The Effect of Delay of Attack of Oats By Heterodera a Venae On the Relation Between Initial Nematode Density and Plant Growth, Plant Weight, Water Consumption and Dry Matter Content

Abstract

The relation in two experiments between egg density P of Heterodera avenae and relative weight y of 97 and 77day-old oat plants in pots inoculated at different times after sowing was in accordance with the equation y = m + (1-m) 0.95P/T-1 for P> T and y = 1 for P> T (1). Values of m were strongly and of Tweakly positively correlated with the time after sowing that the pots were inoculated. Up to egg densities 90Twater consumption of the plants was proportional but at larger egg densities smaller than proportional to dry plant weight, while at densities >90Tdry matter content also was increased (second mechanism of growth reduction). The effect of nematode attack on weight increase of the plants determined in one experiment (growth curves derived from water consumption) was in accordance with Seinhorst's (1979, 1986) growth model: rp/r0 = t0/tp = k + (l-k) 0.9675P/T-1 with Tas in eq. (1) for P>Tand rp/r0 = t0/tp = 1 for P< T(same ratio of growth rates of plants of given weight at given nematode density P, rp, reached at time tp after the start of nematode attack, and of plants of the same weight without nematodes, r0, reached at time to after the start of nematode attack, at all times to). The value of k was the same for all nematode densities at a given inoculation date but it was positively correlated with the time between sowing and the inoculation of the pots.