A review of current and potential applications of remote sensing to study the water status of horticultural crops

Published: 17 January 2020With increasingly advanced remote sensing systems, more accurate retrievals of crop water status are being made at the individual crop level to aid in precision irrigation. This paper summarises the use of remote sensing for the estimation of water status in horticultural crops. The remote measurements of the water potential, soil moisture, evapotranspiration, canopy 3D structure, and vigour for water status estimation are presented in this comprehensive review. These parameters directly or indirectly provide estimates of crop water status, which is critically important for irrigation management in farms. The review is organised into four main sections: (i) remote sensing platforms; (ii) the remote sensor suite; (iii) techniques adopted for horticultural applications and indicators of water status; and, (iv) case studies of the use of remote sensing in horticultural crops. Finally, the authors’ view is presented with regard to future prospects and research gaps in the estimation of the crop water status for precision irrigation.Deepak Gautam and Vinay Paga

Distribution and host range of the grapevine plasmodiophorid Sorosphaera viticola

Sorosphaera viticola, an obligate parasite of grapevine, was first detected in 2003 in roots of Vitis berlandieri x V. riparia rootstocks in a vineyard in the German Rheingau. To estimate the distribution and the abundance of S. viticola, other German and Austrian winegrowing areas (Mosel-Saar-Ruwer, Rhineland-Palatinate, Weinviertel) were screened. Vineyards planted with different rootstocks or own-rooted V. vinifera vines were chosen to elucidate the host range of this plasmodiophorid within the genus Vitis. S. viticola was found in different V. berlandieri x V. riparia hybrids and in roots of V. vinifera. Root samples from wild V. riparia from the Niagara Peninsula (Canada) were also found to be infested by S. viticola. This is the first record of S. viticola outside of Europe

Assessing the Feasibility of Using Sentinel-2 Imagery to Quantify the Impact of Heatwaves on Irrigated Vineyards

Heatwaves are common in many viticultural regions of Australia. We evaluated the potential of satellite-based remote sensing to detect the effects of high temperatures on grapevines in a South Australian vineyard over the 2016-2017 and 2017-2018 seasons. The study involved: (i) comparing the normalized difference vegetation index (NDVI) from medium- and high-resolution satellite images; (ii) determining correlations between environmental conditions and vegetation indices (Vis); and (iii) identifying VIs that best indicate heatwave effects. Pearson's correlation and Bland-Altman testing showed a significant agreement between the NDVI of high- and medium-resolution imagery (R = 0.74, estimated difference ??0.093). The band and the VI most sensitive to changes in environmental conditions were 705 nm and enhanced vegetation index (EVI), both of which correlated with relative humidity (R = 0.65 and R = 0.62, respectively). Conversely, SWIR (short wave infrared, 1610 nm) exhibited a negative correlation with growing degree days (R = -0.64). The analysis of heat stress showed that green and red edge bands-the chlorophyll absorption ratio index (CARI) and transformed chlorophyll absorption ratio index (TCARI)-were negatively correlated with thermal environmental parameters such as air and soil temperature and growing degree days (GDDs). The red and red edge bands-the soil-adjusted vegetation index (SAVI) and CARI2-were correlated with relative humidity. To the best of our knowledge, this is the first study demonstrating the effectiveness of using medium-resolution imagery for the detection of heat stress on grapevines in irrigated vineyards.</p

Regulated deficit irrigation and crop load interaction effects on grape heterogeneity

Aim: To investigate the interaction effects between irrigation and crop load and the resulting impact on grape heterogeneity within a Geographical Indication in South Australia. Methods and Results: Cabernet Sauvignon grapes were sampled at the time of harvest from the Coonawarra Geographical Indication where full and sustained deficit irrigation and crop load manipulations were implemented as a 2 × 2 factorial block design. Grape heterogeneity was quantified for each treatment at three levels (bunch, vine and block) using berry density categories that were related to grape maturity. Furthermore, each density category was characterised in terms of total soluble solids, berry fresh weight, tannin content and tartaric and malic acid concentrations. Irrigation and crop load interaction effects on grape heterogeneity were observed for intra- cluster, vine, and between blocks. Conclusion: This research reveals the extent of heterogeneity existing in the vineyard at the time of harvest, and presents management techniques that may mitigate grape ripeness variation in the vineyard. Significance and Impact of the Study: Grape heterogeneity is an important consideration for the production of high quality red wine, as high proportions of under ripe and/or overripe fruit present at the time of harvest have been shown to negatively impact colour, mouthfeel, and varietal aroma of the wine. Furthermore, the presence of overripe/shrivelled grapes with excessive sugar concentrations can lead to increased ethanol in the wine. Previous research has acknowledged the impact that the three focal aspects of terroir – climate, soil and cultivar – have on grape composition, with the overarching effects of climate being highlighted. Vine water status and vine balance can conceivably mediate some of the influences of climate on grape composition, but there has been limited literature delving into the effects on grape heterogeneity. By investigating vineyard management techniques with a view to minimising grape heterogeneity, this research gives insight into the optimisation of grape production, especially in hotter climates that are more susceptible to producing overripe fruit.Claire Armstrong, Pietro Previtali, Vinay Pagay, Paul Boss, David Jeffer

