由Lasiodiplodia spp.造成之落花生基腐病

Peanuts collar rot caused by Lasiodiplodia spp.

落花生為臺灣重要雜糧作物，栽培過程病蟲害種類繁多，近幾年在雲林地區，落花生於生育中後期出現萎凋現象，罹病植株呈現乾腐症狀，莖部病徵處可見密集凸起之黑色柄子殼，鏡檢可見兩種型態之孢子，分別為卵圓形、透明、單室之未成熟孢子與卵圓形、褐色、中央有一隔膜且具明顯縱紋之成熟孢子。病原菌經分離純化後，於PDA上菌落初呈灰白色，之後轉為灰黑色絨毛狀菌落，並有柄子殼形成，經型態鑑定及親緣關係分析結果，屬Lasiodiplodia屬之真菌，完成柯霍氏法則，確定為落花生上的新興病害。於2021-2022年收集不同田區菌株進行病原性分析、親緣關係分析、溫度生長測試、藥劑感受性測試、種子拌藥防治試驗等，結果發現目前田間常見的品種均可被感染，病原菌親緣關係分析結果顯示，收集到的菌株含L. pseudotheobromae、L. iraniensis、L. hormozganensis與L. theobromae等四個親緣種，其中以L. pseudotheobromae最多，占所收集菌株的58.8%，推測應為田間主要病原菌。病原菌在20-30℃的環境下菌絲生長快速，依普同能完全抑制菌絲生長，而腐絕對大部分L. pseudotheobromae供試菌株抑制效果不佳。使用依普同與腐絕混拌落花生種子，可顯著降低幼苗發病情形，但其中一組種子經腐絕拌藥處理依然有50%左右之罹病率，推測可能為對腐絕具抗藥性菌株所致。臺灣地區並無Lasiodiplodia spp.造成落花生萎凋的紀錄，近年來卻普遍發生，本研究為臺灣首次正式報告，而在觀察罹病植株發現，子房柄與豆莢上可見到病原菌之柄子殼，且種子上能分離出相同的病原菌，播種由罹病植株採集之落花生種子，發芽之植株會產生與田間相同之病徵，因此推測感染源可能來自於種子。

Peanut (Arachis hypogaea) is an important grain crop in Taiwan. There are many kinds of diseases and pests during the cultivation process. In recent years, peanuts in Yunlin area have wilted in the middle and late growth stages. Wilted plants show symptoms of dry rot, pycnidia densely raised at the diseased parts of the stems. Under microscopic examination, two types of spores can be seen: oval, transparent, single-chambered immature spores and oval, brown, mature spores with a septum in the center and obvious longitudinal stripes. The colony of isolated pathogen on PDA was initially off-white, then turned into gray-black fuzzy colonies with pycnidia formed. Morphological identification and phylogenetic analysis showed that the fungus belonged to the genus Lasiodiplodia, completing Koch's postulates and being determined to be an emerging disease on peanuts. In 2021-2022, pathogen strains from different fields were collected for pathogenicity analysis, phylogenetic analysis, temperature growth tests, fungicides sensitivity tests, seed coating for control tests, etc. The results showed that all common varieties of peanut in the field can be infected. The results of the pathogen phylogenetic analysis showed that the collected strains contained four related species, including L. pseudotheobromae, L. iraniensis, L. hormozganensis and L. theobromae. Among them, L. pseudotheobromae was the most, accounting for 58.8% of the collected strains. It is speculated that it should be the main pathogen in the field. The mycelium of the pathogen grew rapidly in an environment of 20-30℃. Iprodione could completely inhibit the mycelium growth, while Thiabendazole had poor inhibition effect on most of the tested strains of L. pseudotheobromae. Seed coating Iprodione and Thiabendazole can significantly reduce the incidence of disease in seedlings, but one group of seeds treated with Thiabendazole still had a disease rate of about 50%, indicating that there may be fungicide-resistant strains in the field. There is no record of Lasiodiplodia spp. causing peanut wilt in Taiwan, but it has become common in recent years. This study is the first official report in Taiwan. On diseased peanut plant, pycnidia were visible on the ovary stalk and pod, and the same pathogen could be isolated from the seeds. When peanut seeds collected from diseased plants were sown, the germinated plants would produce the same symptoms as those in the field, so it is speculated that the first inoculums source of infection may come from the seeds.