Year-Long Assessment of Soil Nematode Diversity and Root Inhibition-Indicator Nematode Genera in Rice Fields

Soil nematodes contribute to nutrient cycling. This year-long study aimed to investigate the changes in the diversity of soil nematodes during the spring, summer, and winter seasons in rice fields at 24 sites and to determine the indicator nematode genera that inhibit the roots of rice plants. A total of 216 soil samples were collected during three seasons, and the collection of 72 root samples was carried out during rice cropping. Forty-four soil nematode genera were identified. They exhibited significant changers in their abundance, which were dependent on the seasons and on soil characteristics. In particular, the abundance of plant-parasitic nematodes (PPNs) and free-living soil nematodes was 49% and 15% higher during the summer than during the spring and winter seasons, respectively. Soil characteristics, such as soil nitrogen (N) contents, carbon (C) contents, and soil moisture were significantly higher during the summer than in the spring and winter seasons, but soil pH was significantly lower during the summer than in the spring and winter seasons. Moreover, Hirschmanniella,Meloidogyne, and Heterodera emerged as good indicators for rice root inhibition, corroborating the frequency, density, and prominence value of PPNs of the sampled soil and rice roots. This study also indicated that free-living nematode genera, such as Rhabdolaimus, Diplogaster, and Rhabditis, might function as ecological indicators for soil health.