内生真菌感染对宿主羊草抗病性的影响

以感染内生真菌的天然禾草羊草为实验材料,通过体外纯培养条件下的内生真菌、感染内生真菌的离体叶片和在体叶片对3种病原菌的抑菌实验,以探讨内生真菌对宿主植物羊草在抗病性方面的贡献。结果表明:体外纯培养条件下,分离自羊草的内生真菌Epichlobromicola对新月弯孢(Curvularia lunata)、根腐离蠕孢(Bipolaris sorokiniana)和枝孢霉(Cladosporium sp.)这3种病原菌都具有抑制作用,抑菌率分别达56.22%,46.93%和45.15%,且内生真菌培养滤液可以有效抑制这3种病原菌的孢子萌发,平均萌发率分别为30.4%,15.7%和16.4%;宿主植物叶片在离体条件下,内生真菌感染可以有效降低羊草叶片受C.lunata和C.sp.侵染后的病斑数或病斑长度,但对B.sorokiniana不起作用,甚至提高了叶片的病斑数及病斑长度,而离体叶片提取液对不同病原菌均有不同程度的抑制作用;在体条件下,内生真菌均可以通过降低叶片病斑数来增强羊草植株对这3种病原菌的抗性。由此看来,内生真菌E.bromicola对宿主植物羊草在抗病原菌侵染方面有一定的增益作用。

Effect of endophyte infection on fungal disease resistance of Leymus chinensis

Endophytes are commonly defined as fungi that live asymptomatically within healthy plant tissue, such as leaves, stems or roots, for a part or all of their life cycle. The largest plant family hosting these endophytes is Poaceae. Studies on the grass-endophyte symbiosis indicate that endophytes can not only protect the host grass from abiotic stresses but also enhance its resistance to biotic disturbance, including herbivores, nematodes, bacteria and pathogens. However, the response of grass-endophyte symbiosis to fungal pathogens is less studied. Most previous reports on resistance of endophytes to pathogens have focused on inhibition of fungal pathogens by endophytes in vitro or by inoculation of fungal pathogens on detached leaves of the symbiont, and these studies have demonstrated that endophytes can inhibit growth of certain species of fungal pathogens to some degree. Up to now, only a few studies have centered on influence of endophyte infection on disease resistance of live plants. In this paper we used the endophyte Epichloë bromicola, which was isolated from Leymus chinensis. L. chinensis is a natural grass, widely distributed in the Inner Mongolian steppe. Three species of fungal pathogens were chosen, i.e. Curvularia lunata, Bipolaris sorokiniana and Cladosporium sp.. The experiment comprised three parts, i.e. fungal pathogens inhibition experiment by endophyte, infected detached leaves and infected intact plants experiments. The questions were: (1) whether E. bromicola could inhibit the growth of the three fungal pathogens in vitro, and (2) whether endophyte-infected (E+) and endophyte-free (E-) plants differed in resistance to the pathogenic fungi in detached leaves and live plants of L. chinensis. The results suggested that E. bromicola significantly inhibited the growth of C. lunata, B. sorokiniana and C. sp. in vitro, but anti-fungal activities of the endophyte to different pathogenic fungi were different. The inhibition rates were 56.22, 46.93 and 45.15%, respectively. Culture filtrate of endophyte also effectively reduced pathogenic spore germination and the average germination rate were 30.4, 15.7 and 16.4%, respectively. The main antagonism mechanisms involved in competition and producing anti-fungal chemical compounds. As for our research, the main strategy was the latter. Leaf inoculation trial showed that all fungal pathogens were able to cause lesions on detached leaves regardless of endophyte status. Either the number or length of disease lesions on E+ L. chinensis leaves caused by C. lunata or C. sp. decreased compared with those on E- leaves. But lesion number and length of B. sorokiniana leaf spots were dramatically higher on E+ leaves compared with E- leaves. Detached leaves extraction inhibited three pathogens to varying degrees. The reason might be that some inhibitory substances differed in vitro and in the whole plant. The intact E+ leaves had greater resistance to all of three species of pathogens than E- leaves. The explanation may be that the defense of plant associated with endophyte increased through resistance enhancement and secondary metabolites production. In a word, the endophyte E. bromicola had a positive effect on disease resistance of the host plant.