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Communication

Outcrossing Levels and Fruit Quality in Single-Cultivar Blocks of a Multi-Cultivar Lychee (Litchi chinensis Sonn.) Orchard

by
Stephen J. Trueman
* and
Joel Nichols
School of Environment and Science, Griffith University, Nathan, QLD 4111, Australia
*
Author to whom correspondence should be addressed.
Horticulturae 2025, 11(3), 244; https://doi.org/10.3390/horticulturae11030244
Submission received: 28 January 2025 / Revised: 20 February 2025 / Accepted: 20 February 2025 / Published: 25 February 2025
(This article belongs to the Special Issue Orchard Management: Strategies for Yield and Quality)
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Abstract

:
Intraspecific diversity is often introduced in orchards to promote cross-pollination, which is essential for self-incompatible crops and beneficial for many self-compatible crops. In lychee, orchards are often planted with multiple cultivars to increase the availability of male flowers, enhancing pollen transfer to female flowers. Typically, this diversity is arranged in single-cultivar blocks, requiring pollinators to transport cross-pollen across rows to reach trees in the middle of each block. We aimed to determine the levels of outcrossing at the edge and in the middle of blocks of Fay Zee Siu, Kaimana, Kwai Mai Pink, Sah Keng, Souey Tung and Wai Chee in a multi-cultivar lychee orchard. We also aimed to determine whether outcrossed fruit have different mass, skin colour and flavour attributes from selfed fruit. All cultivars produced a mixture of outcrossed and selfed fruit. Fay Zee Siu and Kaimana fruit were predominantly outcrossed, Kwai Mai Pink produced slightly more selfed than outcrossed fruit, and Souey Tung displayed high selfing. Outcrossing levels did not differ significantly between the edge and middle rows of these four cultivars. In contrast, Sah Keng and Wai Chee produced more outcrossed fruit in their edge row but more selfed fruit in their middle row. These two cultivars were at the orchard periphery, with another cultivar planted on only one side. Pollinators transported cross-pollen 56–60 m into the middle of blocks when different cultivars were planted on both sides, but this distance decreased to 42–56 m into the blocks when another cultivar was planted on only one side. Cross-pollination had few effects on fruit mass or quality, although pollination by Souey Tung sometimes increased fruit mass or Brix. These findings suggest that interplanting different cultivars of lychee can make effective use of its mixed-mating system, providing additional pollen sources in the orchard, supporting fruitlet retention, and sustaining tree productivity, without contributing greatly to quality variation in each cultivar.

Graphical Abstract

1. Introduction

Intraspecific crop diversity is often established in fruit and nut orchards to ensure that the flowers of each main cultivar have access to a diverse array of pollen sources, allowing cross-pollination [1,2,3]. Cross-pollination is essential for fruit and seed production in crops that are self-incompatible [4,5,6,7,8,9]. Cross-pollination is also beneficial for yield or fruit quality in many crops that are self-compatible [10,11,12,13]. Cross-pollination can increase the fresh mass of avocado, macadamia, pear, plum and strawberry fruit [13,14,15,16,17], improve the flavour or shelf life of blueberry, citrus and strawberry fruit [17,18,19,20], and improve the nutritional profile of almond, avocado, blueberry and strawberry fruit [6,19,20,21,22,23]. Despite these benefits, commercial orchards are often designed with single-cultivar blocks to facilitate uniform, convenient and cost-effective management of pests, diseases, irrigation, crop nutrition, harvesting and post-harvest processing [24,25,26,27]. This approach simplifies orchard operations but it may reduce cross-pollination, especially in the middle of each block where pollinators need to transport pollen across many orchard rows to ensure cross-pollination [13,28,29,30,31,32,33].
Lychee is a tropical and subtropical fruit crop that often has orchards planted with multiple cultivars to increase the opportunities for successful pollination of each flower [34,35,36,37]. Lychee flowers are insect-pollinated, primarily by bees but possibly also by flies and other insects [38,39,40,41,42]. Lychee trees produce numerous panicles that bear, firstly, male (M1) flowers with low-fertility pollen; secondly, female (F) flowers with copious sugary nectar; and thirdly, male (M2) flowers with highly fertile pollen [39,43]. There is little overlap between the M1, F and M2 flowers on the same panicle and so effective pollination requires synchronous flowering of F flowers with M2 flowers among different panicles of the same tree, different trees of the same cultivar or different cultivars within an orchard [38,39]. This means that incorporating intraspecific diversity by planting multiple cultivars can improve the chances of successful lychee pollination [34,38]. Lychee cultivars Floridian and Mauritius exhibit a mixed-mating system in commercial orchards in Israel, producing fruit by both cross-pollination and self-pollination [34,44]. We have found recently that lychee cultivars Kaimana and Kwai Mai Pink also exhibit mixed mating in a commercial orchard in Australia [37]. Cross-fertilised lychee fruit may be larger and have better skin colour than self-pollinated fruit, though the results depend on the cross-pollen parent [34,37,44].
Here, we extended the research to six lychee cultivars in the same orchard in Australia and hypothesised the following: (1) that they would exhibit mixed mating, producing a mixture of self-fertilised and cross-fertilised fruit; (2) outcrossing rates would be higher at the edge than the middle of single-cultivar blocks in a multi-cultivar orchard; and (3) cross-fertilised fruit would generally have superior quality, with greater mass, more intense skin colour, and enhanced flavour attributes than self-fertilised fruit. The findings from this study will contribute to the development of orchard designs that integrate intraspecific diversity, promoting successful pollination and optimising fruit quality.

