Black point in wheat has the potential to cost the Australian industry $A30.4 million a year. It is difficult and expensive to screen for resistance, so the aim of this study was to validate 3 previously identified quantitative trait loci (QTLs) for black point resistance on chromosomes 2B, 4A, and 3D of the wheat variety Sunco. Black point resistance data and simple sequence repeat (SSR) markers, linked to the resistance QTLs and suited to high-throughput assay, were analysed in the doubled haploid population, Batavia (susceptible) × Pelsart (resistant). Sunco and Pelsart both have Cook in their pedigree and both have the Triticum timopheevii translocation on 2B. SSR markers identified for the 3 genetic regions were gwm319 (2B, T. timopheevii translocation), wmc048 (4AS), and gwm341 (3DS). Gwm319 and wmc048 were associated with black point resistance in the validation population. Gwm341 may have an epistatic influence on the trait because when resistance alleles were present at both gwm319 and wmc048, the Batavia-derived allele at gwm341 was associated with a higher proportion of resistant lines. Data are presented showing the level of enrichment achieved for black point resistance, using 1, 2, or 3 of these molecular markers, and the number of associated discarded resistant lines. The level of population enrichment was found to be 1.83-fold with 6 of 17 resistant lines discarded when gwm319 and wmc048 were both used for selection. Interactions among the 3 QTLs appear complex and other genetic and epigenetic factors influence susceptibility to black point. Polymorphism was assessed for these markers within potential breeding material. This indicated that alternative markers to wmc048 may be required for some parental combinations. Based on these results, marker-assisted selection for the major black point resistance QTLs can increase the rate of genetic gain by improving the selection efficiency and may facilitate stacking of black point resistances from different sources.

Quantitative trait loci (QTLs) for black-point resistance have been mapped in two doubled haploid-derived wheat populations, each thought to contain unrelated sources of resistance. In the 'Sunco' x'Tasman'-derived population, QTLs were located on chromosomes 1D, 2B, 3D, 4A, 5A and 7A with each QTL explaining between 4 and 15% of the observed phenotypic variance. QTLs were contributed by both parents. In the 'Cascades' x 'AUS1408'-derived population, QTLs from 'Cascades' were identified on chromosomes 2A, 2D and 7A with each QTL explaining between 12 and 18% of the phenotypic variance. Several markers were identified which are promising candidates for use in marker-assisted selection programmes. If one, two or three of these markers would have been used to select for black-point resistance in the 'Sunco' x 'Tasman' population, then with one marker 34 of 39 resistant lines, with two markers 23 of 32 and with three markers 17 of 32 would have been selected. At the same time, 67 false positives obtained by selecting with one marker are reduced to 24 by selection with two markers and to 11 by selection with three markers. Similarly, if one, two or three markers are used to select for black-point resistance in the 'Cascades' x 'AUS1408' populations, then with one marker 25 of 31 resistant lines, with two markers 26 of 31 and with three markers 10 of 31 are selected. At the same time, 14 false positives are obtained with one marker are reduced to six by selection with two markers and no false positives are selected using three markers.

Black point in wheat has commonly been thought to be caused by Alternaria alternata. To obtain a method for screening for resistance to this problem, the process by which A. alternata infects wheat grain was observed in resistant and susceptible varieties. No association was found between infection with A. alternata and black point symptoms. A technique was developed to produce symptoms in vitro which showed the detection and location of the peroxidase enzymes involved. Isoelectric focusing (IEF) determined considerable differences in peroxidase isoenzyme activity from black point resistant and susceptible wheat varieties. The potential exists for using IEF as a tool for rapid screening for black point resistance.