Far-red radiation increases flower and fruit abortion in sweet pepper (Capsicum annuum L.)

Fruit set is a crucial plant developmental process, determining yield in many crops. Pepper (Capsicum annuum L.) is a crop with poor fruit set as typically about two-thirds of all flowers abort. A higher light integral improves fruit set. However, the role of light spectrum has hardly been investigated. Opportunities for detailed investigation of light spectrum effects on fruit set have strongly increased with the introduction of narrow-band LED lighting. To investigate whether additional far-red light (FR) influences the fruit set of sweet pepper, a climate chamber experiment was conducted. Four light treatments were applied to pepper plants grown under 130 µmol m−2 s−1 of red/white LED light. Treatments consisted of different intensities of FR (0, 50, 100 µmol m−2 s−1) applied throughout the day or applied at the end of day (EOD, 30 min, 30 µmol m−2 s−1). Treatments resulted in phytochrome photostationary state (PSS) values of 0.88, 0.77. 0.70 and EOD 0.16, respectively. Fruit set was determined 3 weeks after the last anthesis of the studied flowers. Additional FR light reduced fruit set in sweet pepper, regardless of whether FR light was provided during the whole day or only at the end of the day. Meanwhile, FR led to more stem elongation, more upright branches, and more dry mass partitioning to stems. Additional FR during the daytime increased total shoot dry weight but not when FR was applied at the end of day. Possible reasons for stimulated flower and fruit abortion by additional FR are discussed.