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Adequate yield and fruit quality are required in commercial plum production. The pollen source has been shown to influence fruit set and fruit characteristics. In this study, ‘Siyueli’, ‘Fenghuangli’ and ‘Yinhongli’ were used as pollinizers of ‘Fengtangli’ plum. Additionally, self-pollination, mixed pollination, and open pollination were performed. We characterized the differences in pollen tube growth, fruit set and fruit quality among pollination combinations. ‘Fengtangli’ flowers pollinated by ‘Fenghuangli’ had more pistils with pollen tubes penetrating the ovary and the highest fruit set rate, while the lowest fruit set rate was obtained from self-pollination. In self-pollinated flowers, 33% of pistils had at least one pollen tube reaching the ovary, implying that ‘Fengtangli’ is partially self-compatible. Pollen sources affected ‘Fengtangli’ fruit size, weight, pulp thickness, soluble solids, and sugar content. Transcriptome analysis of ‘Siyueli’-pollinated and ‘Yinhongli’-pollinated fruits revealed 2762 and 1018 differentially expressed genes (DEGs) involved in the response to different pollen sources. DEGs were enriched in plant hormone signal transduction, starch and sucrose metabolism, and MAPK signaling pathways. Our findings provide a reference for the selection of suitable pollinizers for ‘Fengtangli’ plum and promote future research on the metaxenia effect at the molecular level.

Background Chestnut seeds are important kinds of edible nuts rich in starch and protein. The characteristics and nutrient contents of chestnut have been found to show obvious metaxenia effects in previous studies. To improve the understanding of the effect of metaxenia on chestnut starch and sucrose metabolism, this study used three varieties of chestnut, ‘Yongfeng 1’, ‘YongRen Zao’ and ‘Yimen 1’, as male parents to pollinate the female parent, ‘Yongfeng 1’, and investigated the mechanisms of starch and sucrose metabolism in three starch accumulation stages (70 (S1), 82 (S2), and 94 (S3) days after pollination, DAP) in chestnut seed kernels. Result Most carbohydrate metabolism genes were highly expressed in YFF (self-pollinated ‘Yongfeng 1’) in stage S2 and in YFR (‘Yongfeng 1’ × ‘Yongren Zao’) and YFM (‘Yongfeng 1’ × ‘Yimen 1’) in stage S3. In stage S3, hub genes encoding HSF_DNA-binding, ACT, Pkinase, and LIM proteins and four transcription factors were highly expressed, with YFF showing the highest expression, followed by YFR and YFM. In addition, transcriptome analysis of the kernels at 70, 82 and 94 DAP showed that the starch granule-bound starch synthase (EC 2.4.1.242) and ADP-glucose pyrophosphorylase (EC 2.7 .7.27) genes were actively expressed at 94 DAF. Chestnut seeds regulate the accumulation of soluble sugars, reducing sugars and starch by controlling glycosyl transferase and hydrolysis activity during development. Conclusion These results and resources have important guiding significance for further research on starch and sucrose metabolism and other types of metabolism related to chestnut metaxenia.

Tissue-cultured (TC) date palms produce no fruit or low yield due to abnormal fruit setting. To improve the yield of TC ‘Berhi’ palms, trees were pollinated using five pollen sources (Gantar, Ghannami, Mazafati, Zahedi, and Jarvis). The experiment was carried out in three replications for two successive years in a randomized complete blocks design. The fruit set, the fruit and seed physical traits at the Khalal stage, bunch weight at the Tamar and Khalal stages, ripeness of Tamar bunch, and the fruit quality at both Khalal and Tamar stages were measured and monitored. Year factor significantly affected the fruit set and the fruit and seed characteristics. Pollen sources affected fruit set and some seed characteristics significantly. Zahedi+Jarvis pollen treatment that induced 50% normal fruit set and the highest ratio of pulp to seed was found superior. It was also a top treatment in Khalal’s bunch weight (3.11 Kg). Zahedi+Gantar treatment was realized superior in Tamar’s bunch weight (6.00 Kg). Ghannami, Jarvis+Ghannami, and Zahedi+Jarvis treatments produced Khalal’s fruits with higher quality indices but Zahedi+Jarvis treatment was superior in fruit quality at the Tamar stage. Overall, the combined application of Zahedi and Jarvis pollens yielded the most desired outcomes.

