Characterization of Heterodera carotae from the Tarlton area, South Africa, and determination of its life cycle under field conditions: a baseline study

Identification of Heterodera carotae (carrot cyst nematode), first reported from the Tarlton area in South Africa in 2008, was based on morphometrical and morphological characteristics. Specimens from this area were collected during the summer growing season of 2016 and identified using classical morphometrical and morphological techniques as well as molecular methods. The life cycle of this species was furthermore investigated in a carrot planting. Slight morphological differences were found between the Tarlton-population of H. carotae (South Africa) and its European, Canadian and Mexican counterparts. Second stage juveniles (J2) have a slightly shorter body (270.3–434 µm vs. 375–452 µm from those of Europe; 388–457 µm from Canada; and 360–443 µm from Mexico) and their heads are narrower (5.8–8.7 µm vs. 9–10 µm and 8–10 µm compared to that of specimens from Europe and Mexico, respectively). Spicules were slightly longer than that of both European and Canadian specimens (36.5–40.0 µm vs. 31–36 µm and 33–37 µm, respectively), but compared well with that of the Mexican males (36.5–40.0 µm vs. 32–39 µm). The male stylet is shorter (28.5–29.6 µm vs. 31–38 µm in European and 33–44 µm in Canadian specimens), but is nearer to that of Mexican specimens (28.5–29.6 µm vs. 29–36 µm). Novel golden-yellow cysts were observed. Phylogenetic analysis grouped the Tarlton population together in a clade with H. carotae, H. cruciferae and H. urticae. BLAST results indicated a 99% similarity with H. carotae. Heterodera carotae completed two life cycles during this growing season in Tarlton.