Quality damage on carrots (Daucus carota L.) caused by the root-knot nematode Meloidogyne chitwoodi

In the Belgian provinces Antwerp and Limburg, the root-knot nematode, Meloidogyne chitwoodi, is widespread. These regions are important production areas of carrot, Daucus carota, for the processing industry. Nineteen carrot cultivars were screened for potential resistance for M. chitwoodi. Egg masses of M. chitwoodi were found on all cultivars. However, there were no egg masses on more than 80% of plants of cvs Berlanda, Bolero, Chantenay, Nantucket and Parmex. By contrast, on cvs ABK, Douceur, Maxi and Merida egg masses were formed on all of the tested plants. To gain information about the damage caused by M. chitwoodi, carrots were grown in soil infected with different densities of nematodes. There was no effect of M. chitwoodi on the length, width and weight of the carrot taproot. Damage caused by M. chitwoodi was manifested by severe galling near the lenticels. Inoculation of nematodes 6 weeks after the carrots emerged resulted in a higher percentage of infected carrots and damaged taproots compared with earlier inoculation times. The effect of the time of harvest on nematode infection and damage was examined. When harvested 100 days after sowing in soil with low nematode densities (two second-stage juveniles (J2)/100 g soil), no damage was reported. Harvesting 120 and 140 days after sowing resulted in 10 and 20% damaged carrots, respectively. With initial M. chitwoodi densities of 25 J2/100 g soil, the percentage of damaged taproots increased from 10% when harvested 100 days after sowing to 70% when harvested 140 days after sowing. In a field trial, 11.5% of the carrots were damaged after a field period of 139 days and the initial M. chitwoodi population increased from 3 to I I I J2/100 g soil. It is recommended that growing carrots in M. chitwoodi-infested fields should be avoided. However, damage can be limited in fields with low initial nematode populations when the growing period is reduced.