The effectiveness of proximal remote sensors in plant water status evaluation of grapevine

Abstract

Extensive studies have been conducted on grapevine responses to water deficit, but these responses are difficult to generalise since numerous factors can influence the response(s), including genotype, developmental stage, soil, climate, and season. Plant water stress responses are therefore most relevant in the environmental context in which a study is conducted. Moreover, there is a lack of high throughput methods that enable multi-scale plant water stress assessment for large spatial areas. Remote sensing gained popularity due to its non-destructive nature and generating rapid high throughput data for large spatial areas. However, the effectiveness of these sensors needs to be validated for different cultivars and environmental conditions. This study was conducted on potted own-rooted scion (Cabernet Sauvignon, Petit Verdot, Merlot, Pinotage and Shiraz), rootstock (Ramsey, 101-14 Mgt, 110Richter, USVit 8-7) and their grafted combinations (29 unique combinations) that were established in a randomised block design. The plants were grown under field conditions and phenology and physiological responses (Ψstem and gsw) were followed under full irrigation (FI) and water stress (WS) was implemented via two active drying (AD) cycles. The proximal remote sensors (Thermal infrared, TIR; spectral reflectance) were tested on all genotypes under water stress conditions. The genotypes allowed testing of sensors on plants with variable stress responses to water deficit. Phenology progression was comparable between combinations with the same scion, regardless of grafting status and the development of own-rooted rootstock cultivars varied. The strictest stomatal control in each cultivar category was observed in the own-rooted CS and US and the grafted Me/Mg, Sh/US, PV/Mg and PV/Ra which showed more drastic gsw lowering as Ψstem decreased. Both the proximal thermal and spectral reflectance sensors detected changes in canopy temperature and reflectance patterns in response to water status. However, the TIR sensor was more consistent, although its correlation to the canopy temperature was cultivar-dependant due to the observed differences in stomatal conductance, both within and between genotypes. The proximal spectral reflectance sensor’s ability to detect changes in leaf canopy was variable between wavebands from the same genotypes, and between cultivar combinations.