The pathogen-weed complex: a new perspective on the role of alternative hosts in Meloidogyne graminicola epidemiology

Weeds, especially purple nutsedge, are not just alternative hosts but highly susceptible host that drive the persistence and spread of rice root-knot nematodes. This study provides a comprehensive assessment of the host status of eight plant species, including rice and common rice-associated weeds, to the root-knot nematode Meloidogyne graminicola. By integrating quantitative infection assays with confocal laser scanning microscopy, we combined whole-plant measurements of nematode development with cellular-level visualization of feeding-site structures to characterize host suitability more precisely. The results revealed a continuum of responses ranging from weakly supportive to highly susceptible hosts. Purple nutsedge (Cyperus rotundus) showed the highest susceptibility under controlled conditions, with a reproduction factor (Rf = 77.25) exceeding that of rice (Oryza sativa, Rf = 15.45) and jungle rice (Echinochloa colona, Rf = 19.81). Digitaria sanguinalis also supported considerable nematode multiplication (Rf = 10.92). Confocal imaging provided temporal snapshots of feeding-site formation, giant cell development and gall progression in C. rotundus, complementing the quantitative findings. Several species, including Glinus oppositifolius and Stellaria media, supported minimal development, indicating limited suitability as hosts. Overall, the study demonstrates that multiple weeds commonly present in rice ecosystems can sustain M. graminicola development to varying degrees under experimental conditions. These results highlight the importance of considering weed species when evaluating nematode population dynamics and designing integrated management strategies for rice-based agroecosystems.