Understanding water stress signaling mechanisms and screening for tolerant cocoa cultivars are major challenges when facing prolonged dry and rainy seasons in cocoa-producing areas. While abscisic acid (ABA) and proline are supposed to enhance drought tolerance in cocoa, the role of polyamines remains unclear. The aim of this study was to investigate the biochemical response and phenological adaptation of cocoa (Theobroma cacao) on different soil moisture conditions, with a focus on short-term (20 days) and long-term (89 days) stress conditions, and to compare the performance of three cocoa cultivars. In a split plot design with four blocks, cocoa seedlings of an international high-yielding cultivar (TSH-565) and two locally selected cultivars (IIa-22 and III-06) from the drought-exposed Alto Beni region, Bolivia, were arranged in pots under a roof shelter (cultivar: three levels). The seedlings were exposed to strong (VERY DRY) and moderate (DRY) soil moisture deficits, water logging (WET) and regular irrigation (MOIST) that served as a control (moisture: four levels). We examined the growth performance and the levels of ABA, proline, and polyamines in the leaves. Growth was reduced already at a moderate drought, while severe drought enhanced seedling mortality. Severe drought increased the levels of ABA by 453% and of proline by 935%, inducing a short-term stress response; both compounds were degraded over the long-term period. The polyamine concentration was unrelated to soil moisture. The cocoa cultivars did not differ in their biochemical response to soil moisture stress (proline: p-value = 0.5, ABA: p-value = 0.3), but the local cultivar III-06 showed a stronger height growth increment than the international cultivar TSH-565 (237%, p-value = 0.002) under drought conditions.

中文翻译：

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短期与长期土壤水分胁迫对三种可可 (Theobroma cacao L.) 栽培品种生理反应的影响

在可可产区面临长时间的旱季和雨季时，了解水分胁迫信号机制和筛选耐受性可可品种是主要挑战。虽然脱落酸 (ABA) 和脯氨酸被认为可以增强可可的耐旱性，但多胺的作用仍不清楚。本研究的目的是调查可可（Theobroma cacao）在不同土壤水分条件下的生化反应和物候适应，重点是短期（20 天）和长期（89 天）胁迫条件，并比较三个可可品种的性能。在具有四个区块的裂区设计中，一个国际高产栽培品种 (TSH-565) 的可可幼苗和来自玻利维亚 Alto Beni 地区遭受干旱的两个当地选择的栽培品种 (IIa-22 和 III-06)，被安排在屋顶庇护所下的花盆中（栽培品种：三层）。幼苗暴露于强（非常干燥）和中度（干燥）土壤水分亏缺、积水 (WET) 和作为对照的定期灌溉 (MOIST)（水分：四个级别）。我们检查了叶子中的生长性能和 ABA、脯氨酸和多胺的水平。在中度干旱时生长已经下降，而严重干旱会增加幼苗死亡率。严重干旱使 ABA 水平增加了 453%，脯氨酸水平增加了 935%，诱导了短期应激反应；两种化合物都在长期内降解。多胺浓度与土壤水分无关。可可品种对土壤水分胁迫的生化反应没有差异（脯氨酸：p 值 = 0.5，ABA：p 值 = 0.3），