Marker-trait association analysis for drought tolerance in smooth bromegrass.

BACKGROUND: Little information is available on the application of marker-trait association (MTA) analysis for traits related to drought tolerance in smooth bromegrass. The objectives of this study were to identify marker loci associated with important agronomic traits and drought tolerance indices as well as fining stable associations in a diverse panel of polycross derived genotypes of smooth bromegrass. Phenotypic evaluations were performed at two irrigation regimes (normal and deficit irrigation) during 2 years; and association analysis was done with 626 SRAP markers. RESULTS: The results of population structure analysis identified three main subpopulations possessing significant genetic differences. Under normal irrigation, 68 and 57 marker-trait associations were identified using general linear model (GLM) and mixed linear mode1 (MLM), respectively. While under deficit irrigation, 61 and 54 markers were associated with the genes controlling the studied traits, based on these two models, respectively. Some of the markers were associated with more than one trait. It was revealed that markers Me1/Em5-11, Me1/Em3-15, and Me5/Em4-7 were consistently linked with drought-tolerance indices. CONCLUSION: Following marker validation, the MTAs reported in this panel could be useful tools to initiate marker-assisted selection (MAS) and targeted trait introgression of smooth bromegrass under normal and deficit irrigation regimes, and possibly fine mapping and cloning of the underlying genes and QTLs.

Study of genetic variation in sesame (Sesamum indicum L.) using agro-morphological traits and ISSR markers.

This research was conducted to study the genetic variation among eighteen genotypes of sesame (Sesamum indicum L.) collected from various agro-climatic regions of Iran along with six exotic genotypes from the Asian countries using both agro-morphological and ISSR marker traits. The results showed significant differences among genotypes for all agro-morphological traits and a relatively high genetic coefficient of variation observed for number of fruiting branches per plant, capsules per plant, plant height and seed yield per plant. Cluster analysis based on these traits grouped the genotypes into five separate clusters. Larger inter- than intra cluster distances implies the presence of higher genetic variability between the genotypes of different groups. Genotypes of two clusters with a good amount of genetic divergence and desirable agronomic traits were detected as promising genotypes for hybridization programs. The 13 ISSR primers chosen for molecular analysis revealed 170 bands, of which 130 (76.47%) were polymorphic. The generated dendrogram based on ISSR profiles divided the genotypes into seven groups. A principal coordinate analysis confirmed the results of clustering. The agro-morphological traits and ISSR markers reflected different aspects of genetic variation among the genotypes as revealed by a non significant cophenetic correlation in the Mantel test. Therefore the complementary application of both types of information is recommended to maximize the efficiency of sesame breeding programs. The discordance among diversity patterns and geographical distribution of genotypes found in this investigation implies that the parental lines for hybridization should be selected based on genetic diversity rather than the geographical distribution.

Allele sequencing of the barley stem rust resistance gene Rpg1 identifies regions relevant to disease resistance.

The stem rust resistance gene Rpg1 has protected North American barley cultivars from significant yield losses for over 65 years. The remarkable durability of this gene warrants further study as to its possible origin and allelic variation. Eight Swiss barley (Hordeum vulgare) landraces and eight wild barley (H. vulgare subsp. spontaneum) accessions from diverse geographic regions were analyzed to uncover new alleles of Rpg1 and learn about its possible origin. The two germplasm groups included accessions that were resistant and susceptible to Puccinia graminis f. sp. tritici pathotype MCCF. Allele-specific primers were utilized to amplify 1 kbp overlapping fragments spanning the Rpg1 gene and sequenced if a polymerase chain reaction (PCR) fragment was generated. Variation among the PCR products revealed significant polymorphisms among these Hordeum accessions. Landraces and wild barley accessions susceptible to pathotype MCCF exhibited the highest degree of Rpg1 polymorphism. One resistant landrace (Hv672) and one resistant wild barley accession (WBDC040) yielded all seven Rpg1-specific PCR fragments, but only landrace Hv672 coded for an apparently functional Rpg1 as determined by comparison to previously characterized resistant and susceptible alleles and also resistance to HKHJ, a stem rust pathotype that can specifically detect Rpg1 in the presence of other resistance genes. Accessions resistant to stem rust pathotype MCCF, but completely lacking Rpg1-specific PCR amplification and hybridization with an Rpg1-specific probe, suggested the presence of stem rust resistant gene(s) different from Rpg1 in the Hordeum germplasm pool. Some Rpg1 alleles that retained the ability to autophosphorylate did not confer resistance to Puccinia graminis f. sp. tritici pathotype MCCF, confirming our previous observations that autophosphorylation is essential, but not sufficient for disease resistance. Thus, the RPG1 protein plays a complex role in the stem rust disease resistance-signaling pathway.

The stem rust resistance gene Rpg5 encodes a protein with nucleotide-binding-site, leucine-rich, and protein kinase domains.

We isolated the barley stem rust resistance genes Rpg5 and rpg4 by map-based cloning. These genes are colocalized on a 70-kb genomic region that was delimited by recombination. The Rpg5 gene consists of an unusual structure encoding three typical plant disease resistance protein domains: nucleotide-binding site, leucine-rich repeat, and serine threonine protein kinase. The predicted RPG5 protein has two putative transmembrane sites possibly involved in membrane binding. The gene is expressed at low but detectable levels. Posttranscriptional gene silencing using VIGS resulted in a compatible reaction with a normally incompatible stem rust pathogen. Allele sequencing also validated the candidate Rpg5 gene. Allele and recombinant sequencing suggested that the probable rpg4 gene encoded an actin depolymerizing factor-like protein. Involvement of actin depolymerizing factor genes in nonhost resistance has been documented, but discovery of their role in gene-for-gene interaction would be novel and needs to be further substantiated.

Inheritance of flower color and spininess in safflower (Carthamus tinctorius L.).

Safflower (Carthamus tinctorius L.) flowers are used for coloring and flavoring food and also as fresh-cut and dried flowers. The most important characteristics which contribute to the ornamental value of safflower are flower color and spinelessness. The objective of this study was to determine the inheritance mode and the number of genes controlling spininess and flower color in some Iranian genotypes of safflower. The results indicated that the existence of spines on the leaves and bracts of safflower is controlled by a single dominant gene in which the spiny phenotype was completely dominant to spineless. In some crosses, flower color was controlled by two epistatic loci each with two alleles, resulting in a ratio of 13:3 in the segregating F2 population for plants with orange and yellow flowers. Also, other mechanisms of genetic control, such as duplicate dominance and duplicate recessive types of epistasis, were observed for flower color in other crosses that led to ratios of 7:9 and 15:1 for plants with orange and yellow flowers, respectively. The results suggest that for ornamental use or in the food dying industry, genotypes with orange or yellow flowers and without spines on the leaves and bracts can be produced.