How a rare haploid peach gives birth to triploid offspring
image: The morphological and cytological traits of '9-D' and its offspring.
Credit: Horticulture Research
Haploid plants, which carry only a single set of chromosomes, are typically sterile, making them valuable but difficult to use in breeding. A rare peach haploid mutant, '9-D', surprisingly exhibited partial fertility and produced triploid offspring. Through detailed cytological observation, researchers discovered that abnormal meiosis in '9-D' led to the formation of unreduced (2x) pollen grains capable of fertilization. These diploid male gametes fused with haploid female gametes to generate triploid progeny. The findings illuminate how chromosome doubling can restore fertility in haploids and provide key insights into ploidy breeding, offering a potential pathway for creating novel polyploid fruit cultivars with improved traits.
Peach (Prunus persica) is one of the world's most important fruit crops, with China leading global production. Ploidy manipulation—altering the number of chromosome sets—is a core strategy for generating new varieties with enhanced quality and stress resistance. However, haploid peaches are extremely rare (0–0.7% natural occurrence) and usually sterile due to abnormal meiosis that prevents viable gamete formation. Triploids, in contrast, often exhibit superior vigor and seedlessness, making them valuable breeding targets. Understanding how haploids regain fertility through natural chromosome doubling can bridge this gap. Due to these challenges, it is necessary to investigate the cytological mechanisms underlying haploid fertility and triploid formation in peach.
A research team from the Beijing Academy of Agriculture and Forestry Sciences and the China Agricultural University has uncovered the cytological mechanism that enables a haploid peach mutant to produce triploid offspring. The study, published (DOI: 10.1093/hr/uhae316) online in Horticulture Research on February 1, 2025, reveals how the haploid peach '9-D' partially restores fertility through the formation of 2x pollen grains during meiosis. The researchers used cytological analysis, flow cytometry, and microscopy to identify abnormal chromosome division that results in diploid gamete formation—a key process driving triploid development.
The team first confirmed that the mutant '9-D' was a pure haploid with eight chromosomes (n = x = 8) through flow cytometry and cytogenetic analysis. Morphologically, '9-D' plants exhibited smaller leaves, flowers, and fruits compared with normal diploids. Microscopic and scanning electron microscopy revealed that about 50.4% of its pollen grains were viable, yet only 7.6% could germinate normally. During meiosis, pollen mother cells in '9-D' lacked the typical transition between anaphase I and prophase II, leading to the appearance of dyads—cells with two real nuclei instead of four. These meiotic abnormalities caused some pollen to retain a doubled chromosome set (2x). Pollen diameter measurements supported this finding, showing that about 4.5% of grains were diploid. When such 2x pollen fertilized haploid female gametes (x), triploid (3x) offspring were produced. This rare fertility mechanism, known as “pseudomeiosis,” resembles the process in Arabidopsis mutants that bypass the second meiotic division. The discovery provides the first cytological evidence explaining how haploid peaches can yield viable triploid progeny through spontaneous chromosome doubling.
“Our findings show that haploid fertility can be restored through cytological anomalies that generate unreduced gametes,” said lead author Quan Jiang from the Beijing Academy of Agriculture and Forestry Sciences. “The haploid peach '9-D' offers a unique natural model to study chromosome doubling and ploidy breeding. Understanding how these 2x gametes form and function could help us develop new seedless or improved peach cultivars without relying on artificial chromosome manipulation. This mechanism also deepens our understanding of polyploid evolution in fruit trees.”
The discovery of naturally doubled 2x gametes in a haploid peach highlights a new path for polyploid breeding. Triploid peaches generated via such mechanisms may exhibit enhanced fruit quality, stress tolerance, or seedlessness—traits highly desirable in modern horticulture. Moreover, this study provides theoretical foundations for haploid breeding and genome stability research across other fruit trees such as apple, pear, and citrus. Beyond its practical breeding value, the work sheds light on how unreduced gametes contribute to plant evolution and speciation, offering new opportunities to harness natural ploidy variation for sustainable crop improvement.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhae316
Funding information
We are grateful to Weichao Fang (Zhengzhou Fruit Research Institute, Chinese Academy of Agricultural Sciences) and Zhixiang Cai (Institute of Pomology, Jiangsu Academy of Agricultural Sciences), who provided the partial pictures of peaches. This research was supported by the earmarked fund for China Agriculture Research System of Peach (CARS-30), National Natural Science Foundation of China (31301734), and Beijing Academy of Agriculture and Forestry Sciences Innovation Capability Construction Special Project (KJCX20230118).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.