类和七酮类化合物的合成。
