ارزیابی ژنوتیپ‌های گیاه هویج نسبت به آلودگی نماتد ریشه‌گرهی Meloidogyne javanica

Root-knot nematodes are the most critical plant parasitic nematodes that cause significant damage in carrot fields. In light of growing environmental worries related to chemical pesticide usage, it is crucial to locate plant genetic resources that exhibit resistance and tolerance to nematodes. This research aimed to screen of resistance level of 26 different genotypes of carrot plants to the M. javanica. For this purpose, the plants were inoculated with population of 2 eggs and J2s per gram of soil, and the nematode pathogenicity and reproduction factors were analyzed 60 days post-inoculation. Upon assessing the resistance of the genotypes to the nematode, the levels of chlorophylls and carotenoids in the leaves were examined to explore the impact of the nematode on the plant's photosynthesis activity, which is the primary function of plants. The roots of the resistant genotype and one of susceptible genotypes were exposed to newly hatched J2s. Chlorophyll a, b, total chlorophyll, and carotenoid levels were evaluated after one nematode life cycle (35 days). The obtained data indicated that the nematode caused the most and least number of galls and egg mass in the roots of TN-99-62 and TN-99-129 varieties, respectively. Four studied genotypes had a gall index of 5, while twenty had a gall index of 4. Only one genotype had a gall index of 3, and TN-99-129 was the only genotype with a gall index of 2. In six genotypes, egg mass index was 4, eleven genotypes had an egg mass index of 3, eight genotypes had an egg mass index of 2, and TN-99-129 genotype had an egg mass index of 1. The gall index was used to assess plant damage, while the reproduction factor was used as an indicator of nematode reproduction, to determine the level of resistance of the genotypes. In eight genotypes, Ashil, HC104, HC105, HC108, HC109, TN-99-75, TN-99-86, and TN-99-134, the reproduction factor was less than 1 and the gall index was more than 2, so they were diagnosed as hypersusceptible. The gall index for genotype TN-99-129 was 2, and its reproduction factor was below 1, so it was the only resistant genotype. The other genotypes had a gall index of more than 2 and a reproduction factor of more than 1 and were identified as susceptible genotypes. The analysis of leaf pigments indicated that in the TN-99-129 genotype, although the nematode reproduction factor was low, there was a significant decrease in the levels of chlorophyll a, b, total, and carotenoids in response to nematode infection. The evaluation provided in this report is the first step in assessing the resistance of carrot varieties in Iran to root-knot nematode, which is a crucial accomplishment in considering them for inclusion in plant breeding programs.