Analysis of fruit quality and spatial distribution of soluble solids content in four new kiwifruit cultivars

【Objective】Kiwifruit has become a high-value agricultural commodity in China, where the development of new cultivars is critical for maintaining market competitiveness. Fruit quality traits such as sweetness, acidity, and nutritional composition are heavily dependent on genotype-environment interactions. Shiyan City in northwestern Hubei Province, characterized by a subtropical monsoon climate with annual rainfall of 800-1200 mm and elevations spanning 300-1500 meters, offers ideal ecological conditions for kiwifruit cultivation. Despite this potential, the region remains underutilized in terms of optimized production systems. Four new cultivars, Wudang No. 1, Hanxiang, Hanmei, and Zhongmi No. 2, bred for enhanced stress resilience and flavor profiles, require comprehensive evalua-tion of their phenotypic adaptability and biochemical characteristics under local conditions. This study aimed to assess the fruit quality traits of these cultivars, and investigate spatial variations in soluble solids content (SSC) across fruit segments to guide cultivar selection, harvest timing, and scientific sampling protocols.【Methods】Fruits of four cultivars were harvested when SSC levels reached 6.5%- 7.0%. The single fruit mass was measured using a precision electronic scale. Fruit dimensions (longitudinal, transverse, and lateral diameters) were recorded with vernier calipers, and the shape index was calculated as the ratio of longitudinal to transverse diameter. The SSC was analyzed using a PAL-1 digital refractometer, with fruits longitudinally divided into three segments (stalk end, middle part, and beak end) prior to juice extraction. The soluble sugar content was determined via the 3,5-dinitrosalicylic acid colorimetric method (NY/T 2742—2015), expressed as glucose equivalents. Total acidity was quantified using an automatic titrator with 0.1 mol·L-1 NaOH titrant to pH 8.2, reported as citric acid equivalents based on a modified GB/T 12456—2008 protocol. The vitamin C content was analyzed through high- performance liquid chromatography (HPLC) following GB 5009.86—2016 standards.【Results】 The results revealed significant varietal differences: Hanmei and Zhongmi No. 2 exhibited the highest single fruit mass (132.99 g and 124.47 g, respectively), while Hanxiang (59.26 g) was markedly smaller. In terms of the SSC, Hanxiang (20.04%) surpassed all other cultivars, followed by Zhongmi No. 2 (18.34% ), Wudang No. 1 (15.78% ), and Hanmei (15.51% ). The soluble sugar content of Hanxiang (12.04% ) and Zhongmi No. 2 (11.36% ) was higher than that of Hanmei (10.47% ) and Wudang No. 1 (10.23%) showed no significant differences. The total acidity was nearly similar among the four cultivars (1.24%-1.41%), whereas the dry matter content varied from 17.37% (Hanmei) to 20.37% (Hanxiang). Vitamin C levels ranged narrowly from 96.67 to118.53 mg · 100 g- 1 . The correlation analysis showed strong positive associations between fruit size parameters and negative correlations between single fruit mass and SSC, dry matter. Notably, the SSC showed strong linkages to soluble sugars and dry matter, while vitamin C exhibited no significant correlations with other metrics. The comprehensive analysis of SSC across three anatomical regions (stalk end, middle part, and beak end) revealed distinct spatial patterns among cultivars. All four kiwifruit cultivars exhibited a consistent SSC gradient, with the highest concentration at the beak end and gradual decrease toward the stalk end. However, inter-cultivar differences emerged in the magnitude of these gradients. In Zhongmi No. 2 and Wudang No. 1, the SSC remained statistically uniform across segments, with mean values ranging narrowly. In contrast, Hanmei demonstrated pronounced compartmentalization: stalk end SSC (15.05% ) was significantly lower than that of middle part (15.60%) and beak end (15.89%). The most striking variation occurred in Hanxiang, which beak end SSC reached 20.50% over stalk end levels (18.8% ) and middle part values (19.98% ), and the difference between the beak end and the stalk end of the fruit was significant. Among all recorded SSC values, the maximum values of Zhongmi No. 2, Wudang No. 1, and Hanmei were consistently observed at the beak end, while the minimum values were uniformly detected at the stalk end. In contrast, both the maximum and minimum SSC values in Hanxiang kiwifruit were recorded from the middle part. The coefficients of variation (CV) for SSC in fruits of Zhongmi No. 2, Wudang No. 1 Hanmei, and Hanxiang exhibited a decreasing trend, measuring 5.24%, 4.73%, 4.03%, and 3.67% respectively. These spatial disparities showed the importance of sampling position for quality assessments.【Conclusion】The four cultivars demonstrated superior fruit quality in Shiyans Qinba Mountain region. Hanxiang and Zhongmi No. 2 had higher sweetness and dry matter content, while Wudang No. 1 was advantageous in vitamin C enrichment. The observed SSC spatial gradients underscored the need for cultivarspecific harvest strategies, for instance, mixed sampling of different parts (covering the whole fruit) forHanmei and Hanxiang to ensure accurate quality assessments.