Breeding and Analysis of Two New Grapefruit-Like Varieties with Low Furanocoumarin Content

Abstract

Furanocoumarins (FCs) are a group of related plant defense metabolites occurring in several plant families, including some species in the genus citrus, such as grapefruit and pummelo. FCs function as toxins against pathogens, insects and other plant pests and some are toxic to humans at high levels. Although the levels of FCs in grapefruits are non-toxic to humans, they inhibit the intestinal enzyme CYP3A, thus preventing degradation of medicines, such as statins, and causing dangerous overdose effects. This overdosing can cause devastating side effects, ranging from stomach bleeding to kidney problems, muscle aches and irregular heartbeats. In the present study, we utilize LC/MS to characterize the levels of FCs pathway intermediates and end products in twelve citrus cultivars, including mandarin (Citrus reticulata), orange [Citrus sinensis (L.) Osbeck], Pummelo [Citrus maxima (Burm.) Merr.], grapefruit (Citrus paradisi Macf.), and two newly selected grapefruit like varieties [(Citrus reticulata) X [Citrus maxima (Burm.) Merr]. The orange and mandarin varieties do not contain FCs or FCs precursor compounds suggesting that this biosynthetic pathway is absent or inactive in mandarins and oranges and therefore a good genetic source for null alleles to FCs biosynthesis. We report the selection and characterization of two new low FCs and seedless grapefruit-like varieties, "Aliza" and "Coocki", developed by a cross between pummelo and mandarin. Fruits of these varieties resemble grapefruit and contain high levels of the flavanone naringin, typical of grapefruit, but contain only trace amounts of FCs (based on LC/MS analysis). Based on the variability of FCs content and inheritance in citrus species, the results suggest that future development of new low-FCs grapefruit varieties is an achievable objective.

Strategies to Produce Grapefruit-Like Citrus Varieties With a Low Furanocoumarin Content and Distinctive Flavonoid Profiles

“…Some attempts have already been made in different breeding programs worldwide to recover of new grapefruit-like citrus varieties with low FC contents. Fidel et al (2016) reported the selection of two low FCs and seedless grapefruit-like varieties, named Aliza and Coocki, recovered by a cross between pummelo and mandarin. Fruits of these varieties resemble orange-fleshed grapefruits, and contain high levels of the flavanone naringin and only trace amounts of FCs.…”

“…To overcome this problem, sexual hybridization could be a useful strategy, but would not recover true-to-type grapefruit varieties; however, this strategy could be suitable for the production of new grapefruit-like varieties with low FCs content and distinctive flavonoid profiles, together with other characteristics attractive to the consumers, as shape and size of the fruit, color of the peel and pulp or seedlessness. This strategy, at diploid and triploid levels, is one of the most promising approaches and in fact has been used in breeding programs in Florida, Spain, Israel, and Italy ( Grosser et al, 2015 ; Navarro et al, 2015 ; Fidel et al, 2016 ; Russo et al, 2016 ), respectively. Citrus diploid hybrids can be recovered by classical sexual hybridization between diploid parents, whereas triploid hybrids can be produced directly from crosses between two diploid genotypes resulting from the union of a 2n megagametophyte with haploid pollen ( Aleza et al, 2010 ) or by hybridization between diploid and tetraploid parents ( Aleza et al, 2012a , b ).…”