Grape Heterogeneity Index: Assessment of Overall Grape Heterogeneity Using an Aggregation of Multiple Indicators

Uniform grape maturity can be sought by producers to minimise underripe and/or overripe proportions of fruit and limit any undesirable effects on wine quality. Considering that grape heterogeneity is a multifaceted phenomenon, a composite index summarising overall grape heterogeneity was developed to benefit vineyard management and harvest date decisions. A grape heterogeneity index (GHI) was constructed by aggregating the sum of absolute residuals multiplied by the range of values from measurements of total soluble solids, pH, fresh weight, total tannins, absorbance at 520 nm (red colour), 3-isobutyl-2-methoxypyrazine, and malic acid. Management of grape heterogeneity was also studied, using Cabernet Sauvignon grapes grown under four viticultural regimes (normal/low crop load, full/deficit irrigation) during the 2019/2020 and 2020/2021 seasons. Comparisons of GHI scores showed grape variability decreased throughout ripening in both vintages, then significantly increased at the harvest time point in 2020, but plateaued on sample dates nearing the harvest date in 2021. Irrigation and crop load had no effect on grape heterogeneity by the time of harvest in both vintages. Larger vine yield, leaf area index, and pruning weight significantly increased GHI score early in ripening, but no significant relationship was found at the time of harvest. Differences in the Ravaz index, normalised difference vegetation index, and soil electrical conductivity did not significantly change the GHI score.Claire E. J. Armstrong, Pietro Previtali, Paul K. Boss, Vinay Pagay, Robert G. V. Bramley, and David W. Jeffer

Vascular connections into the grape berry: the link of structural investment to seededness

Vascular bundles in the grape pedicel and berry contain the conduits, phloem and xylem, for transport of water, sugar, nutrients and signals into and through the grape berry and play a critical role in berry growth and composition. Here, we assess the vascular anatomy within the proximal region of the berry. Guided using a 3D berry model generated by micro-CT, differential staining of transverse sections of berries and receptacles was followed by fluorescent microscopy. Morphometric and vascular characteristics were analyzed within the central proximal region (brush zone, a fibrous extension from the pedicel vascular system into the berry) of the seeded cultivars Shiraz and Sauvignon Blanc, as well as the stenospermocarpic cultivars Ruby Seedless and Flame Seedless. Observations revealed a change in vascular arrangement from the receptacle into the berry brush zone and differences in xylem element size as well as xylem and phloem area relationships. Xylem anatomical and derived hydraulic parameters, as well as total tissue area of xylem and phloem varied between cultivars and in receptacle and berry components. Variation in vascular growth between grape pedicels and berries was independent of seededness. Differences in receptacle xylem vessel size and distribution could contribute to cultivar-dependent xylem backflow constraint.Zeyu Xiao, Sabrina Chin, Rosemary G. White, Aude M. Gourieroux, Vinay Pagay, Stephen D. Tyerman, Leigh M. Schmidtke and Suzy Y. Rogier

3D visualisation of voids in grapevine flowers and berries using X‐ray micro computed tomography

First published: 06 January 2021Background and Aim: X-ray micro computed tomography (micro-CT) is a non-destructive 3D imaging technique that has been applied to plant morphology and anatomical studies to gain a better understanding of physiological phenomena in vivo. It is particularly useful for imaging voids in undisturbed fragile tissues and therefore may be applied to the delicate flowers and soft berries of Vitis vinifera. The characterisation of gas spaces and channels can offer insights into the process of tissue aeration and this may have implications on cell function and vitality. We assessed the use of micro-CT to visualise voids within these reproductive organs. Methods and Results: The internal structures of flowers and berries were captured through rapid micro-CT scanning and subsequently were recreated in 3D using image processing. The relative positions of the developing flower parts encased within the flower cap were visualised. Low density/porous tissue was identified within the pedicel and receptacle, con- necting the lenticels with the interior of the berry. Voids were present in the proximal mesocarp of mature berries forming a ‘detachment zone’ in both seeded and seedless cultivars. Voids permeated the mesocarp of mature seedless grape cultivars, but not seeded grapes. Conclusion: Micro-CT offers new insights regarding the distribution of voids on the morphology and compositional hetero- geneity of organs that are difficult to dissect and/or view with light microscopy. Significance of the Study: A better understanding of the physiology and functionality of grapevine reproductive tissues may be achieved by 3D visualisation of internal structure in vivo.Z. Xiao, T. Stait-Gardner, S.A. Willis, W.S. Price, F.J. Moroni, V. Pagay … et al