Ultrastructure of the tail region of the second stage preparasitic larva of the root-knot nematode

Abstract

Studies on the tail of second-stage infective larvae (L 2s) of Meloidogyne javanica, M. incognita and M. hapla from a region anterior to the rectal gland to the tail tip have revealed the presence of a previously undescribed sensory organ, the caudal sensory organ, in the posterior region of the tail. The extreme tip of the tail consists of solid cuticle and the different zones of this structure are described throughout the tail region. Longitudinal sections through the anus and rectum have revealed that the cortical (external cortical, epicuticle) layer gradually decreases in thickness until its outermost layer appears to merge with the plasma membrane of the rectal inflation or gland. This gland appears to be similar in all three species studied. The two phasmidial glands and their canals are described from transverse sections. Somatic muscle is first found in the region of the anus and it extends anteriorly throughout most of the length of the L 2. Depressor ani muscles which insert on the dorsal surface of the rectum are also described. The rectal gland in the dilated state occupies about three quarters of the diameter of the L 2. It contains a matrix which resembles that extruded from the adult female rectal gland cells. The rectal gland cells contain large amounts of rough endoplasmic reticulum and desmosomes are found close to the junction of these cells and the plasma membrane of the gland itself. More anteriorly in the L 2 most of the area is taken up by large lipid droplets which function as an energy reserve. It is suggested that the rectal gland should not be used as a taxonomic criterion for separating the La 2 S of Meloidogyne because it can vary so much in appearance within the same species.