Carrot Breeding for Alternaria Leaf Blight Resistance

Studies were conducted in a field research plot of the Kazakh Research Institute of Potato and Vegetable Growing on furrow-irrigated, clay-loam, dark-chestnut soils. Carrot selections were visually screened over three seasons for Alternaria leaf blight (ALB) (Alternaria ssp.) resistance. Field evaluation of carrot leaf infection by ALB was visually scored one month before harvest, at maximum display of foliage infection. The rating scale was: 0 - disease symptoms are absent; 1 - low susceptible (1-10% of foliage); 2 - moderately susceptible (11-25% of foliage); 3 - susceptible (26-50% of foliage); and 4 - highly susceptible (more than 51% of foliage). For the assessment of carrot plants' resistance to leaf infection by ALB, the coefficients of weighted-mean infection, intensity of distribution and degree of infection development were calculated. Of the 86 carrot selections screened visually, 69 carrot selections exhibited very low susceptibility to ALB (0.1-1.0 points), 16 accessions were considered low susceptible (1.1-2.0 points), and selection number CR425 was moderately susceptible (2.1-3.0 points) to ALB. Correlation analysis indicated the lack of any association between ALB infection rates and yield or other carrot quality traits (R=-0.002-0.115).