在墨西哥,鳄梨生产是重要的经济来源。在上个赛季中,它产生了$3。该国有270亿美元的外币。Irpexspp.是木材腐烂真菌。在2019-2022年期间,在米却肯州(19°13\'N;101°55\'W),墨西哥,Irpexsp。在5岁和更老的鳄梨(Perseaamericana)树的树干和树冠的基部观察到。树木表现出疾病症状,包括白根腐烂,叶子变黄,小叶子,分支死回,广义落叶,顶端松弛,由于缺乏叶子,水果丰富但很少晒伤,在2-4年的第一次疾病出现后,受感染的树木死亡。在真菌建立的地方,形成了丰富的白色和棉质菌丝体,导致树木腐烂。在采样果园中,该病的发病率估计为每公顷30%,有350-400棵树,这是通过一个简单的采样设计确定的,重点是由于植物病原体引起的疾病的体征和症状的树木。从90棵树(每个果园5-6棵)中收集了感染的组织(根和茎)和真菌孢子的样品。从17个果园中随机选择了有症状的鳄梨树。对于真菌的宏观表征,使用了Gilbertson和Ryvarden(1986)和Largent(1973)描述的天气键。样品显示出对应于Irpexsp的典型结构。,包括玫瑰花,一年生子体,单质菌丝系统,和近球形负孢子。根据Agrios(2004)的方案,从担子体和感染的树组织中进行体外真菌分离。将真菌菌株维持在28°C的PDA上。在孵育16天时,菌落是不透明的,白色,有蓬松和软木菌丝。真菌的显微镜分析显示典型的淡黄色孢子,椭圆体形状为3-4x4-5.5µm(每个分离物50个占结构[N=19]),基底为20-25x4.5-5.5µm(n=20个基底)。对于分子表征,使用了两个分子标记,内部转录间隔区rDNA-ITS15.8rDNA-ITS2(ITS;White等人。1990)和大核糖体亚基(LSU;Vilgalys和Hester1990)。如Martínez-González等人所述进行PCR反应。(2017)。将共有序列与保存在NCBI-GenBank中的序列进行比较,使用BLASTN2.2.19工具(Zhang等人2000),样本显示与该物种99%匹配,Irpex玫瑰花形。提交的分离株的GenBank登录号总结在补充表4中。为了测试科赫的假设,将在温室条件下生长的3个月大的鳄梨植物接种在根上(每个分离株n=10[N=19])。该实验用20株未接种的植物作为对照进行两次。67天后,观察到基部(平均50x70x1.5mm),其中疾病发生率>77%,随后的树木下降。在PDA中体外重新分离病原体,并通过菌丝体的形态特征确认其身份。这项工作表明,玫瑰花形不仅是一种木材腐烂真菌,也是一种植物病原体,美洲白根腐病的致病因子。双歧杆菌,品种\'Hass\',这为监测和防止其扩散到美洲大陆其他地区和出口苗圃鳄梨幼苗的世界建立了先例。
In México, avocado production is an important economic source. In the last season it generated $ 3. 27 billion USD of foreign currency in the country. Irpex spp. are wood decay fungi. In the period 2019-2022, in the state of Michoacán (19°13\' N; 101°55\' W), México, basidiomes of Irpex sp. were observed on the base of trunks and crowns of 5-years-old and older avocado (Persea americana) trees. The trees exhibited disease symptoms that included white root rot, leaf yellowing, small leaves, branch diebacks, generalized defoliation, apical flaccidity, abundant but small sun burnt fruits due to the lack of foliage, and after 2-4 years of first disease appearance, the infected trees died. In the place where fungus was established, abundant white and cottony mycelium was formed, which caused trees decay. The incidence of the disease in the sampled orchards was estimated to be 30% per ha with 350 - 400 trees, which was determined through a simple sampling design focused on trees with signs and symptoms of the disease due to the phytopathogen. Samples of infected tissue (roots and stems) and fungal basidiomes were collected from 90 trees (5-6 per orchard). The symptomatic avocado trees studied were randomly selected from 17 orchards. For the fungal macroscopic characterization, the synoptic keys described by Gilbertson and Ryvarden (1986) and by Largent (1973) were used. The samples showed typical structures corresponding to Irpex sp., including rosettes, annual basidiomes, a system of monomitic hyphae, and subglobose basidiospores. In vitro fungal isolation from basidiomes and infected tree tissues was done according to the protocol of Agrios (2004). The fungal strains were maintained on PDA at 28 °C. At 16 days of incubation the colonies were opaque, whitish with fluffy and corky mycelium. Microscopic analysis of the fungus showed typical yellowish spores, with an ellipsoid shape of 3-4 x 4-5.5 µm (50 accounted structures per isolate [N=19]) and basidia of 20-25 x 4.5-5.5 µm (n=20 basidiomes). For molecular characterization, two molecular markers were used, the internal transcribed spacer rDNA-ITS1 5.8 rDNA-ITS2 (ITS; White et al. 1990) and the large ribosomal subunit (LSU; Vilgalys and Hester 1990). The PCR reaction was performed as described by Martínez-González et al. (2017). The consensus sequences were compared with those deposited in the NCBI-GenBank, using the BLASTN 2.2.19 tool (Zhang et al. 2000), the samples showed 99% match with the species, Irpex rosettiformis. GenBank accession numbers of the submitted isolates are summarized in supplementary Table 4. To test Koch\'s postulates, 3-months old avocado plants grown in greenhouse conditions were inoculated (n = 10 per each isolate [N= 19]) on the roots with 3 g of I. rosettiformis mycelium. The experiment was done twice with 20 non-inoculated plants as control. After 67 days, basidiomes (50 x 70 x 1.5 mm in average) were observed where the disease incidence was >77%, with subsequent tree decline. The pathogen was re-isolated in vitro in PDA and its identity was confirmed by morphological characteristics of mycelium. This work shows that I. rosettiformis is not only a wood decay fungus, but also a phytopathogen, the causative agent of white root rot disease in P. americana var. drymifolia, cultivar \'Hass\', which establishes a precedent for monitoring and preventing its proliferation to other regions in the American continent and the world where nursery avocado seedlings are exported.