PHENOLOGY, PATHOGENICITY AND PATHOTYPES OF CEREAL CYST NEMATODES, HETERODERA-AVENAE AND H-LATIPONS (NEMATODA, HETERODERIDAE) IN ISRAEL

Cereal cyst nematodes were found in varying population densities in the majority of wheat fields surveyed in Israel. The dominant species was Heterodera avenae (Ha), while H. latipons (Hl) occurred mainly in the more arid (southern) areas. The phenology and life cycle of the two species was basically similar: both species completed a single generation per year, life-stage development being closely related to climate and plant development. The two species differed in their etiology; whereas Ha attacked the root tip region inducing typical branching and swelling of roots with ensuing adherence of soil particles, juveniles of Hl penetrated at sites along roots more distant from the apex and, therefore, did not produce clearly visible root symptoms in the early seedling stage. In field conditions, the presence of Hl could be recognized only when cysts appeared on the roots. Moreover, the growth inhibition caused by Ha was more severe than that due to Hl. All local wheat cultivars tested were found to be excellent hosts for both Ha and Hl, as were all tested cultivars of barley and Phalaris sp.; oat cultivars were extremely poor hosts of Ha, but good hosts of Hl. Seven Ha populations showed the predominance of two pathotypes: Ha21, in the northern and the coastal regions, and Ha41 in the southern areas. Soil temperature affected both Heterodera' species hatching and damage to roots: at 6-degrees-C, life-stage development took 4 months, and it shortened as temperature increased up to 18-degrees-C, when it took only 40 days. At 24-degrees-C, juveniles failed to penetrate the roots. The effects on plant growth of early vs later sowing in dry and wet soils were recorded and are discussed.