Relationship Between Paratrichadorus sp. Density, and Growth of Wheat in Pots.

The effect of a Paratrichodorus sp. (close to P. tunisiensis) on the growth of wheat (Triticum durum Desf.) was investigated in pots containing different nematode densities and maintained in a growth chamber at 20 C for 40 days. The relation between fresh weight of tops and initial nematode density was according to the equation y = m + (1 - m)z(PT). This suggests a tolerance limit of 1.4 nematodes/cm(3) of soil under the conditions of the experiment; taking into account the effect of the great nematode mortality, it is estimated to be between 0.15 and 0.35 nematodes/cm(3) soil. Models of the growth of the plants and the multiplication of the nematodes (assuming a constant mortality of the nematodes in the absence of roots) which explain the relation between initial and tinal nematodes densities at initial densities greater than 1 nematode/cm(3) soil are described in an appendix. Sections of nematode infested roots showed disorganization of root structure clue to abnormal proliferation of lateral roots. Nematode feeding on the root cap and apical meristem caused cessation of root elongation and induced abnormal production of lateral root primordia.