Plant-nematode interactions: novel insights to sustainable management
Rice (Oryza sativa L.) is one of the most important food crops in the world. It is used as a staple food for the majority of the world populations, predominantly in Asia where more than 90% of world rice is grown and consumed. Among the biotic stressors that deplete rice production, the root knot nematode, Meloidogyne graminicola (Mg) is considered to be one of the most damaging causal agents in the tropical aerobic rice system, contributing to 20-80% yield loss. The two of the most effective control measures, soil flooding and nematicide applications are of increasingly limited utility for controlling Mg. In the case of floodwater management, the recent adoption of labour and water conserving practices could potentially increase the pest potential of Mg. Management using chemical nematicides is not only hazardous to the environment but are economically prohibitive to the small and marginal farmers. Given the paucity of control options, the development of novel strategies against Mg is crucial for maintaining rice production sustainability. By studying the interaction between Rice and Mg, the overarching goal of my research programme is to generate sustainable cost effective management options for this important nematode. To this front, my research focus will broadly involve the following two mechanistic routes: host plant resistance and chemical ecology of the interaction
Schematic representation of our research plan. We are studying the plant nematode interaction using the rice-M. graminicoal model under two major domains: host plant resistance and chemical ecology of the interaction. Graphs (a, b, c) in the right side shows preliminary data generated in our lab. (c) shows the modified dual choice olfactometer used to study nematode chemotaxis behaviour.
A) Host plant resistance (HPR): The innate ability of a plant to avoid, tolerate or recover itself from herbivory, HPR, offers an effective and economic alternative to other nematode controlling practices. Screening for Mg resistance in Oryza germplasm has already been successful. To date, we have collected 523 rice germplasms across the country. These are currently being maintained in our research farm in ISI, Giridih. Screening of the rice germplasms against Giridih isolate of Mg resulted in the identification of three highly resistant lines (Graph a). Resistant reactions were confirmed in both host sensitivity and host efficacy assays. Expression profiles of 59 genes, known to provide nematode resistance in rice (including reference genes) are currently being analysed to understand the molecular basis of the resistance. To determine the effectiveness of resistance of selected lines against multiple isolates, challenge inoculation studies were conducted with six isolates of Mg collected from different rice-growing regions of the country (Graph b).
B) Chemical ecology of interaction: Chemotaxis is known to be the primary means by which nematodes locate host plants. Mg hatch from eggs in the soil into non-feeding infective juveniles (J2). J2s must find a suitable host to establish a feeding site. They are preferentially attracted to and penetrate the region of the rice root just above the root tip, corresponding approximately to the elongation zone, likely responding to multiple sensory inputs, perceiving hosts over a long distance through volatile compounds (smell) and more locally through water soluble chemical signals (taste). Preliminary experiments conducted using a modified dual choice olafactometer (Picture c) in our lab showed that under choice tests, Mg J2s are preferentially attracted towards susceptible rice cultivars (Fig 1c). To fully characterise the chemical ecology of rice- Mg interactions, we have initiated a bioassay-guided chemical analysis to identify root semiochemicals of susceptible and resistant rice cultivars that modulates host finding behaviour. Another important aspect that remains to be investigated is the transcriptional plasticity of nematodes in response to different host chemical cues in Mg. Given that transcriptional variability has been linked to the success of generalist pathogens indicate that polyphagous nematodes like Mg might also have this ability. Differential gene expressions will be determined by extracting total RNA from nematodes treated with root exudates of resistant and susceptible lines. The results could elucidate the role of transcriptional plasticity as an adaptive mechanism for host recognition and increased root invasion by this polyphagous species.
Ongoing projects
Completed projects
2021 - 2024
A study on chemical constituents of rice root modulating herbivory by Meloidogyne graminicola: a chemical ecology perspective
Funding: DST SERB Core Research Grant
2014 - 2015
Spatial distribution of and community structure of nematodes associated with Betel Vine growing regions of West Bengal
Funding: ISI Intramural funding
2018 - 2021
Host-parasite interaction between the rice root knot nematode and rice
Funding: ISI Intramural funding
2015 - 2018
Phytonematode problems of rice in Jharkhand: density, diversity and pathogenesis
Funding: ISI Intramural funding