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Figure 1. 

Phenotypic and morphological characterization of watermelon plants from G42 and G42cs. (a) Seedling morphology of G42 and G42cs at the early growth stage. (b) Vine architecture: G42 exhibits longer, more elongated vines, whereas G42cs shows compacted vine growth. (c) Leaf and floral morphology: the G42cs line exhibits shallower leaf lobation and shorter tendrils compared to its counterpart, while floral structure remains unchanged. (d) Plant architecture: G42 produces a taller, more extended vine, whereas G42cs forms a shorter, more compact vine. (e) Fruit phenotype: G42 yields a larger fruit, while G42cs produces a smaller fruit. (f) Quantitative trait analysis. Main vine length; temporal dynamics of main vine elongation over 37 d after transplanting (DAT), with G42 consistently outperforming G42cs. Vine elongation rate, fruit longitudinal diameter, fruit transverse diameter, fruit pedicel length, hypocotyl length, petiole length, tendril length, and fruit weight: G42 shows significantly greater values than G42cs (p < 0.01 or p < 0.05). Fruit central/edge soluble solids content, flesh hardness, rind thickness, rind hardness, and seed length/width/thickness: no significant differences (ns) between G42 and G42cs. Statistical significance: *, p < 0.05, **, p < 0.01; ns = not significant (p ≥ 0.05). All data represent mean ± standard error (SE) from at least three biological replicates. Scale bars = 10 cm.

Figure 2. 

(a), (b) Shoot apical meristem of wild-type G42 and short-vine mutant G42cs, scale bar = 500 μm (yellow arrows indicate bud axis, red arrows indicate leaf primordia). (c), (d) Observation of longitudinal stem section cells in wild-type and short-vine mutant, scale bar = 200 μm. (e), (f) Comparison of stem cell size and cell number per unit area between wild-type and short-vine mutant. **, p < 0.01.

Figure 3. 

Preliminary mapping of the short-vine gene by BSA-seq. Manhattan plot of SNP-index values across chromosomes (Chr01–Chr11). The red dashed lines indicate significance thresholds (± 0.7), and the blue dashed lines represent the baseline (0.0). A prominent peak is observed on Chr01, suggesting a strong association with vine length. Genotype-phenotype correlation for vine length (cm) in G42cs (44 cm), G42 (208 cm), F₁ hybrid (205 cm), and F₂ progeny (F₂-183, F₂-45, F₂-176, F₂-429, F₂-632). Black bars indicate homozygous G42cs genotype, gray bars indicate heterozygous genotype, and white bars indicate homozygous G42 genotype. The red dashed line indicates that the differential SNP located within the candidate interval is in linkage with the vine length phenotype, and this SNP resides within the coding sequence (CDS) of the gene ClG42_01G0099100.10.

Figure 4. 

F₂ individuals were genotyped using the 12982321-dCAPS marker, and the resulting restriction fragments were separated by polyacrylamide gel electrophoresis. Genotypes were scored as follows: lower band, homozygous for the short-vine allele; upper band, homozygous for the long-vine allele; two bands, heterozygous. The size marker is 250 bp. L indicates that the plant exhibits the long-vine phenotype (plant height > 80 cm), and S indicates that the plant exhibits the short-vine phenotype (plant height < 80 cm). CK represents the parental lines of the F₂ population, and F₁.

Figure 5. 

A novel small-fruit watermelon hybrid was developed utilizing a dwarf trait: the short-vine gene was introgressed into the maternal parent G42cs-1, which was then crossed with a paternal parent to produce the new cultivar (Scale bar = 10 cm).