Myrtle rust (MR) caused by Austropuccinia psidii is one of the most important diseases affecting eucalypt (Eucalyptus) plantations in Brazil. Over the years, selection and planting of MR‐resistant clones has been the primary strategy for MR management. In May 2013, young trees of the GG100 hybrid (E. grandis × E. urophylla) clone—widely planted in Brazil and previously classified as resistant to MR—were infected by A. psidii in Minas Gerais, Brazil. In this study, artificial inoculations of a eucalypt clone set with differential reactions to A. psidii races were used to discover a new race of A. psidii (race 5) that was highly aggressive on the majority of eucalypt clones tested. In addition, only this new race successfully infected eucalypt G26 and 847 genotypes, which were formerly classified as resistant to the four previously known races of A. psidii. Since G26 genotype is homozygous for Ppr1 (a major resistance gene against A. psidii), this is the first report of MR resistance breakdown in a eucalypt genotype homozygous for Ppr1. Our findings demonstrate that this new A. psidii race is highly aggressive and capable of infecting a larger number of eucalypt genotypes compared with the previously known A. psidii races 1, 2, 3, and 4.

中文翻译：

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一个新的，具有侵略性的澳洲紫薇种族感染了巴西种植广泛的，具有桃金娘防锈，桉树的基因型

澳洲紫薇引起的紫薇锈病（MR）是影响巴西桉树（Eucalyptus）种植园的最重要疾病之一。多年来，MR抗性克隆的选择和种植一直是MR管理的主要策略。在2013年5月，该GG100混合幼树（ē。桉 × 尾叶桉）克隆广泛种植在巴西和以前列为耐MR-被感染A. psidii在米纳斯吉拉斯州，巴西。在这项研究中，通过人工接种桉树克隆而对A. psidii小种产生不同的反应，从而发现了一个新的A. psidii小种。（竞赛5）对大多数测试的桉树克隆都具有很高的攻击性。此外，只有这一新种族成功感染了桉树G26和847基因型，它们先前被归类为对四个已知的A. psidii种族具有抗性。由于G26基因型对Ppr1是纯合子（对A. psidii的主要抗性基因），因此这是关于Ppr1纯合子的桉树基因型的MR耐药性分解的首次报道。我们的发现表明，与以前已知的psidii种族1、2、3和4相比，这种新的psidii种族具有很高的侵略性，并且能够感染更多的桉树基因型。