THE PARASITIC BEHAVIOR OF 2ND-STAGE JUVENILES OF MELOIDOGYNE-INCOGNITA IN ROOTS OF ARABIDOPSIS-THALIANA

The parasitic behaviour of second-stage juveniles (J2) of Meloidogyne incognita in roots of Arabidopsis thaliana was recorded at 25 +/- 1-degrees-C with the aid of video-enhanced contrast light microscopy and time lapse techniques. The J2 invaded the root primarily in the region of elongation, close to the meristematic zone. Invasion was achieved, in most cases, by destroying epidermal and subepidermal cells, while intercellular invasion between epidermal cells was less frequent. Inside the root the J2 oriented themselves always in the direction of the root-tip and migrated towards it between cortical and meristematic cells without causing any damage. Occasional attempts at intracellular migration through cortical cells were observed but these failed due to insurmountable barriers. When the J2 reached the apex of the root, they turned round and migrated backwards between the cells towards the differentiating vascular cylinder. Within the differentiated cylinder migration eventually stopped and giant-cell induction was initiated. After a period of induction, the J2 became surrounded by young multinucleate giant-cells within about 24 h. A characteristic behavioural pattern, composed of continuous head and stylet movements, interspersed by periods of stylet-tip protrusion and metacorpal bulb pumping, was maintained throughout all phases of parasitism, also when the J2 fed from the young giant-cells.