Relationships between the Number of First-Flush Flowers and Leaf Water Potential or Leaf ABA Content Affected by Varying Degrees of Water Stress in Meiwa Kumquat (Fortunella crassifolia Swingle)

Abstract

The effect of water stress on the number of first-flush flowers was investigated in Meiwa kumquat trees. Treatments of soil water deficit (SWD), soil water deficit combined with mist (SWM), and non-treated controls (CONT) were established in a greenhouse in 2009 and 2010. The leaf water potential in SWD and SWM decreased significantly after 10 d of the treatment. In 2009, the number of first-flush flowers in SWD and SWM was 133.8 and 142.4, respectively, and these were significantly greater than that in CONT. Second- or third-flush flowers were significantly greater in CONT. In 2010, the number of first-flush flowers increased with a decrease in the leaf water potential down to −1.7 MPa. It was also positively correlated with leaf abscisic acid (ABA) content, but did not significantly change once ABA levels exceeded 5 nmol g⁻¹. These results suggest that water stress increases the number of first-flush flowers. The severe water stress represented by leaf water potentials below −1.7 MPa, or over 5 nmol g⁻¹ of leaf ABA content, did not appear to have the same effect. Approximately 150 flowers per 100 nodes of shoots appeared to be the maximum number of first-flush flowers produced by Meiwa kumquat trees.