Analysis of endogenous hormones in different organs reveals the critical role of phthalanilic acid in the yield and quality of pepper (Capsicum annuum) fruits

Abstract

Phthalanilic acid (PPA), a plant growth regulator, has advantageous biological effects on fruit trees. However, little is known about its effects on vegetables. Thus, field trials were conducted on pepper (Capsicum annuum) plants by spraying with PPA at concentrations of 133.3, 200.0, and 266.7 mg·L−1. The key physiological indicators of peppers were investigated, including the number of flowers and fruits, yield, yield components, quality, and endogenous hormones. Results showed that PPA greatly boosted the number of flowers and fruits on pepper plants. The fruit shape index, dry matter content, single fruit weight, and yield in the PPA treatment of 133.3 mg·L−1 were particularly higher than those of the control, with increasing rates of 28.73%, 22.97%, 26.85%, and 35.75%, respectively. PPA considerably decreased the levels of titratable acid and nitrate while noticeably increasing the levels of soluble protein, soluble sugar, l-ascorbic acid, and capsaicin in mature green or red pepper fruits. PPA may also increase the levels of indole-3-acetic acid (IAA) in flowers, buds, and leaves, elevate the levels of abscisic acid (ABA) in leaves, raise the levels of zeatin riboside (ZR) in young fruits, but decrease the ABA content in buds. PPA actively controls fruit quality and yield in the concentration range of 133.3–200.0 mg·L−1. This beneficial outcome might ultimately be connected to the regulation of endogenous hormones.