Abstract
Drought is one of the most severe and unpredictable abiotic stresses, occurring at any growth stage and affecting crop yields worldwide. Therefore, it is essential to develop drought tolerant varieties to ensure sustainable crop production in an ever-changing climate. High-throughput digital phenotyping technologies in tandem with robust screening methods enable precise and faster selection of genotypes for breeding. To investigate the use of digital imaging to reliably phenotype for drought tolerance, a genetically diverse safflower population was screened under different drought stresses at Agriculture Victoria’s high-throughput, automated phenotyping platform, Plant Phenomics Victoria, Horsham. In the first experiment, four treatments, control (90% field capacity; FC), 40% FC at initial branching, 40% FC at flowering and 50% FC at initial branching and flowering, were applied to assess the performance of four safflower genotypes. Based on these results, drought stress using 50% FC at initial branching and flowering stages was chosen to further screen 200 diverse safflower genotypes. Measured plant traits and dry biomass showed high correlations with derived digital traits including estimated shoot biomass, convex hull area, caliper length and minimum area rectangle, indicating the viability of using digital traits as proxy measures for plant growth. Estimated shoot biomass showed close association having moderately high correlation with drought indices yield index, stress tolerance index, geometric mean productivity, and mean productivity. Diverse genotypes were classified into four clusters of drought tolerance based on their performance (seed yield and digitally estimated shoot biomass) under stress. Overall, results show that rapid and precise image-based, high-throughput phenotyping in controlled environments can be used to effectively differentiate response to drought stress in a large numbers of safflower genotypes.
Highlights
Safflower (Carthamus tinctorius L) is one of the oldest oilseed crops, currently grown in more than 25 countries, with Kazakhstan, USA, Mexico and India being major producers in 2018 [1]
Growth curves for each treatment were identical during initial growth stages until 66 DAS, when the majority of plants reached initial branching (IB), and stress was imposed for two groups (Fig 3B)
The ability to select genotypes with increased tolerance to water stress is paramount, as recent climate change models have forecast a substantial increase in global temperatures and drought conditions, resulting in a scarcity of water for growing of crops [74]
Summary
Safflower (Carthamus tinctorius L) is one of the oldest oilseed crops, currently grown in more than 25 countries, with Kazakhstan, USA, Mexico and India being major producers in 2018 [1]. Safflower is an undervalued yet highly versatile crop, with young plants consumed as a vegetable, petals used to produce the dye carthamin, and seed oil used in various industries [5,6,7]. With the preference for the plant-based renewable oil, there has been an increased demand for safflower oil, with its use in biofuel [9, 10], textile [10], food [11, 12], pharmaceutical [13] and cosmetic [14] industries. Due to increased demand in the biofuel and biolubricant industries, recent breeding programs have been directed towards selection of superior safflower genotypes with over 75% oleic acid, a higher purity than any other oil seed crops [18,19,20,21]
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