Asynchronous flowering between male and female date palms (Phoenix dactylifera L.) makes pollen storage a practical necessity for growers, especially for cultivars like ‘Mejhoul’, which require artificial pollination. This study examined the stainability of pollen as an indicator of cytoplasmic integrity, from four male date plant pollen donor genotypes (‘Mejhoul’, ‘Deglet Nour’, ‘Khadrawy’, and ‘Zahidi’) stored at 4 °C for different durations (fresh, one-year, and two-year storage) and their effects on fruit set and physical fruit characteristics of the Mejhoul cultivar in Mexico. Pollen stainability was assessed in vitro using 1% acetocarmine. Fruit and seed set percentages were evaluated as indicators of the practical effectiveness of stored pollen under field conditions, but not as direct measures of viability. Results showed that fresh pollen exhibited the highest stainability (91.2–95.6%), followed by one-year-stored pollen (59.4–68.3%), and two-year-stored pollen (38.8–45.4%). Fruit set percentages were highest with fresh pollen (63.8–81.7%), decreasing with storage duration. ‘Deglet Nour’ pollen consistently showed superior compatibility with ‘Mejhoul’ females. Physical fruit characteristics (weight, length, diameter) and seed traits were minimally affected by reduced pollen stainability, indicating that there were enough viable grains for effective pollination. The study also observed Metaxenia and Xenia effects, where pollen genotypes influenced fruit and seed size. Overall, these findings suggest that pollen stored at 4 °C for short and medium terms can be used in Mejhoul production, but longer storage significantly reduces efficacy, recommending sub-zero temperatures for extended preservation.

Metaxenia, an intriguing phenomenon in fruit crops, refers to the influence of the pollen parent on fruit characteristics beyond the maternal plant’s genetic makeup. This phenomenon holds significant implications for fruit crop production and improvement. Through a range of scientific studies, it has been observed that metaxenia can lead to diverse changes in fruit attributes such as size, color, flavor, and nutritional content. The practice allows for rapid trait enhancement, targeted breeding, and customization of fruit varieties to align with consumer preferences and market trends. Further, trials are required to examine the impact of varying pollen origins on biochemical processes linked to fruit quality. Additionally, identifying optimal pollinators for specific cultivars is essential. There exists a necessity to ascertain the physiological and genetic underpinnings of metaxenia concerning both qualitative and quantitative attributes in fruit crops. This paper delves into the practical implications of metaxenia, highlighting its role in shaping modern fruit cultivation, fostering innovation, and meeting the evolving demands of consumers and markets.

This study evaluated the influence of different male date palm cultivars, distinguished by their chloroplast haplotypes, on pollen quality, pollination efficiency, metaxenia effects, and gene expression during fruit development. Chloroplast DNA analysis of 37 male trees revealed multiple haplotypes, from which cultivars B25, P8, C22, and B46 were selected for further investigation. Pollen viability varied significantly among cultivars, with P8 and B25 exhibiting the highest germination rates and pollen tube elongation, while C22 showed the lowest. These differences correlated with pollination success: P8 and B25 achieved fertilization rates near 99%, whereas C22 remained below 43%. Pollination outcomes also varied in fruit traits. Despite its low pollen performance, C22 induced the production of larger fruits at the Bleh (Kimri) stage, potentially due to compensatory physiological mechanisms. Phytochemical profiling revealed significant cultivar effects: fruits from B25-pollinated trees had with lower moisture and polyphenol content but the higher sugar levels and soluble solids, suggesting accelerated maturation. Ripening patterns confirmed this finding, with B25 promoting the earliest ripening and B46 causing the most delayed. Gene expression analysis supported these phenotypic differences. Fruits pollinated by P8, B25, and B46 exhibited elevated levels of cell-division-related transcripts, particularly the PdCD_1 gene (PDK_XM_008786146.4, a gene encoding a cell division control protein), which was most abundant in P8. In contrast, fruits from C22-pollinated trees had the lowest expression of growth-related genes, suggesting a shift toward cell expansion rather than division. Overall, the results show the critical role of male genotype in influencing fertilization outcomes and fruit development, offering valuable insights for targeted breeding strategies at enhancing date palm productivity and fruit quality.

Fruits of hickory ( ) are larger and their peel is greener after interspecific pollination by pecan ( ; later pp fruits) than after intraspecific pollination by hickory (later ph fruits). Previous studies have found little genetic differences between offspring and their maternal parent, indicating that the observed trait differences between pp and ph fruits are due to metaxenia. Fruit development depends on the amount of photosynthetic assimilate available. Since there is no difference in photosynthesis of the associated leaves between pp and ph fruits, the larger size of the pp fruits might be attributed to changes in fruit photosynthesis caused by the different pollen sources. To elucidate to the photosynthetic mechanisms behind the metaxenia effect on fruit development in hickory, the effects of intraspecific and interspecific pollination regimes were examined in the present study. We observed the photosynthetic capacity in the peel of fruits and the related ecophysiological and morphological traits of both ph and pp fruits over a period of 120 days after pollination. Significant differences in the appearance and dry weight between ph and pp fruits were observed at 50 days after pollination (DAP). More than 70% of dry matter accumulation of the fruits was completed during 60-120 DAP, while the true photosynthetic rate of the associated leaves significantly decreased by about 50% during the same period. In several cell layers of the peel, the number of chloroplasts per cell was significantly higher in pp than in ph fruits. Similarly, the ribulose 1, 5-bisphosphate carboxylase (Rubisco) activity, the total chlorophyll content, and the nitrogen content were all significantly higher in pp than in ph fruits during all growth stages; and all of these physiological quantities were positively correlated with the gross photosynthetic rate of the fruits. We conclude that the enhanced photosynthetic capacity of pp fruits contributes to their fast dry matter accumulation and oil formation. This result will provide a theoretical basis for improving hickory fruit yields in practical cultivation.

