| Summary: | <p>Abstract</p> <p>Background</p> <p>Parthenocarpy is a desirable trait in <it>Capsicum annuum </it>production because it improves fruit quality and results in a more regular fruit set. Previously, we identified several <it>C. annuum </it>genotypes that already show a certain level of parthenocarpy, and the seedless fruits obtained from these genotypes often contain carpel-like structures. In the <it>Arabidopsis bel1 </it>mutant ovule integuments are transformed into carpels, and we therefore carefully studied ovule development in <it>C. annuum </it>and correlated aberrant ovule development and carpelloid transformation with parthenocarpic fruit set.</p> <p>Results</p> <p>We identified several additional <it>C. annuum </it>genotypes with a certain level of parthenocarpy, and confirmed a positive correlation between parthenocarpic potential and the development of carpelloid structures. Investigations into the source of these carpel-like structures showed that while the majority of the ovules in <it>C. annuum </it>gynoecia are unitegmic and anatropous, several abnormal ovules were observed, abundant at the top and base of the placenta, with altered integument growth. Abnormal ovule primordia arose from the placenta and most likely transformed into carpelloid structures in analogy to the <it>Arabidopsis bel1 </it>mutant. When pollination was present fruit weight was positively correlated with seed number, but in the absence of seeds, fruit weight proportionally increased with the carpelloid mass and number. <it>Capsicum </it>genotypes with high parthenocarpic potential always showed stronger carpelloid development. The parthenocarpic potential appeared to be controlled by a single recessive gene, but no variation in coding sequence was observed in a candidate gene <it>CaARF8</it>.</p> <p>Conclusions</p> <p>Our results suggest that in the absence of fertilization most <it>C. annuum </it>genotypes, have parthenocarpic potential and carpelloid growth, which can substitute developing seeds in promoting fruit development.</p>
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