Tolerance and resistance of onion (Allium cepa) to stem and bulb nematode (Ditylenchus dipsaci)

Resistance is known as a defense mechanism of plant, while tolerance is ability to give good yield where there is a pathogen. Both mechanisms provide advantage to plant under unfavorable conditions. Onion is an economically important plant species grown in the world for human nutrition and the important constrain of it is stem and bulb nematode (Ditylenchus dipsaci). Both tolerance and resistance of onion cultivars were investigated under greenhouse conditions to D. dipsaci. Totally 28 onion cultivars were evaluated for resistance and tolerance reactions to D. dipsaci under growth room and greenhouse conditions, respectively. 'Valenciana' cultivar had the lowest nematode multiplication in growth room resistance experiment (MR: 0,5). Plant height and plant diameter of cultivars statistically significantly changed with nematode treatment in greenhouse tolerance experiment. Plant weight of 'Biotek Boran' and plant height, diameter and weight of 'Taraz' had statistically significant positive correlations with nematode multiplication. It is recommended growing 'Valenciana' for lower nematode multiplication, and 'Biotek Boran' and 'Taraz' for better plant development under nematode multiplication in stem and bulb nematode infested onion growing areas.