Spray application factors and plant growth regulator performance. I. Bioassays and biological response
1998
Knoche, M. | Bukovac, M.J. | Nakagawa, S. | Crabtree, G.D.
Bioassays were adapted to investigate effects of droplet size and carrier volume on performance of daminozide, gibberellic acid (GA3) and 2,4-D using Phaseolus vulgaris L. as a model system. Response to plant growth regulators was indexed by inhibition (daminozide), promotion of internode elongation (GA3) or ethylene production (2,4-D). Elongation of first plus second internodes above primary leaves was evaluated 14 days after treatment of primary leaves, while ethylene production was determined from head-space samples of incubated leaves 24 h after treatment. Daminozide inhibition of internode elongation was related to decreased cell size and number in pith and epidermis (range 49-70% of the untreated control). GA3 increased cell size and number in both tissues 2.3- to 4.8-fold. Responsiveness to daminozide and 2,4-D markedly decreased as seedling age increased from 8 to 12 days, but responsiveness to GA3 increased. Decreasing droplet size (10-0.5 microliter) and increasing carrier volume (10-200 microliter per leaf) at constant dose of daminozide (100 microgram per leaf) and 2,4-D (100 microgram per leaf) significantly increased performance, but had little effect on performance of GA3 (2 microgram per leaf). Effects of application factors on performance were related to their effects on the interface area between droplets and leaf surface. Significant positive linear relationships were obtained between plant response and the logarithm of the droplet/leaf interface area for all growth regulators.
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