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Citrus is a highly valued tree crop worldwide, while, at the same time, citrus production faces many biotic challenges, including bacterial canker and Huanglongbing (HLB). Breeding for disease‐resistant varieties is the most efficient and sustainable approach to control plant diseases. Traditional breeding of citrus varieties is challenging due to multiple limitations, including polyploidy, polyembryony, extended juvenility and long crossing cycles. Targeted genome editing technology has the potential to shorten varietal development for some traits, including disease resistance. Here, we used CRISPR/Cas9/sgRNA technology to modify the canker susceptibility gene CsLOB1 in Duncan grapefruit. Six independent lines, DLOB2, DLOB3, DLOB9, DLOB10, DLOB11 and DLOB12, were generated. Targeted next‐generation sequencing of the six lines showed the mutation rate was 31.58%, 23.80%, 89.36%, 88.79%, 46.91% and 51.12% for DLOB2, DLOB3, DLOB9, DLOB10, DLOB11 and DLOB12, respectively, of the cells in each line. DLOB2 and DLOB3 showed canker symptoms similar to wild‐type grapefruit, when inoculated with the pathogen Xanthomonas citri subsp. citri (Xcc). No canker symptoms were observed on DLOB9, DLOB10, DLOB11 and DLOB12 at 4 days postinoculation (DPI) with Xcc. Pustules caused by Xcc were observed on DLOB9, DLOB10, DLOB11 and DLOB12 in later stages, which were much reduced compared to that on wild‐type grapefruit. The pustules on DLOB9 and DLOB10 did not develop into typical canker symptoms. No side effects and off‐target mutations were detected in the mutated plants. This study indicates that genome editing using CRISPR technology will provide a promising pathway to generate disease‐resistant citrus varieties.

In citrus cultivation, rootstocks are of fundamental importance and affect several characteristics of the variety used as canopy. Despite the great diversity within Citrus and related genera, the production of rootstocks in Brazil is restricted to a small number of varieties, making the citrus culture vulnerable to the appearance of phytosanitary problems. The aim of this study was to agronomically characterize fruits and seeds of seven citrandarins [Citrus sunki (Hayata) hort. ex Tanaka x Poncirus trifoliata cv. Rubidoux (L.) Raf.], obtained by controlled crossing. The orchard was installed in randomized blocks, with three replicates, in the municipality of Cordeirópolis, SP, where 20 fruits were collected in each replicate, obtained from free pollination of seven citrandarins, Swingle citrumelo and Rangpur lime. The following variables were evaluated: fruit mass, height, diameter, total number of seeds and percentage of viable seeds per fruit; number of embryos per seed, mass of one thousand seeds, number of seeds in 1.0 kg, final emergence rate, number of seedlings per seed, polyembryony rate, emergence speed index and seedling height at 60 days after sowing. For fruit size, the highest values were obtained for Swingle citrumelo. For number of embryos per seed, seedlings obtained through seed and polyembryony, citrandarin TSxPT 245 showed the highest values. Although citrandarin fruits had smaller size than fruits from commercial Rangpur lime and Swingle citrumelo rootstocks, characteristics related to seeds such as viability, polyembryony and emergence rate, were similar or superior, and can be considered potential new rootstocks for the production of citrus plants.

A synopsis is provided of different expressions of whole-animal vertebrate clonality (asexual organismal-level reproduction), both in the laboratory and in nature. For vertebrate taxa, such clonal phenomena include the following: human-mediated cloning via artificial nuclear transfer; intergenerational clonality in nature via parthenogenesis and gynogenesis; intergenerational hemiclonality via hybridogenesis and kleptogenesis; intragenerational clonality via polyembryony; and what in effect qualifies as clonal replication via self-fertilization and intense inbreeding by simultaneous hermaphrodites. Each of these clonal or quasi-clonal mechanisms is described, and its evolutionary genetic ramifications are addressed. By affording an atypical vantage on standard vertebrate reproduction, clonality offers fresh perspectives on the evolutionary and ecological significance of recombination-derived genetic variety.

A typical seed of rice (Oryza sativa L.) gives rise to a single seedling. In contrast, seeds from multiple embryos may develop into two or more seedlings, one of which is generated via sexual reproduction, while the others are likely to originate through apomictic pathways. Therefore, the occurrence of multiple embryos is often considered a hallmark of apomixis in rice. Apomixis refers to an asexual reproductive strategy wherein unreduced gametes form through modified meiosis (apomeiosis) without fertilization, thereby generating clonal offspring generally genetically identical to the maternal plant. This process is of great relevance in fixing heterosis in hybrid rice breeding. This review discusses the origin, frequency, genetic regulation, and candidate genes related to multiple embryos in rice and provides a systematic summary of the latest research advances in rice apomixis. The insights presented in this study provide a theoretical foundation for the application of apomixis in rice breeding.

Chondrichthyans (sharks, rays and chimaera) are a fascinating case study through which to examine reproductive biology. While most vertebrate lineages have converged upon either placental viviparity or oviparity, chondrichthyans exhibit unparalleled diversity in reproductive mode and other aspects of reproductive biology. Despite this, our understanding of reproductive variation in this clade remains incomplete. Namely, several ‘unusual’ reproductive traits have been repeatedly observed in some chondrichthyan taxa, but we have little to no understanding of their adaptive value. Here, I focus on two traits (facultative parthenogenesis and the deposition of multiple embryos with separate yolks within a single eggcase (MEPE)), which theoretically result in exponential increases in fecundity. I discuss the theoretical fitness consequences of these traits, the range of species and eco-evolutionary contexts in which they have been documented and major open questions regarding their prevalence and evolutionary consequences. It appears likely that both facultative parthenogenesis and MEPE are adaptive in at least some chondrichthyan taxa and ecological contexts. However, additional data are needed to determine the true effect of these traits on lifetime fecundity, the frequency with which they occur, potential population-level effects and cues or triggers that might favour switches from ‘typical’ sexual reproduction to parthenogenesis or MEPE.