2. Materials and Methods

2.1. Study Site

We sampled lychee fruit in a commercial orchard at Welcome Creek (24°47′0″ S, 152°16′40″ E), near Bundaberg, Queensland, Australia. The orchard contained eight cultivars, six of which were planted in single-cultivar blocks: Fay Zee Siu, Kaimana, Kwai Mai Pink, Sah Keng, Souey Tung and Wai Chee (Figure 1). The trees of these six cultivars were 6–19 years old. Tree spacing in the orchard was 6–7 m between rows × 3–4 m within rows, with the exact spacing tailored to each of the six different cultivars. Additionally, a few Bengal and Salathiel trees were also scattered throughout the orchard. No honeybee hives had been placed in the orchard, but managed hives were present in nearby macadamia orchards.

2.2. Fruit Sampling and Quality Analysis

We sampled mature fruit in December 2022 and January 2023 from the six cultivars planted in single-cultivar blocks. From each cultivar, fruit were sampled from twelve trees—six from an edge row and six from a middle row (Figure 1). Whenever possible, sampled trees were separated by at least one other tree. We harvested 12 fruits from each tree (i.e., 72 fruits from the edge row and 72 fruits from the middle row of each cultivar), selecting 3 fruits from each of four quadrants (NE, SE, SW and NW) around the canopy. Each fruit was selected from either a high or low position within the canopy using a random-number generator. Each fruit was weighed, and its skin colour was assessed on its reddest side using a CR-10 colorimeter (Konica Minolta, Chiyoda, Japan) that measured brightness (L*), colour along the green–red axis (a*) and colour along the blue–yellow axis (b*). To assess fruit quality, each fruit was then dissected, and one-quarter of the flesh was squeezed through filter paper to measure total soluble solid concentration (°Brix), acid concentration, and the Brix:acid ratio using a PAL-BX|ACID15 sugar and acidity metre (Atago, Tokyo, Japan) [19].

2.3. Paternity Analysis

To identify the pollen parent of each fruit, we extracted DNA from a 50 mg seed subsample using the glass-fibre plate protocol for DNA extraction [45]. Extracted DNA was amplified at eight microsatellite loci used for identifying the pollen parent of lychee fruit [37,46], and PCR reactions were performed as described previously [37]. We generated genotypes using a 3130xl Genetic Analyser (Applied Biosystems, Foster City, CA, USA). Allele sizes were scored using the software, GeneMarker version 2.6.3 (SoftGenetics, State College, PA, USA), relative to an internal standard (600 LIZ® Size Standard, Applied Biosystems). The pollen parent of each fruit was assigned using the software, CERVUS version 3.0.7 [47]. Pollen parents were considered possible if CERVUS assigned a positive logarithm of odds (LOD) score. Specific pollen parents were assigned if only one pollen parent was assigned a positive LOD score, or if the best match achieved an 80% confidence level. Simulations on paternity were performed by setting the parameters to the following: (a) proportion of mistyped loci at 0.01; (b) proportion of candidate fathers sampled at 1.0; and (c) offspring simulated at 100,000.

2.4. Statistical Analysis

For cross-paternity and self-paternity analyses, we used paired t tests, treating two trees at corresponding positions in edge and middle rows as a pair. We analysed data for fruit mass, skin colour components and flavour attributes by analysis of variance (ANOVA). Brix data were square-root or log-transformed, when necessary, to achieve homogeneous variance. Post hoc Tukey’s Honest Significant Difference (HSD) tests were used when differences among means were detected by ANOVA. Statistical significance was set at p < 0.05. Statistical analyses were performed using IBM SPSS Statistics v. 30.0.0.0 (172) (IBM, Armonk, NY, USA). Means are reported with standard errors.

