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13 pages, 4522 KB

Open AccessArticle

CRISPR/Cas9-Mediated Knockout of ClMLO5b Confers Powdery Mildew Resistance in Watermelon

by Lihuan Wang, Weide Sun, Jingyi Zhang, Zicheng Zhu, Shuang Pei, Yao Cheng and Peng Gao

Horticulturae 2025, 11(12), 1517; https://doi.org/10.3390/horticulturae11121517 - 15 Dec 2025

Viewed by 179

Abstract

Powdery mildew poses a significant threat to watermelon production. The development of disease-resistant varieties through gene editing represents a major focus in current breeding research. In this study, we identified an MLO family gene in watermelon, denoted by ClMLO5b, which is phylogenetically [...] Read more.

Powdery mildew poses a significant threat to watermelon production. The development of disease-resistant varieties through gene editing represents a major focus in current breeding research. In this study, we identified an MLO family gene in watermelon, denoted by ClMLO5b, which is phylogenetically closely related to cucumber CsaMLO8 and melon CmMLO5. Homology modeling revealed high conservation of the three-dimensional protein structures among these orthologs. Expression analysis demonstrated that ClMLO5b is significantly up-regulated upon powdery mildew infection, and the protein localizes to the plasma membrane. To validate its function, we first employed an Agrobacterium rhizogenes-mediated hairy root transformation system to rapidly verify the editing efficiency of two CRISPR/Cas9 targets designed for ClMLO5b. Subsequently, stable transgenic watermelon plants were generated via Agrobacterium tumefaciens-mediated transformation, and a mutant line with homozygous substitutions at target site 2 was obtained. Disease resistance assays showed that, compared to wild-type plants, the Clmlo5b exhibited strongly inhibited mycelial growth, significantly reduced disease severity, and a substantial decrease in spore production after inoculation with powdery mildew. Our findings confirm that ClMLO5b is a key susceptibility gene in watermelon and provide both a promising genetic target and valuable breeding material for developing powdery mildew-resistant watermelon varieties. Full article

(This article belongs to the Special Issue Germplasm Resources and Genetics Improvement of Watermelon and Melon)

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22 pages, 8822 KB

Open AccessArticle

A Comparative Analysis of High-Throughput and Conventional Phenotyping: Validation of Plantarray System and Dynamic Physiological Traits for Drought Tolerance in Watermelon

by Rui Cheng, Shiyu Zhao, Xiaolong Shi, Xin Liu, Yan Tang, Wenzhao Xu, Binghua Xu, Cong Jin, Yudong Sun and Xuezheng Wang

Horticulturae 2025, 11(11), 1374; https://doi.org/10.3390/horticulturae11111374 - 14 Nov 2025

Viewed by 597

Abstract

Drought stress is a major constraint on watermelon production worldwide. Conventional phenotyping methods for drought tolerance are often low-throughput and fail to capture dynamic physiological responses. This study validated the high-throughput phenotyping platform (Plantarray 3.0) against conventional methods by dynamically evaluating drought tolerance [...] Read more.

Drought stress is a major constraint on watermelon production worldwide. Conventional phenotyping methods for drought tolerance are often low-throughput and fail to capture dynamic physiological responses. This study validated the high-throughput phenotyping platform (Plantarray 3.0) against conventional methods by dynamically evaluating drought tolerance across 30 genetically diverse watermelon accessions. The Plantarray system quantified key dynamic traits, including transpiration rate (TR), transpiration maintenance ratio (TMR), and transpiration recovery ratios (TRRs), revealing distinct drought-response strategies. Principal component analysis (PCA) of these dynamic traits explained 96.4% of the total variance (PC1: 75.5%, PC2: 20.9%), clearly differentiating genotypes. A highly significant correlation (R = 0.941, p < 0.001) was found between the comprehensive drought tolerance rankings derived from Plantarray and conventional phenotyping. We identified five genotypes as highly tolerant and four as highly sensitive. The elite drought-tolerant germplasm, notably the wild species PI 537300 (Citrullus colocynthis) and the cultivated variety G42 (Citrullus lanatus), exhibited superior physiological performance and recovery capacity. The results demonstrate that the Plantarray system not only efficiently screens for drought tolerance but also provides deep insights into dynamic resistance mechanisms, offering a powerful tool and valuable genetic resources for breeding climate-resilient watermelon cultivars. Full article

