Abstract
Ponkan mandarin (Citrus reticulata Blanco) trees were subjected to shading for three weeks at two levels: high (70-75%) and low (55-65%), either at the end of anthesis (stage I), during major fruit drop (stage IIA) or at the onset of fruit expansion (stage IIB) . The objective was to monitor effects on source-leaf non-structural carbohydrate content, photosynthetic rate, fruit set, growth and quality; and thus evaluate fruit developmental responses to source limitations. Early shading (stage I) did not affect the fruit set and quality, whereas shading during the major fruit drop period (stage IIA) reduced the fruit set. Late shading (duringg high fruit growth rate) reduced the fruit size and increased the titratable acidity. Compared to early shading, late shading reduced the content of leaf non-structural carbohydrates and the photosynthetic activity of fruitless shoots significantly. High shading level caused larger reductions in fruit size, quality and weight than low shading although differences were not always significant.
