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  • Author or Editor: A. Mujeeb-Kazi x
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The B(S) genome diploids (2n = 2x = 14) are a unique reservoir of genetic diversity that can provide wheat breeders a rich source of allelic variation for stress traits that limit productivity. Restricted in practical use essentially due to their complex chromosomal behavior, these diploids have been in limited practical usage. The classic utilization example has been the suppression activity of the Ph locus and role in alien genetic transfer aspects that has been a standard in cytogenetic manipulation studies. For applied efforts focusing on Aegilops speltoides researchers in CIMMYT initiated an ambitious program to make AABBBB(SS) synthetics and made progress by generating over 50 such synthetics. Of these 20 were available for this study in which phenology and powdery mildew screening were evaluated. Four of these 20 synthetics appeared to be useful sources for further exploitation in breeding. These were entries 6, 9, 10 and 11 suited for exploitation in pre-breeding, with positive phenological characters particularly high thousand-kernel weight and are cytologically near euploid at 2n = 6x = 42. The subtle hyper (43) and hypoploid number would not negate their applied use potential. Preference however goes to genotypes 9 and 11.

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Bridge crosses utilizing the D genome synthetic hexaploids (SH), Triticum turgidum / Aegilops tauschii (2n = 6x = 42, AABBDD), are a potent means of improving bread wheat ( T. aestivum ) for biotic and abiotic stresses. The synthetic germplasm enables incorporation of the genetic diversity of T. turgidum cultivars together with the attributes of the Ae. tauschii accessions. In this research, SH wheats were screened for karnal bunt in Obregon, Mexico over six crop cycles and several SHs were earlier identified with an immune response. These SHs have unique Ae. tauschii accessions as parents. Phenologically descriptors and additional trait evaluations led us to develop a sub-set of the most desirable combinations for wheat breeding. The SH wheats are generally tall, late to mature, have good agronomic type, and are non-free threshing with a high 1000 kernel weight. All have a spring growth habit with several possessing multiple stress resistances. The resistance exhibited by SH wheats has been transferred into elite but KB susceptible bread wheat cultivars thus generating a new and unique genetic resource that can be readily exploited by conventional breeding programs.

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A panel of 94 diverse hexaploid wheat accessions was used to map quantitative trait loci (QTL) underlying the yield related traits on chromosome 3A. Population structure and kinships were estimated using unlinked SSR markers from all 21 chromosomes. Analysis of variance revealed significant difference among accessions; however, genotype × year interaction was non-significant for majority of yield related traits. A mixed linear model (MLM) approach identified six QTLs for four traits that individually accounted for 10.7 to 17.3% phenotypic variability. All QTLs were consistently observed for both study years. New putative QTLs for the maximum fertile florets per spike and spike length were identified. This report on QTLs for yield related traits on chromosome 3A will extend the existing knowledge and may prove useful in marker-assisted selection (MAS) for development of high yielding cultivars.

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Cereal Research Communications
Authors: J. Díaz De León, R. Escoppinichi, R. Zavala-Fonseca, T. Castellanos, M. Röder and A. Mujeeb-Kazi

To determine limits of tolerance, provide information about genetic diversity, and explore potential as progenitors for a salt-tolerant wheat improvement program, we collected several landraces and genotypes reputed to be salt-tolerant. Salt tolerance was tested by irrigation with a diluted solution of seawater with 12 dS.m −1 electrical conductivity for two years. Phenotypic parameters of percent of emergence, days to flowering to spike emergence, and physiological maturity were not significantly affected. Leaf area was sensitive to salt stress and inhibited about 30%. Plant height was inhibited 30%, while spike length and number of grains per spike were not. Total yield of Shorawaki and Kharchia landraces confirmed their reputation as salt-tolerant. Cultivars Mepuchi, Pericu, Calafia, WH157, and SNH-1 were inhibited at a moderate level of tolerance; cultivars Cochimí, Lu26S, and KRL 1–4 were inhibited, as was the control cultivar Oasis by up to 50%. To amplify microsatellites from genomes A, B, and D, 33 pairs of primers were used. The microsatellite WMS169-6A was highly polymorphic, with 10 different alleles distinguishing the genotype set. Also, the short arm of chromosome 4D microsatellites were amplified and found to be monomorphic, which suggests highly conserved alleles. The other microsatellites had variable polymorphism. In total, 120 alleles were obtained and used to define genetic diversity. The resulting dendrogram showed that landraces Shorawaki and Kharchia are distantly grouped from all other cultivars, as well as the cultivar Chinese Spring. Strikingly, KRL1–4, a derivative of Kharchia, did not show a close relationship to its source. The geographic origin did not influence pair-wise combinations. However, pedigree did influence pair-wise combinations.

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