Mango (Mangifera indica) is an economically and nutritionally important tropical/subtropical tree fruit crop. Most of the current commercial cultivars are selections rather than the products of breeding programs. To improve the efficiency of mango breeding, molecular markers have been used to create a consensus genetic map that identifies all 20 linkage groups in seven mapping populations. Polyembryony is an important mango trait, used for clonal propagation of cultivars and rootstocks. In polyembryonic mango cultivars, in addition to a zygotic embryo, several apomictic embryos develop from maternal tissue surrounding the fertilized egg cell. This trait has been associated with linkage group 8 in our consensus genetic map and has been validated in two of the seven mapping populations. In addition, we have observed a significant association between trait and single nucleotide polymorphism (SNP) markers for the vegetative trait of branch habit and the fruit traits of bloom, ground skin color, blush intensity, beak shape, and pulp color.

The species of the family Malpighiaceae are mainly diversified in the Neotropical Region as a consequence of a specialized pollination system. Due to the production of floral oils as a reward to pollinators, and their interaction with Centris, Epicharis (Centridini) and Monoeca (Tapinotaspidini) oil-collecting bee species in most neotropical species, many studies were focused on this interesting mutualistic interaction. However, a few have approached the reproductive biology of these species. The aim of this study was to gather all the existing information to date on the reproductive biology, megagametophyte development and apomixis of the Malpighiaceae species and analyze it together. We found 39 studies on the reproductive biology of 66 species, of which 47% are self-compatible, 33.3% self-incompatible, 18.2% have a mixed system, showing variable behavior among populations and 1.5% agamospermic species. We also found studies/reports on apomixis for eight species (three genera), polyembryony for six species (five genera) and on the development of megagametophyte for 14 species. We showed that our knowledge about the reproductive biology of Malpighiaceae species is scarce and fragmented, obtaining data for only 70–80 species (6–7% out of the total), most of which belonged to one population and/or few analyzed individuals. Further studies about the integral reproductive biology of these species that focus on the analysis of inter-population variations of the reproductive characters should be carried out to better understand how certain reproductive traits of Malpighiaceae species might have evolved and to provide valuable information on the mechanisms of population differentiation.

The breeding of tropical fruit trees for improving fruit traits is complicated, due to the long juvenile phase, generation cycle, parthenocarpy, polyploidy, polyembryony, heterozygosity and biotic and abiotic factors, as well as a lack of good genomic resources. Many molecular techniques have recently evolved to assist and hasten conventional breeding efforts. Molecular markers linked to fruit development and fruit quality traits such as fruit shape, size, texture, aroma, peel and pulp colour were identified in tropical fruit crops, facilitating Marker-assisted breeding (MAB). An increase in the availability of genome sequences of tropical fruits further aided in the discovery of SNP variants/Indels, QTLs and genes that can ascertain the genetic determinants of fruit characters. Through multi-omics approaches such as genomics, transcriptomics, metabolomics and proteomics, the identification and quantification of transcripts, including non-coding RNAs, involved in sugar metabolism, fruit development and ripening, shelf life, and the biotic and abiotic stress that impacts fruit quality were made possible. Utilizing genomic assisted breeding methods such as genome wide association (GWAS), genomic selection (GS) and genetic modifications using CRISPR/Cas9 and transgenics has paved the way to studying gene function and developing cultivars with desirable fruit traits by overcoming long breeding cycles. Such comprehensive multi-omics approaches related to fruit characters in tropical fruits and their applications in breeding strategies and crop improvement are reviewed, discussed and presented here.

Apomixis is a horticultural trait that enables clonal propagation of hybrids by producing asexual embryos from maternal cells in the ovule without meiosis. Many mango cultivars exhibit apomictic polyembryony, where one embryo develops from zygotic tissues and the rest from nucellar tissues, resulting in seedlings that are genetically identical to the mother tree. In Mangifera indica L. commercially important rootstocks are raised from apomictic seeds, which are then grafted with desired cultivars. Identifying molecular markers for polyembryony and understanding its genetics would facilitate introducing this trait in commercially important cultivars. In this report, genome-wide association studies were conducted on a diversity panel consisting of 42 polyembryonic and 42 monoembryonic M. indica cultivars using high-density single nucleotide polymorphism (SNP) markers. These studies revealed that the polyembryony locus is in a 360-kb region on linkage group 17 of the ‘Alphonso’ reference genome. This locus contains the MiRWP/MiRKD4 gene, which codes for an RWP–RK domain-containing protein previously implicated in citrus apomixis. Comparative genomic analyses revealed synteny between the citrus and the mango polyembryony loci, suggesting a common evolutionary mechanism for this trait. A total of 29 SNP markers in this locus were significantly associated with polyembryony in M. indica . Five of these markers were developed into convenient genotyping assays using competitive allele-specific PCR chemistry implemented in two different genotyping platforms – Kompetitive Allele-Specific PCR (KASP) and PCR allele competitive extension (PACE). The utility of these assays was validated and demonstrated in diverse germplasm collection and open-pollinated mango breeding populations with known pedigrees and polyembryony phenotypes. These SNP markers, especially those flanking the MiRWP/MiRKD4 gene, provide a valuable tool for mango breeders to select polyembryonic progenies at the seedling stages in mango breeding programs.