Alteraciones histológicas inducidas por Meloidogyne hapla y M. arenaria en zanahoria (Daucus carota L.) en el Valle de Tepeaca, Puebla, México

The aim was to describe anatomical changes induced by M. arenaria and M. hapla in carrot roots. In 2008, 19 carrot fields from Tepeaca Valley, Puebla, central Mexico were sampled. Galled and not galled roots were collected, fixed in FAA, and embedded in paraffin for sectioning (9-10 μm) in longitudinal and transverse planes. Sections were stained with fuchsin-fast green and mounted in synthetic resin. M. hapla was identified in six of the 19 fields (31.6%) inducing small galls (diameter 1-4 mm) and proliferation of lateral roots; 2-9 giant cells with dense granular cytoplasm were observed and a large compact mass of nuclear material in the center was observed in most cases. Giant cells were located in vascular cylinder replacing the xylem and phloem. Meloidogyne arenaria was mixed with M. hapla in four fields (21.1%) and induced galls larger than those induced by M. hapla (0.5-1.5 cm diameter) and with no lateral roots. Four to twelve multinucleate giant cells were observed, containing dense granular cytoplasm and thick walls; nuclei and nucleoli were enlarged. These cells were located in cortical tissue mainly, but sometimes also invaded the vascular cylinder.