Unraveling the off-season survival of rice root-knot nematode, Meloidogyne graminicola, in wetland rice ecosystem

One of the basic foods consumed by humans globally is rice, and a variety of biotic factors, most notably weeds and plant parasitic nematodes (PPN), hinder the production of rice. The impact of weeds on rice production is well established, and among PPN, Meloidogyne graminicola, a rice root-knot nematode (RRKN), is becoming a major issue. Although the weeds and RRKN share the same habitat, it is yet unknown how these weeds contribute to the off-season survival of RRKN. Consequently, the current study was done to determine the susceptibility of weeds in the rice wetland ecosystem to RRKN. The weed survey was carried out in rice fields during both crop season and off season, followed by its susceptibility study against RRKN in pot experiment. 24 weed species were discovered to be prevalent including 17 broadleaved weeds (BLW), 5 grassy weeds (GRW) and 2 sedges (SED). Among them the GRW were more frequent (93.33%) and predominant (48.20/0.25 m², 64.71% of all weeds) in the crop season. On the other hand, during the off season, the BLW predominated (55.17/0.25 m², 58.16% of all weeds). Based on our susceptibility test against RRKN, we discovered that, among the 24 weed species, 9 act as good hosts with Build Up Index (BUI) > 10, 4 function as poor hosts with a BUI between 1 and 10, and 11 act as non-hosts with a BUI < 1. We are presenting information on five novel weed species that act as alternate hosts of RRKN for the first time: Macerdonia procumbens, Leptochloa chinensis, Ipomea aquatica, Ammannia baccifera and Eragrostis racemose. The weeds that were observed in both seasons such as Cyanotis axillaris (BUI-16.67), Phyllanthus niruri (BUI-15.97), Macerdonia procumbens (BUI-14.33), Eclipta alba (BUI-14.00), Sphenoclea zeylanica (BUI-13.00) and Echinocloa colona (BUI-15.00) could therefore constitute a serious threat to rice wetland cultivation by assisting the off-season survival of RRKN. The findings underline the importance of weed management strategies in managing the RRKN in rice wetland ecosystem.