Identification and a culture method for a Helicotylenchus microlobus from tomato in China

The nematodes of the genus Helicotylenchus are root parasites of a wide variety of plants, and certain species can cause serious damage to their hosts. During a survey of the plant-parasitic nematode associated with tomato, a population of Helicotylenchus was collected from tomato roots and soil samples. Thus, one of the objectives of the study was to confirm the specie of Helicotylenchus obtained from the tomato samples based on morphological and molecular characteristics. In addition, a mass pure culture of plant-parasitic nematodes is key to pathogenicity studies and many other biological studies. However, a successful mass rearing method for Helicotylenchus has not been reported. Thus, the other objective of the study was to establish a method of culturing Helicotylenchus.

Based on both the morphological characteristics and molecular analysis of the internal transcribed spacer (ITS) and D2-D3 expansion region of 28S ribosomal RNA (rRNA) sequences the specimens were identified as Helicotylenchus microlobus. Phylogenetic analysis with the rRNA sequences of the ITS and 28S D2-D3 regions was consistent with molecular identification, suggesting this population formed a highly supported clade with other H. microlobus populations. Additionally, a method for culture of H. microlobus on carrot disks was established, and the effect of temperature on the reproduction rate (Rr) of H. microlobus was investigated. The optimum temperature for culturing H. microlobus on carrot disks was 27.5 °C and, after inoculation with 30 females of H. microlobus at 27.5 °C for 90 days, Rr reached 406.

To our knowledge, this is the first detailed description of H. microlobus from tomato in China. This study also demonstrated that the carrot disk method is suitable for the culture of H. microlobus. This study lays a foundation for other related research on H. microlobus, and has significance for the study of Helicotylenchus.