Wheat rust diseases are a major cause of yield losses of this crop. Yellow (Puccinia striiformis f. sp. tritici) rust is of the most widespread and dangerous disease of wheat and is the major factor that adversely affects wheat yield and quality. The use of genetic host resistance is the most effective, economical and environmentally safe method of controlling stripe rust that allows elimination of fungicides and minimize crop losses from this disease. Due to the threat of the development of epiphytoties of rust disease it is necessary to identify new donors of resistance to yellow rust and to develop resistant wheat breeding material. In the present study, attention was drawn to the effective yellow rust resistance genes Yr5, Yr10 and Yr15, which were identified in the process of molecular screening of wheat germplasm. Genetic analysis using S23M41 molecular marker linked to Yr5 revealed the presence of this gene in 17 out of 136 promising lines. Thirteen genotypes screened with Xbarc8 generated the DNA fragment associated with Yr15. Three advanced lines with Yr10 were identified using the SCAR marker. Three lines carrying two Yr genes (Yr5 and Yr15) were detected. Combination of Yr5 and Yr10 were found in 15 wheat lines. We identified a number of wheat genotypes highly resistant to stripe rust, which could be further evaluated to release new resistant varieties or to be used in the breeding program.
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Rust diseases are among the most important affecting wheat because they are responsible for a significant yield reduction globally. Different types of conventional breeding approaches are currently underway to protect wheat from these diseases. The involvement of molecular genetics and biotechnology tools in conventional plant breeding sets new directions to develop crop varieties with desired traits more efficiently and accurately. An array of molecular markers linked to rust resistant genes and dense molecular genetic maps are now available for use. Marker assisted selection (MAS) is now a routine activity in various crops especially for agronomic traits that are otherwise difficult to tag like resistance to pathogens, insects, nematodes etc. Gene pyramiding involves the stacking of many genes leading to real-time expression of all genes in single variety to develop durable resistance. This method is gaining significant popularity as it would enhance the efficiency of conventional breeding methods and precise development of broad spectrum resistant capabilities. Keeping in view the significance of MAS, rust resistant wheat parental lines were selected and molecular information was tagged using gene linked markers through PCR. Conventional breeding plane was designed on the basis of molecular data and maximum crosses were made between high yielding susceptible and resistant wheat genotypes. Molecular screening and other yield parameters were keenly noted on each stage of segregating population. Three rust resistant genes i.e. Lr-34/Yr-18, Lr-46/Yr-29 and Lr-19 were successfully combined in three cross combinations. Twenty crosses were found positive for two resistant genes i.e. Lr-46/Yr-29 and Lr-19, Moreover, one cross was positive for Lr-34/Yr-18 and Lr-46/Yr-29, and one was positive for Lr-34/Yr-18 and Lr-19. Introduction of more genes is also continued to develop superior resistance against a wide range of rust pathogen in wheat.
In the context of climate change, drought is one of the most important and complex abiotic stresses affecting crop production worldwide. The adoption of an appropriate technological package, principally drought tolerant varieties, may overcome these challenges to meet global food security needs for the rapidly growing human population, particularly in developing countries. Therefore, this research was carried out to identify efficient phenotypic and genetic selection criteria to identify drought tolerant wheat varieties. In this perspective, 200 diverse elite bread wheat lines from ICARDA and CIMMYT were evaluated under four Moroccan environments during the 2015 and 2016 seasons for yield and 15 agro-physiological traits. The same set of genotypes was genotyped using 15k SNPs. Significant environment and genotype environment interaction effects were observed for yield. Average yield reached 3.18t/ha and ranged from 2.45 to 4.27t/ha. The secondary traits were mostly dominated by the environment effect (p<0.001). Based on correlation and regression analysis between grain yield and phenotypic data, the biomass, grain number per m<sup>2</sup> and to a lesser extent fertile spikes number and thousand kernel weights (depending of drought scenarios) can be more reliable traits than yield for the identification of drought tolerant genotypes. Moreover, the ground cover and canopy temperature depression can be used as supplementary criteria for more accurate selection. Slow selection on the basis of phenotypic traits may be accelerated and improved by using molecular markers. The genetic analysis highlighted significant SNPs and identified new QTLs linked to yield and the most efficient phenotypic traits under drought conditions. These findings could be useful for breeding drought-resistant wheat cultivars using marker-assisted selection to accumulate these favorable alleles of SNPs associated with yield-related traits to increase grain yield.
