Since the advent of Huanglongbing (HLB) disease, Florida’s citrus production has dropped by 70%. HLB-affected trees decline rapidly under high pH growing conditions. Limited nutrient availability at high soil pH has been speculated to be the cause of such rapid decline in HLB-affected trees; however, such decline is not observed in healthy citrus trees. Therefore, the objective of this study was to understand the nutrient uptake, physiological, and molecular responses of healthy (HLY) and HLB-affected (HLB) sweet orange (Citrus sinensis (L.) Osbeck) trees when grown in media maintained at different pH levels 6.0, 7.0, or 8.0. Overall, the performance of HLY and HLB trees decreased with the increase in pH conditions. HLB trees showed a significant inverse correlation between growth parameters (leaf number, shoot growth, SPAD value, stem water potential) and growing media pH whereas no such correlation was observed for HLY trees. Interesting, superior performance of HLB trees at pH 6.0 coincided with higher accumulation of Fe, Mn, and N in whole plant body as compared to high pH treatments. In contrast, HLY tree performance was significantly better at pH 7.0 compared to other pH conditions. At pH 7.0, stress related genes were upregulated in HLB leaves as compared to HLY leaves, indicating the stress response in terms of leaf abscission, reduced growth, and natural aging process was exacerbated in HLB trees at higher pH treatments. Altogether, all the physiological and molecular observations supports an interaction between HLB trees and pH, where HLB trees at pH 6.0 perform better than at higher pH.

中文翻译：

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培养基pH值对黄龙病影响的柑桔幼树生长性能的影响

自从黄龙病（HLB）疫情出现以来，佛罗里达州的柑橘产量下降了70％。在高pH值生长条件下，受HLB影响的树木会迅速下降。据推测，在高土壤pH下有限的养分利用率是造成受HLB影响的树木迅速下降的原因。但是，在健康的柑橘树中未观察到这种下降。因此，本研究的目的是了解健康（HLY）和受HLB影响（HLB）的甜橙（Citrus sinensis）的养分吸收，生理和分子响应（L.）Osbeck）树在培养基中生长时保持在不同的pH值6.0、7.0或8.0。总体而言，HLY和HLB树的性能随pH条件的增加而降低。HLB树显示出生长参数（叶数，枝条生长，S​​PAD值，茎水势）与生长培养基pH之间存在显着的反相关关系，而HLY树未观察到这种相关性。有趣的是，与高pH处理相比，HLB树在pH 6.0时的优异性能与整个植物体内更高的Fe，Mn和N积累相吻合。相反，与其他pH条件相比，在pH 7.0时HLY树的性能明显更好。在pH 7.0时，与HLY叶片相比，HLB叶片中与胁迫相关的基因上调，表明在叶片脱落，生长减少，在较高pH的处理下，HLB树的自然衰老过程更加严重。总的来说，所有的生理和分子观察结果都支持HLB树与pH之间的相互作用，其中pH 6.0的HLB树的性能优于较高pH的树。