Differentiation of Cysts of Heterodera schachtii and H. trifolii by Fenestral Length.

The sugarbeet cyst nematode, Heterodera schachtii Schmidt, 1871, was discovered by Mai et al. (4) in fields of 16 New York State commercial red table beet growers during a survey in 1970-1971. They reported that the clover cyst nematode, H. trifolii Goffart, 1932, which also has lemon-shaped cysts with bullae, was present in very low numbers in many of the fields sampled. Thus a rapid and reliable method was needed to differentiate cysts of these nematodes in the many soil samples collected. Several workers have suggested that lemon-shaped cysts ofHeterodera spp. could be separated by vulval cone structures (1, 2, 3, 5, 6). Oostenbrink and Den Ouden (6) suggested that for practical advisory work fenestral length may be useful in differentiating cysts of H. schachtii and H. trifolii. They reported that the average fenestral lengths of H. schachtii and H. trifolii were 32.1 and 45.6/l, respectively. They also concluded that "an average of five specimens is adequate to place a population below or above 38.7, which is the limiting value between the two species according to statistical treatment of the presented data". Fenestral lengths reported by Mulvey (5) and Jimenez (3) substantiated this finding. Mulvey (5 ) a l so reported that no statistical correlation occurred