Transfer of resistance to the northern root-knot nematode (Meloidogyne hapla) from carrot wild relatives to the cultivated carrot
Plant-parasitic root-knot nematodes of the genus Meloidogyne, causing significant yield and quality losses, are a major economic risk for carrot cultivation. The northern root-knot nematode (Meloidogyne hapla Chitwood) is the nematode with the greatest importance for central and northern Europe. Commercial usage of the produced carrots can be completely prevented by extensive galling and forking of the taproot as well as enhanced lateral root formation. As no commercial cultivars with resistance to M. hapla are available and effective nematicides are withdrawn from use, breeding of resistant cultivars is highly important. Among other carrot wild relatives, Daucus carota subsp. azoricus was identified as resistance source. Backcross progenies of crosses carrot wild relative × carrot breeding lines were tested for resistance to the northern root-knot nematode along with their parental lines using a climatic chamber test. After four weeks of cultivation in a sandy substrate, each plant was inoculated with 400 M. hapla second-stage juveniles and cultivated for further ten weeks. After washing, the root systems were stained with cochineal red A. The number of galls and stained egg masses was determined. The ratio of resistant and susceptible plants in four independent F2 progenies of the cross D. c. azoricus × D. c. sativus was in agreement with a monogenic dominant inheritance of the resistance.
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