3. Results and Discussion

All six lychee cultivars displayed a mixed-mating system, producing both self-fertilised and cross-fertilised fruit, but with varying levels of outcrossing among cultivars (Figure 2). Fay Zee Siu and Kaimana were predominantly outcrossed, with 83 ± 7% and 71 ± 8% of Fay Zee Siu fruit and 70 ± 3% and 83 ± 4% of Kaimana fruit identified as cross-fertilised in their edge and middle rows, respectively (Figure 2a,b). Kwai Mai Pink produced slightly more self-fertilised than cross-fertilised fruit, with 45 ± 7% and 33 ± 5% of the fruit identified as outcrossed in the edge and middle rows, respectively (Figure 2c). Souey Tung had high levels of selfing, with only 18 ± 6% and 10 ± 2% of fruit identified as outcrossed in the edge and middle rows, respectively (Figure 2e). Kaimana was found 2 years earlier to have higher levels of outcrossing than selfing, while Kwai Mai Pink was found to have high levels of selfing, in the same orchard blocks [37]. The results demonstrate a consistency of outcrossing levels in each cultivar across two different years.
The levels of outcrossing did not differ significantly between the edge and middle rows of the Fay Zee Siu, Kaimana, Kwai Mai Pink and Souey Tung blocks (Figure 2a–c,e), consistent with findings from the two cultivars studied previously, i.e., Kaimana and Kwai Mai Pink [37]. This suggests that insect visitors, mainly the honeybee, Apis mellifera, but also a rhiniid fly, Stomorhina discolor and other bees such as Tetragonula carbonaria and Homalictus dampieri [37], transported cross-pollen at similar levels into the middle of these four blocks as they did into the edge rows. The middle rows of the Fay Zee Siu, Kaimana, Kwai Mai Pink and Souey Tung blocks were 60 m, 56 m, 70 m and 56 m, respectively, from the nearest other cultivar (Figure 1). Interestingly, the outcrossing levels were not clearly related to tree age. The highest outcrossing levels were in a block of young trees, i.e., 6-year-old Kaimana, as well as a block of older trees, i.e., 17-year-old Fay Zee Siu. Lower outcrossing was found in the 19-year-old Kwai Mai Pink trees, and the lowest outcrossing was found in the 14-year-old Souey Tung trees. We had surmised previously [37] that lower outcrossing in Kwai Mai Pink than Kaimana might be due to a larger floral display on the older Kwai Mai Pink trees because bees often prefer to forage on plants that have a large floral display [48,49] and because foraging on many flowers within a single plant or cultivar may cause a high rate of selfing [1,50]. The results instead suggest that the realised mating system of lychee trees is influenced by other factors such as the synchronicity of flowering between cultivars [34,36,38,44] and different levels of pollen-pistil self-incompatibility or selective abortion of selfed fruitlets among the cultivars [36,44,51]. Further research is needed to examine selfing and outcrossing levels at early fruitlet stages, before fruitlet abscission [11,16,36,44,51,52,53].
Outcrossing levels were significantly higher in the edge than the middle row of two cultivars, Sah Keng and Wai Chee (Figure 2d,f), unlike the other four cultivars. The levels of outcrossing were 59 ± 9% and 23 ± 8% in the edge and middle rows, respectively, of the Sah Keng block (Figure 2d) and 61 ± 5% and 31 ± 8% in the same respective rows of the Wai Chee block (Figure 2f). This suggests that pollinators were less effective at transporting cross-pollen into the middle rows of these blocks. The middle rows of the Sah Keng and Wai Chee blocks were 42 m and 56 m, respectively, from the nearest other cultivar (Figure 1). These two cultivars (and Kwai Mai Pink) were located at the periphery of the orchard, with another cultivar located on only one side, rather than two sides, of their blocks. Therefore, pollinators transported cross-pollen 56–60 m into the middle of single-cultivar lychee blocks (i.e., at similar levels to the amount in the edge rows) when different cultivars were located on both sides of the block. However, cross-pollen flow was often limited at 42–56 m into the middle of the blocks when another cultivar was located on only one side.
The main cross-pollen parent for each cultivar was usually the neighbouring cultivar (for Fay Zee Siu, Kaimana and Sah Keng) or a cultivar in the very close vicinity (for Wai Chee) (Table 1, Figure 3). This suggests that pollen dispersal is limited and random mating does not occur across the entire orchard. The paternity results are similar to those from single-cultivar blocks of avocado and macadamia in multi-cultivar orchards, where the predominant cross-pollen parent was typically the cultivar in the neighbouring block [8,13,32,54]. Declining outcrossing levels have been observed by 12–30 m into the middle of single-cultivar blocks of Floridian and Mauritius lychee in Israel where another cultivar was planted on only one side [34,44]. Lower yields accompanied the lower outcrossing levels in the Floridian blocks, but not in the Mauritius blocks even at 48–132 m from another cultivar [34,44]. Declining yields have been observed by 12–30 m in single-cultivar blocks of Mauritius in two other orchards in Israel where polliniser trees were only planted as a single row rather than wide blocks [36].
Outcrossing rates also decline between the edge and the middle of single-cultivar blocks of avocado [13,52,53,55,56,57]. Similarly to lychee, declining outcrossing rates in the middle of single-cultivar avocado blocks are sometimes [13,52,55], but not always [52,53], associated with declining yields. Lower avocado yields have been observed at 42–60 m from polliniser trees in Israel [52,55] and at 160 m from polliniser trees in Australia [13]. Tree yields were not measured in the current study. However, the mating-system results indicate that the pollination of many female (F) flowers in the middle of the peripheral blocks (rather than the central blocks) of the orchard was highly reliant on having synchronous flowering of fertile M2 flowers on different panicles of the same cultivar, rather than different cultivars, within the orchard [38,39].
Cross-pollination typically had no significant effect on the fresh mass, skin colour or flavour attributes of lychee fruit (Table 1). Cross-pollination had no significant effect previously on the mass or quality of Kwai Mai Pink fruit in the same orchard [37], 73-S-20 fruit in Taiwan [58], or Mauritius fruit in one orchard in Israel [34]. However, Sah Keng fruit that were cross-fertilised by Souey Tung had 25% higher fresh mass than self-fertilised Sah Keng fruit (Table 1), similar to the 20% increase found previously following pollination of Kaimana by Souey Tung [37]. In addition, Kaimana fruit that were cross-fertilised by Souey Tung had 14% higher Brix than self-fertilised Kaimana fruit, and Wai Chee fruit that were cross-fertilised by Sah Keng had 14% higher acid concentration than self-fertilised Wai Chee fruit (Table 1). Despite these three exceptions, we reject the hypothesis that cross-fertilised lychee fruit often have higher mass, more intense skin colour, and better flavour attributes than self-fertilised fruit.
Changes in fruit mass, flavour or nutritional profile have been observed following cross-fertilisation of almond, citrus, macadamia and strawberry flowers [6,7,8,18,19,21,32,59]. The current results for lychee instead reflect findings from mango, where few significant differences are found between self-fertilised and cross-fertilised fruit [33]. Therefore, the planting of a diversity of pollen sources in lychee orchards might often contribute little to variation in fruit quality within each cultivar, assisting growers to provide consistent-grade fruit for processing and marketing [60].
Closer interplanting of different lychee cultivars, especially in the peripheral blocks of an orchard, can improve access to synchronously flowering M2 flowers on the panicles of different cultivars, thus improving pollen transfer and fruitlet set [34,38]. Lychee trees selectively retain cross-fertilised fruitlets [36,44,51] and so increasing the opportunities for cross-pollination may also help to reduce fruitlet abscission. Our results suggest that establishing intraspecific crop diversity in lychee orchards can make effective use of the mixed-mating system of this species, improving pollination, supporting fruitlet retention to maturity, and sustaining tree productivity, while maintaining stable fruit quality within cultivars.

