Histological study of syncytia induced in cereals by the Mediterranean cereal cyst nematode Heterodera latipons

Abstract

AbstractFeeding sites of Heterodera latipons in wheat, barley and Lolium rigidum were studied and compared with those of Heterodera avenae in wheat. Juveniles of H. latipons penetrated mainly differentiated roots and chose a root cortical cell as their initial syncytium cell (ISC) in wheat and barley, whilst H. avenae chose a vascular parenchymal cell as an ISC. The cell associated with females in wheat root underwent hypertrophy, and incorporated endodermis, pericycle and parenchyma cells of the vascular cylinder by cell wall dissolution. Syncytia of H. latipons contained a high number of organelles, including endoplasmic reticulum, mitochondria, plastids and amoeboid nuclei, whilst those of H. avenae were highly vacuolated. The syncytium partly occupied both the cortex and the vascular cylinder in contrast to those of H. avenae, which occupied most of the space within the vascular cylinder near the infection site. The cortical cell associated with H. latipons males did not undergo hypertrophy, but had dense cytoplasm, and incorporation of other cells by cell wall dissolution was rare. A similar syncytium formation process was observed with barley, but a cortical cell, several cell layers away from the endodermis, was chosen for the ISC. In resistant L. rigidum, H. latipons juveniles chose an endodermal cell or its neighbouring cortical cell as an ISC. Partial dissolution of cell wall was observed in neighbouring parenchymal cells, although the nematode did not develop into adults.