Xu Hao, Watanabe Yoichiro, Ediger Danielle, Yang Xiaotang, Iritani Davis
Summerland Research and Development Centre, Agriculture and Agri-Food Canada, Summerland, BC V0H 1Z0, Canada.
Plants (Basel). 2022 Apr 29;11(9):1201. doi: 10.3390/plants11091201.
The 2021 summer heat waves experienced in the Pacific Northwest led to considerable fruit damage in many apple production zones. Sunburn browning (SB) was a particularly evident symptom. To understand the mechanism underlying the damage and to facilitate the early assessment of compromised fruit quality, we conducted a study on external characteristics and internal quality attributes of SB 'Ambrosia' apple ( var. Ambrosia) and evaluated the fruit loss on five rootstocks. The cell integrity of the epidermal and hypodermal layers of fruit skins in the SB patch was compromised. Specifically, the number of chloroplasts and anthocyanin decreased in damaged cells, while autofluorescent stress-related compounds accumulated in dead cells. Consequently, the affected sun-exposed skin demonstrated a significant increase in differential absorbance between 670 nm and 720 nm, measured using a handheld apple DA meter, highlighting the potential of using this method as a non-destructive early indicator for sunburn damage. Sunburn browning eventually led to lower fruit weight, an increase in average dry matter content, soluble solids content, acidity, deteriorated weight retention, quicker loss of firmness, and accelerated ethylene emission during ripening. Significant inconsistency was found between the sun-exposed and shaded sides in SB apples regarding dry matter content, firmness, and tissue water potential, which implied preharvest water deficit in damaged tissues and the risk of quicker decline of postharvest quality. Geneva 935 (G.935), a large-dwarfing rootstock with more vigor and higher water transport capacity, led to a lower ratio of heat-damaged fruits and a higher yield of disorder-free fruits, suggesting rootstock selection as a long-term horticultural measure to mitigate summer heat stress.
2021年太平洋西北地区经历的夏季热浪在许多苹果产区造成了相当严重的果实损害。日灼褐变（SB）是一种特别明显的症状。为了解损害背后的机制并促进对受损果实品质的早期评估，我们对SB“安波罗斯”苹果（安波罗斯品种）的外部特征和内部品质属性进行了研究，并评估了五种砧木上的果实损失情况。SB斑块处果实表皮和皮下层的细胞完整性受到损害。具体而言，受损细胞中的叶绿体和花青素数量减少，而与应激相关的自发荧光化合物在死亡细胞中积累。因此，使用手持式苹果差分吸收仪测量，受影响的暴露在阳光下的果皮在670纳米至720纳米之间的差分吸收显著增加，这突出了使用该方法作为日灼损害非破坏性早期指标的潜力。日灼褐变最终导致果实重量降低、平均干物质含量增加、可溶性固形物含量增加、酸度增加、重量保持率下降、硬度更快丧失以及成熟期间乙烯释放加速。在SB苹果中，暴露在阳光下的一侧和遮荫一侧在干物质含量、硬度和组织水势方面存在显著不一致，这意味着受损组织在收获前存在水分亏缺，并且采后品质有更快下降的风险。日内瓦935（G.935）是一种具有更强活力和更高水分运输能力的大矮化砧木，它导致热损伤果实的比例较低，无病害果实的产量较高，这表明选择砧木是减轻夏季热应激的一项长期园艺措施。
