The effects of growth regulators on the photosynthetic apparatus of the sweet pepper (Capsicum annuum L.) in relation to the productivity

Abstract

The effects of growth stimulants 6-benzylaminopurine (6-BAP), gibberellic acid (GA3) and 1-naphthaleneacetic acid (1-NAA) as well as gibberellin inhibitors tebuconazole (EW-250), ethephon (2-chloroethylphosphonic acid, 2-CEPA) and chloromequate chloride (ССС-750), which differ in their action mechanism, on growth, development, leaf apparatus formation, CO2 and H2O gas exchange, photochemical activity of Photosystem II (PSII) and productivity traits of sweet pepper plants were studied. It was shown that treatment with growth stimulants increased, and gibberellin inhibitors decreased the linear sizes of sweet pepper plants of the Antei variety. It was established that all growth regulators, except for 2-CEPA, increased the number and the mass of leaves on the plant. Under the action of all preparations, except for 2-CEPA, the area of the leaves increased. Gibberellin inhibitors and 6-BAP significantly increased the amount of chlorophyll in pepper leaves. However, it decreased under the action of GA3 and did not practically change in treatment with 1-NAA. All growth substances, except GA3, increased the total chlorophyll content in the plant. The impact of growth regulators on the activity of photosynthetic processes was more pronounced at the stage of fruit formation than at the flowering stage. The CO2 assimilation rate at the flowering stage increased under the treatment of 1-NAA, 6-BAP, 2-CEPA and EW-250, but decreased under the action of GA3 and CCC-750. At the same time, all studied growth regulators increased the CO2 assimilation rate at the stage of fruit formation. Changes in the CO2 assimilation rate were closely correlated with changes in stomatal conductance (r = 0.79—0.85). Growth regulators increased transpiration in the light at fruit formation stage while the transpiration in the dark was reduced at the flowering stage. Growth regulators increased the operating quantum efficiency of PSII in the light, photochemical quenching of chlorophyll fluorescence, and intensity of linear electron transport in chloroplasts, and reduced non-photochemical quenching (NPQ) fluorescence. The specified morphological, physiological and biochemical changes in plants of sweet pepper of the Antei variety contributed to improvement of crop productivity traits. The use of growth stimulants 6-BAP and GA3, and retardants EW-250 and ССС-750 was most effective.