Kiwiberry (Actinidia arguta) is dioecious species which is now commercially grown in several countries worldwide. A study was conducted to determine the influence of five pollen sources derived from A. arguta (three cultivars), A. arguta var. purpurea ‘Rot’ and A. chinensis var. deliciosa ‘Tomuri’ on fruit and seed characteristics for three female A. arguta cultivars. Average fruit weight and biochemical features—fruit total phenolic concentration (TPC), ascorbate (ASC), pigments, total antioxidant activity and seed proteins profile were evaluated. TPC was determined using the Folin–Ciocalteu reagent assay. ASC, individual phenolic compounds and pigments composition were analysed using HPLC technique. Seed protein composition was analysed based on SDS-PAGE. Fruit phenolic and dry matter contents were influenced to a large degree by pollen sources while ASC content did not. The type of male and female parents used in the study were found to have a considerable effect on these parameters. The biggest differences in fruit phytocompound contents were found between female parents. The ‘Geneva’ cultivar showed the highest concentration of the most bioactive compounds tested. Four phenolic acids and five flavonoids were present in the highest concentrations in tested kiwiberry fruit. Actinidia chinensis var. deliciosa ‘Tomuri’ pollen clearly modified the seed protein spectrum with a 17 and 23 kDa protein. The obtained results indicate that to achieve desired fruit biochemical characteristics, the pollen source (male vines) should be selected individually for particular female cultivars, especially in the case of polyphenol content. Our findings suggest that not only A. arguta but also A. arguta var. purpurea and A. chinensis var. deliciosa ‘Tomuri’ males may be suitable as pollinizers for kiwiberry fruit production.

The deposition of lignin in flesh parenchyma cells for pear stone cells, and excessive stone cells reduce the taste and quality of the fruit. The effect of metaxenia on the quality of fruit has been heavily studied, but the effect of metaxenia on stone cell formation has not been fully elucidated to date. This study used P. bretschneideri (Chinese white pear) cv. ‘Yali’ (high-stone cell content) and P. pyrifolia (Sand pear) cv. ‘Cuiguan’ (low-stone cell content) as pollination trees to pollinate P. bretschneideri cv. ‘Lianglizaosu’ separately to fill this gap in the literature. The results of quantitative determination, histochemical staining and electron microscopy indicated that the content of stone cells and lignin in YL fruit (‘Yali’ (pollen parent) × ‘Lianglizaosu’ (seed parent)) was significantly higher than that in CL fruit (‘Cuiguan’ (pollen parent) × ‘Lianglizaosu’ (seed parent)). The transcriptome sequencing results that were obtained from the three developmental stages of the two types of hybrid fruits indicated that a large number of differentially expressed genes (DEGs) related to auxin signal transduction (AUX/IAAs and ARFs), lignin biosynthesis, and lignin metabolism regulation (MYBs, LIMs, and KNOXs) between the CL and YL fruits at the early stage of fruit development. Therefore, metaxenia might change the signal transduction process of auxin in pear fruit, thereby regulating the expression of transcription factors (TFs) related to lignin metabolism, and ultimately affecting lignin deposition and stone cell development. In addition, we performed functional verification of a differentially expressed gene, PbC4H2 (cinnamate 4-hydroxylase). Heterologous expression of PbC4H2 in the c4h mutant not only restored its collapsed cell wall, but also significantly increased the lignin content in the inflorescence stem. The results of our research help to elucidate the metaxenia-mediated regulation of pear stone cell development and clarify the function of PbC4H2 in cell wall development and lignin synthesis, which establishes a foundation for subsequent molecular breeding.

Phoenix species are interfertile and crossing distinct species leads to fertile hybrid offspring. The introduction of a species in the wild generates gene flows leading to the creation of new hybrids and has conservation implications. In cultivation, such crossings may be spontaneous or are the result of artificial pollination, as several reasons impel doing so. Crossing gives rise to beautiful hybrids and is also useful for the conservation of old palm groves threatened by pests. Thus, an increasing need of hybrid detection and characterization exists, particularly as morphology alone is not sufficient for this task. Besides new methods such as traditional and geometric morphometrics that may bring new clues, the advent of genetic and molecular markers helps to detect hybrids, especially based on the combination of nuclear and chloroplastic data. The application of methods such as near-infrared reflectance spectroscopy is currently under examination to estimate their potential use for hybrid characterization.