Variation of Cicer Germplasm to Manganese Toxicity Tolerance.

Karthika Pradeep,Richard W. Bell,Wendy Vance

doi:10.3389/fpls.2020.588065

Abstract

After aluminum, manganese toxicity is the most limiting factor for crops grown in acidic soils worldwide. But overall, research on Mn toxicity is still limited. The poor acid tolerance of chickpea may be related to Mn toxicity, but there has been no previous screening of chickpea germplasm (nor in its wild Cicer relatives, Cicer reticulatum and Cicer echinospermum) for tolerance to Mn toxicity. A screening technique was developed for tolerance to Mn toxicity using three released cultivars of chickpea (Cicer arietinum L), Ambar, PBA HatTrick, and PBA Striker; one accession each of C. reticulatum and C. echinospermum; and lupin (Lupinus angustifolius) as a Mn-tolerant check, with eight Mn concentrations of 2, 25, 50, 100, 150, 200, 250, and 500 μM Mn as MnSO4 in a low-ionic-strength nutrient solution. The plants were harvested at 14 and 28 days after Mn treatments. The nutrient uptake in shoots (young, old leaves, and the rest of the shoot) and roots was investigated. The best discrimination between tolerant and intolerant Cicer genotypes based on relative shoot dry weight, root dry weight, total root length, and scoring of toxicity symptoms was achieved at 150 μM Mn after 14 days of growth in Mn solution. Among the chickpea cultivars, the greater relative plant growth (both shoot and root) of Ambar and PBA Striker at 100–200 μM Mn contrasted with that of PBA HatTrick, while the C. echinospermum accession was more tolerant to Mn toxicity than C. reticulatum. Manganese tolerance in both domestic cultivars and wild accessions was associated with internal tolerance to excess Mn following greater uptake of Mn and translocation of Mn from roots to shoots.

Highlights

Manganese (Mn) toxicity is one of the important constraints limiting crop growth in acid soils worldwide
The plants were scored for Mn toxicity symptoms weekly after Mn treatment additions to study the Mn effect over the experiment period, using a score card developed for chickpeas ranging from 0 to 5
Among the current prominent chickpea cultivars in Australia, PBA Striker was more tolerant than PBA HatTrick, suggesting that there is genotypic variation in Mn toxicity tolerance among chickpea cultivars currently grown in Australia

Summary

Introduction

Manganese (Mn) toxicity is one of the important constraints limiting crop growth in acid soils worldwide. Manganese toxicity occurs because of increased Mn2+ concentration with increased acidity even through increased H+ in the root zone decreases the rate of Mn uptake by roots (Edwards and Asher, 1982). While aluminum (Al) toxicity is most common in severely acid soils, Mn is a likely growth-limiting factor in moderately–strongly acid soils, and the problem further worsens under waterlogged conditions and with environmental factors such as high soil temperature, which increases the concentration of Mn2+ (Foy et al, 1988; Khabaz-Saberi et al, 2010). Manganese toxicity reduced leaf CO2 assimilation rate, stomatal conductance, and leaf pigments (chlorophylls a and b) in different plant species in various studies (Stoyanova et al, 2009; Santos et al, 2017). Excess Mn enhanced production of reactive oxygen species (ROS) (Santos et al, 2017), triggering oxidative stress in plant cells (Demirevska-Kepova et al, 2004), and was associated with elevated peroxidase activity and lower activities of catalase, ascorbic acid oxidase, glutathione oxidase, and cytochrome C oxidase (Hannam and Ohki, 1988)

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