Endophytic fungi of Tectona grandis L. (Teak)
Taxonomic diversity, biology and ecological aspects of fungal endophytes of Tectona grandis (teak) from Chiang Mai Province, Thailand were investigated. It was found that the endophyte assemblages of mature leaves sampled from natural forest and plantation teak were not significantly different. Members of the Xylariaceae, especially Daldinia eschscholzii, Nemania subannulata, Hypoxylon haematostroma and Xylaria cubensis were frequent isolates. Widely reported endophytic fungi such as Phomopsis, Colletotrichum, Cladosporium and Fusarium were also isolated. There is little evidence to support host specificity for the majority of the isolates. Differences in endophyte assemblages between young and mature leaves were shown to occur with a much lower infection percentage in the young leaves. Species of Phomopsis and Colletotrichum were dominant in the young leaves but members of the Xylariaceae dominated in mature leaves. This pattern was the same for both natural forest and plantation samples. However comparison of taxa isolated from leaf lamina, midrib and veins gave conflicting results. Samples from mature leaves from natural forest trees exhibited little variation with greater variation in taxa recovered being found to occur between sampling years than between position of isolation from the leaf. In plantation leaves, although the results were similar to those from natural forest tree leaves for two of the years sampled, in 1997 the overall recovery rate was highest for the lamina, followed by veins and then the midrib. There was no evidence obtained to link individual taxa with specific regions of the leaf. It is now possible to devise a sampling strategy to obtain suitable diversity of endophytic isolates from teak leaves for industrial screening of these fungi. Techniques were developed to overcome current problems of identification of xylariaceous endophytes in the absence of their teleomorph. Inoculation of suitable woody substrata combined with selective incubation was used to induce teleomorph formation in many of the isolates and this together with chemical profiling enabled identification to species of many of these isolates. Rates of development of specific species were obtained and differences in environmental conditions necessary for development of teleomorphs to maturity were noted for members of different genera. Thus species of Daldinia and Hypoxylon required drier conditions than species of Xylaria and Nemania which only developed under wet shaded conditions. Xylariaceae from the natural forest, plantation, and forest surrounding the plantation were surveyed and a number of the Xylariaceae recovered as endophytes were found to be new to science, new records for Thailand or were recorded as endophytes for the first time.