4. Conclusions

All six lychee cultivars produced a mixture of outcrossed and selfed fruit, with pollinators transporting cross-pollen up to 60 m into single-cultivar blocks. Introducing a range of pollen sources into lychee orchards has great potential to improve the access of female flowers to pollen from the male flowers of different cultivars, increasing the opportunities for successful pollination and decreasing fruitlet abscission. Very few differences in quality existed between outcrossed and selfed fruit, suggesting that introducing a diversity of pollen sources will not introduce significant variation in the quality of fruit within each cultivar. The results demonstrate some of the benefits of intraspecific crop diversity in orchards, including increasing the efficiency of pollinators by providing them with an optimal pollen supply at a time when there is a growing shortfall in the global stock of managed honeybee hives and a decreasing abundance of wild pollinators.

Autor Contributions

Conceptualization, S.J.T. and J.N.; formal analysis, S.J.T. and J.N.; funding acquisition, S.J.T.; investigation, J.N. and S.J.T.; methodology, S.J.T. and J.N.; project administration, S.J.T.; writing—original draft preparation, S.J.T. and J.N.; writing—review and editing, J.N. and S.J.T. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by project PH20001 of the Frontiers strategic partnership initiative developed by Hort Innovation, with co-investment from Griffith University, Plant & Food Research Ltd., Western Sydney University, The University of New England, and contributions from the Australian Government.

Data Availability Statement

The data presented in this study are available upon request from the corresponding author and with the permission of Hort Innovation.

Acknowledgments

We thank Chris Searle (MacAvo Consulting) for advice, assistance and access to the orchard, Ryan Newis, Nimanie Hapuarachchi, Nicole Hogg and Jean Barcelon (Griffith University) for technical assistance, and Wiebke Kämper (University of Göttingen) for the original photograph adapted for the graphical abstract.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; or in the writing of the manuscript; but they approved publication of the results.