(This article belongs to the Special Issue Germplasm Resources and Genetics Improvement of Watermelon and Melon)

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16 pages, 3414 KB

Open AccessArticle

Genome-Wide Identification of GW5-LIKE Family Revealed the Function of ClGL1 Involved in Fruit and Seed Shape by Mediating Brassinosteroid Signaling in Watermelon

by Peng Tian, Lei Zhang, Jingjing Zhang, Bowen Liu, Wei Liu, Bing Li, Xiurui Gao, Jie Zhang, Yanrong Wu and Yong Xu

Horticulturae 2025, 11(11), 1326; https://doi.org/10.3390/horticulturae11111326 - 4 Nov 2025

Viewed by 509

Abstract

The regulatory mechanism of brassinolide (BR) signaling in cucurbitaceae crops remains incompletely understood. Previous research demonstrated that the rice genes GW5 and GW5L modulate seed morphology via the BR pathway. However, the conservation of their orthologs in watermelon and their evolutionary trajectory are [...] Read more.

The regulatory mechanism of brassinolide (BR) signaling in cucurbitaceae crops remains incompletely understood. Previous research demonstrated that the rice genes GW5 and GW5L modulate seed morphology via the BR pathway. However, the conservation of their orthologs in watermelon and their evolutionary trajectory are yet to be elucidated. In this study utilizing the watermelon 97103v2 genome, we identified 15 GW5-LIKE genes. Through structure, phylogenetic tree construction, collinearity, promoter and spatiotemporal expression analysis, we determined that ClGL1 to ClGL3 are the most closely related to GW5 and GW5L. Subsequently, two crucial materials were acquired: the inbred line Jing L6M harboring the homozygous mutant Clgl1, and the near-isogenic line Changhong, a Jing L6M backcross containing the wild-type allele ClGL1. Apart from the disparity in fruit morphology, a clear difference in seed shape was observed between the two. Furthermore, exogenous BR treatment demonstrated that ClGL1 positively regulated the BR signal, aligning with the positive impact of GW5 and GW5L. In conclusion, ClGL1 modulates the morphology of watermelon fruit and seed by enhancing BR signaling, which provides a key gene and theoretical basis for BR signaling evolution and molecular design breeding in Cucurbitaceae. Full article

(This article belongs to the Special Issue Germplasm Resources and Genetics Improvement of Watermelon and Melon)

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19 pages, 4057 KB

Open AccessArticle

Towards Introgression Between Watermelon (Citrullus lanatus) and Its Wild Relative, Bitter Apple (C. colocynthis)

by Lana W. Al-Qadumii, Monther T. Sadder, Bayan Alkharabsheh, Samih Y. Salem, Mohammad S. Salem and Karam Bani-Yaseen

Horticulturae 2025, 11(11), 1304; https://doi.org/10.3390/horticulturae11111304 - 31 Oct 2025

Viewed by 817

Abstract

The genetic diversity of cultivated crops is limited, largely as a result of domestication bottlenecks and the selective pressures imposed during modern breeding. An introgression cross was initiated by mating bitter apple (Citrullus colocynthis), as a wild founder parent, with ‘Charleston [...] Read more.

The genetic diversity of cultivated crops is limited, largely as a result of domestication bottlenecks and the selective pressures imposed during modern breeding. An introgression cross was initiated by mating bitter apple (Citrullus colocynthis), as a wild founder parent, with ‘Charleston Grey’ watermelon (Citrullus lanatus) commercial cultivar, focused on identifying and utilizing trait-enhancing alleles from crop wild relative (CWR). Successful crosses resulted in diverse families, including F₁ hybrids, F₂ population, and backcross (BC) progenies. The study revealed substantial variation among the founder parents and their derived progeny in plant growth and major agronomic fruit traits, highlighting the value of this genetic diversity for breeding programs and demonstrating the potential of Citrullus introgression lines to enhance desired traits in cultivated watermelon. Morphological analysis demonstrated that F₁ progeny resembled the maternal parent for the majority of investigated fruit traits. A considerable proportion of the introgression progeny in the F₂ generation outperformed both parents in total soluble solids and lycopene content, suggesting that crop wild relatives hold strong breeding value through beneficial allelic recombination. BC₁ siblings were closer to the wild watermelon, which is presumably maternally controlled through plastome and mitogenome in crosses between cultivated watermelon and wild bitter apple, which is expected to be retained in successive backcrosses. The study uncovers novel alleles of CWR that preserve extensive genetic variation that is essential for enhancing resilience traits in current breeding lines. These introgression-derived resources provide a critical platform for advancing genetic studies and enhancing crop resilience. Full article

