Induction of Seedlessness in Citrus: From Classical Techniques to Emerging Biotechnological Approaches

Abstract

<jats:p>Seedlessness can be obtained through parthenocarpy (i.e., fruit formation without fertilization or embryo abortion). In practice, the actual reduction in seed number in parthenocarpic plants is often exaggerated by coupling parthenocarpy with self-incompatibility or male sterility. Traits related to seedlessness, such as parthenocarpy, can be introduced into genetic accessions through conventional cross-breeding. However, conventional breeding in <jats:italic>Citrus</jats:italic> L. species faces several limitations. First, these species have long juvenile (nonflowering) periods during which a relatively thick canopy develops, which limits the size of seedling populations that can be maintained for further evaluation. Second, they have a narrow genetic base, which limits the availability of alternative alleles that could be introgressed into other lines for the formation of a particular phenotype such as parthenocarpy. Third, breeding efforts are limited by the lack of knowledge of the mode of inheritance of specific characteristics. Fourth, and last, breeding efforts are limited by the polygenic nature of many important traits. Despite these limitations, conventional breeding in fruit trees has yielded improved cultivars and will most likely continue to be a very important strategy. However, emerging biotechnological approaches should be continuously evaluated for their potential for expediting such breeding efforts. The objective of this review is to present, evaluate, and discuss conventional and emerging biotechnological approaches for the induction and maintenance of seedlessness in a variety of crops. Particular attention will be paid to citrus crops, including the presentation and discussion of some preliminary data on the genetic inheritance of parthenocarpy.</jats:p>

Production and molecular characterization of two new Citrus somatic hybrids for scion improvement

“…Seedlessness is a quality character of great economic importance for new fresh-market citrus cultivars (Deng 2005;Vardi et al 2008). Although emerging novel approaches reviewed by Vardi et al (2008) have been developed for seedlessness, including somatic cybridization targeted to transfer cytoplasmic male sterility, transgenic and biotechnological techniques, seedless citrus cultivars have hitherto been obtained mainly by several classical methods, such as bud mutation selection, chance seedling selection, induced mutation and cross breeding (Deng 2005).…”

“…Although emerging novel approaches reviewed by Vardi et al (2008) have been developed for seedlessness, including somatic cybridization targeted to transfer cytoplasmic male sterility, transgenic and biotechnological techniques, seedless citrus cultivars have hitherto been obtained mainly by several classical methods, such as bud mutation selection, chance seedling selection, induced mutation and cross breeding (Deng 2005). In the present study, we successfully obtained allotetraploid somatic hybrid plants from the 'Murcott' tangor ?…”

“…Therefore, reduced seed numbers per fruit or seedlessness has continued to be one of the most important breeding objective in citrus improvement programs (Grosser and Gmitter 2005;Deng 2005;Vardi et al 2008). Triploid fruits generally do not contain seeds due to the abnormal meiosis, and interploid crosses between diploid and tetraploid parent or reciprocally followed by embryo rescue has been an efficient method to generate triploid Communicated by J. van Huylenbroeck.…”

Re‐evaluating strategies for pollinator‐dependent crops: How useful is parthenocarpy?

“…Parthenocarpy (fruit set in the absence of fertilization) is a trait which has the potential to make many ‘pollinator‐dependent’ species produce fruit without pollination (Vardi, Levin & Carmi ). Parthenocarpy is thought to increase fruit quantity as plants are able to set fruit in conditions adverse for fertilization, for example due to poor pollen maturation or few pollinating species, typically seen in greenhouses or during periods of poor light and cold temperatures (Pandolfini ).…”

“…), is advantageous in fruit processing, such as tinned tomatoes (Pandolfini et al . ), and is generally favoured by consumers for convenience in preparation and consumption (Vardi, Levin & Carmi ). However, evidence suggests that some parthenocarpic plants may still produce a greater quantity and quality [including higher sugar content (Hayata et al .…”