Pepper Photosynthesis, Stomatal Conductance, Transpiration, and Water Use Efficiency Differ with Variety, Indigenous Habitat, and Species of Origin

The instantaneous photosynthetic rate (P n ), transpiration rate (E), and stomatal conductance ( g S ) were measured for 33 outdoor-grown Capsicum varieties (varying in species of origin and indigenous habitat) between 29 July and 22 Aug. 2017 using a portable gas exchange meter. Cuvette leaf temperature (T leaf ) and relative humidity (RH) were recorded at that same time. P n differed from 3.6 to 3.7 for ‘Malawi Piquante’ and ‘Korean Long Green’ peppers to 16.3 μmol CO 2 /m 2 /s (fixed) for ‘Thai Hot’ peppers. The g S differed from 0.01 to 0.05 among 13 varieties to 0.28 mmol H 2 O/m 2 /s for ‘Thai Hot’ peppers. E differed from 0.43 to 0.59 among three varieties to 4.14 to 4.20 mmol H 2 O/m 2 /s for ‘CGN 22091’ and ‘Peruvian Purple’ peppers. Water use efficiency (WUE; P n /E) varied from 2.92 to 3.43 among three varieties to 5.10 to 7.20 for 16 other varieties. C . annuum derived varieties had higher P n (9.4 μmol CO 2 /m 2 /s fixed) than varieties derived from other species (4.5–8.6 μmol CO 2 /m 2 /s fixed). Varieties originating from dry climates had higher P n (12.5 μmol CO 2 /m 2 /s fixed) than those originating from temperate or tropical climates (8.0–8.8 μmol CO 2 /m 2 /s fixed). T leaf (27 to 33 °C) and RH (38% to 39% and 57% to 59%) differed among varieties. P n was positively correlated with g S , E, and RH and was negatively correlated with WUE. We found that Capsicum P n , E, and g S varied more than has been previously reported, and our data suggested that P n , g S , and E data of outdoor-grown peppers should be used only when selecting parents for a breeding program (unless progeny is intended for greenhouse production).