Morphology and morphometrics of six species of pratylenchus.

Six species of Pratylenchus (P. penetrans, P. vulnus, P. coffeae, P. scribneri, P. zeae and P. brachyurus) were propagated aseptically on alfalfa callus tissue at 27 C and in greenhouse pot culture on suitable hosts. Morphological and morphometric comparisons revealed a high degree of variability of most taxonomic characters studied. The number of annules in the lip region, the number and arrangement of incisures in the lateral field, the shape of stylet knobs and tail varied considerably within most of the species. Of 20 morphometric characters, vulva percent and stylet length had the lowest coefficients of variability and were found to be of diagnostic value. A slightly greater morphometric variability was encountered in P. vulnus females and males from greenhouse than from callus cultures. A small spermatotheca containing no spermatozoa was present in the monosexual species P. scribneri, P. zeae and P. brachyurus. A few males were found only in P. brachyurus. The distal part of the uterus was composed of 12 cells arranged in three rows of four cells each (tricolumella). A detailed description of each species is given.