ALBERT

Notes: Greenbug and Russian wheat aphid (RWA) are two devastating pests of wheat. The first has a long history of new biotype emergence and recently. RWA resistance has just started to break down. Thus, it is necessary to find new sources of resistance that will broaden the genetic base against these pests in wheat. Seventy-five doubled haploid recombinant (DHR) lines for chromosome 6A from the F1 of the cross between “Chinese Spring’ and the “Chinese Spring (Synthetic 6A) (Triticum dicoccoides × Aegilops tauschii)” substitution line were used as a mapping population for testing resistance to greenbug biotype C and to a new strain of RWA that appeared in Argentina in 2003. A quantitative trait locus (QTL) (br antixenosis to greenbug was significantly associated with the marker loci Xgwm1009 and Xgwm1185 located in the centromere region of chromosome 6A. Another QTL which accounted for most of the antixenosis against RWA was associated with the marker loci Xgwm1291 and Xiinni1150. both located on the long arm of chromosome 6A. This is the first report of greenbug and RWA resistance genes located on chromosome 6A. It is also the first report of antixenosis against the new strain of RWA. As most of the RWA resistance genes present in released cultivars have been located in [he D-genome, it is highly desirable to find new sources in other genomes to combine the existing resistance genes with new sources.

Notes: In hexaploid bread wheat, Triticum aestivum (2n = 6x = 42), little work has been carried out to study the genetic control of the synthesis of reduced, non-reduced and total non-structural carbohydrates and soluble proteins in aerial and rooting structures. The aim of this paper was to determine the chromosomal location of genes determining carbohydrate and protein synthesis that could be used for diagnostic selection in segregating breeding populations. A set of wheat intervarietal chromosome substitution lines [‘Chinese Spring’ (CS) × synthetic wheat (Triticum diccocoides×Aegilops squarrosa) (Syn)], was used. Plants were cultivated in hydroponic solutions to the fully expanded third leaf stage. Carbohydrate and protein contents and dry matter were determined for aerial and root parts. The root dry weight did not show significant differences between the parental varieties and the substitution lines, except for 5A, 2B and 6B, which had significantly lower dry weights. The aerial dry weight was significantly higher for Syn and the 2A substitution line. The ratio aerial dry weight/root dry weight was significantly higher in Syn, 1A, 2A and 4B. The protein content of the plant showed highly significant differences between both parental lines but 6A and 1D of the substitution lines showed highly significant differences, with contents as high as that for Syn. Syn produced significantly lower total aerial carbohydrates. The substitution lines 2A, 5A, 6A, 7A, 2B, 3D, 5D and 6D showed highly significant total carbohydrate content increases in the aerial parts compared with both parental lines. The non-reduced carbohydrate contents showed a pattern similar to that of the total carbohydrates. Syn had a lower reduced carbohydrate content than CS. Only the 5A, 2B, and 1D substitution lines had a highly significantly different content of reduced carbohydrates than CS. In roots, Syn produced the lowest values for every type of sugar. The highest significant values for total carbohydrates were found in substitution lines 2B, 4B, 5B, 6B, 1D and 6D. The non-reduced carbohydrate levels were significantly higher than CS in 2B, 5B, 6B and 6D substitution lines. Only the substitution lines 3B and 1D showed a significantly higher reduced carbohydrate content in roots compared with CS. The photoassimilate partitioning in Syn, 1 A, 2A and 4B favoured the aerial parts but, in contrast, higher partitioning to the roots was found in the 7B, 1D and 3D substitution lines. Both groups appear to carry interesting patterns worth incorporating in wheat cultivars.

Notes: Breeding for genetic resistance against greenbug and Russian wheat aphid (RWA) is the most effective way of controlling these widespread pests in wheat. Earlier work had shown that chromosome 7D of a synthetic hexaploid wheat, ‘Synthetic’ (T. dicoccoides × Ae. squarrosa) (AABB × DD) gave resistance when transferred into the genetic background of an aphid-susceptible cultivar, ‘Chinese Spring’, as the recipient. To map the genes involved, a set of 103 doubled haploid recombinant substitution lines was obtained from crossing the 7D substitution line with the recipient, and used to determine the number and chromosomal location of quantitative trait loci (QTL) controlling antixenosis and antibiosis types of resistance. Antixenosis to RWA was significantly associated with marker loci Xpsr687 on 7DS, and Xgwm437 on 7DL. Antibiosis to greenbug was associated with marker loci Xpsr490, Rc3 (on 7DS), Xgwm44, Xgwm111, Xgwm437, Xgwm121 and D67 (on 7DL). Similarly, antibiosis to RWA was linked to loci Xpsr490, Rc3, Xgwm44, Xgwm437 and Xgwm121. At least two QTL in repulsion phase, one close to the centromere either on the 7DS or 7DL arms, and a second distal on 7DL could explain antibiosis to RWA and, partially, this mechanism against greenbug.