Variation in cucumber (Cucumis sativus L.) fruit size and shape results from multiple components acting pre-anthesis and post-pollination

Variation in cucumber (Cucumis sativus L.) fruit size and shape is highly quantitative, implicating interplay of multiple components. Recent studies have identified numerous fruit size and shape quantitative trait loci (QTL); however, underlying factors remain to be determined. We examined ovary and fruit development of two sequenced cucumber genotypes with extreme differences in fruit size and shape, Chinese Long ‘9930’ (CL9930), and pickling type ‘Gy14’. Differences were observed in several independent factors that can influence size and shape: ovule number, rate and period of cell division in longitudinal and cross section in ovaries and fruit, timing and rate of fruit expansion in length and diameter, and cell shape. Level and timing of expression of select fruit growth stage marker genes and candidate fruit size gene homologs associated with cucumber fruit size and shape QTL were examined from 5-day pre-anthesis to 20-day post-pollination. Our results indicate that variation in fruit size and shape results from differences in cell number and shape in longitudinal and cross section, driven in turn by differences in orientation, timing, and duration of cell division and expansion, both pre- and post-anthesis, and suggest candidate genes contributing to determination of cucumber fruit size and shape.