IASMA Research and Innovation Centre, Fondazione Edmund Mach, Via E. Mach 1, 38010 S. Michele all'Adige (TN), Italy.
J Agric Food Chem. 2009 Nov 11;57(21):10038-43. doi: 10.1021/jf902342b.
Erwinia amylovora causes fire blight, a serious disease of apple and pear. The bacterial pathogen colonizes the flower stigma and hypanthium, where it multiplies and then invades through natural openings (nectarthodes). E. amylovora requires nicotinic acid as growth factor, and competition for nicotinic acid is being explored as a novel biocontrol strategy. The ability of E. amylovora to substitute nicotinic acid with analogues or derivates as growth factors has not been investigated yet. Furthermore, the presence and/or variable concentration of nicotinic acid and its analogues/derivates in the hypanthium could be associated with the different susceptibilities to fire blight of hosts and nonhosts and with the differential sensitivity to the disease among apple and pear varieties. Currently, no methods to specifically quantify nicotinic acid and nicotinic acid analogues/derivates in the hypanthium of apple and pear blossoms are available. This study demonstrates that E. amylovora can grow using nicotinamide and 6-hydroxynicotinic acid as alternative growth factors to nicotinic acid, but not using 2-hydroxynicotinic acid. A novel HPLC/ES-MS method was developed for the detection and quantification of nicotinic acid and its analogues/derivates directly in the hypanthium of apple and pear blossoms. Analyses established the presence of nicotinic acid and nicotinamide, whereas no detectable amounts of 6-hydroxynicotinic acid and 2-hydroxynicotinic acid were observed. Mean nicotinic acid content in the pear hypanthium was found to be approximately 2 orders of magnitude higher than in the apple hypanthium, which may contribute to the differential susceptibility of these two host species to fire blight. Contents of nicotinamide were in contrast similar. Nicotinic acid can therefore be considered a relevant factor in the pathogen establishment in pear blossoms, whereas nicotinamide could cover a primary role in apple blossoms.
果胶杆菌引起火疫病，这是苹果和梨的一种严重疾病。该细菌病原体定植于花托和花被筒，在那里繁殖，然后通过自然开口（蜜腺）入侵。果胶杆菌需要烟酸作为生长因子，目前正在探索烟酸竞争作为一种新的生物防治策略。果胶杆菌是否能够用烟酸类似物或衍生物替代烟酸作为生长因子尚未得到研究。此外，花被筒中烟酸及其类似物/衍生物的存在和/或可变浓度可能与宿主和非宿主对火疫病的不同易感性以及苹果和梨品种对该病的不同敏感性有关。目前，尚无专门在苹果和梨花朵的花被筒中定量检测烟酸和烟酸类似物/衍生物的方法。本研究表明，果胶杆菌可以使用烟酰胺和 6-羟基烟酸作为替代生长因子来替代烟酸生长，但不能使用 2-羟基烟酸。开发了一种新的 HPLC/ES-MS 方法，用于直接在苹果和梨花朵的花被筒中检测和定量分析烟酸及其类似物/衍生物。分析结果表明存在烟酸和烟酰胺，但未检测到 6-羟基烟酸和 2-羟基烟酸。在梨花被筒中发现烟酸的含量大约比苹果花被筒高 2 个数量级，这可能导致这两个宿主物种对火疫病的不同易感性。烟酰胺的含量则相反相似。因此，烟酸可以被认为是该病原体在梨花朵中建立的一个相关因素，而烟酰胺在苹果花朵中可能发挥主要作用。
