Abstract The apple (Malus × domestica) fruit consists of two main fleshy tissues, cortex and pith, that are of diverse origins and contribute differentially to final fruit size. The contribution of these fruit spatial constituents to variation in fruit morphology has not been determined previously. We developed an image-analysis based method that uses two-dimensional images of the fruit sectioned in the proximo-distal plane to determine fruit, cortex, and pith volumes, and key shape descriptors. Fruit volume determined by image-analysis was compared to that determined using water displacement. These two methods were strongly correlated (R2 = 0.95) and displayed good agreement. The cortex volume constituted majority (> 86 %) of the fruit. Variation in cortex volume explained most of the variation in fruit volume (R2 = 0.99), while that of the pith explained a relatively minor portion (R2 = 0.32). Further, variation in pith volume explained only a minor part of cortex volume variation (R2 = 0.24), suggesting that growth in these tissues is regulated by a combination of shared and differential mechanisms. Proportion of the fruit constituted by cortex displayed limited variability across 28 apple cultivars. However, proportion of cortex was substantially lower, and that of pith higher, in a crabapple (Malus sp.) cultivar, Callaway, suggesting that change in tissue proportions contributes to increase in fruit size from that observed in crabapples. Limited variation in the fruit aspect ratio, a key shape descriptor, was noted in the apple cultivars analyzed. A weak relationship was observed between the fruit aspect ratio and that of the core (R2 = 0.29), indicating that differential mechanisms determine shapes of the fruit and its internal tissues. Together, data from this study suggest that growth of cortex and pith tissues is mediated in part by shared, and substantially by differential mechanisms.

中文翻译：

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使用图像分析确定皮层和髓对苹果（Malus×domestica Borkh.）果实形态的贡献

摘要 苹果（Malus ×domestica）果实由两个主要的肉质组织，皮层和髓组成，它们具有不同的来源，对最终果实的大小有不同的影响。这些水果空间成分对水果形态变化的贡献以前尚未确定。我们开发了一种基于图像分析的方法，该方法使用在近远端平面中切片的水果的二维图像来确定水果、皮质和髓体积以及关键形状描述符。将通过图像分析确定的果实体积与使用水置换确定的果实体积进行比较。这两种方法具有很强的相关性 (R2 = 0.95) 并显示出良好的一致性。皮质体积占果实的大部分 (> 86 %)。皮质体积的变化解释了果实体积的大部分变化（R2 = 0.99），而髓的解释相对较小（R2 = 0.32）。此外，髓体积的变化仅解释了皮层体积变化的一小部分（R2 = 0.24），表明这些组织的生长受共享和差异机制的组合调节。由皮质构成的果实比例在 28 个苹果品种中显示出有限的变异性。然而，在海棠 (Malus sp.) 栽培品种 Callaway 中，皮层的比例明显较低，而髓部的比例较高，这表明组织比例的变化有助于增加果实大小，而不是在海棠中观察到的。在分析的苹果品种中注意到果实纵横比的有限变化，这是一个关键的形状描述符。在果实纵横比和核心之间观察到微弱的关系（R2 = 0.29），表明差异机制决定了果实及其内部组织的形状。总之，来自这项研究的数据表明皮层和髓组织的生长部分是由共享机制介导的，主要是由不同机制介导的。