A quantitative scale for assessing chickpea reaction to Ascochyta rabiei

Hybrid generations obtained from crosses between several chickpea cultivars were used to develop a quantitative scale to assess the reaction of chickpea (Cicer arietinum) to Ascochyta rabiei under controlled conditions. The number of lesions, their average and total lengths, and the linear infection index were used to establish a quantitative scale. The distribution frequency of the number of lesions, average and total lengths of lesions, and the linear infection index showed that the latter best described the reaction of chickpea seedlings to A. rabiei. This index provided a satisfactory separation between resistant and susceptible plants. The linear infection index was based on a quantitative measurement of the disease expression on plants, whereas the 1–9 scale developed at the International Crops Research Institute for the Semi-Arid Tropics uses mostly visual disease assessment. The linear infection index was used to establish a new scale of eight classes in which plants rated from class 0 to class 3 were considered resistant, and those rated from class 4 to class 7 were considered susceptible. Key words: Cicer arietinum, Ascochyta rabiei.