Apple trees tend to bear an excess of young fruits (fruitlets). Chemical thinning with an application of bioregulators early in the season is currently the most common solution to adjust fruit load. However, the results of this approach are highly inconsistent between seasons. In the present study, we identified the most informative bands in the visible-near infrared range for forecasting fruitlet destiny in response to the thinner application, which could be used to support grower decisions. “Golden Delicious” apple trees were monitored during two consecutive seasons, following the application of synthetic auxins commonly used in commercial orchards. Simple bands, band differences, and band ratios were investigated as features for forecasting fruitlet destiny from the first week of monitoring. Optimal threshold values and best wavelengths combinations were determined via the receiver operating characteristic (ROC) curve. At the early stage of fruitlet development (4–6 days after treatment, DAT), applying thresholding to the band difference R 973 − R 404 was preferable (accuracies ranging from 66% to 87%), while applying thresholding to the band ratio R 693 / R 674 was preferable at 7–12 DAT (accuracies ranging from 76% to 95%). The present results indicate that the development of a simplified portable device for forecasting apple fruitlet drop seems feasible. Complimentary measurements performed on intact vs. denuded fruitlets revealed that the spectral differences observed can be explained by substantial changes in trichomes density that occur naturally during fruitlet development and affect the apparent pigment absorption.

中文翻译：

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选择 Vis-NIR 波段来预测化学处理后苹果落果

苹果树往往结出过多的幼果（小果）。在季节早期应用生物调节剂进行化学疏伐是目前最常见的调整果实负荷的解决方案。然而，这种方法的结果在季节之间高度不一致。在本研究中，我们确定了可见-近红外范围内信息最丰富的波段，用于预测小果的命运，以响应更薄的应用，可用于支持种植者的决策。在应用商业果园常用的合成生长素后，连续两个季节对“金冠”苹果树进行了监测。研究了简单条带、条带差异和条带比率，作为从监测的第一周起预测小果命运的特征。通过接收器操作特性 (ROC) 曲线确定最佳阈值和最佳波长组合。在果实发育的早期阶段（处理后 4-6 天，DAT），对带差 R 973 - R 404 应用阈值是可取的（准确度从 66% 到 87%），同时对带比 R 应用阈值693 / R 674 在 7–12 DAT（准确度范围为 76% 到 95%）时更可取。目前的结果表明，开发一种用于预测苹果落果的简化便携式设备似乎是可行的。对完整与裸果进行的免费测量表明，观察到的光谱差异可以通过在果实发育过程中自然发生的毛状体密度的实质性变化来解释，并影响表观色素吸收。