PARASITISM OF TIMBER BAMBOO ROOTS BY GRACILACUS LATESCENS RASKI, 1976 AND MORPHO-BIOLOGICAL NOTES ON MATURE AND IMMATURE LIFE STAGES
Keywords:biology, feeding tube, florida, gracilacus latescens, histopathology, host response, morphology, nematode development, pin nematodes, syncytium
AbstractColonies of Gracilacus latescens consisting of swollen females, males, second-stage juveniles (J2) and eggs were observed on timber bamboo (Phyllostachys bambusoides) roots collected in central Florida. These nematode life stages were embedded in a hardened gelatinous matrix adhering to the root surface. Microscopical examination of the roots indicated that the vermiform female inserts its long stylet into root tissues and remains attached to the root surface by the stylet. The female body swells with gonad maturation. Eggs are deposited in a gelatinous matrix, which embeds and protects the female and newly hatched J2s. Third (J3) and fourth stage juveniles (J4) are inactive, coiled, and lack a developed stylet. They retain the cuticle after molting and produce motile males and vermiform females, which are enclosed in the juvenile cuticles. Newly hatched J2, kept in water at 25ºC, completed the postembryogenic development without feeding in 8-9 days. Histological examination of bamboo root sections infected by the nematode showed nematode feeding on the epidermis, cortical parenchyma and sclerenchyma. Feeding induces cell wall thickening of the epidermis at the feeding site. Up to 3-4 layers of cells are perforated by the stylet, which becomes encased in a cytoplasmic feeding tube. The feeding tube has been observed only in the epidermal, sclerenchymal and peripheral cortical parenchymal cells, which are usually the tissues explored and reached by the nematode stylet. Continuous feeding on these tissues results in the formation of a syncytium, which expands in the cortical parenchyma and extends into the central cylinder incorporating endodermis, pericycle, phloem and vascular parenchyma cells. Densely stained, discrete cells with hypertrophied nuclei and nucleoli, and granular cytoplasm are visible in the syncytium. Endodermal cells incorporated in the syncytium lose cell wall thickening. The morphological examination of the Florida population of G. latescens provides further indications that specimens described originally as putative J4s are actually J2s. The J2s of the Florida population have shorter stylets than reported in the original description (10µm vs. 15µm).