Study on two nematode species suggests climate change will inflict greater crop damage

Food security has become one of the greatest challenges of the millennium and it is predicted to be exacerbated by climate change due to the adverse effects of soil temperature on crop productivity. Although plant-parasitic nematodes are one of the most important limiting factors of agricultural production, the fate of soil temperature in their biology is not fully understood. Here we present the effects of soil temperature on survival, reproduction, virulence, and disease severity from the perspective of two nematode species Rotylenchulus reniformis and Meloidogyne floridensis. The two nematode species were purposefully selected to represent a significant threat to annual and perennial crops. We employed novel approaches of direct as well as indirect heat exposure to evaluate nematode biology. The direct heat exposure assay involved the exposure of nematodes to hot water in a heating block at 32, 33, and 34 °C for 7 h, and subsequent evaluation of their survival after 18 h. The indirect exposure assay employed a commercial heat mat to raise soil temperatures to 32, 33, and 34 °C for 7 h during the daytime, and subsequent evaluation of nematode reproduction, virulence, and/or disease severity over the period of 6 weeks after inoculation. When directly exposed to hot water at 34 °C, the survival of R. reniformis increased by 10% while the survival of M. floridensis decreased by 12% relative to that at 32 °C. Upon increasing soil temperatures from 32 to 34 °C, the reproduction of R. reniformis and M. floridensis decreased by 49% and 53%, respectively. A significant reduction in the reproduction of M. floridensis occurred when soil temperature was increased from 33 to 34 °C, however, the same condition did not significantly affect R. reniformis reproduction suggesting the latter species has a greater ability to adapt to increasing soil temperature. Additionally, the virulence of R. reniformis was greater at 33 and 34 °C relative to that at 30 °C indicating increased aggressiveness of the nematode at higher soil temperatures. The virulence of M. floridensis appeared to be decreased as evident from increased root biomass when soil temperature was increased from 32 to 34 °C, however, the greater root biomass may have resulted from increased root galling at the higher temperatures. Results of the current study suggest that while higher soil temperatures due to climate change may lead to reduced nematode reproduction, crop losses will likely increase due to increased nematode virulence. Through the current study, we report practical evidence of the quantitative impact of climate change on the biology of plant-parasitic nematodes. Further studies involving a wider range of temperature and exposure time are needed to better understand nematode biology under climate change.