Seeds of weeds as an alternative host of phytopathogens

ABSTRACT: Weeds compete with agricultural crops for water, light, nutrients and space, besides having an extensive seed bank. However, another aspect to be considered relates to few studies pointing out weeds as hosts of phytopathogenic fungi. Many fungi, the main cause of diseases in plants, are known to use seeds as an efficient means of survival and dispersal. The objective of this work was to evaluate the health of weed seeds and the pathogenicity of fungi associated to plants of agricultural importance. The seeds were collected manually in Cerrado areas located in the municipality of Gurupi, Tocatins, Brazil. The blotter test method was used to evaluate seed health. The incidence of fungi was evaluated through an individual analysis of seeds using a stereoscopic and an optical microscope. The pathogenicity of fungi from weed seeds was evaluated by inoculation in plants of agronomic interest and, when pathogenic, we inoculated them in the host plant of the fungus. Weed seeds have been identified in fungi of the genus Alternaria, Aspergillus, Bipolaris, Cladosporium, Curvularia, Fusarium, Nigrospora, Papularia, Rhizopus and Pythium. The seeds of Acanthospermum australe, Bidens pilosa, Cenchrus echinatus, Digitaria horizontalis, Echinochloa crus-pavonis, Eleusine indica, Ipomoea sp., Pennisetum setosum, Sida rhombifolia, Spermacoce latifolia, Tridax procumbens and Vernonia polyanthes carry and disseminate fungi that, once inoculated, cause infection in plants of agricultural importance, such as Oryza sativa, Phaseolus vulgaris, Vigna unguiculata, Zea mays and Glycine max.

摘要：杂草会与农作物争夺水分、光照、养分与生长空间，同时还会形成庞大的种子库。然而，尚有一个亟待关注的研究层面：目前仅有少量研究将杂草列为植物病原真菌的宿主。作为植物病害的主要致病原，多数真菌以种子作为高效的存活与传播载体。本研究旨在评估杂草种子的健康状况，以及可侵染重要农业作物的病原真菌的致病性。本研究的杂草种子采集自巴西托坎廷斯州古鲁皮市的塞拉多（Cerrado）生态区域，采集方式为人工采集。采用吸水纸检测法（blotter test method）评估杂草种子的健康状况。通过体视显微镜与光学显微镜对单粒种子进行逐一分析，以此评估真菌的侵染率。通过将分离自杂草种子的真菌接种至具有农艺价值的植物上来评估其致病性；若该真菌具有致病性，则进一步将其接种至该真菌的天然宿主植物上进行验证。研究从杂草种子中分离鉴定出链格孢属（Alternaria）、曲霉属（Aspergillus）、离蠕孢属（Bipolaris）、芽枝霉属（Cladosporium）、弯孢霉属（Curvularia）、镰孢菌属（Fusarium）、黑孢霉属（Nigrospora）、粉束霉属（Papularia）、根霉属（Rhizopus）以及疫霉属（Pythium）的真菌。澳洲苍耳（Acanthospermum australe）、鬼针草（Bidens pilosa）、蒺藜草（Cenchrus echinatus）、止血马唐（Digitaria horizontalis）、野稗（Echinochloa crus-pavonis）、牛筋草（Eleusine indica）、番薯属植物（Ipomoea sp.）、狼尾草（Pennisetum setosum）、黄花稔（Sida rhombifolia）、长瓣牛眼草（Spermacoce latifolia）、羽芒菊（Tridax procumbens）以及多花斑鸠菊（Vernonia polyanthes）的种子可携带并传播真菌，这些真菌在接种后可侵染水稻（Oryza sativa）、菜豆（Phaseolus vulgaris）、豇豆（Vigna unguiculata）、玉米（Zea mays）以及大豆（Glycine max）等重要农业作物。