探討以印度梨型孢菌防治樹木褐根病與抵抗非生物性逆境

Abstract

都市樹木之生長環境中，普遍有土壤缺乏營養或植穴狹小等問題，而樹木也因生長不良而容易受到病蟲害感染。Phellinus noxius引起的褐根病為熱帶和亞熱帶地區的重要樹木病害，罹病樹木若因根部受損而傾倒，容易造成公共安全風險。內生菌印度梨型孢菌 (Serendipita indica) 目前主要應用在非木本植物如大麥、大豆和玉米等，有助植物抵抗生物及非生物性逆境，因此本研究嘗試以固態發酵之S. indica接種適合臺灣生長的行道樹苗，以探討其應用於樹木保護之潛力。本研究從六種穀物中，選取小米製作S. indica固態接種源，接種苦楝、烏桕、青剛櫟、茄苳及枇杷等樹苗後，發現S. indica可成功定殖於所有樹種的根部。其後以茄苳進行S. indica及P. noxius固態發酵接種，以及營造缺磷和缺氮的生長環境，期間觀察樹的萎凋率、P. noxius 分離率、S. indica的厚膜孢子量，並以專一性引子對偵測S. indica及P. noxius之DNA，並測量植株的濕乾重及葉子的氮磷含量等指標，以評估S. indica對於褐根病菌感染茄苳及茄苳的氮磷吸收之影響。本研究發現：(1) S. indica可長期定殖於茄苳根部 (觀察期84天)，但其數量在接種後第七天最高，之後大幅下降；(2) 不論是否先接種S. indica，茄苳苗於接種褐根病菌後均於五天內急速萎凋，但曾接種S. indica之處理組，其主根的褐根病菌分離率降低~50%；(3) 先接種S. indica再接種P. noxius的處理組，相較於僅接種S. indica者，可觀察到S. indica的厚膜孢子數量增加約37倍；(4) 在缺氮或缺磷之營養液澆灌八週後，已接種S. indica與未接種S. indica之茄苳的生長及氮磷吸收指標等均無明顯差異。本研究也發現，使用小米固態接種源對於茄苳根部可能有不良影響，建議未來可針對接種源的製備和接種方法做改良。

The common problems occurring in the environment for growth of urban trees include nutrient deficiency and narrow tree pits. Moreover, trees become more susceptible to pests and diseases because of the unhealthy growth. Brown root rot (BRR) disease of trees, caused by Phellinus noxius, is a serious disease in tropical and subtropical areas. Safety risk to public may be posed by BRR if the infected trees topple due to their root damage. The endophytic fungus Serendipita indica, known to enhance plant resistance to biotic and abiotic stresses, is currently mainly applied to non-woody plants such as barley and soybean. This study attempted to apply solid-state fermentation for inoculation of S. indica on urban tree species suitable for growing in Taiwan, with a view to exploring the possibility of application on tree protection. Proso millet was selected from six types of grains to act as grain substrate for inoculum preparation in this study. After inoculation of Melia azedarach, Sapium sebiferum, Bischofia javanica, Cyclobalanopsis glauca and Eriobotrya japonica seedlings, we discovered that S. indica successfully colonize the roots of all those tree species. B. javanica was then chosen for inoculation of S. indica and/or P. noxius, and evaluation under nitrogen and/or phosphorous deficiency growing environments. To evaluate the effects of S. indica on the infection of P. noxius and acquisition of nitrogen and phosphorous, indexes such as the incidence of wilting, isolation rate of P. noxius, root colonization rate of S. indica, DNA of S. indica and P. noxius (detected by specific primers), wet and dry weights and N and P contents of seedlings, were investigated. Our findings include: (1) S. indica could colonize inside the root of B. javanica for a long time (observation period was 84 days), but the colonization percentage decreased sharply after reaching maximum at seven-day-post-inoculation. (2) No matter S. indica was inoculated at first or not, B. javanica seedlings declined quickly five days after the inoculation of P. noxius. But the isolation rate of P. noxius from the tap roots of S. indica-inoculated seedlings decreased by ~50%. (3) Compared to the seedlings inoculated with S. indica only, root colonization index of S. indica in the seedlings inoculated with S. indica first and then P. noxius was 37 times higher. (4) After supplementing nitrogen and/or phosphorous deficient nutrient solutions for eight weeks, difference was not observed on the growth and absorption of nitrogen and phosphorous in seedlings inoculated with or without S. indica. We also discovered that application of fermented proso millet inoculum may cause negative effects on the roots of B. javanica, and therefore, inoculum preparation and inoculation method should be improved in the future.