Intra-specific morphological and morphometric variability of Radopholus similis (Cobb, 1893) Thorne, 1949

Abstract

All the root inhabiting migratory endoparasitic nematode populations of Radopholus procured from banana crop of Vellayani, Thiruvananthapuram, Kerala were identified as Radopholus similis. Heat killed females were straight to slightly ventrally curved posteriorly. Female’s head was low, rounded, continuous or slightly setoff with the body contour. Females were 500-660 µm long and were comparatively longer than males. Males had button shaped head set off by a constriction; female with three to five lip annuli, four crenate and areolated lateral incisures, stylet 14-18 µm long with rounded knobs, vulva post-equatorial (58%), sometimes with slight protuberant lips, ovary paired and equally developed, oesophageal gland overlapped the intestine dorsally, tail elongate-conoid with narrowly rounded terminus. The stylet length (µm), width of stylet knob (µm), distance of excretory pore from anterior end (µm), distance from head to basal bulb (µm), lateral field structure, shape of stylet knob, head region, position of phasmid, tail shape with its terminus, morphometric values like m%, o% and v% and a, c and c´ ratios of females were stable (CV<12%) features. There is an existence of intra-specific variability in the morphological and morphometric features of R. similis. The main morphological diversity was observed with P% of male and female, b ratio of female and stylet length, distance of DEGO from stylet base, o% and T% of male. All the root inhabiting migratory endoparasitic nematode populations of Radopholus Thorne, 1949 procured from banana of Vellayani, Thiruvananthapuram, Kerala were identified as Radopholus similis (Cobb, 1893) Thorne, 1949. A high degree of intra-specific morphometric variability was observed with regard to the total body length (µm), body width (µm), stylet length (µm), distance of dosrsal oesophageal gland orifice (DEGO) from stylet base (µm), number of lip annuli, lip height (µm), distance from head to basal bulb (µm), distance of anus from anterior end (µm), tail length (µm), anal body width (µm), distance of phasmid from tail terminus (µm), number of lateral lines, width of lateral field (µm), b ratio and P % among females of R. similis. Morphometric features like m%, o% and v% of females of R. similis showed least variability. These can be considered as the stable morphometric characters for discrimination of females of R. similis. Ratios like ‘a’ and ‘c’ of females of R. similis were found moderately variable. The morphometric feature and of male i.e. distance from head to basal bulb (µm) was found least variable; while number of lip annuli and spicule length (µm) were moderately variable.