Apple Leaf Spot

The main types of leaf spots include phyllosticta leaf spot (pathogens Phyllosticta mali, P. briardi), marssonina blotch (Marssonina coronaria), alternaria blotch (Alternaria alternata), and pestalotia leaf spot caused by Pestalotia malorum. The diseases vary in the nature of the lesions: from small brown spots with pycnidia to large areas with a bright yellow halo, as well as viral ribbon patterns characteristic of ACLSV.

Genetic control is most studied in alternaria blotch, where resistance is determined by the Alt locus on chromosome 11. The presence of the dominant Alt allele causes cultivar susceptibility to the fungus's AM-toxins. Molecular markers are used in breeding to identify resistant genotypes, whereas resistance to marssonina blotch is polygenic in nature, which requires the search for genomic regions responsible for tolerance.