Polyploidy in Fruit Tree Crops of the Genus Annona (Annonaceae)

Abstract

Genome duplication or polyploidy is one of the main factors of speciation in plants. It is especially frequent in hybrids and very valuable in many crops. The genus Annona belongs to the Annonaceae, a family that includes several fruit tree crops, such as cherimoya (Annona cherimola), sugar apple (Annona squamosa), their hybrid atemoya (A. cherimola × A. squamosa) or pawpaw (Asimina triloba). In this work, genome content was evaluated in several Annona species, A. triloba and atemoya. Surprisingly, while the hybrid atemoya has been reported as diploid, flow cytometry analysis of a progeny obtained from an interspecific cross between A. cherimola and A. squamosa showed an unusual ploidy variability that was also confirmed karyotype analysis. While the progeny from intraspecific crosses of A. cherimola showed polyploid genotypes that ranged from 2.5 to 33%, the hybrid atemoyas from the interspecific cross showed 35% of triploids from a total of 186 genotypes analyzed. With the aim of understanding the possible implications of the production of non-reduced gametes, pollen performance, pollen size and frequency distribution of pollen grains was quantified in the progeny of this cross and the parents. A large polymorphism in pollen grain size was found within the interspecific progeny with higher production of unreduced pollen in triploids (38%) than in diploids (29%). Moreover, using PCR amplification of selected microsatellite loci, while 13.7% of the pollen grains from the diploids showed two alleles, 41.28% of the grains from the triploids amplified two alleles and 5.63% showed up to three alleles. This suggests that the larger pollen grains could correspond to diploid and, in a lower frequency, to triploid pollen. Pollen performance was also affected with lower pollen germination in the hybrid triploids than in both diploid parents. The results confirm a higher percentage of polyploids in the interspecific cross, affecting pollen grain size and pollen performance. The occurrence of unreduced gametes in A. cherimola, A. squamosa and their interspecific progeny that may result in abnormalities of ploidy such as the triploids and tetraploids observed in this study, opens an interesting opportunity to study polyploidy in Annonaceae.

Assessing Ploidy Level Analysis and Single Pollen Genotyping of Diploid and Euploid Citrus Genotypes by Fluorescence-Activated Cell Sorting and Whole-Genome Amplification

“…The “Mexican” lime is a interspecific hybrid between C. micrantha × C. medica (Nicolosi et al, 2000; Garcia-Lor et al, 2013b; Curk et al, 2016). It is known that interspecific hybrids of other plant genera show a tendency towards the formation of unreduced gametes (Van Tuyl et al, 1989; Ramanna et al, 2003; Mason et al, 2011; Chung et al, 2013; Martin et al, 2019). In addition, Curk et al (2016) proposed that C. latifolia (“Tahiti” lime like accessions) resulted from the fertilization of a haploid lemon ovule by a diploid gamete of a diploid “Mexican” like lime.…”

“…On the other hand, there is a lack of knowledge about citrus pollen genotyping. A limiting factor of this technique is the small amount of DNA per pollen and, thus, limiting the number of markers that can be used for analyzing single pollen grains (Matsuki et al, 2007; Martin et al, 2019). Citrus pollen genotyping has been previously only performed by multiplex PCR (Honsho et al, 2016).…”

Synthetic Polyploidy in Grafted Crops

“…In the genus Annona , which includes edible fruits like cherimoya ( A. cherimola Mill.) and sugar apple ( A. squamosa L.), the production of non-reduced gametes has been identified after unusual polyploid progenies were observed ( Martin et al, 2019 ). Also, analyses based on molecular markers can be used to estimate the PHR rates for 2n gametes in polyploid progenies and, therefore, to identify the mechanisms underlying unreduced gamete formation ( Cuenca et al, 2011 , 2015 ).…”

Accelerated diversification correlated with functional traits shapes extant diversity of the early divergent angiosperm family Annonaceae

“…Polyploidy is undoubtedly a major force in angiosperm evolution [70]. It has been reported in several genera of Annonaceae, including: Cyathocalyx , with 2 x and 8 x taxa recorded [71]; Duguetia , with 2 x , 3 x , 4 x , and 6 x taxa [58,72,73]; Annona , with 2 x , 4 x , 6 x , and 8 x taxa [71,72,73,74]; and Guatteria , which are uniformly 4 x [71,75,76]. In particular, these four genera all exhibit rapid diversification rates (Fig.…”