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

SIMPLE SUMMARY: Nematodes are the soil microbes that function for nutrient regulation and biological degradation. Nematode diversity changes during different seasons of a year due to changes in ecological factors. Soil characteristics change significantly due to lowland rice cultivation. This research investigated soil nematode diversity and seasonal changes in rice fields during three months of the year. Soil nematode abundance was different during the three seasons, and plant-parasite nematodes were more abundant during summer than in spring or winter. Soil characteristics, such as soil moisture, carbon content, and nitrogen content, were more common during the summer season than in the spring and winter seasons, while soil pH was low in the summer season. The plant-parasitic nematodes showed a stronger correlation with the soil characteristics during the summer season than in the spring and winter seasons. In addition, the abundance of some free-living nematode genera functioned as ecological indicators. The community and diversity indices of this study will help farmers and microbiologists in nematode management in crop fields. ABSTRACT: 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.