(Genes and QTLs Controlling Aluminum Toxicity Tolerance in Crop Plants and Their Applications for Plant Breeding in Indonesia)

Genetic knowledge of loci controlling Al toxicity tolerance is the key for a successful breeding program in developing Al tolerant cultivars. Tolerance level of crop plants to Al toxicity is genetically controlled. The gene inheritance pattern is mainly resulted from intensive studies of cereal crops, such as wheat, sorghum, maize, and rice. The trait can be controlled by a single dominant gene, a single dominant gene with many alleles, a pair of dominant genes, or by many genes (QTL). The majority of the Al tolerance genes identified so far belongs to two independent groups of gene families, i.e. aluminumactivated malate transporter (ALMT) and multidrug and toxic compound extrusion (MATE), both encoding transport proteins involved in Al-activated organic acid release, mainly citrate and malate. The variations in Al toxicity tolerance phenotypes are strongly correlated with the expressions of such genes in the root apical cells. Many Al tolerance QTLs have been mapped in the genomes of various crop species and were found to be colocated with the ALMT and MATE genes. The genetic maps of the Al tolerance genes and QTLs facilitate breeding programs for developing Al-tolerant cultivars through marker-assisted breeding methods. Al tolerance genes that have been isolated from genetically unrelated species can be used in genetic transformation studies of crop genotypes sexually incompatible to the gene source genotypes. The application of these molecular breeding methods expedites breeding programs to develop crop cultivars tolerance to Al toxicity and acid soils. Genomic technologies by using next-generation sequencing and high-throughput genotyping system accelerate Al toxicity tolerance gene and QTL discoveries of various crop species. The modern genomic technologies also facilitate more comprehensive PGR characterization and utilization to accelerate identification and isolation of the Al tolerance genes and QTLs to be used in a more comprehensive breeding program to support national food self sufficiency and food security programs.