Capsicum annuum (pepper) is an emerging crop for controlled environment production that is susceptible to intumescence. Intumescence is a physiological disorder characterized by unrestricted cellular growth causing protruding lesions, ultimately leading to epidermal rupture. While the causative factor for this disorder remains unknown, water stress is commonly implicated and end-of-day (EOD) lighting has been identified as a potential strategy for mitigating intumescence development. However, the timing of pepper leaf area expansion and intumescence development as well as appropriate lighting strategies for their control have yet to be determined. The objectives of this work were to 1) determine the timing of leaf area expansion to better inform EOD or pre-dawn (PD) lighting applications for intumescence suppression; 2) quantify the impact of low-intensity lighting applications on pepper leaf morphology; and 3) determine the role of water stress in the occurrence of intumescence development for pepper. Pepper ‘Pot-a-Peño’, ‘Spicy Jane’, and ‘California Wonder’ were grown in 15-cm pots in a common greenhouse environment. For Objective 1, three weeks after transplant, one uniform leaf on each plant was tagged and plants were evaluated twice a day (0700 and 1900) for one week. For Objective 2, plants were subjected to 30-minute lighting treatments at an intensity of 25 μmol·m·−2·s−1 for two weeks provided at either EOD with blue (EOD-B; 447 nm), red (EOD-R; 659 nm), or far-red light (EOD-FR; 734 nm), or PD with blue light (PD-B; 447 nm). For Objective 3, plants were either maintained at 70% field capacity (control) or allowed a single event of reaching 40% field capacity prior to watering. Intumescence development was visually monitored twice a day (0900 and 1700) during the water stress event. For Objective 1, leaf area expansion was 46%, 34%, and 94% greater at night (1900-0700) compared to the day (0700-1900) for ‘Spicy Jane’, ‘Pot-a-Peño’, and ‘California Wonder’, respectively. For Objective 2, responses to lighting treatments were cultivar specific. For example, after two weeks, imaged leaf area was lowest under EOD-B for ‘Pot-a-Peño’ and greatest under EOD-FR for ‘Spicy Jane’. For Objective 3, intumescence development was observed on all cultivars subjected to water stress post returning to field capacity, with no incidence of the disorder for control plants. These results will help in the prediction of intumescence development for pepper produced in controlled environments and inform decisions regarding the timing of possible suppression methods to control this disorder.
