梭梭新病害霜霉病的发现

Discovery of the New Disease of Downy mildew on Haloxylon ammodendron

为了给梭梭病害的诊断和科学防治提供依据。对2018年7月甘肃省民勤县大滩镇梭梭苗圃中的梭梭苗发生的病害进行了病原菌形态学鉴定,依据孢囊梗、孢子囊和卵孢子的形态特征,初步确认是由霜霉科(Peronosporaceae)卵菌引起的霜霉病。病原菌形态特征为孢囊梗自气孔生出,单生或丛生,主轴基部有时膨大,冠部多次二叉状锐角分枝,通常末端正直或呈极叉开张,末枝枝端尖细;孢囊梗长178.0~630.0μm,宽6.9~13.7μm,孢囊梗主轴长79.2~352.5μm,主轴长/全长=0.4~0.6;孢子囊灰褐色,卵圆形至橄榄形,27.4~44.1μm×13.7~21.6μm,长/宽=1.5~2.5。卵孢子在病组织内大量产生:藏卵器球形、近球形、广椭圆形,或多角形,44.1~63.7μm×42.1~60.8μm;卵孢子球形,金黄褐色至红褐色,30.4~47.0μm×28.4~44.1μm,卵孢子壁厚、粗糙,上有瘤突或锥状突。鉴于目前尚缺乏梭梭霜霉病菌的分子生物学和寄主专化性试验数据,因此将病菌暂定为(Peronosporaceae sp.),归属于有色孢子囊霜霉组的霜霉属(Peronospora)或假霜霉属(Pseudoperonospora)。由于梭梭与已发现的霜霉菌的藜科寄主植物的亲缘关系较远,因此梭梭霜霉病菌极有可能是一个新种。这是梭梭及梭梭属植物霜霉病在世界范围内的首次报道。

In order to provide the reference for the diagnosis and scientific prevention and control of diseases in Haloxylon ammodendron,in July 2018,morphological identification of pathogens was carried out on diseased seedlings of Haloxylon ammodendron in Haloxylon ammodendron nursery,Datan Township,Minqin County,Gansu Province.According to the morphological characteristics of sporangiophores,sporangia and oospores,the primary identification was downy mildew caused by oomycetes from Peronosporaceae family.Morphological characteristics of the pathogen were described as that the sporangiophores arised from the stomata,solitary or clustered,the base of trunk was sometimes enlarged,and the crown branched dichotomously in multi-orders,the ultimate branchlets were in pairs or single,usually straight or extremely angle and tapering.Sporangiophore length was 178.0 to 630.0μm,sporangiophore width was 6.9 to 13.7μm,the main trunk length was 79.2 to 352.5μm and the main trunk length/total length ratio was between 0.4 to 0.6.The sporangia were grayish brown,ovoid to olive-shaped,27.4 to 44.1μm×13.7 to 21.6μm with a length/width ratio of 1.5 to 2.5.The oogonia were produced abundantly in diseased tissues,spherical,nearly spherical,broadly elliptical,or polygonal in shape,44.1 to 63.7μm×42.1 to 60.8μm.Oospores were aplerotic,spherical,golden brown to reddish brown,30.4 to 47.0μm×28.4 to 44.1μm,the wall of oospores was thick and rough,with tuberculate or paniculate protrusions.Due to the lack of molecular biology and host specificity test data of the pathogen at present,the pathogen is tentatively named Peronosporaceae sp.(the group of downy mildews with colored sporangia:Peronospora or Pseudoperonospora).Since the genetic relationship of the discovered downy mildews between H.ammodendron and the other Chenopodiaceae host plants is relatively far away,the pathogen is highly probablya new species.This is the first report of downy mildew on H.ammodendron and Haloxylon genus worldwide.