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Extreme anatomical modifications of roots of Anadenanthera colubrina var. cebil parasitized by Lophophytum mirabile subsp. bolivianum (Balanophoraceae).
Encuentro; 2012 PAN-AMERICAN MEETING; 2012
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The vegetative body of L. mirabile is a subspherical ?tuber?, which completely lacks all vegetative organs. All tubers were subterranean, only inflorescences emerged above soil level. Normal, uninfected roots of A. colubrina had diffuse porous wood with vessels in clusters of 1-3. The wood matrix was mostly fibers. Axial parenchyma was paratracheal vasicentric and aliform, and rarely apotracheal in bands only one or two cells thick. Rays were uni- or biseriate and homogeneous. The phloem consisted of tangential strata of sieve tube members and companion cells, parenchyma cells, and bands of crystalliferous cells and fibers. Rays were uni- or biseriate. The attachment point with A. colubrina is a discrete woodrose: a ?coralloid? interface caused by localized proliferation of host wood. The host root stopped elongation growth after infection, and instead developed a broad, club-shaped end. In the hypertrophied and infected region, host wood anatomy was extremely modified. Vessels were narrower and more abundant, and oriented in concentric rings, with L. mirabile cells at their centers. Most of the infected wood consisted of lignified parenchyma cells with darkly stained contents, oriented radially rather than longitudinally. Rays were almost completely absent as were fibers. In this infected region, the phloem?s tangential banding became disorganized, and instead phloem appeared to consist almost entirely of parenchyma cells with darkly-stained contents with very few, scattered fibers. We did not detect any sieve tube members, rays or crystalliferous cells in this region. The infected region also had hundreds of tiny nodules of L. mirabile cells located in the host secondary phloem and outermost wood. Infection causes many changes in A. colubrina wood development, most of which favor the success of the parasite. The only defensive reaction is that the host stops producing sieve tube members near the infection site.