Damage thresholds and population dynamics of Pratylenchus penetrans on carrot (Daucus carota L. cv. Nerac) at three different seed densities

Yield and quality loss of carrot (Daucus carota L. cv. Nerac) caused by Pratylenchus penetrans and the population dynamics of this nematode were studied in a climate controlled glasshouse. A range of 12 nematode densities was used at three different seed densities of carrot; 2, 4 and 18 seeds pot−1. Seinhorst’s yield loss model; y = m + (1 - m) 0.95Pi/T-1 for Pi > T; y = 1 for Pi ≤ T for Tylenchina was fitted to the yield and quality loss data. Seinhorst’s model for population dynamics of migratory nematodes with multiple generations; Pf=M∗Pi/(Pi+M/a)Pf=M∗Pi/(Pi+M/a) was fitted to the data of the final population densities (Pf). P. penetrans had a significant impact on carrot taproot yield and its quality. The tolerance limits for the relative carrot taproot yield (Ty) were 1.51, 1.88, and 1.37 and those of quality yields (Tq) were 0.67, 0.18, and 0.40 P. penetrans (g dry soil)−1 at 2, 4 and 18 seeds pot−1, respectively. Both the minimum yield (0.20, 0.29, and 0.60) and the minimum quality yield (0.05, 0.07, and 0.20), expressed as a proportion, increased with seed density at 2, 4 and 18 seeds pot−1, respectively. The model for population dynamics fitted well to the Pf data obtained. The maximum multiplication rates (a) were 19.58, 9.99, and 17.54, while the maximum population densities (M) were 49.86, 43.21, and 60.37 P. penetrans (g dry soil)−1 at 2, 4, and 18 seeds pot−1, respectively. Carrot cv. Nerac can be considered a good host for P. penetrans.