Towards the isolation of boron tolerance genes from barley and wheat

Abstract

Boron toxicity in many low yielding environments is a significant limitation to crop productivity. In barley and wheat, genetic variation exists for tolerance to soil boron and the location of major loci is known from previous work. The major controlling loci in barley are on chromosomes 4H and 6H, and on 7B in wheat. In each case the favorable allele reduces the accumulation of boron in shoots and the deleterious morphological symptoms of growth under toxic conditions. We report on progress to identify these genes using positional cloning. In the first instance double haploid populations have been used to obtain moderate mapping resolution, and larger F2 and F3 populations have been developed and are currently in use for fine mapping to a sub-centimorgan scale. To achieve targeted PCR-based marker generation for both species we have exploited colinearity with related regions of the rice genome (on chromosomes 2, 3 and 6) in combination with wheat and barley EST databases. BAC (bacterial artificial chromosome) and TAC (transformation-competent artificial chromosome) libraries from a boron tolerant line have been constructed in-house to enable the recovery and sequencing of target loci and determine the molecular basis for boron tolerance in cereals.