Germplasm collections are an important source for plant breeding, especially in fruit trees which have a long duration of juvenile period. Thus, efforts have been made to study the diversity of fruit tree collections. Even though mango is an economically important crop, most of the studies on diversity in mango collections have been conducted with a small number of genetic markers. We describe a de novo transcriptome assembly from mango cultivar ‘Keitt’. Variation discovery was performed using Illumina resequencing of ‘Keitt’ and ‘Tommy Atkins’ cultivars identified 332,016 single-nucleotide polymorphisms (SNPs) and 1903 simple-sequence repeats (SSRs). Most of the SSRs (70.1 %) were of trinucleotide with the preponderance of motif (GGA/AAG)n and only 23.5 % were di-nucleotide SSRs with the mostly of (AT/AT)n motif. Further investigation of the diversity in the Israeli mango collection was performed based on a subset of 293 SNPs. Those markers have divided the Israeli mango collection into two major groups: one group included mostly mango accessions from Southeast Asia (Malaysia, Thailand, Indonesia) and India and the other with mainly of Floridian and Israeli mango cultivars. The latter group was more polymorphic (FS = −0.1 on the average) and was more of an admixture than the former group. A slight population differentiation was detected (FST = 0.03), suggesting that if the mango accessions of the western world apparently was originated from Southeast Asia, as has been previously suggested, the duration of cultivation was not long enough to develop a distinct genetic background. Whole-transcriptome reconstruction was used to significantly broaden the mango’s genetic variation resources, i.e., SNPs and SSRs. The set of SNP markers described in this study is novel. A subset of SNPs was sampled to explore the Israeli mango collection and most of them were polymorphic in many mango accessions. Therefore, we believe that these SNPs will be valuable as they recapitulate and strengthen the history of mango diversity.

Off-types are quite common among tissue culture-produced date palm trees. The present study characterises a low fruit setting phenotype, found widely among tissue culture-produced date palms of the cultivar ‘Barhee’. Most flowers in such trees turn into parthenocarpic fruitlets having three carpels. In severe cases, supernumerary carpels are formed. Other flower abnormalities include distortions of carpels and stigmas. The phenotype is alleviated in older trees, with about 50% of trees reverting to normal within 10 years from planting. Many flowers on the abnormal trees have impaired pollen tube elongation, with growth being limited to the stigma or to regions near its point of joining the carpel. Directional growth of pollen tubes ceases and tubes grow in different directions or stop growing completely. Possible mechanisms for this off-type phenotype, and its resemblance to other cases of somaclonal variation are discussed.

Colour accumulation and expression of the anthocyanin biosynthetic pathway were analysed in four variants of ‘Red Delicious’ apple (Malus x domestica) that differed in their levels of red colouration. Colour characteristics were assessed by analysing the percentage red colour skin coverage, colour quality, colour intensity, and anthocyanin concentration during maturation and fruit ripening in two seasons: a typical one, and a high-colouration season. Anthocyanins and their precursors were analysed by HPLC, while expression of structural genes in the anthocyanin biosynthetic pathway was followed by quantitative real-time RT-PCR. Colour characteristics varied between the apple variants. In one variant, a large fraction of the fruit skin turned red at an early stage, while in others the red colour accumulated only close to ripening. Red variants showed earlier appearance and higher levels of anthocyanins and several quercetin derivatives as well as higher expression of genes encoding most of the anthocyanin biosynthetic enzymes. Our results suggest that in the redder variants, the entire anthocyanin biosynthetic pathway, rather than any specific gene, is highly induced in the early stages of fruit maturation. Differences in overall expression patterns of genes that regulate anthocyanin biosynthesis are probably the cause of the different colouration patterns observed in these variants.

In mango (Mangifera indica L.), fruitlet abscission limits productivity. The INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) peptide acts as a key component controlling abscission events in Arabidopsis. IDA-like peptides may assume similar roles in fruit trees. In this study, we isolated two mango IDA-like encoding-genes, MiIDA1 and MiIDA2. We used mango fruitlet-bearing explants and fruitlet-bearing trees, in which fruitlets abscission was induced using ethephon. We monitored the expression profiles of the two MiIDA-like genes in control and treated fruitlet abscission zones (AZs). In both systems, qRT-PCR showed that, within 24 h, both MiIDA-like genes were induced by ethephon, and that changes in their expression profiles were associated with upregulation of different ethylene signaling-related and cell-wall modifying genes. Furthermore, ectopic expression of both genes in Arabidopsis promoted floral-organ abscission, and was accompanied by an early increase in the cytosolic pH of floral AZ cells—a phenomenon known to be linked with abscission, and by activation of cell separation in vestigial AZs. Finally, overexpression of both genes in an Atida mutant restored its abscission ability. Our results suggest roles for MiIDA1 and MiIDA2 in affecting mango fruitlet abscission. Based on our results, we propose new possible modes of action for IDA-like proteins in regulating organ abscission.

Sexual reproduction in plants is the main pathway for creating new genetic combinations in modern agriculture. In heterozygous plants, after the identification of a plant with desired traits, vegetative propagation (cloning) is the primary path to create genetically uniform plants. Another natural plant mechanism that creates genetically uniform plants (clones) is apomixis. In fruit crops like citrus and mango, sporophytic apomixis results in polyembryony, where seeds contain multiple embryos, one of which is sexually originated and the others are vegetative clones of the parent mother tree. Utilizing the mango genome and genetic analysis of a diverse germplasm collection, we identified MiRWP as the gene that causes polyembryony in mango. There is a strong correlation between a specific insertion in the gene’s promoter region and altered expression in flowers and developing fruitlets, inducing multiple embryos. The MiRWP gene is an ortholog of CitRWP that causes polyembryony in citrus. Based on the data, we speculate that promoter insertion events, which occurred independently in citrus and mango, induced nucellar embryogenesis. The results suggest convergent evolution of polyembryony in the two species. Further work is required to demonstrate the utility of these genes (mango and citrus) in other biological systems as a tool for the clonal production of other crops.