References

  1. Hung, K.-L.J.; Fan, S.L.; Strang, C.G.; Park, M.G.; Thomson, J.D. Pollen carryover, pollinator movement, and spatial context impact the delivery of pollination services in apple orchards. Ecol. Appl. 2023, 33, e2917. [Google Scholar] [CrossRef] [PubMed]
  2. Chabert, S.; Eeraerts, M.; DeVetter, L.W.; Borghi, M.; Mallinger, R.E. Intraspecific crop diversity for enhanced crop pollination success. A review. Agron. Sust. Dev. 2024, 44, 50. [Google Scholar] [CrossRef]
  3. Tscharntke, T.; Ocampo-Ariza, C.; Kämper, W. Pollinator, pollen, and cultivar identity drive crop quality. Trends Plant Sci. 2025, in press. [Google Scholar] [CrossRef] [PubMed]
  4. Sapir, G.; Goldway, M.; Shafir, S.; Stern, R.A. Multiple introduction of honeybee colonies increases cross- pollination, fruit-set and yield of ‘Black Diamond’ Japanese plum (Prunus salicina Lindl.). J. Hortic. Sci. Biotechnol. 2007, 82, 590–596. [Google Scholar] [CrossRef]
  5. Aranzana, M.J.; Decroocq, V.; Dirlewanger, E.; Eduardo, I.; Gao, Z.S.; Gasic, K.; Iezzoni, A.; Jung, S.; Peace, C.; Prieto, H.; et al. Prunus genetics and applications after de novo genome sequencing: Achievements and prospects. Hortic. Res. 2019, 6, 58. [Google Scholar] [CrossRef]
  6. Kämper, W.; Thorp, G.; Wirthensohn, M.; Brooks, P.; Trueman, S.J. Pollen paternity can affect kernel size and nutritional composition of self-incompatible and new self-compatible almond cultivars. Agronomy 2021, 11, 326. [Google Scholar] [CrossRef]
  7. Trueman, S.J.; Kämper, W.; Nichols, J.; Ogbourne, S.M.; Hawkes, D.; Peters, T.; Hosseini Bai, S.; Wallace, H.M. Pollen limitation and xenia effects in a cultivated mass-flowering tree, Macadamia integrifolia (Proteaceae). Ann. Bot. 2022, 129, 135–146. [Google Scholar] [CrossRef] [PubMed]
  8. Trueman, S.J.; Penter, M.G.; Malagodi-Braga, K.S.; Nichols, J.; De Silva, A.L.; Ramos, A.T.M.; Moriya, L.M.; Ogbourne, S.M.; Hawkes, D.; Peters, T.; et al. High outcrossing levels among global macadamia cultivars: Implications for nut quality, orchard designs and pollinator management. Horticulturae 2024, 10, 203. [Google Scholar] [CrossRef]
  9. Cuevas, J.; Chiamolera, F.M.; Pinillos, V.; Rodríguez, F.; Salinas, I.; Cabello, D.; Arbeiter, A.B.; Bandelj, D.; Raboteg Božiković, M.; Vuletin Selak, G. Arbosana olive is self-incompatible, but inter-compatible with some other low-vigor olive cultivars. Horticulturae 2024, 10, 739. [Google Scholar] [CrossRef]
  10. Denney, J.O. Xenia includes metaxenia. HortScience 1992, 27, 722–728. [Google Scholar] [CrossRef]
  11. Dag, A.; Eisenstein, D.; Gazit, S.; El-Batsri, R.; Degani, C. Effect of pollenizer distance and selective fruitlet abscission on outcrossing rate and yield in ‘Tommy Atkins’ mango. J. Am. Soc. Hortic. Sci. 1998, 123, 618–622. [Google Scholar] [CrossRef]
  12. Bayer, I.; Stösser, R. Effect of self- and cross-pollination on fruit set, yield and pollen tube growth in plum. Erwerbsobstbau 2002, 44, 97–104. [Google Scholar]
  13. Trueman, S.J.; Nichols, J.; Farrar, M.B.; Wallace, H.M.; Hosseini Bai, S. Outcrossing rate and fruit yield of Hass avocado trees decline at increasing distance from a polliniser cultivar. Agronomy 2024, 14, 122. [Google Scholar] [CrossRef]
  14. Fountain, M.T.; Mateos-Fierro, Z.; Shaw, B.; Brain, P.; Delgado, A. Insect pollinators of Conference pear (Pyrus communis L.) and their contribution to fruit quality. J. Pollinat. Ecol. 2019, 25, 103–114. [Google Scholar] [CrossRef]
  15. Deng, L.; Wang, T.; Hu, J.; Yang, X.; Yao, Y.; Jin, Z.; Huang, Z.; Sun, G.; Xiong, B.; Liao, L.; et al. Effects of pollen sources on fruit set and fruit characteristics of ‘Fengtangli’ plum (Prunus salicina Lindl.) based on microscopic and transcriptomic analysis. Int. J. Mol. Sci. 2022, 23, 12959. [Google Scholar] [CrossRef] [PubMed]
  16. De Silva, A.L.; Kämper, W.; Ogbourne, S.M.; Nichols, J.; Royle, J.W.L.; Peters, T.; Hawkes, D.; Hosseini Bai, S.; Wallace, H.M.; Trueman, S.J. MassARRAY and SABER analyses of SNPs in embryo DNA reveal the abscission of self-fertilised progeny during fruit development of macadamia (Macadamia integrifolia Maiden & Betche). Int. J. Mol. Sci. 2024, 25, 6419. [Google Scholar] [CrossRef] [PubMed]
  17. Dung, C.D.; Wallace, H.M.; Hosseini Bai, S.; Ogbourne, S.M.; Trueman, S.J. Fruit size and quality attributes differ between competing self-pollinated and cross-pollinated strawberry fruit. Int. J. Fruit Sci. 2023, 23, 1–12. [Google Scholar] [CrossRef]
  18. Wallace, H.M.; Lee, L.S. Pollen source, fruit set and xenia in mandarins. J. Hortic. Sci. Biotechnol. 1999, 74, 82–86. [Google Scholar] [CrossRef]
  19. Dung, C.D.; Wallace, H.M.; Hosseini Bai, S.; Ogbourne, S.M.; Trueman, S.J. Cross-pollination affects fruit colour, acidity, firmness and shelf life of self-compatible strawberry. PLoS ONE 2021, 16, 0256964. [Google Scholar] [CrossRef]
  20. Liu, J.; Xu, J.; Wang, Y.; Li, K.; Zong, Y.; Yang, L.; Chen, W.; Liao, F.; Guo, W. The xenia effect promotes fruit quality and assists in optimizing cross combinations in ‘O’Neal’ and ‘Emerald’ blueberry. Horticulturae 2022, 8, 659. [Google Scholar] [CrossRef]
