Abstract

Theobroma cacao L. is cultivated in Mexico, primarily in Tabasco, a southern state where the climatic conditions are suitable for producing cacao, the source of chocolate. However, these conditions are also suitable for cacao pathogens such as Phytophthora spp., the causative agents of black pod rot, a disease that is difficult to eradicate once established. In this study, we collected cacao pods exhibiting the symptoms and signs of black pod rot from different locations in Tabasco. Several recovered isolates exhibited the typical colony morphology of Phytophthora, including a white mycelium, stellate with chrysanthemum shape and appressed appearance with slightly torulose hyphae. Both sporangia and chlamydospores were absent in culture media, but were observed after induction in a sterile soil solution. Sporangia were papillated, and the sporangial shapes were globose, ellipsoid, and obturbinate, while the sporangiospores were umbrella shaped and simple sympodial. Chlamydospores were spherical, terminal, and subterminal. The concatenated analysis of the internal transcribed spacer region (ITS1-5.8S-ITS2 = ITS), the cytochrome c oxidase subunit II (COXII), the translation elongation factor 1α (TEF1) and β-tubulin (BT) placed strain PtCa-14 among several P. tropicalis strains, confirming the identity of this species. The pathogenicity tests on pear and peach fruit and cacao pods showed the ability of this oomycete to induce rot. Taken together, these results indicated the presence of P. tropicalis in the Mexican state of Tabasco and demonstrated its ability to cause black pod rot.

摘要

Theobroma cacao L. 在墨西哥种植，主要是在南部的塔巴斯科州，那里的气候条件适合生产巧克力的来源可可。然而，这些条件也适用于可可病原体，例如疫霉属，黑荚腐病的病原体，这种病害一旦发生就很难根除。在这项研究中，我们从塔巴斯科州的不同地点收集了表现出黑荚腐病症状和迹象的可可豆荚。几个回收的分离株表现出典型的疫霉菌落形态，包括白色菌丝体，星状菊花状，外观紧贴，菌丝略呈圆环状。孢子囊和厚壁孢子在培养基中均不存在，但在无菌土壤溶液中诱导后观察到。孢子囊具乳头状，孢子囊形状为球状、椭圆形和钝形，孢子囊呈伞状，单瓣。厚壁孢子呈球形、末端和亚末端。内部转录间隔区 (ITS1-5.8S-ITS2 = ITS)、细胞色素 c 氧化酶亚基 II ( COXII )、翻译延伸因子 1α ( TEF1 ) 和 β-微管蛋白 ( BT ) 放置菌株 PtCa-14 的串联分析在几个热带假单胞菌中菌株，确认该物种的身份。对梨、桃果实和可可豆荚的致病性试验表明，这种卵菌具有诱导腐烂的能力。综上所述，这些结果表明在墨西哥塔巴斯科州存在热带假单胞菌，并证明其有引起黑荚腐病的能力。