Venturia inaequalis is an ascomycete. The photo shows its perithecia, the flask-shaped ascrocap with single vent for releasing spores. Inside it, there are asci, which contain sexual spores called ascospores.
After dispersal (e.g. by wind) to other leaves, they will germinate and penetrate the cuticle, growing between it and the leaf epidermis.

Lesions are formed on plants after in infection by this fungi, in which it will expand more rapidly when it is infected by conidia rather than ascospores of this species.
Q) What causes such differences in infection efficiency between asexual and sexual spores?

Yin Nam, interesting info. Can you provide the source of the information?