Boron Toxicity

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Plant and Soil 193: 181–198, 1997. c 1997 Kluwer Academic Publishers. Printed in the Netherlands.

181

Chapter 12

Boron toxicity
Ross O. Nable1 , Gary S. Ba˜ uelos2 and Jeffrey G. Paull3 n 1

CSIRO Land and Water, P.M.B., P.O. Aitkenvale, QLD 4814, Australia , 2 Water Management Research Laboratory, USDA-ARS, 2021 S. Peach Av., CA 93727, USA and 3 Department of Plant Science, Waite Campus, University of Adelaide, Glen Osmond, SA 5064, Australia

Abstract Whilst of lesser prevalence than B deficient soils, B-rich soils are important, causing B toxicity in the field and decreased crop yields in different regions of the world. The highest naturally occurring concentrations of soil B are in soils derived from marine evaporites and marine argillaceous sediment. In addition, various anthropogenic sources of excess B may increase soil B to levels toxic for plants. The most important source is irrigation water, but others include wastes from surface mining, fly ash, and industrial chemicals. Ameliorating high-B soils is extremely difficult. A commonly used method of reclaiming high B soils is to extensively leach with low B water. Though used successfully, leaching may not be a permanent solution and causes difficulties with the disposal of the leachates. Other amelioration methods include the use of soil amendments (e.g. lime, gypsum) and the planting of plant genotypes that are tolerant of high external B concentrations. Although there are various methods available to determine the levels of B in soils, soil analysis can provide little more than a general risk assessment for B toxicity. Similarly, diagnosing B toxicity in plants, either by visible symptoms or tissue analysis has limited applicability. Thus at present, neither soil nor plant analysis can be recommended to precisely predict the growth of plants on high soil B. Recent physiological and genetic studies have provided some understanding of genetic variation in the response of plants to high concentrations of B. Moreover, these studies have facilitated the breeding of tolerant genotypes for cultivation on high B soils. Considerable genetic variation in response to high B has been identified in a wide range of plant species, most of which share a similar tolerance mechanism – reduced uptake of B in both shoots and roots. The tolerance mechanism appears to be under the control of several major additive genes, and specific chromosomal locations have been identified for the genes in some species. Considerable success has been achieved in breeding for tolerance to B toxicity, a process that is greatly aided by the ease with which genotypic variation for this characteristic can be assessed and the range of methods available to screen breeding populations. Introduction Boron toxicity is an important disorder that can limit plant growth on soils of arid and semi arid environments throughout the world. High concentrations of B may occur naturally in the soil or in groundwater, or be added to the soil from mining, fertilisers, or irrigation water. Although of considerable agronomic importance, our understanding of B toxicity is rather fragmented and limited. The present paper attempts to review the available literature on a broad range of topics, from the occurrence and detection of B toxic soils, to the effects of high B on plants, through to the management of B toxicity. It differs from earlier reviews on B toxicity (e.g. Gupta et al. 1985; Leyshon and Jame, 1993) by exploring in detail the physiology and genetypic variation for tolerance to B toxicity and how this variation can be utilised to maximise plant growth on high B soils.

Formation and distribution of boron laden soils Sources of boron Boron, the only non-metal among the elements of Group III in the periodic table, is not uniformly distributed in the earth’s crust. The primary sources of



E-mail: Ross.Nable@tvl.clw.csiro.au

182 B in most soils are tourmaline and the volatile emanations of...
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