GLUTAMIC-ACID CONTENT OF PHLOEM SAP IS NOT A GOOD PREDICTOR OF PLANT-RESISTANCE TO RHOPALOSIPHUM-PADI

The phloem sap content of glutamic acid was determined in EDTA leaf ex udate samples from a collection of Hordeum vulgare subsp. spontaneum p reviously screened for Rhopalosiphum padi resistance. Segregating popu lations of crosses between subsp. spontaneum X cultivated barley were also evaluated. The concentration of glutamic acid was significantly i nversely correlated with aphid performance on the spontaneum lines. Ho wever, no relationship between glutamic acid concentration and R. padi resistance was observed in segregating material. Causes for this are discussed.