Intumescence incidence and growth characteristics of pepper and tomato grafted seedlings under different photoperiods in a light-emitting diode (LED) healing chamber

Abstract

This study aimed to identify methods to minimize intumescence in grafted pepper and tomato seedlings by controlling the photoperiod in a light-emitting diode (LED) healing chamber. Intumescence, a non-pathogenic physiological disorder affecting leaves and stems, occurs primarily in solanaceous crops, such as pepper (Capsicum annuum L.) and tomato (Solanum lycopersicum L.). The disorder is triggered by ultraviolet radiation (100-400 nm) deficiency and high humidity, which are conditions typical of LED healing chambers used for grafted seedling production. However, studies on the inhibition of intumescence in grafted seedlings are limited. In this study, three cultivars each of pepper and tomato were used as scions, and one cultivar was selected as the rootstock. Immediately after grafting, they were placed in an LED healing chamber for six days with a light intensity of 30 +/- 5 mu mol center dot m-2 center dot s-1 photosynthetic photon flux density, an air temperature of 22 +/- 0.7 degrees C, and a relative humidity of 93 +/- 5%. The seven photoperiods were as follows: 0/24, 8/16, 10/14, 12/12, 14/10, 16/8, and 24/0 (light/dark) hours (h). Peppers exhibited the lowest intumescence under 0/24 h and 8/16 h photoperiods, with increased severity as the photoperiod lengthened. The graft-take rate for tomatoes significantly improved under a 12/12 h photoperiod, with the lowest intumescence observed at 14/10 h. Therefore, the optimal photoperiods for minimizing intumescence were 8/16 h for peppers and 14/10 h for tomatoes. These findings highlight the importance of optimizing photoperiod in LED healing chambers to curb intumescence without compromising seedling quality.