A Comparison of Watermelon Flesh Texture across Different Ploidy Levels Using Histology and Cell Wall Measurements

Abstract

Watermelon fruits of different ploidy levels exhibit significant variations in texture. This study aimed to investigate the primary factors that influence texture differences. To achieve this, we conducted an investigation into the differences in fruit texture development using homozygous autogamous diploid (2×) lines and their autotriploid (3×) and autotetraploid (4×) lines ‘Yixuan’. The study investigated fruit development, flesh texture profile analysis (TPA), flesh cell wall polysaccharide content, and flesh cell microstructure analysis in 2×, 3×, and 4× watermelon fruits. The study found that as watermelon fruits matured, several characteristics increased, including fruit weight, TSS (total soluble solids) content, rind hardness, flesh cell size, and cell wall polysaccharide contents such as crude fiber, cellulose, hemicellulose, lignin, and protopectin. In contrast, the flesh texture parameters and soluble pectin content of the flesh cell wall decreased over time. Significant differences in fruit flesh texture and flesh cell structure were observed among fruits of different ploidy levels at the 32 DAP. Specifically, the 2× fruits displayed considerably lower rind hardness, reduced flesh texture (Hardness, Fracturability, Chewiness, Gumminess), and cell density compared to the 3× and 4× fruits. Additionally, the 2× fruits had larger cell sizes than the 3× and 4× fruits. However, there were no significant differences observed in the flesh cell wall polysaccharide contents across various ploidy levels. These findings suggest that the variation in texture among watermelon fruits of different ploidy levels can be attributed to the size and arrangement of the flesh cells. This research provides a foundation for the further exploration of the intrinsic regulatory factors and molecular mechanisms contributing to texture variation in polyploid watermelon fruits.