Effect of plant age on resistance toAscochyta rabieiin chickpea

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Abstract
The impact of plant age on resistance to ascochyta blight of chickpea (Cicer arietinum) was assessed on kabuli cvs. UC27 (susceptible) and Sanford and B90 (partially resistant) and desi cv. Myles (partially resistant) using two isolates of Ascochyta rabiei. Tests were conducted under controlled conditions and in field trials in 1999 and 2000. Seed was sown at regular intervals to produce plants at different growth stages (seedling, vegetative, flowering, podding), which were all inoculated at the same time in randomized complete block experiments with four replications. Cultivar UC27 was highly susceptible at all stages of plant development. However, plant age had a large impact on the reaction of resistant cultivars to A. rabiei. In growth chamber studies, blight severity was low in seedlings of the resistant cultivars (range, 4-20%) and highest in podding plants (41-82%) 2 weeks after inoculation. In the field trials, severity at 2 weeks after inoculation showed a similar pattern, with mean severity among resistant cultivars ranging from 1 to 2% in seedlings and 3 to 28% in podding plants. Severity at 8 weeks after inoculation on plants of resistant cultivars inoculated as seedlings was low (6-14% in 1999, 10-23% in 2000) relative to those inoculated at podding (65-91% in 1999; 54-83% in 2000) in the field trials. These results indicate that resistance decreases with plant age in the partially resistant chickpea cultivars adapted to western Canada and that resistance alone may not provide adequate disease control.