  21. Brittain, C.; Kremen, C.; Garber, A.; Klein, A.-M. Pollination and plant resources change the nutritional quality of almonds for human health. PLoS ONE 2014, 9, e90082. [Google Scholar] [CrossRef] [PubMed]
  22. Doi, K.; Inoue, R.; Iwasaki, N. Seed weight mediates effects of pollen on berry weight, ripening, and anthocyanin content in highbush blueberry. Sci. Hortic. 2021, 288, 110313. [Google Scholar] [CrossRef]
  23. Kämper, W.; Ogbourne, S.M.; Hawkes, D.; Trueman, S.J. SNP markers reveal relationships between fruit paternity, fruit quality and distance from a cross-pollen source in avocado orchards. Sci. Rep. 2021, 11, 20043. [Google Scholar] [CrossRef] [PubMed]
  24. Kron, P.; Husband, B.C.; Kevan, P.G.; Belaoussoff, S. Factors affecting pollen dispersal in high-density apple orchards. HortScience 2001, 36, 1039–1046. [Google Scholar] [CrossRef]
  25. Trueman, S.J.; McConchie, C.A.; Turnbull, C.G.N. Ethephon promotion of crop abscission for unshaken and mechanically shaken macadamia. Aust. J. Exp. Agric. 2002, 42, 1001–1008. [Google Scholar] [CrossRef]
  26. Sánchez-Estrada, A.; Cuevas, J. Pollination strategies to improve fruit set in orchards of ‘Manzanillo’ olive in a nontraditional producing country, Mexico. HortTechnology 2019, 29, 258–264. [Google Scholar] [CrossRef]
  27. Carisio, L.; Díaz, S.S.; Ponso, S.; Manino, A.; Porporato, M. Effects of pollinizer density and apple tree position on pollination efficiency in cv. Gala. Sci. Hortic. 2020, 273, 109629. [Google Scholar] [CrossRef]
  28. Wallace, H.M.; King, B.J.; Lee, L.S. Pollen flow and the effect on fruit size in an ‘Imperial’ mandarin orchard. HortScience 2002, 37, 84–86. [Google Scholar] [CrossRef]
  29. Cuevas, J.; Hueso, J.J.; Puertas, M. Pollination requirements of loquat (Eriobotrya japonica Lindl.), cv. ‘Algerie’. Fruits 2003, 58, 157–165. [Google Scholar] [CrossRef]
  30. Matsumoto, S.; Eguchi, T.; Maejima, T.; Komatsu, H. Effect of distance from early flowering pollinizers ‘Maypole’ and ‘Dolgo’ on ‘Fiji’ fruit set. Sci. Hortic. 2008, 117, 151–159. [Google Scholar] [CrossRef]
  31. Müller, J.L.; Steyn, W.J.; Theron, K.I. The effect of cross-pollination of southern highbush blueberries on fruit set and fruit characteristics. Acta Hortic. 2013, 1007, 571–578. [Google Scholar] [CrossRef]
  32. Kämper, W.; Trueman, S.J.; Ogbourne, S.M.; Wallace, H.M. Pollination services in a macadamia cultivar depend on across-orchard transport of cross pollen. J. Appl. Ecol. 2021, 58, 2529–2539. [Google Scholar] [CrossRef]
  33. Kämper, W.; Nichols, J.; Tran, T.D.; Burwell, C.J.; Byrnes, S.; Trueman, S.J. Flower visitors, levels of cross-fertilisation, and pollen-parent effects on fruit quality in mango orchards. Agronomy 2023, 13, 2568. [Google Scholar] [CrossRef]
  34. Stern, R.A.; Gazit, S.; El-Batsri, R.; Degani, C. Pollen parent effect on outcrossing rate, yield, and fruit characteristics of ‘Floridian’ and ‘Mauritius’ lychee. J. Am. Soc. Hortic. Sci. 1993, 118, 109–114. [Google Scholar] [CrossRef]
  35. Froneman, I.J.; Bijzet, Z.; Sippel, A.D.; Bower, J.P. Effect of different pollen parents on fruit retention and fruit characteristics in ‘Wai Chee’ litchi. Acta Hortic. 2012, 932, 51–58. [Google Scholar] [CrossRef]
  36. Raz, A.; Goldway, M.; Sapir, G.; Stern, R.A. “Hong Long” lychee (Litchi chinensis Sonn.) is the optimal pollinizer for the main lychee cultivars in Israel. Plants 2022, 11, 1996. [Google Scholar] [CrossRef]
  37. Trueman, S.J.; Nichols, J.; Burwell, C.J.; Kämper, W. Strategic selection of polliniser trees can improve fruit quality of lychee, a crop that exhibits mixed-mating. Basic Appl. Ecol. 2025, 83, 80–87. [Google Scholar] [CrossRef]
  38. Stern, R.A.; Gazit, S. Lychee pollination by the honeybee. J. Am. Soc. Hortic. Sci. 1996, 120, 152–157. [Google Scholar] [CrossRef]
  39. Stern, R.A.; Gazit, S. The reproductive biology of the lychee. Hortic. Rev. 2003, 28, 393–453. [Google Scholar]
  40. Abrol, D.P. Diversity of pollinating insects visiting litchi flowers (Litchi chinensis Sonn.) and path analysis of environmental factors influencing foraging behaviour of four honeybee species. J. Apic. Res. 2006, 45, 180–187. [Google Scholar] [CrossRef]
  41. Sapir, G.; Goldway, M.; Stern, R.A. Supplementing bumblebees to ‘Mauritius’ lychee improves yield. Sci. Hortic. 2019, 251, 162–166. [Google Scholar] [CrossRef]
  42. Sinhaseni, K.; Catterall, C.P. Tropical fruit production depends on wild insect communities: Bees and lychees in Thailand. J. Trop. Ecol. 2021, 37, 26–34. [Google Scholar] [CrossRef]
  43. Lee, Y.-C.; Chang, J.-C. Leafless inflorescence produces more female flowers and fruit yield than leafy inflorescence in ‘Yu Her Pau’ litchi. HortScience 2019, 54, 487–491. [Google Scholar] [CrossRef]
  44. Degani, C.; Stern, R.A.; El-Batsri, R.; Gazit, S. Pollen parent effect on the selective abscission of ‘Mauritius’ and ‘Floridian’ lychee fruitlets. J. Am. Soc. Hortic. Sci. 1995, 120, 523–526. [Google Scholar] [CrossRef]
