Abstract
Self-incompatibility (SI) is present in around half of all species of flowering plants. SI limits endogamy and contributes to increased genetic diversity. SI is a very important trait in citrus because, when coupled with parthenocarpy, it allows seedless fruit production. Otherwise, SI is an impediment to genetic studies and breeding programs. Temperature stress, bud pollination and polyploidization can induce the breakdown of the SI mechanism in several species. In this work, we investigated how the SI mechanism can be broken down in two self-incompatible diploid citrus genotypes: ‘Fortune’ mandarin and ‘Clemenules’ clementine. The influence of temperature stress on the SI mechanism was assessed in self-pollinated flowers of ‘Fortune’ mandarins subjected to 2 temperature regimes (10 °C and 30 °C), whereas the bud pollination effect was investigated in the same genotype and in ‘Clemenules’ clementines cultivated under field conditions. The tetraploid ‘Clemenules’ clementine cultivated under field conditions was used to study if tetraploidization can bypass the SI reaction. Histological observations of pollen tube growth and seed production in self-pollinated flowers were used to evaluate the breakdown of SI, while the genetic analysis with SSR and SNP markers confirmed that all recovered plants were zygotic and had been originated by selfing. Our results confirm that the SI reaction can be surpassed by temperature stress, bud pollination and tetraploidy. To our knowledge, this is the first report in citrus in which the SI reaction breakdown by these three different strategies is demonstrated by molecular markers.
Highlights
Introduction iationsSelf-incompatibility (SI), called self-sterility, is defined as “the prevention of selffertilization by otherwise normal and viable gametes, due to their genetic similarity” [1] and was described by Darwin in 1876
We analyzed the influence of three potential approaches to induce the breakdown of the SI system in mandarins and clementines: temperature stress, bud pollination and chromosome doubling
The SI phenotype was characterized by a histological study of pollen tube growth and ovule fertilization
Summary
Introduction iationsSelf-incompatibility (SI), called self-sterility, is defined as “the prevention of selffertilization by otherwise normal and viable gametes, due to their genetic similarity” [1] and was described by Darwin in 1876. The Brassicaceae and Solanaceae families have been important models for elucidating the molecular mechanism of SI [8,9,10]. SI has been described in most of the species included in the Rosaceae [11,12,13,14], Malvaceae [15], Oleaceae [16] and Rutaceae families [17]. SI avoids endogamy by favoring cross-pollination and contributes to increasing genetic diversity. It is crucial for species’ adaptation and evolution [18,19,20,21]. SI is widespread in angiosperm species, and it is estimated that
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