Quantitative resistance of barley cultivars to Rhynchospohum secalis

Abstract

Quantitative resistance in spring barley cultivars with different genetic bases of resistance to scald was investigated in field trials conducted in 1993, 1995, and 1996. The variables measured included area under the disease progress curve (AUDPC), apparent infection rate (AIR), infection frequency (IF), lesion length (LL), lesion width (LW), time to disease onset at 5% severity (T5), final severity (FS), and sporulation (SP). Grain yield and thousand-kernel weight (TKW) of each cultivar in plots protected with Tilt® were compared with those in nonprotected plots. The eight cultivars evaluated were statistically separated into susceptible and resistant groups according to the variables measured. 'Argyle,' 'Harrington,' 'Klages,' and 'Jackson' were placed in the susceptible group and 'AC Stacey,' 'Johnston,' and 'Leduc' were placed in the resistant group. 'CDC Guardian' became progressively more susceptible each growing season, indicating that its resistance was overcome by new pathotype(s) of the scald pathogen. Scald caused significant yield and TKW losses based on a combined analysis of the three-year data. Grain yield and TKW of susceptible cultivars were reduced more than those of resistant cultivars. AUDPC, FS, AIR, T5, IF, LL, and LW were significantly correlated to each other. Percent TKW relative to plots protected with Tilt® was negatively correlated with AUDPC, FS, AIR, IF, LL, and LW, positively correlated with T5, but percent yield relative to plots protected with Tilt® was not correlated with any of these variables. 'Leduc' retarded disease development, as evidenced by a smaller AUDPC, lower AIR, reduced IF, longer T5, and lower FS. 'Leduc' was consistently tolerant to scald, having the lowest reduction in yield among the eight cultivars. Therefore, 'Leduc' can be used as a source of durable resistance by breeding programs in western Canada.