Relationship between Water Potential and Leaf and Inflorescence Initiation in Helianthus annuus

Abstract

The total number of leaves produced by the primary stem of Helianthus annuus L. cv. Pole Star and cv. Peredovik, was reduced from 29 leaves to 21–22 leaves when water stress ranging from −2000 to −3000 kPa was imposed over the period from day 10 to day 20 after sowing, by withholding water from the soil. Extending the stress period by 10 days did not cause any further significant reduction in leaf number. Examination of the shoot apex showed that the leaf initiation rate was depressed by low water potential, the greatest effect occurring in the range 0 to −1000 kPa. It was established that inflorescence initiation commenced about 18 days after planting in control plants and this was delayed by only about 4 days by low water potentials in the range −1000 to −3000 kPa.