(This article belongs to the Special Issue Germplasm Resources and Genetics Improvement of Watermelon and Melon)

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13 pages, 8290 KB

Open AccessArticle

Construction and Phenotypic Characterization of a Recombination Inbred Line (RIL) Population from a Melo-agrestis Melon Hybrid

by He Liu, Jianquan Wang, Shoujun Cao, Yongjie Guo, Qinghua Shi and Xiaoyu Yang

Horticulturae 2025, 11(9), 1087; https://doi.org/10.3390/horticulturae11091087 - 9 Sep 2025

Viewed by 796

Abstract

Melon (Cucumis melo L.) is an economically important horticultural crop worldwide, while its production is continuously endangered by powdery mildew (PM), a fungal disease mainly caused by Podosphaera xanthii, due to the insufficiency of disease resistant germplasms. Here, a melon recombinant [...] Read more.

Melon (Cucumis melo L.) is an economically important horticultural crop worldwide, while its production is continuously endangered by powdery mildew (PM), a fungal disease mainly caused by Podosphaera xanthii, due to the insufficiency of disease resistant germplasms. Here, a melon recombinant inbred line (RIL) population that consisted of 188 independent individuals was obtained through the crossing of ‘SN-1’ (C. melon L. ssp. melo) and ‘YJM’ (C. melon L. ssp. agrestis), two parents with contrasting PM resistance, followed by 7-round selfings. Comprehensive phenotypic investigation revealed substantial variations in key agronomic traits among these RILs, such as stem diameters of 3.7~12.6 mm and internode lengths of 1.6~12.2 cm at the anthesis stage, as well as peduncle lengths of 0.5~9.5 cm and soluble solid content of 1.6~17.4% at the maturation stage. Particularly, 95 RILs, of which 60 and 35 belonged to thin-peel and netted types, respectively, were identified to be highly resistant to P. xnathii infection, providing new germplasms for melon improvement. Altogether, the generation of this melo-agrestis RIL population, together with the phenotypic observations, lays a solid foundation for mechanistic investigation of the traits with economic importance and could contribute to future breeding programs of melon cultivars with PM resistance. Full article

(This article belongs to the Special Issue Germplasm Resources and Genetics Improvement of Watermelon and Melon)

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15 pages, 5873 KB

Open AccessArticle

A Point Mutation of the Alpha-Tubulin Gene ClTUA Causes Dominant Dwarf Phenotype in Watermelon (Citrullus lanatus)

by Ziwei Hu, Leichen Zhang, Jun Shi, Quansheng Ying, Huafeng Zhang, Xingping Zhang, Yun Deng and Yuhong Wang

Horticulturae 2025, 11(6), 562; https://doi.org/10.3390/horticulturae11060562 - 22 May 2025

Viewed by 849

Abstract

Vine length is a crucial plant architecture trait in watermelon, which determines its height. In this study, we identified a dominant dwarf watermelon mutant by treating G42 with Ethyl methanesulfonate (EMS). In order to clarify the causes of the dwarfism in mutants, genetic [...] Read more.

