FREEZING TOLERANCE OF BARLEY SEEDLINGS INFESTED BY APHIDS

The effects of the aphids Schizaphis graminum (Rondani) and Rhopalosip hum padi L. infestation on freezing tolerance of barley cv. Aramir and Atlas were studied. Seven day-old plants were infested with two aphid s each. After 6 d, the freezing tolerance of the leaves was determined . Non infested leaves of cv. Atlas were significantly more tolerant th an leaves of cv. Aramir (LT50 = -6.65 and -5.75 degrees C, respectivel y). The freezing tolerance of cv. Aramir did not vary when these plant s were infested with aphids. However, the Freezing tolerance of cv. At las infested by S. graminum and R. padi, decreased in 1.5 and 3.3 degr ees C, respectively. Basal ABA content in non infested plants was high er in cv. Aramir than Atlas, 285 and 69 nmol/kg, fresh mass, respectiv ely. When plants were infested with S. graminum or R. padi, ABA conten t increased to 389 and 364 nmol/kg. Fresh mass respectively, only in A ramir. Sucrose content in cv. Atlas infested with R. padi or with S. g raminum 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.