Factors Influencing the Number of Larvae of Heterodera Avenae Within Susceptible Wheat and Barley Seedlings

The number of larvae of Heterodera avenae which penetrated a root of wheat (cv. Halberd) increased linearly as density of inoculum increased until a maximum was reached. Which root of the seedling was inoculated did not affect the number penetrating but placing sand on the root tip before inoculation increased the number of larvae which penetrated. When the roots were exposed to larvae for longer periods there was generally a similar change in the numbers penetrating a root, except that there was an initial lag phase and that a constant number was not maintained at high densities. The duration of the lag phase decreased as inoculum density increased. With increased duration of exposure of the root the number of larvae established or immobile within the root increased linearly till constant. Longer storage of larvae prior to inoculation increased the number of immobile larvae within the root. The number of larvae penetrating single roots of wheat and barley (cv. Clipper) was the same, but barley developed more seminal roots during early seedling growth than wheat. Tolerance in barley to H. avenae was attributed to the dilution of the number of larvae in each root tip because of the increased number of roots.