Optimal inoculum levels for the resistance screening of sugar beet to root- knot nematode under greenhouse condition

Sugar beet (Beta vulgaris) is one of the hosts for different root-knot nematode species. In this study, firstly the effect of different inoculum levels including 250+250, 500, 500+250, 750, 500+500 and 1000 second stage juveniles of Meloidogyne javanica were evaluated on a susceptible variety named Jolgeh. The results showed that all inoculum levels were suitable for infection on sugar beet plants and that the gall numbers at one and two time inoculations were not statistically different (p≥0.01). Therefore, 500 second stage juvenile of root-knot nematode was the lowest inoculum level that could be used to infect sugar beet plants in the greenhouse. In the second experiment, the best treatment was applied on Jolgeh (susceptible to root-knot nematode) and Pauletta (commercial resistant variety to cyst nematode) varieties and also seven half-sib families derived from SB33 population (carrying root-knot nematode resistance gene), to evaluate its generalization for screening of resistant/susceptible genotypes. The total number of root galls was taken as nematode resistance criterion. Results showed that Jolgeh and Pauletta varieties with average number of more than 100 galls were considered as highly susceptible varieties whereas the seven half-sib families with average number of 10 galls (<10)were classified as resistant varieties.