  45. Ivanova, N.V.; Fazekas, A.J.; Hebert, P.D.N. Semi-automated, membrane-based protocol for DNA isolation from plants. Plant Mol. Biol. Rep. 2008, 26, 186–198. [Google Scholar] [CrossRef]
  46. Viruel, M.A.; Hormaza, J.I. Development, characterization and variability analysis of microsatellites in lychee (Litchi chinensis Sonn., Sapindaceae). Theor. Appl. Genet. 2004, 108, 896–902. [Google Scholar] [CrossRef]
  47. Kalinowski, S.T.; Taper, M.L.; Marshall, T.C. Revising how the computer program CERVUS accommodates genotyping error increases success in paternity assignment. Mol. Ecol. 2007, 16, 1099–1106. [Google Scholar] [CrossRef] [PubMed]
  48. Evans, L.J.; Jesson, L.; Read, S.F.J.; Jochym, M.; Cutting, B.T.; Gayrard, T.; Jammes, M.A.S.; Roumier, R.; Howlett, B.G. Key factors influencing forager distribution across macadamia orchards differ among species of managed bees. Basic Appl. Ecol. 2021, 53, 74–85. [Google Scholar] [CrossRef]
  49. Mitchell, R.J.; Karron, J.D.; Holmquist, K.G.; Bell, J.M. The influence of Mimulus ringens floral display size on pollinator visitation patterns. Funct. Ecol. 2004, 18, 116–124. [Google Scholar] [CrossRef]
  50. Karron, J.D.; Holmquist, K.G.; Flanagan, R.J.; Mitchell, R.J. Pollinator visitation patterns strongly influence among-flower variation in selfing rate. Ann. Bot. 2009, 103, 1379–1383. [Google Scholar] [CrossRef]
  51. Xie, D.-R.; Ma, X.-S.; Rahman, M.Z.; Yang, M.-C.; Huang, X.-M.; Li, J.-G.; Wang, H.-C. Thermo-sensitive sterility and self-sterility underlie the partial seed abortion phenotype of Litchi chinensis. Sci. Hortic. 2019, 247, 156–164. [Google Scholar] [CrossRef]
  52. Degani, C.; El-Batsri, R.; Gazit, S. Outcrossing rate, yield, and selective fruit abscission in ‘Ettinger’ and ‘Ardith’ avocado plots. J. Am. Soc. Hortic. Sci. 1997, 122, 813–817. [Google Scholar] [CrossRef]
  53. Alcaraz, M.L.; Hormaza, J.I. Influence of physical distance between cultivars on yield, outcrossing rate and selective fruit drop in avocado (Persea americana, Lauraceae). Ann. Appl. Biol. 2011, 158, 354–361. [Google Scholar] [CrossRef]
  54. Hapuarachchi, N.S.; Kämper, W.; Wallace, H.M.; Hosseini Bai, S.; Ogbourne, S.M.; Nichols, J.; Trueman, S.J. Boron effects on fruit set, yield, quality and paternity of Hass avocado. Agronomy 2022, 12, 1479. [Google Scholar] [CrossRef]
  55. Degani, C.; Goldring, A.; Gazit, S. Pollen parent effect on outcrossing rate in ‘Hass’ and ‘Fuerte’ avocado plots during fruit development. J. Am. Soc. Hortic. Sci. 1989, 114, 106–111. [Google Scholar] [CrossRef]
  56. Degani, C.; Goldring, A.; Adato, I.; El-Batsri, R.; Gazit, S. Pollen parent effect on outcrossing rate, yield, and fruit characteristics of ‘Fuerte’ avocado. HortScience 1990, 25, 471–473. [Google Scholar] [CrossRef]
  57. Kobayashi, M.; Lin, J.-Z.; Davis, J.; Francis, L.; Clegg, M.T. Quantitative analysis of avocado outcrossing and yield in California using RAPD markers. Sci. Hortic. 2000, 86, 135–149. [Google Scholar] [CrossRef]
  58. Chu, Y.-C.; Lin, T.-S.; Chang, J.-C. Pollen effects on fruit set, seed weight, and shriveling of ‘73-S-20’ litchi- with special reference to artificial induction of parthenocarpy. HortScience 2015, 50, 369–373. [Google Scholar] [CrossRef]
  59. Kodad, O.; Socias i Company, R. Fruit quality in almond as related to the type of pollination in self-compatible genotypes. J. Am. Soc. Hortic. Sci. 2008, 133, 320–326. [Google Scholar] [CrossRef]
  60. Jiang, Y.M.; Wang, Y.; Song, L.; Liu, H.; Lichter, A.; Kerdchoechuen, O.; Joyce, D.C.; Shi, J. Postharvest characteristics and handling of lychee fruit—An overview. Aust. J. Exp. Agric. 2006, 46, 1541–1556. [Google Scholar] [CrossRef]
Horticulturae 11 00244 g001
Figure 1. Schematic diagram of the lychee orchard with blocks of Kwai Mai Pink, Kaimana, Souey Tung, Sah Keng, Fay Zee Siu and Wai Chee trees. The approximate locations of the sampled trees are indicated with red lines.
Figure 1. Schematic diagram of the lychee orchard with blocks of Kwai Mai Pink, Kaimana, Souey Tung, Sah Keng, Fay Zee Siu and Wai Chee trees. The approximate locations of the sampled trees are indicated with red lines.
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Horticulturae 11 00244 g002
Figure 2. Percentages of self-fertilised and cross-fertilised (a) Fay Zee Siu, (b) Kaimana, (c) Kwai Mai Pink, (d) Sah Keng, (e) Souey Tung and (f) Wai Chee lychee fruit in the edge row and the middle row of single-cultivar blocks of each cultivar. The percentages of fruit with unassigned paternity (i.e., <80% confidence level) are also shown. Different letters within a cultivar indicate that the two means (+SE) for cross-paternity are significantly different, as are the two means (+SE) for self-paternity (paired t test; p < 0.05, n = 6 trees).
