Xylaria species are common endophytes in tropical plants.
It is not known, however, whether transmission of Xylaria occurs
horizontally or vertically, whether individual Xylaria
strains have wide host ranges or are host-specific, or how they are dispersed.
We compared frequency of Xylaria endophytes in leaves and seeds
of two tree species in Puerto Rico, Casuarina equisetifolia
(Australian pine) and Manilkara bidentata (ausubo). These
trees were chosen because they differ markedly in morphology, habitat,
distribution, and origin. In C. equisetifolia Xylaria was
significantly more frequent in leaves than in seeds. Xylaria was
isolated from
seeds of trees in inland parks, but never from seeds of trees growing on
beaches. This suggests that vertical transmission of Xylaria
may be possible but is not necessary for infection. In M. bidentata,
Xylaria was isolated from 97% of leaves but was never isolated
from seeds, suggesting that transmission is entirely horizontal.
Seedlings raised in a greenhouse far from other M. bidentata trees
had
a level of Xylaria infection as high as seedlings in
the forest, suggesting that inocula can come from other sources and endophytic
strains are not host-specific.