Increasing harvestability of Phacelia hastata seed using plant growth regulators

Abstract

Phacelia hastata, an excellent pollinator plant that is highly drought resistant, winter hardy, and tolerant of acid and heavy metal soils, has limited commercial availability due to inadequate seed supplies. Indeterminate flowering, lodging and seed shatter of this species make mechanical seed harvest difficult. This study was undertaken to evaluate the effects of four plant growth regulator formulations (PGRs) on seed yield, seed quality and growth characteristics of P. hastata. These PGRs were gibberellin, paclobutrazol, ethephon, and a hormone compound containing gibberellic acid, cytokinin and indolebutyric acid. In field experiments, foliar sprays of PGRs were applied at two rates and two timings. Plots were sprayed once, at early vegetative stage, or twice, with a sequential spray three weeks later. The exception was ethephon, which was sprayed once at time of full bloom. Treatments included plots sprayed with (1) 100 and 200 ppm gibberellic acid (2) 30 ppm paclobutrazol, (3) 2000 ppm ethephon, (4) 2500 ppm Ascend (a hormone compound consisting of cytokinin, gibberellic acid and indolebutyric acid), and (5) deionized water (Control). Two foliar applications of paclobutrazol, at a rate of 30 ppm, at one-month rosette stage and three weeks later, increased seed yield of P. hastata in thinned plots by 337%. In plots treated with ethephon, seed shatter was eliminated but seed yield and germination decreased. Results suggest foliar sprays of the plant growth regulator paclobutrazol on P. hastata regulate the flowering process, increasing harvestable seed.