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落花生果莢黑斑病研究之回顧與展望
Review and Prospect of Studies on Pod Rot of Peanut
摘要
落花生果莢黑斑病從何時開始在本省發生，沒有明確的記載可查。因為其病原菌有好幾種，因此可以推斷由來已久，只是過去落花生以收穫乾莢果為主，而且本病發生不若目前嚴重，所以未被重視。直到十年前冷凍花生上市以後才浮出抬面，該病也因為本省過份依賴農藥與化學肥料之生產模式，導致土壤中生態系不平衡而病害日益嚴重，且缺乏有效之防治方法可供農民使用。對本病害之生態及防治方法之研究，台南場自1986年開始前後共進行約十年，其研究結果如下：造成本病之病原微生物主要有Fusarium solani、Rhizoctonia solani（AG-4）、Sclerotium rolfsii、Pythium myriotylum及寄生性線蟲等。P. myriotylum及S. rolfsii多在粘質土壤而且排水不良時造成水浸狀腐爛型病徵，F. solani及R. solani則多在較乾燥之土壤造成點狀黑斑型病斑，砂質土壤中寄生性線蟲較多，其所造成之傷口有利於病菌之侵入。一般而言砂質土壤比粘質土壤發病輕微，同一種土壤則含水量高者其發病較嚴重。花生田土壤之pH值與病害之發生並沒有相關性。前作物包括水稻、玉米、甘藷、根菜類、葉菜類或瓜果類與果莢黑斑病之發生情形亦無相關性，唯與水稻輪作可降低土壤中線蟲之密度。處女地或多年未種花生及客新土之落花生田，其發病均低於15%以下，河床新生地發病率亦低。目前推廣之栽培品種間，台南選九號之發病比台南十一號略輕，但兩種均屬感病型。至於配合育種所進行之抗病檢定工作，雖有一些較抗病品系，但表現不大穩定，亦即在不同期作其表現常不一致，因此仍缺乏具良好抗性之品系，可供育種之利用。種植前施用土壤添加物或殺線蟲劑，然後於結莢初期分別灌注免賴得可濕性粉劑或鋅錳滅達樂可濕性粉劑，其防治效果因地而異，此乃因不同試區其土壤微生物相不一樣所致，而且使用藥劑成本太高，無法推廣。土壤用溴化甲烷或蒸氣消毒，可有效殺死病原菌，再種落花生，可以明顯降低病害之發生，但使用溴化甲烷危險性高，該藥也將禁用，加上成本太高，因此不可行。使用蒸氣全面消毒土壤，雖無危險性，但實際上之可行性尚待評估。本場曾採行提早採收、輪作、施用尿素及深耕打破犁底層等各種耕作方式，但均未能有效且經濟的控制病害的發生。
並列摘要
No record can be traced for the first occurrence of peanut pod rot in Taiwan. Because it is a disease-complex caused by many species of fungi and nematodes, the disease may have existed in Taiwan for many decades. This disease was not noticed or emphasized until the consumption of frozen boiled-peanut pod became popular about 10 years ago. It is also believed that the change of cropping system and cropping pattern, which greatly caused the imbalance of the eco-system of soil microorganisms, increased the importance and severity of the disease. So far, this disease is lack of effective and practical control measures for the farmers to use. Results of the studies on this disease in the last decade at the station are summarized. The disease is a disease-complex caused by species of fungi including Fusarium solani, Rhizoctonia solani (AG-4), Sclerotium rolfsii, Pythium myriotylum and species of nematodes. P. myriotylum and S. rolfsii were commonly observed in the soil with high percentage of clay and they caused water-soaking and rotting symptoms on the pods, while F. solani and R. solani were in the dry soil and caused black spot and dry rot on the pods. Nematodes are more frequently presented in the sandy soils. Injuries or wounds on the pods by nematodes are favored to the infection by the pathogenic fungi. Distribution or importance of each causal organism in the soil varied in locations and seasons. Disease was more severe in the clay soil than that in the sandy soil. More disease also was found in the same soil with higher moisture. Soil pH did not greatly affect the occurrence or severity of the diseases. Previous crop such as paddy rice, corn, sweet potato, root vegetables, leaf vegetables or fruit vegetables might slightly affect the severity of pod rot in the subsequent peanut plantings without consistent results. Rotation with paddy rice can obviously decrease the population of nematodes in the soil. Less disease (＜15%) was found in the peanut pods harvested from the virgin soil; the soil had not planted peanut for many years; and the surface soil had been renewed with clean soil. Low incidence of the disease also was found in the new land of riverbeds. All the currently grown cultivars were susceptible to the disease, but Tainan sel. No.9 was slightly less than Tainan No. 11. In cooperation to the breeding program, some lines were found with a certain level of resistance but they were not stable or varied in location and seasons. The use of Ridomil MZ W.P. was effective in the field when Pythium spp. is dominant and Benlate W.P. was only effective in the sandy soils. Due to the high cost of fungicides, it was not recommended to the farmers. Results of the high cost of fungicides, it was not recommended to the farmers. Results of the experiments conducted in an isolated cement box with soil fumigent methyl bromide reduced the infection rate of pod to 4.5%, while the non-treated ones was found with 21.5% of infected pod. Due to the high cost and application danger of methyl bromide, it was also not recommended to the farmers. Soil pasteurization with water steam before planting is very effective to kill the pathogens. However, large scale of application is very difficult and expensive, it is not practical. Other cultural measures such as early harvesting of the pods; rotation with other crops on the same land planted with one crop of peanut in one, two, or three years; application of urea to nullify the sclerotia of the pathogen before planting; and deep plowing of the surface soil to reduce the pathogen population, were all tested, and failed to control the disease effectively at the economic or accepted levels.