circular pattern of mold on quince
Looks like you may have Monilinia fructigena, brown rot, or at something similar (possibly also called brown rot, but from a different species). This pattern isn't special to quince, but to this fungus.
The formation of these rings is called &quot;zonation&quot;, and the concentric rings are from areas of growth that are primarily spore-forming versus not.
Hall (1933) gives an extensive description of the different factors necessary for observing this growth pattern, but ultimately the key factor is light. Patterns of light-and-dark conditions while the fungus spreads causes alternating phases of growth, with one phase comprised of more sporulation.
Another source: https://www.cabi.org/isc/datasheet/34747

Byrde, R. J. W., &amp; Willetts, H. J. (2013). The brown rot fungi of fruit: their biology and control. Elsevier.
Hall, M. P. (1933). An analysis of the factors controlling the growth form of certain fungi, with especial reference to Sclerotinia (Monilia) fructigena. Annals of Botany, 47(187), 543-578.