Abstract The rabbiteye blueberry (Vaccinium virgatum Aiton) is a promising new fruit crop in the subtropical lowland. However, mid-day temporary wilting of young shoot tips often occurs in the high summer heat and strong irradiance, warranting breeding for heat tolerance. Differences in leaf color among rabbiteye blueberry genotypes are visually distinguishable. To test the hypothesis that leaf color can be a morpho-physiological index for early screening in heat tolerance breeding with lighter leaf color preferred, leaf color of selected ‘Blueshower’ open-pollinated siblings was quantified using CIE L*a*b* color space. Diurnal leaf to air temperature differences (ΔTleaf-air), chlorophyll content (Chl), mid-day gas exchange parameters and water use efficiency (WUE) were measured. The collected data were correlated with L*a*b* information. In hot sunny days, the genotypes with dark leaf color or low L* absorbed heat quicker than those with light leaf color or high L*, resulting in greater ΔTleaf-air in the morning hours. The differences in ΔTleaf-air were similar among the genotypes after mid-day, likely due to the negative correlation between L* and transpiration (E) that facilitates heat dissipation. Maximum leaf net CO2assimilation (An) was recorded at leaf temperature around 35°C in all genotypes and was positivly corrected with b*. a* was positively correlated with leaf Chl content but not with any gas exchange parameters, suggesting that the effect of Chl content on An was overpowered by the effect of leaf lightness derived from cuticular wax layers on leaf surface. Although increasing L* reduced E and thus improved WUE, the genotype with the highest L* value had the lowest mid-day stomatal conductance and intercellular CO2 concentration, resulting in a significantly low An than that in the genotypes with moderate L*. We concluded that leaf lightness is a feasible index for heat tolerance breeding. For hot and arid climates, genotypes with high L* are recommended for their outstanding WUE but in the expense of An. For the hot humid subtropical climate, genotypes with moderate L* and high b* will be better candidates for their high An in well-watered conditions.

中文翻译：

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叶色作为筛选耐热性和提高兔眼蓝莓（Vaccinium v​​irgatum Aiton）水分利用效率的形态生理指标

摘要 兔眼蓝莓（Vaccinium v​​irgatum Aiton）是亚热带低地地区极具发展前景的新型水果作物。然而，在夏季高温和强光照射下，幼芽尖部的中午临时萎蔫往往发生，需要耐热性繁殖。兔眼蓝莓基因型之间叶子颜色的差异在视觉上是可区分的。为了检验叶色可以作为早期筛选耐热性育种的形态生理指标的假设，叶色较浅，选择的“Blueshower”开放授粉兄弟姐妹的叶色使用 CIE L*a*b* 颜色空间进行量化. 测量了昼夜叶片与空气温度差异 (ΔTleaf-air)、叶绿素含量 (Chl)、中午气体交换参数和水分利用效率 (WUE)。收集的数据与 L*a*b* 信息相关联。在炎热的晴天，深叶色或低L*的基因型比浅叶色或高L*的基因型吸收热量更快，从而导致早晨的ΔTleaf-air更大。中午过后，基因型之间 ΔTleaf-air 的差异相似，这可能是由于 L* 与促进散热的蒸腾 (E) 之间的负相关。在所有基因型中，在大约 35°C 的叶温下记录了最大叶净 CO2 同化 (An)，并用 b* 进行了正校正。a* 与叶 Chl 含量呈正相关，但与任何气体交换参数无关，这表明 Chl 含量对 An 的影响被叶表面表皮蜡层衍生的叶亮度影响所压倒。尽管增加 L* 降低了 E 从而提高了 WUE，具有最高L*值的基因型具有最低的中午气孔导度和细胞间CO2浓度，导致An显着低于具有中等L*值的基因型。我们得出结论，叶片亮度是耐热育种的可行指标。对于炎热和干旱的气候，推荐具有高 L* 的基因型，因为它们具有出色的 WUE，但代价是 An。对于炎热潮湿的亚热带气候，具有中等 L* 和高 b* 的基因型将是它们在良好浇水条件下高 An 的更好候选者。推荐具有高 L* 的基因型，因为它们具有出色的 WUE，但以 An 为代价。对于炎热潮湿的亚热带气候，具有中等 L* 和高 b* 的基因型将是它们在良好浇水条件下高 An 的更好候选者。推荐具有高 L* 的基因型，因为它们具有出色的 WUE，但以 An 为代价。对于炎热潮湿的亚热带气候，具有中等 L* 和高 b* 的基因型将是它们在良好浇水条件下高 An 的更好候选者。