Figure 2. Percentages of self-fertilised and cross-fertilised (a) Fay Zee Siu, (b) Kaimana, (c) Kwai Mai Pink, (d) Sah Keng, (e) Souey Tung and (f) Wai Chee lychee fruit in the edge row and the middle row of single-cultivar blocks of each cultivar. The percentages of fruit with unassigned paternity (i.e., <80% confidence level) are also shown. Different letters within a cultivar indicate that the two means (+SE) for cross-paternity are significantly different, as are the two means (+SE) for self-paternity (paired t test; p < 0.05, n = 6 trees).
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Figure 3. Schematic diagram using arrows to show the potential direction of pollen dispersal from the most frequent cross-pollen parents to flowers of lychee cultivars Fay Zee Siu, Kaimana, Sah Keng and Wai Chee. Potential long-distance dispersal of Wai Chee pollen to Kwai Mai Pink flowers is also indicated.
Figure 3. Schematic diagram using arrows to show the potential direction of pollen dispersal from the most frequent cross-pollen parents to flowers of lychee cultivars Fay Zee Siu, Kaimana, Sah Keng and Wai Chee. Potential long-distance dispersal of Wai Chee pollen to Kwai Mai Pink flowers is also indicated.
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Table 1. Fruit mass, skin colour components and flavour attributes of Fay Zee Siu, Kaimana, Kwai Mai Pink, Sah Keng, Souey Tung and Wai Chee lychee fruit with different pollen parents.
Table 1. Fruit mass, skin colour components and flavour attributes of Fay Zee Siu, Kaimana, Kwai Mai Pink, Sah Keng, Souey Tung and Wai Chee lychee fruit with different pollen parents.
Mother Cultivar
× Pollen Parent		Fruit Mass (g)Skin Colour ComponentsFlavour Attributes
Brightness
(L*)		Green–Red (a*)Blue–Yellow (b*)°BrixAcidity
(%)		Brix:Acid
Fay Zee Siu
×Fay Zee Siu26.4 ± 1.4 a33.3 ± 0.6 a32.5 ± 1.3 ab16.7 ± 0.8 a19.6 ± 0.5 a0.55 ± 0.03 a37.4 ± 2.5 a
×Bengal27.9 ± 1.8 a33.5 ± 0.5 a36.3 ± 0.7 a15.1 ± 0.7 a19.4 ± 0.2 a0.58 ± 0.02 a33.7 ± 1.1 a
×Kaimana26.7 ± 0.8 a33.9 ± 1.5 a31.4 ± 0.9 b16.3 ± 1.4 a19.7 ± 0.5 a0.52 ± 0.04 a40.1 ± 4.0 a
×Kwai Mai Pink *25.7 ± 0.7 a34.9 ± 0.4 a35.2 ± 0.8 ab16.9 ± 0.4 a19.1 ± 0.2 a0.59 ± 0.03 a33.8 ± 1.6 a
Kaimana
×Kaimana22.2 ± 1.0 a37.7 ± 0.8 a33.0 ± 2.2 a19.0 ± 0.9 a17.7 ± 0.5 b0.59 ± 0.03 a31.3 ± 2.0 a
×Bengal23.7 ± 0.8 a36.5 ± 0.6 a37.2 ± 1.2 a17.8 ± 0.4 a18.2 ± 0.2 b0.56 ± 0.02 a34.0 ± 1.4 a
×Kwai Mai Pink *24.4 ± 0.6 a37.4 ± 0.6 a37.8 ± 1.4 a18.2 ± 0.4 a18.7 ± 0.3 ab0.57 ± 0.02 a33.8 ± 1.2 a
×Sah Keng22.3 ± 0.8 a38.2 ± 1.1 a35.5 ± 2.9 a19.5 ± 0.8 a18.7 ± 0.7 ab0.54 ± 0.02 a35.5 ± 1.8 a
×Souey Tung24.7 ± 1.3 a37.2 ± 0.7 a38.6 ± 2.2 a17.8 ± 0.8 a20.1 ± 0.7 a0.61 ± 0.04 a33.6 ± 1.2 a
×Wai Chee24.6 ± 0.9 a36.3 ± 0.7 a37.8 ± 2.5 a17.4 ± 0.8 a18.1 ± 0.5 b0.57 ± 0.03 a32.9 ± 2.1 a
Kwai Mai Pink
×Kwai Mai Pink18.2 ± 0.3 a39.1 ± 0.3 a34.4 ± 0.5 a19.6 ± 0.2 a21.4 ± 0.2 a0.64 ± 0.01 a34.5 ± 0.6 a
×Fay Zee Siu19.3 ± 0.7 a37.9 ± 1.3 a34.6 ± 1.6 a18.5 ± 0.6 a21.7 ± 0.7 a0.60 ± 0.04 a36.6 ± 1.6 a
×Wai Chee *19.0 ± 0.6 a37.7 ± 0.8 a35.0 ± 0.8 a19.4 ± 0.3 a21.8 ± 0.4 a0.63 ± 0.02 a35.3 ± 1.0 a
Sah Keng
×Sah Keng24.3 ± 0.5 b33.3 ± 0.3 a32.6 ± 0.9 a15.4 ± 0.4 a18.2 ± 0.2 a0.54 ± 0.01 a34.7 ± 0.9 a
×Kwai Mai Pink26.6 ± 1.4 b31.6 ± 0.6 a36.0 ± 1.1 a13.8 ± 0.5 a17.5 ± 0.9 a0.53 ± 0.03 a34.4 ± 2.2 a
×Souey Tung *30.4 ± 1.6 a32.1 ± 0.5 a34.8 ± 1.6 a14.4 ± 0.6 a16.7 ± 0.7 a0.48 ± 0.03 a36.2 ± 1.7 a
Souey Tung
×Souey Tung †20.4 ± 0.41 a41.7 ± 0.5 a31.3 ± 0.7 a23.2 ± 0.4 a17.9 ± 0.2 a0.66 ± 0.01 a27.8 ± 0.5 a
Wai Chee
×Wai Chee17.3 ± 0.3 a33.6 ± 0.3 a33.7 ± 0.7 a14.0 ± 0.3 a20.1 ± 0.2 a0.48 ± 0.01 a43.3 ± 0.9 a
×Kwai Mai Pink *17.1 ± 0.3 a33.2 ± 0.3 a31.6 ± 0.9 a13.6 ± 0.3 a20.6 ± 0.3 a0.50 ± 0.01 ab42.0 ± 0.9 a
×Sah Keng17.0 ± 0.9 a33.3 ± 1.3 a29.6 ± 1.8 a13.4 ± 0.8 a20.8 ± 0.9 a0.54 ± 0.03 b38.9 ± 1.6 a
* Asterisks indicate the most frequent cross-pollen parent for each mother cultivar. † Insufficient cross-fertilised fruit were available to allow comparisons among pollen parents of Souey Tung fruit. Means ± SE with different letters within a mother cultivar are significantly different (ANOVA and Tukey’s HSD test; p < 0.05; n = 8–93 fruit).
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Trueman, S.J.; Nichols, J. Outcrossing Levels and Fruit Quality in Single-Cultivar Blocks of a Multi-Cultivar Lychee (Litchi chinensis Sonn.) Orchard. Horticulturae 2025, 11, 244. https://doi.org/10.3390/horticulturae11030244

AMA Style

Trueman SJ, Nichols J. Outcrossing Levels and Fruit Quality in Single-Cultivar Blocks of a Multi-Cultivar Lychee (Litchi chinensis Sonn.) Orchard. Horticulturae. 2025; 11(3):244. https://doi.org/10.3390/horticulturae11030244

Chicago/Turabian Style

Trueman, Stephen J., and Joel Nichols. 2025. "Outcrossing Levels and Fruit Quality in Single-Cultivar Blocks of a Multi-Cultivar Lychee (Litchi chinensis Sonn.) Orchard" Horticulturae 11, no. 3: 244. https://doi.org/10.3390/horticulturae11030244

APA Style

Trueman, S. J., & Nichols, J. (2025). Outcrossing Levels and Fruit Quality in Single-Cultivar Blocks of a Multi-Cultivar Lychee (Litchi chinensis Sonn.) Orchard. Horticulturae, 11(3), 244. https://doi.org/10.3390/horticulturae11030244

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