A Comparison of Hydroponics, Soil, and Root Staining Methods for Evaluation of Aluminum Tolerance in Medicago truncatula (Barrel Medic) Germplasm

Abstract

Aluminum toxicity and soil acidity are major constraints in alfalfa (Medicago sativa subsp. sativa) production in the world. Despite intense research efforts, neither an effective screening procedure nor an Al‐tolerant alfalfa germplasm is available. This dictates the need for identifying a new source of Al‐tolerant genes in the closely related species M. truncatula (barrel medic). Our objectives were to compare three Al tolerance screening methods: (i) a seedling‐based hydroponics method, (ii) a soil‐based plant method, and (iii) an Al‐stressed seedling‐based lumogallion root staining method in 32 M. truncatula accessions. The soil system compared the genotypes for dry root and shoot weights in unlimed soil and for relative weights. The lumogallion root staining of Al‐stressed seedlings compared the genotypes for fluorescence intensity of Al‐bound lumogallion within the root tips. In the hydroponics system, the genotypes were compared for root elongation and relative growth. The three methods were different from each other, with altered rankings for genotypes across the methods. The soil assay demonstrated a higher capacity for discriminating Al response among genotypes with a higher reproducibility. Most of the genotypes that were Al‐tolerant in soil were also Al‐tolerant using the hydroponics and root staining methods. The results suggested that a combination of soil‐based and hydroponics screening might be essential to identify Al‐tolerant genotypes possessing multiple Al tolerance mechanisms.

New genetic sources of resistance in the genus Phaseolus to individual and combined aluminium toxicity and progressive soil drying stresses

“…Several authors have examined the relationship of response with different screening methods with varying results. Narasimhamoorthy et al (2007) compared three methods including hydroponics, soil, and root staining for evaluation of Al tolerance in Medicago truncatula (Barrel Meic) germplasm and found a weak correlation, suggesting that each technique is distinct and cannot be substituted for each other. A large discrepancy between hydroponics-based ratings of seedlings and sand-culture-based ratings of soybean plants was found when Al tolerance was expressed as percentage of controls, and correlations between sand culture and hydroponics-based results were found to be low (Villagarcia et al 2001).…”

The response of Medicago sativa to aluminium toxicity under laboratory and field conditions

“…Possibly, only hydroponic screening could be comparable by efficiency but only in the case of further growing of selected seedlings (Narasimhamoorthy et al, 2007;Scott et al, 2008). Other methods, especially based on soil techniques, are hardly suitable for screening of thousands of seeds per accession in temperate climate.…”

“…These methods contribute to the evaluation of physiological processes underlying this trait. The genetics and physiology of M. sativa tolerance to Al as well as tolerance screening techniques have been comprehensively studied during the last decade (Sledge et al, 2002;Narasimhamoorthy et al, 2007;Pan et al, 2008;Bouton, 2012;Khu et al, 2012). Comparisons of screening techniques revealed medium to high correlations of tolerance factors among them.…”

Proteomic Response of Alfalfa Subjected to Aluminum (Al) Stress at Low pH Soil

“…Approximately 40% of world's total arable lands are acidic, and excessive Al containing soil may lose about 25~80% yield of various crop plants (Narasimhamoorthy et al, 2007). In acidic soil, when pH drops below five (<5.0), Al 3+ is solubilized in to the soil which is extremely toxic to plant growth.…”