Vine length is a crucial plant architecture trait in watermelon, which determines its height. In this study, we identified a dominant dwarf watermelon mutant by treating G42 with Ethyl methanesulfonate (EMS). In order to clarify the causes of the dwarfism in mutants, genetic statistics, phenotypic observation, and cytological observation were carried out. Meanwhile, individual resequencing combined with molecular markers was used to map the candidate gene. Our results demonstrated that the dwarf mutant exhibited incomplete dominance. The dwarf plants showed a decrease in the number of internodal cells, shortened internodes, and reduced vine length. Gene mapping indicated that the target gene responsible for this mutation was ClTUA, which encodes α-tubulin. A point mutation in the dwarf plants was identified, specifically, a change from C to T at the 1851st base pair. Further experiments, including transcriptome analysis and Liquid Chromatography–Tandem Mass Spectrometry (LC-MS/MS), revealed that this gene mutation affected auxin synthesis, leading to the dwarfing of the plants. This study provides new germplasm resources and a theoretical foundation for plant architecture breeding in watermelon. Full article

(This article belongs to the Special Issue Germplasm Resources and Genetics Improvement of Watermelon and Melon)

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Review

Jump to: Research

22 pages, 2064 KB

Open AccessReview

Advances in Functional Genomics for Watermelon and Melon Breeding: Current Progress and Future Perspectives

by Huanhuan Niu, Junyi Tan, Wenkai Yan, Dongming Liu and Luming Yang

Horticulturae 2025, 11(9), 1100; https://doi.org/10.3390/horticulturae11091100 - 11 Sep 2025

Cited by 1 | Viewed by 1843

Abstract

Watermelon (Citrullus lanatus) and melon (Cucumis melo) are globally important cucurbit crops, with China being the largest producer and consumer. Traditional breeding methods face difficulties in significantly improving yield and quality. Smart breeding, which combines genomics, gene editing, and [...] Read more.

Watermelon (Citrullus lanatus) and melon (Cucumis melo) are globally important cucurbit crops, with China being the largest producer and consumer. Traditional breeding methods face difficulties in significantly improving yield and quality. Smart breeding, which combines genomics, gene editing, and artificial intelligence (AI), holds great promise but fundamentally depends on understanding the molecular mechanisms controlling important agronomic traits. This review summarizes the progress made over recent decades in discovering and understanding the functions of genes that control essential traits in watermelon and melon, focusing on plant architecture, fruit quality, and disease resistance. However, major challenges remain: relatively few genes have been fully validated, the complex gene networks are not fully unraveled, and technical hurdles like low genetic transformation efficiency and difficulties in large-scale trait phenotyping limit progress. To overcome these and enable the development of superior new varieties, future research priorities should focus on the following: (1) systematic discovery of genes using comprehensive genome collections (pan-genomes) and multi-level data analysis (multi-omics); (2) deepening the study of gene functions and interactions using advanced gene editing and epigenetics; (3) faster integration of molecular knowledge into smart breeding systems; (4) solving the problems of genetic transformation and enabling efficient large-scale trait and genetic data collection (high-throughput phenotyping and genotyping). Full article

(This article belongs to the Special Issue Germplasm Resources and Genetics Improvement of Watermelon and Melon)

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19 pages, 636 KB

Open AccessReview

Advances in Cold Stress Response Mechanisms of Cucurbits

by Lili Li, Juan Hou, Jianbin Hu and Wenwen Mao

Horticulturae 2025, 11(9), 1032; https://doi.org/10.3390/horticulturae11091032 - 1 Sep 2025

Cited by 1 | Viewed by 1132

Abstract

Cold stress can inhibit the growth of cucurbits, disrupt pollination and fertilization, induce fruit deformities, reduce plant resistance, and increase susceptibility to diseases, ultimately resulting in yield reduction, quality deterioration, or even complete crop failure. This review focuses on the main cucurbits, such [...] Read more.

Cold stress can inhibit the growth of cucurbits, disrupt pollination and fertilization, induce fruit deformities, reduce plant resistance, and increase susceptibility to diseases, ultimately resulting in yield reduction, quality deterioration, or even complete crop failure. This review focuses on the main cucurbits, such as melon, cucumber, and watermelon, systematically expounding the roles of plant hormones, signaling molecules, soluble sugars, key regulatory factors, molecular mechanisms, and network interactions in their response to cold stress. Furthermore, it highlights future research directions and application potential. By analyzing existing challenges and prospective advancements in this field, the review aims to provide a comprehensive reference for facilitating genetic improvement in cold tolerance. Full article

(This article belongs to the Special Issue Germplasm Resources and Genetics Improvement of Watermelon and Melon)

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