Species characterization and population dynamics of Hirschmanniella mucronata in lowland rice fields managed under conservation agriculture in Cambodia

Abstract

The rice root nematodes, Hirschmanniella spp., are considered the predominant plant-parasitic nematode in the clay soils of Battambang’s lowland rice fields in Cambodia. In this study, we compared the nematode population dynamics, rice yield parameters, and soil organic matter content in lowland rice fields under conservation agriculture (CA) system with conventional tillage systems with green manure management (GMCT) or with plough-based tillage (CT) systems. Results demonstrated that GMCT for one year (GMCT1) and the long-term CA for seven years (CA7) reduced nematode densities in both soil and in rice roots, almost throughout the study period, compared to the CT. In the GMCT with tillage for two years (GMCT2), however, the Hirschmanniella spp. densities were high at the beginning, but reduced at later stages of the cycle. For rice yield components and soil fertility, CA7 proved to be effective in increasing plant height, the number of tillers/plant and soil organic matter. Based on molecular, morphometric and morphological features, the nematodes were identified as H. mucronata. The phylogenetic trees of three nuclear markers displayed similarity among 18S, 18S-ITS1-5.8S and D2D3 regions, identifying nematodes as H. mucronata clade I (bootstrap values of 79–100) and related to H. kwazuna and H. loofi sisters. Morphologically the long body (1,512–2,665 µm), long stylet (25–29 µm) and obvious mucron at the end of terminus matched with H. mucronata . Therefore, long term CA, with reduced tillage and using leguminous cover crops provides a promising system to control H. mucronata and promote rice yields and soil organic matter in Cambodian lowland rice fields.