Heritable variation in quinone-induced haustorium development in the parasitic plant Triphysaria

We are using the facultative hemiparasite, Triphysaria, as a model for stud ying host-parasite signaling in the Scrophulariaceae. Parasitic members of this family form subterranean connections, or haustoria, on neighboring hos t roots to access host water and nutrients. These parasitic organs develop in response to haustorial-inducing factors contained in host root exudates. A well-characterized inducing factor, 2, 6-dimethoxy-p-benzoquinone (DMBQ) , can be used to trigger in vitro haustorium formation in the roots of Trip hysaria. We have assayed three species, Triphysaria eriantha (Benth.) Chuan g and Heckard, Triphysaria pusilla (Benth.) Chuang and Heckard, and Triphys aria versicolor Fischer and C. Meyer, for haustorium development in respons e to DMBQ. There were significant differences between the species in their ability to recognize and respond to this quinone. Ninety percent of T. vers icolor individuals responded, whereas only 40% of T. pusilla and less than 10% of T. eriantha formed haustoria. Within field collections of self-polli nating T. pusilla, differential responsiveness to DMBQ was seen in distinct maternal families. Assaying haustorium development in subsequent generatio ns of self-pollinated T. pusilla showed that DMBQ responsiveness was herita ble. Reciprocal crosses between T, eriantha and T. versicolor demonstrated that DMBQ responsiveness was influenced by maternal factors. These results demonstrate heritable, natural variation in the recognition of a haustorial -inducing factor by a parasitic member of the Scrophulariaceae.