Abstract
Basil is one of the most widespread aromatic and medicinal plants, which is often grown in drought- and salinity-prone regions. Often co-occurrence of drought and salinity stresses in agroecosystems and similarities of symptoms which they cause on plants complicates the differentiation among them. Development of automated phenotyping techniques with integrative and simultaneous quantification of multiple morphological and physiological traits enables early detection and quantification of different stresses on a whole plant basis. In this study, we have used different phenotyping techniques including chlorophyll fluorescence imaging, multispectral imaging, and 3D multispectral scanning, aiming to quantify changes in basil phenotypic traits under early and prolonged drought and salinity stress and to determine traits which could differentiate among drought and salinity stressed basil plants. Ocimum basilicum “Genovese” was grown in a growth chamber under well-watered control [45–50% volumetric water content (VWC)], moderate salinity stress (100 mM NaCl), severe salinity stress (200 mM NaCl), moderate drought stress (25–30% VWC), and severe drought stress (15–20% VWC). Phenotypic traits were measured for 3 weeks in 7-day intervals. Automated phenotyping techniques were able to detect basil responses to early and prolonged salinity and drought stress. In addition, several phenotypic traits were able to differentiate among salinity and drought. At early stages, low anthocyanin index (ARI), chlorophyll index (CHI), and hue (HUE2D), and higher reflectance in red (RRed), reflectance in green (RGreen), and leaf inclination (LINC) indicated drought stress. At later stress stages, maximum fluorescence (Fm), HUE2D, normalized difference vegetation index (NDVI), and LINC contribute the most to the differentiation among drought and non-stressed as well as among drought and salinity stressed plants. ARI and electron transport rate (ETR) were best for differentiation of salinity stressed plants from non-stressed plants both at early and prolonged stress.
Highlights
Basil (Ocimum basilicum L.) is the most important species from the genus Ocimum of the subfamily Nepetoideae under the family Lamiaceae (Chowdhury et al, 2017)
Transplanted plants were transferred to growth chamber under 25/20◦C, 16/8 h day/night regime, 70% relative air humidity, and 250 μmol m−2 s−1 of photosynthetic photon flux density (PPFD) provided by Valoya L35, NS12 spectrum light-emitting diodes (LEDs) lights (Valoya Oy, Helsinki Finland), and grown for 10 days allowing plants to adjust to the chamber conditions
Soil volumetric water content (VWC) and electrical conductivity (EC) were daily monitored, and differences among treatments in VWC and EC were obtained at T1 (Supplementary Figure SF1)
Summary
Basil (Ocimum basilicum L.) is the most important species from the genus Ocimum of the subfamily Nepetoideae under the family Lamiaceae (Chowdhury et al, 2017). Because it is exceptionally rich in essential oils, it is commonly produced for economic purposes (Caliskan et al, 2017) It has a wide range of applications; it is used as a spice in many cuisines, as an ingredient for commercial fragrances, flavors, to improve the food products shelf life, in traditional medicine and phytotherapy (Labra et al, 2004; Carovic-Stanko et al, 2010; Radácsi et al, 2010; Mishra et al, 2012; Carovic-Stanko et al, 2013; Purushothaman et al, 2018). It is essential to define plants’ morphophysiological status in the early stages of drought and salinity stress before plants are severely damaged
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