Freezing tolerance of barley seedlings infested by aphids

The effects of the aphids Schizaphis graminum (Rondani) and Rhopalosiphum padi L. infestation on freezing tolerance of barley cv. Aramir and Atlas were studied. Seven day-old plants were infested with two aphids each. After 6 d, the freezing tolerance of the leaves was determined. Non infested leaves of cv. Atlas were significantly more tolerant than leaves of cv. Aramir (LT50 = -6.65 and -5.75 degrees C, respectively). The freezing tolerance of cv. Aramir did not vary when these plants were infested with aphids. However, the Freezing tolerance of cv. Atlas infested by S. graminum and R. padi, decreased in 1.5 and 3.3 degrees C, respectively. Basal ABA content in non infested plants was higher in cv. Aramir than Atlas, 285 and 69 nmol/kg, fresh mass, respectively. When plants were infested with S. graminum or R. padi, ABA content increased to 389 and 364 nmol/kg. Fresh mass respectively, only in Aramir. Sucrose content in cv. Atlas infested with R. padi or with S. graminum decreased to 1.2 and 5.0 mmol/kg, fresh mass respectively. The results show that aphid infestation could affect the capacity of some cultivars of barley to tolerate freezing stress.