Occurrence of triploids in oil palm and their origin

Abstract

Background and Aims Oil palms showing exceptional vigour and dubbed as “giant palms” were identified in some progenies in breeding. A panel of phenotypical traits were studied to characterize these trees. Hypothesis that gigantism and other anomalies might be linked to polyploidy was investigated. Methods Twenty sib pairs of palms from different crosses, each comprising of a giant and a normal oil palm, were studied by flow cytometry with rice Nipponbare as standard reference. Parallelly, palms were assessed in the field using eleven phenotypic traits. A principal component analysis (PCA) was conducted to define relationships between these phenotypical traits and a linear discriminant analysis (LDA) to predict ploidy level and giant classification. Finally, a co-dominant molecular marker study was implemented to highlight the sexual process leading to the formation of 2n gametes. Key Results A first group of oil palms presented an oil palm/rice peak ratio around 4.8 corresponding to diploid oil palms, whereas the second group presented a ratio around 7, classifying these plants as triploid. The PCA let to classify the plant in 3 classes: 21 were normal diploid palms, 10 were giant diploid palms while 11 were giant triploid palms. The LDA revealed three predictors for ploidy classification: phyllotaxy, petiole size and circumference of the plant but surprisingly not height. The molecular study revealed that triploid palms resulted from 2n gametes issued of the second division restitution of meiosis in parents. Conclusions This study confirms and details the process of sexual polyploidization in oil palm. It also identifies three phenotypical traits to assess ploidy level of the giant oil palms in the field. In practical, our results provide a cheap scientific method to identify polyploids palms in the field.

Polyploidy: its consequences and enabling role in plant diversification and evolution

“…1 is essential today. The measurement of genome size, via flow cytometry in correlation with ploidy where there is no or limited loss or gain of DNA, is another important cytogenetic method to measure ploidy, and is often easier than making chromosome preparations, showing distinct peaks with different numbers of genomes ( Elliott et al , 2022 ; Pomies et al , 2022 ; Semberova et al , 2022 ; Tomaszewska et al , 2022 ; Fig. 2A ).…”

“…Alternative mechanisms of propagation, involving either apomictic seed production or vegetative propagation, enable reproduction of taxa without regular meiosis, and allow taxa with odd numbers of ancestral genomes: for example, triploid dessert banana, Musa acuminata ( Heslop-Harrison and Schwarzacher, 2007 ); heptaploid dog rose, Rosa canina ( Hertzklotz and Ritz, 2017 ); and triploid saffron, Crocus sativus ( Schmidt et al , 2019 ). Important examples of vegetatively or seed-propagated triploids discussed in this Special Issue are aspen trees ( Populus tremuloidies ; Eisenring et al , 2022 ) and palms ( Pomies et al , 2022 ), but also some sexual or mixed apomictic–sexual systems, such as Urochloa forage grasses, including multiple ploidies ( Tomaszewska et al , 2022 ). However, beyond chromosomal explanations for sterility of polyploid hybrids, morphology ( Šemberova et al , 2022 ), ecological niche differentiation ( Chase et al , 2022 ) or isolation of populations on islands ( Joshi et al , 2022 ) lead to separation of polyploid lineages allowing evolution independent from the original diploid species, diversification and speciation.…”

“…Polyploidy has been correlated with gigantism, for example an increase in fruit size in kiwi, Actinidia chinensis ( J. H. Wu et al , 2012 ). Pomies et al (2022) characterized oil palms ( Elaeis guineensis ) in a breeding programme and identified ‘giant palms’ based on 11 phenotypic traits: half of the giant palms were triploids, originating from 2 n gametes, although field experience suggests the bunches will have poor fruit set so will not be useful for breeding. Notably too, half of the ‘giant palms’, rigorously defined by a principal components analysis of 21 characters, were diploids, suggesting alternative mechanisms are also responsible for the increase in size.…”

The Promising Potential of Triploidy in Date Palm (Phoenix dactylifera L.) Breeding

“…This report utilized crosses between the tetraploid shoot of ‘Deglet Nour’ and diploid male genotypes. Although triploids have recently been reported in the African oil palm by Pomiès et al [ 5 ], to our knowledge, this is the first report on triploid date palms. This study provides a way to leap forward in date palm breeding in a straightforward manner.…”

“…Within the palm family, the oil palm serves as the only reference. Pomiès et al [ 5 ] reported that spontaneously induced triploid African oil palms exhibit greater vigor, thicker petioles, thicker stems, and a larger habit than diploid palms. They also noted that polyploidy impacts phyllotaxy.…”