ABSTRACT
Apple scab is caused by Venturia inaequalis Wint., and the disease is of economic importance in most apple-growing regions of the world. Scab lesions that develop on the fruit during growing season or in storage reduce the value of fruit, and severe infections can cause premature fruit drop. An application of the basidiomycete Athelia bombacina Pers. to scab-infected apple leaves at leaf fall inhibits the springtime production of V. inaequalis ascospores. Pathogenic and nonpathogenic mutants of V. inaequalis have been selected that require a single amino acid for growth on artificial media. Scab can develop on fruit in storage as an enlargement of existing lesions with additional sporulation beyond the margin, small, blackish lesions that are smooth and devoid of sporulation, and small, brown or black lesions that are rough with an occasional cluster of annellophores that erupts through the surface. Apple scab lesions have been detected on the abaxial and adaxial surfaces of the outermost scales of apple buds.
