Effects of changing temperature regimes on resistance to races of Melampsora medusae in a cultivar of poplar

Abstract

SUMMARYLeaf discs of Populus deltoides cv. W‐79/307 inoculated with race 4–C of Melampsora medusae, give a compatible reaction when incubated at 16°C (LT), but an incompatible reaction at 26°C (HT). When, over a 12–day period, sets of inoculated leaf discs were reciprocally transferred between the temperature regimes (LT to HT, or HT to LT), incubation for as short as 15 h at HT resulted in incompatibility which was not reversed by subsequent incubation at LT. In contrast, incubation of the inoculated discs at LT for at least 4 days was necessary for the development of a compatible reaction following transfer to HT. Further, incompatibility induced in discs by inoculation with race 4–C and incubation at HT is epistatic to expected compatibility following subsequent inoculation with race 4–M, a temperature non‐sensitive biotype. The rapidity, irreversibility and epistatic nature of the temperature‐induced incompatibility suggests that initial recognition in this pathosystem may be for incompatibility. The significance of these results in this host/pathogen system is discussed.