1995年9月於台中區農業改良場薏苡栽培育種試驗田中，發現所栽培薏苡有黑穗病發生蔓延情形。經田間發病調查，夏作薏苡台中選育一號黑穗病發病率在0~23%之間，翌年春作發病則僅在0~4%。調查不同品種薏苡對黑穗病之抗感病性，調查品種包含有尾花澤在來種、岡山在來種、台中選育一號、台中選育五號、紅殼之馬援種及泰國種等品種，其中以台中選育一號最為感病，罹病率可高達23%，而以馬援種及泰國種最為抗病，發病率僅在1%以下。薏苡黑穗病罹病穗之病徵為花器與葉片肥大、畸形，受害花器形成之厚膜孢子堆大小自2至14 mm之間，危害初期穗部外皮呈淡綠色至深綠色，末期呈紅褐色至褐色。厚膜孢子圓形或橢圓形，黃褐色，表面有刺，直徑在7.5~15 mm之間，平均12.8 mm；成熟之厚膜孢子可隨其外皮裂開而四散傳播。本病原菌依其引起病徵、孢子型態特性鑑定為Ustilago coicis Bref.。探討環境因子對其孢子發芽的影響，結果顯示孢子發芽適溫在32℃，低於24℃則降低。光照刺激可明顯促進發芽，增加孢子發芽率，顯示高溫可促進厚膜孢子發芽，但是在水分潛勢低於-5 bars以下，發芽率明顯的減少。由結果顯示薏苡黑穗病菌的厚膜孢子在高溫多濕的條件下易促使發芽。
The coix smut disease symptoms included the conspicuous smut gall of the inflorescence and the hypertrophic malformation on leaves. The infested staminate and pistillate tissues were both totally replaced by smut fungal sori at the later stage of disease development. The infected staminates were conical and 2~4 mm in diameter and pistillates were 4~14 mm. The sori were pale to dark green in color at the initial stage, which turned to brownish black and contained mainly a mass of teliospore. The teliospore were dark brown, round or ellipsoidal and 7.5~15 m m (mean 12.8 m m) in diameter; the surface was a serrate appearance with minute echinulations. The morphological and pathological characteristics indicated that the causal agent is Ustilago coicis Bref. as that described by Small (1927). From summer of 1995 to spring of 1996, which covers 2 construtive crop seasons of coix cultivation, disease survey on smut incidence of Job's tear millet in cultivated field were conducted. On Taichung-Sen-Yu No. 1, one of the main cultivars cultivated in Taiwan, the smut infection appeared to be more severe among summer crops as compared to that among spring crops. The disease severity of summer crops reached approximately 23% at the late stage of crop season; whereas that of spring crops was only 4%. The disease incidence coincided well with the timing whilst daily temperature reached 28℃. The smut teliospores collected from the field germinated well at temperature ranged from 28 to 36℃, with the optimum at 32℃. Beyond this range, the teliospore germination was greatly inhibited. The provision of light illumination greatly stimulated the germination. Moreover the spore germinate well at water potential greater than -5 bars whereas its was greatly inhibited below -10 bars. Other than Taichung-Sen-Yu No. 5, Obanazawa Native, Okayama Native, Mayuen and Thailand cvs.were also examined during the experiment peroid. Among them, Taichung-Sen-Yu No.1 appeared to be most susceptible, while Mayuen was most resistant. Consequently, the application of the resistant cultivar or as breeding sources will be worth for the disease control.
Key words: Job's tears millet, smut, Ustilago coicis, varietal resistance.