Alteration in endospore attachment of H. cajani specific Pasteuria to different age groups of H. cajani J2 exposed to host and non-host root exudates.

Abstract

Plant root exudates and rhizosphere microbes, including nematodes, are involved in highly specific chemical communication that we know little about. Freshly hatched J2 of the pigeon-pea cyst nematode Heterodera cajani and those left in water for 7 and 14 days were separately exposed for 24 h to the root exudates of their host plant (cowpea) and non-host plants (tomato and potato). These J2 were then used for performing spore attachment tests with the Pasteuria isolate from H. cajani. Exposure to the root exudates of tomato resulted in a significant decrease in attachment by 57.7%, 65.1% and 77.6% in fresh, 7 and 14 days old J2 respectively, over the water control. On the contrary, incubation of fresh and 7 days old J2 in root exudates from potato, which is also a non-host for H. cajani, the attachment of endospores was found to be on par with cowpea root exudates and the water control. As expected, the increase in J2 age was inversely proportional with ensdospore attachment. However, the14 day old J2 when incubated in cowpea and potato root exudates, showed a significant increase in attachment by 73.8% and 90.6% over the water control. Interestingly root exudates from potato, a non-host for H. cajani, were able to stimulate cuticular changes in the J2 that promoted Hcp endospore attachment. This population of Hcp, originally isolated from H. cajani exhibits cross-generic attachment and life cycle completion on the potato cyst nematode Globodera spp. In a more time-sensitive assay, incubation of fresh J2 in tomato root exudates for 1 h reduced the attachment significantly by 28.3% which further decreased to 52% after 2 h incubation over the water control. Endospore attachment performed with J2 of H. cajani retrieved from cowpea roots after 24 and 48 h of penetration showed a drastic reduction in attachment by 83.4% and 98.3%, respectively over un-inoculated control.These results show that the nematode cuticle is highly dynamic and that the host plant has unpredictable consequences regarding Pasteuria endospore attachment and therefore biocontrol outcomes.