2.9.11
FREQUENTLY ISOLATED ENDOPHYTIC FUNGI FROM THE JAPANESE BEECH: DETECTION OF MAJOR FUNGAL ENDOPHYTES, THEIR SEASONAL VARIATIONS IN COLONIZATION RATE AND ORGAN SPECIFICITY

N SAHASHI, Y MIYASAWA, T KUBONO and S ITO

Laboratory of Forest Pathology, Tohoku Research Center, Forestry and Forest Products Research Institute, Morioka, Iwate, 020-0123, Japan

Background and objectives
Endophytic fungi, which induce asymptomatic infections of healthy plant tissues, have been the subject of many studies. These studies, which have focused on endophyte communities in woody plants mainly in Europe and in North America, have covered such subjects as methods of detection, taxonomy, species composition, distribution at a variety of scales, biological, ecological and physiological aspects, and interactions and mutualistic symbiosis between endophytes and host plants[l,2]. In Japan, although there have been some reports on endophytic fungi in conifers, little is known about the species composition of endophytic fungi in deciduous broad-leaved trees. Moreover, only limited information is available on seasonal changes in the endophyte communities. Clarifying the fungal species composition and seasonal variations of endophyte colonization is an important first step in understanding the ecology and physiology of endophytes and host-endophyte interactions. The objectives of this study were (1) to isolate the dominant fungal endophytes from various organs of the Japanese beech (Fagus crenataBiume), and (2) to monitor their seasonal variations in colonization rate.

Materials and methods

Several organs of beech which included healthy and symptomless leaves, current-year and 1- to 5-year-old twigs, and petioles were collected twice per month. These samples were cut into small pieces, surface-sterilized and incubated on potato dextrose agar at 15C for 3 ;weeks or more. The incidence of isolation for each fungus was expressed as a percentage of the total number of segments cultured in each sample category and was regarded as the colonization rate.

Results and conclusion
Discula sp. and an unidentified isolate, Lb, were frequently found in the leaves, and Phomopsis sp. was frequently found in the twigs after surface sterilization. In early May, just after expansion of the current leaves, no fungal isolates were detected in the leaves. Discula sp. was detected for the first time on May 26 and continued to be isolated with a relatively high incidence until July 11. The fungus then decreased gradually until August 8, and continued to be detected at low incidence until the end of September. In early October, at the end of the growing season, there appeared to be a slight increase in the frequency of this fungus. Conversely, the fungus Lb started to appear in late June. The fungus then increased rapidly and continued to have a high incidence (over 80%) until the end of the growing season. Thus, the isolation profiles of Discula sp. and Lb appeared to be different. In the old (1- to 5-year-old) twigs, only one fungal species, Phomopsis sp., was found with a high incidence. From early May in 1995 to late April in 1996, it was found in more than 85% of the segments. Discula sp., which was a major endophytic fungus in the leaves, and Phomopsis sp., was isolated at a high frequency in the newly developing current-year twigs. In petioles, the dominant isolates were Discula sp. and Lb, which were the same fungal taxa as those isolated from the leaves, and Phomopsis sp., which was the dominant endophytic fungus in the twigs. Discula sp. and Lb had similar profiles of colonization, even in petioles and current-year twigs, although colonization rates of a given species differed slightly among organs. A certain degree of organ specificity within a given host was observed, as described above. These three fungal species were considered to be the dominant endophytes of the Japanese beech.

References
1. Carroll GC, 1986. Microbiology of the Phyllosphere. Cambridge: Cambridge University Press, pp. 205-222.
2. Petrini O, 1991. Microbial Ecology of Leaves. New York: Springer-Verlag, pp. 179-197.