How much water citrus trees receive during fruit development can have a major impact on fruit size and internal quality, according to new research published in the journal Horticulturae. The study shows that while moderate water stress may improve some aspects of fruit quality, severe drought significantly reduces fruit size and can make fruit much more acidic.
Researchers in China examined how different soil moisture levels affected Himekoharu mandarin trees grown under greenhouse conditions. The team included Longfei Jin, Yanmei Wu, Yueting Sun, Feng Liu and Peng Wang from the Zhejiang Academy of Agricultural Sciences, and Liqin Pan from Taizhou Vocational College of Science & Technology.
The researchers compared trees grown under normal irrigation with those exposed to moderate and severe drought during the critical fruit expansion period. As expected, drought reduced fruit growth. Trees under severe water stress produced fruit that was dramatically smaller and lighter than fruit from well-watered trees. Moderate drought had a much smaller effect on fruit size.
Interestingly, drought also changed fruit quality. Both moderate and severe water stress increased soluble solids, meaning the fruit contained more sugars. However, drought also caused acidity to increase, especially under severe stress. While some increase in sugars can improve flavor, excessive acidity can make fruit less desirable for fresh markets. The researchers concluded that moderate water control may improve fruit quality, but severe drought reduces overall marketability.
To better understand why these changes occur, the scientists analyzed thousands of citrus genes. They found that drought altered genes responsible for plant hormones that regulate cell division and fruit enlargement. Under drought conditions, these growth-promoting hormones became less active, helping explain why fruit remained smaller. At the same time, genes involved in producing and storing citric acid became more active, leading to greater acid accumulation inside the fruit.
For growers, the practical message is clear: Irrigation management during the fruit expansion stage can strongly influence both yield and fruit quality. Moderate water deficits may help increase sugars and improve eating quality under certain production systems, but allowing trees to experience severe drought can reduce fruit size, increase acidity and ultimately lower crop value.
The researchers say their findings provide new insight into how citrus responds to water stress at the molecular level. A better understanding of these responses could eventually help breeders develop varieties that maintain fruit size and quality under increasingly common drought conditions. The researchers plan future studies combining gene expression with plant physiology and metabolomics to further understand how water availability affects citrus fruit development.
Read the full study here.
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