Vettraino A M, Lucero G, Pizzuolo P, Franceschini S, Vannini A
Department of Plant Protection, University of Tuscia, Via San Camillo de' Lellis 01100, Viterbo, Italy.
Department of Biology, National University of Cuyo, Alte. Brown 500, Luján de Cuyo 5505 Mza., Argentina.
Plant Dis. 2009 Jul;93(7):765. doi: 10.1094/PDIS-93-7-0765B.
In Argentina, olives (Olea europaea) are planted on approximately 90,000 ha located primarily in the northwest continental regions. During a 2005 survey, root rot was recorded at several olive plantations in Catamarca, La Rioja, and San Juan provinces (3). Aboveground symptoms associated with root rot were twigs wilting with or without chlorosis, defoliation, and death. Symptoms were initiated on lateral branches and sometimes affected the entire crown. Even if young (5-year-old) trees displayed root rot, aerial symptoms may or may not be seen until years later. Disease incidence varied from 3 to 30%. Rotted rootlets were associated mainly with the infection of Phytophthora palmivora Butler and less frequently with another Phytophthora species. Isolates of this species were heterothallic, had a fluffy growth on carrot agar, and arachnoid growth on potato dextrose agar. Chlamydospores approximately 36 μm in diameter were also produced. The species developed prominent, papillate, noncaducous sporangia of different shapes ranging from ellipsoid to spherical when submerged in saline solution. Sporangia were 35 to 57 × 25 to 45 μm (average 44 × 33 μm), L:B ratio from 1.1 to 1.7. Isolates formed oogonia and amphyginous antheridia following mating type assays. On the basis of morphological features, these isolates were identified as P. nicotianae Breda de Haan. Identity was confirmed by sequencing the rDNA internal transcribed spacer (GenBank Accession No. FJ746693) (1). One-year-old O. europea seedlings were challenged with P. nicotianae (A1 isolates 306G and 339) through soil infestation assay in a growth chamber at 25°C. Infested and uninfested autoclaved millet grains moistened with V8 juice were used to inoculate 15 olive seedlings per isolate and controls, respectively. Fifty days after inoculation, seedlings showed foliar symptoms similar to those observed in the field and had an average of 50% reduction in the root system. Control plants remained healthy. P. nicotianae was always reisolated from symptomatic roots. P. nicotianae was reported on Citrus aurantium in Argentina in 1947 and is currently associated with several hosts (2). In 2002, the same species was reported associated with olive root rot in southern Italy (4). It is possible that P. nicotianae was recently introduced into Argentina through importation of Mediterranean olive varieties. The demonstrated pathogenicity of P. nicotianae on olive together with the recently reported detection of P. palmivora (3) presents a serious threat to olive cultivation in Argentina. References: (1) D. E. L. Cooke et al. Fungal Genet. Biol. 30:17, 2000. (2) M. J. Frezzi. Rev. Investig. Agric. 4:47, 1950. (3) G. Lucero et al. Plant Pathol. 56:728, 2007. (4) F. Nigro and A. Ippolito. Acta Hortic. 586:777, 2002.
在阿根廷，油橄榄（油橄榄属）种植面积约为9万公顷，主要分布在西北大陆地区。在2005年的一项调查中，卡塔马卡省、拉里奥哈省和圣胡安省的几个橄榄种植园发现了根腐病（3）。与根腐病相关的地上症状包括小枝枯萎，伴有或不伴有黄化、落叶和死亡。症状首先出现在侧枝上，有时会影响整个树冠。即使是幼龄（5年生）树木出现根腐病，地上症状可能在数年之后才会显现，也可能不显现。发病率在3%至30%之间。腐烂的细根主要与棕榈疫霉的感染有关，较少与另一种疫霉属物种有关。该物种的分离株是异宗配合的，在胡萝卜琼脂上生长蓬松，在马铃薯葡萄糖琼脂上呈蛛网状生长。还产生了直径约36μm的厚垣孢子。当浸入盐溶液中时，该物种会形成不同形状的突出、具乳突、不脱落的孢子囊，从椭圆形到球形不等。孢子囊大小为35至57×25至45μm（平均44×33μm），长宽比为1.1至1.7。经过交配型测定，分离株形成了藏卵器和双游卵器。根据形态特征，这些分离株被鉴定为烟草疫霉。通过对核糖体DNA内转录间隔区进行测序（GenBank登录号FJ746693），确认了其身份（1）。在生长室中，将一年生油橄榄幼苗置于25°C环境下，通过土壤侵染试验，用烟草疫霉（A1分离株306G和339）进行挑战。分别用经V8汁浸湿的接种和未接种的高压灭菌小米粒对每个分离株的15株橄榄幼苗和对照进行接种。接种50天后，幼苗出现了与田间观察到的类似的叶片症状，根系平均减少了50%。对照植株保持健康。总是能从有症状的根部分离到烟草疫霉。1947年在阿根廷的酸橙上报道过烟草疫霉，目前它与多种寄主有关（2）。2002年，在意大利南部报道了该物种与橄榄根腐病有关（4）。烟草疫霉可能是最近通过进口地中海橄榄品种传入阿根廷的。烟草疫霉对橄榄的致病性以及最近报道的棕榈疫霉的检测（3）对阿根廷的橄榄种植构成了严重威胁。参考文献：（1）D.E.L.Cooke等人，《真菌遗传学与生物学》30:17，2000年。（2）M.J.Frezzi，《农业研究评论》4:47，1950年。（3）G.Lucero等人，《植物病理学》56:728，2007年。（4）F.Nigro和A.Ippolito，《园艺学报》586:777，2002年。
