Response of sugar beet to population densities of Heterodera schachtii in microplots in Iran.

Two experiments were conducted in microplots in Iran, in 2002 and 2003, to relate a range of population densities of the sugar beet cyst nematode, Heterodera schachtii, to yield of sugar beet and reproduction of the nematode. Microplots consisted of clay pots and contained 12 kg soil infested with 0, 0.25, 0.50, 1, 2, 4, 8, 16, 32, 64 or 128 eggs of H. schachtii g(-1) and each inoculum level was replicated eight times. At harvest, weights of sugar beet tap roots were fitted to the Seinhorst's model. Tolerance limits of sugar beet to H. schachtii were 0.62 egg g(-1) soil in 2002 and 1.16 eggs g(-1) soil in 2003 with all average of 0.8 egg g(-1) soil for both years. Average yield losses of 20, 50, and 80% occurred at population densities of tile nematode at sowing of 5, 14, and 40 eggs g(-1) soil, respectively. The reproduction rate of the nematode decreased with the increase of nematode population at sowing and maximum rates of 79.6 and 86.0-fold occurred at the lowest initial population density of 0.25 egg g(-1) soil in 2002 and 2003, respectively. The largest nematode density (84.6 eggs g(-1) soil) occurred at the highest inoculum density. The equilibrium density of the nematode was less than 64 eggs g(-1) soil and all average population decline of 55.5% was observed in the microplots left fallow.