Abstract
BackgroundParthenocarpy is a desirable trait in Capsicum annuum production because it improves fruit quality and results in a more regular fruit set. Previously, we identified several C. annuum genotypes that already show a certain level of parthenocarpy, and the seedless fruits obtained from these genotypes often contain carpel-like structures. In the Arabidopsis bel1 mutant ovule integuments are transformed into carpels, and we therefore carefully studied ovule development in C. annuum and correlated aberrant ovule development and carpelloid transformation with parthenocarpic fruit set.ResultsWe identified several additional C. annuum 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 C. annuum 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 Arabidopsis bel1 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. Capsicum 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 CaARF8.ConclusionsOur results suggest that in the absence of fertilization most C. annuum genotypes, have parthenocarpic potential and carpelloid growth, which can substitute developing seeds in promoting fruit development.
Highlights
Parthenocarpy is a desirable trait in Capsicum annuum production because it improves fruit quality and results in a more regular fruit set
To understand the relationship between parthenocarpic potential and the presence of carpelloid structures, we investigated ovule development and the occurrence of abnormal ovules in C. annuum genotypes possessing a range of high (Chinese Line 3), moderate (Bruinsma Wonder) and low (Orlando) potential for parthenocarpic fruit set
Parthenocarpy is widely present in Capsicum annuum L. genotypes To test whether parthenocarpy is widely present in C. annuum, twelve genotypes were evaluated for their parthenocarpic potential by emasculating flowers (Table 1)
Summary
Parthenocarpy is a desirable trait in Capsicum annuum production because it improves fruit quality and results in a more regular fruit set. Various Arabidopsis mutants have been identified where ovules show disrupted integument growth, such as aintegumenta (ant; lacks inner and outer integuments), aberrant testa shape (ats; contains a single integument), inner no outer integument (ino; the absence of outer integument growth on the ovule primordium), short integuments (sin; where both integuments are short), and bel and apetala (ap2) [7,8,9,10,11,12] In the latter two loss-of-function mutants ovule integuments are converted into carpelloid structures [11,12,13]. Parthenocarpic fruit development was enhanced in the bel fwf-1 double mutant, and at the same time a higher frequency of carpelloid structures was observed compared to the bel single mutant [14]. This suggests on the one hand that carpelloid structures enhance parthenocarpic fruit development, and on the other hand that the development of carpelloid structures is enhanced in the absence of seed set [14]
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