Population dynamics of the citrus nematode Tylenchulus semipenetrans Cobb, 1913 in an infested orchard in Fars province, southern Iran

Abstract The citrus nematode Tylenchulus semipenetrans Cobb, 1913 is one of the most important threats limiting the growth of citrus trees around the world. In recent years, efforts have been made to control this pathogen. Determining the number of generations and population peaks of this nematode is necessary for its control. This study was conducted to investigate the fluctuations of the citrus nematode population in Fasa, an important citrus growing city in Fars province, southern Iran, between 2018 and 2019. The results showed that the lowest levels of soil nematodes including second-stage juveniles (J2s) and males, and root nematodes (eggs, juveniles and females) occurred in July. However, the peak of population levels were different for root and soil nematodes. For root nematodes, two peaks were recorded in late May and November, while for soil nematodes, two peaks were recorded in late May and December. From the results, the nematode population in the roots (especially the female ones) was less subject to fluctuations compared to the soil population. In most samples, the nematode populations in the roots decreased with increasing distance from the tree trunk. Overall, the results showed that there are two population peaks per year, suggesting that two generations of the citrus nematode occur in Fasa orchards. From a management perspective, the results of this study can be generalized to all citrus orchards with the same geographic and environmental factors.