Combining ability analysis of root-knot nematode resistance in air-cured tobacco

Root-knot nematode (RKN) [Meloidogyne incognita] is one of the main pests of tobacco. Determination of genetic behavior for RKN resistance can be useful to improve the resistance of tobacco against RKN. This study was conducted to determine the combining abilities and genetic parameters of RKN resistance in tobacco using a five-parent diallel analysis by Griffing’s method. Three resistant parents (Urmia3, KY9, K17) and two susceptible parents (Ergo, Burley TMV4) were crossed based on half diallel. Fifteen genotypes (Parents and F1s) were planted in the greenhouse based on completely randomized design with five replications and inoculated with 2500 J2 M. incognita race 2 one week after transplanting. Investigation of Gall Index (GI), Number of Egg Masses (NEM) and Average of Eggs per Mass (AEM) showed significant differences among genotypes. The general combining ability was more important than the specific combining ability in GI and NEM. Non-additive effects in AEM and additive effects in GI and NEM had more important role. Narrow-sense heritability was 0.73, 0.54 and 0.07 for GI, NEM and AEM, respectively, which revealed that GI and NEM are suitable traits for RKN resistance identification. KY9 had the highest negative GSA in all traits. So this genotype is appropriate donor parent for RKN resistance.