Resistance and Tolerance of Commercial Onion Cultivars to Stem and Bulb Nematode Ditylenchus dipsaci

Nematode resistance and tolerance reactions of 28 onion cultivars grown commercially in Turkey to stem and bulb  nematode were studied at 20 °C, 70% RH and 16:8 h L:D photoperiod in growth chamber with 10 replications and at  27±4 °C and 16:8 h L:D photoperiod in greenhouse with 3 replications, respectively. Ditylenchus dipsaci multiplied in all  cultivars tested. The lowest multiplication was determined in cv. Valenciana from Ataturk Horticultural Central Research  Institute with 91 nematodes/pot and a multiplication rate of 0.5. Plant height of cultivars were significantly different in  the first tolerance experiment with having an average plant hight of 33.5 and 103.1 mm for inoculated and inoculated  plants, respectively (P<0.05). Onion shoot diameter was statistically greater in nematode inoculated plants with 7.4 mm  than inoculated plants with 6.0 mm in second tolerance experiment (P<0.05). Plant weight was not found different in both  tolerance experiments with nematode inoculation. There was not any statistically difference among cultivars for plant  height, plant diameter, plant weight and nematode multiplication in the experiments. Plant diameter for cv. Betapanko  in first tolerance experiment and plant height for the Banko type onion in the second tolerance experiment sustained  significant negative correlations with nematode numbers. Plant weight for cv. Biotek Boran in second experiment, plant  height for cv. Taraz in second experiment and, plant diameter and plant weight for cv. Taraz in first tolerance experiment  sustained significant positive correlations with nematode multiplication. It could be recommended that Valenciana could  lower nematode multiplication and Biotek Boran and Taraz could maintain a better plant development in nematode  infested onion growing areas.