Leaf rust is the most common rust in wheat production areas of Syria and causes significant annual yield losses. Using genotypes with durable resistance is the most economical way of controlling the disease. One of the best-known leaf rust resistance genes is Lr46 that confers a slow rusting type of adult plant resistance. The main objective of this study was to identify Lr46 in durum wheat genotypes using morphological and molecular markers. Thirty-two durum wheat genotypes were evaluated for response to leaf rust at the seedling and adult plant stages. Twelve genotypes (37.5%) were resistant (R), 10 (31.25%) were moderately resistant (MR), seven (21.87%) were moderately susceptible (MS), and three (9.37%) were susceptible (S). Molecular marker analyses using SSR marker wmc44 showed that 16 genotypes (50%) carried Lr46/Yr29. The genotypes possessing the marker linked to Lr46/Yr29 could be used for selection of Lr46/Yr29 in breeding for slow rusting resistance in durum.
A wheat genotype PBW343+Gpc-B1+LR24 containing the high grain protein content (GPC) gene Gpc-B1 linked to marker Xucw108 was used as the donor parent to transfer Gpc-B1 and Lr24 into Eastern Gangetic Plains (EGP) cv. HUW234 and HUW468 that were released in 1986 and 1999, respectively. The backcrossing program involved the following steps: (i) foreground selection, (ii) marker selection, and (iii) recovery of recipient parent genome. Grain protein contents were recorded for all selected plants from the BC2F2:3 generation. The dominant marker Xucw108 was used for foreground selection, and heterozygous plants were identified through progeny testing. For RPG recovery, both genotypic and phenotypic selection was used. Introgression of the high GPC gene into the recipient background without yield loss was completed in 5 years, starting from 2009-10 (F1) and completed in 2013-14 (BC2F5). A conventional selection program would take the same time to reach BC2F5 but ensuring the transfer of GPC would not not be possible. Ten selected single plants from the BC2F3:4 generation had comparable yields of the parents with 26% higher GPC than the recurrent parent HUW 234. Eight selected plants had comparable yields and 34% higher GPC than HUW 468. Multi-row progenies (BC2F4 and BC2F5) of each selected plant were evaluated in yield traits with the donor and recipient parents as controls during 2012-13 and 2013-14. Two lines based on each recurrent parent were identified with significantly higher GPC with no yield penalty. The study reinforced the belief that MAS in combination with phenotypic selection could be a useful strategy to develop high GPC genotypes without sacrificing grain yield. These lines will be submitted to national trial where MAS derived lines require only two years of testing compared to four years for conventionally bred lines.
Breeding for durable leaf rust resistance is a priority for our breeding programs; however, the availability of new resistance genes is a limiting factor. Two spring wheat populations totaling 186 lines derived from three resistant donors and two Uruguayan susceptible cultivars were used to detect genomic regions associated with seedling and field resistance to LR in Uruguay. AUDPC were recorded in three environments in the 2012 and 2013 cropping seasons, and seedling responses were determined using three Puccinia triticina races. The lines were also genotyped using GBS. A total of 5,222 SNP markers were used for genome-wide association analysis. Molecular markers were used to genotype APR genes Lr34 and Lr68. We identified 43 SNP markers significantly associated with seedling resistance and 19 for field resistance on chromosomes 1A, 1B, 1D, 2B, 2D, 3A, 4A, 5B, 6B, 7A, 7B and 7D. We confirmed the presence of Lr10 and Lr16 in seedling tests and Lr34 and Lr68 in field tests. Novel genomic regions were identified on chromosomes 4A associated with APR, and 5B associated with seedling resistance. These new resistance genes will be useful in breeding for durable LR resistance.
Many of the catalogued leaf rust resistance genes in wheat deployed in agriculture have been overcome by variants of Puccinia triticina (Pt), the causal pathogen of leaf rust. Discovery and characterization of new sources of resistance in various germplasms using multipathotype tests and molecular markers could permit future diversification of the genetic base of leaf rust resistance in wheat. In searching for new sources of leaf rust resistance, 140 wheat lines from 14 African countries were tested with 8 Australian Pt pathotypes. Seedling tests revealed that 41% of the lines were susceptible to all pathotypes, 31% were postulated to carry either one of 10 resistance genes (Lr1, Lr2a, Lr3a, Lr13, Lr18, Lr23, Lr24, Lr26, Lr37 or Lr73) or one of five gene combinations (Lr2a+Lr3a, Lr1+Lr13, Lr1+Lr23, Lr1+Lr13+Lr73 and Lr23+Lr73). Twenty-eight percent of the lines were postulated to carry uncharacterized seedling resistance genes. Based on average coefficients of infection (ACI), 101, 25 and 11 lines showed high (ACI 0-19), moderate (ACI 21-38) and low (ACI 41-56) levels adult plant resistance, respectively, whereas three lines were moderately susceptible to susceptible (ACI 63-76). Genotyping of 74-78 lines that were anticipated to carry APR genes, using the molecular markers: csLV34 (linked to Lr34) and KASP SNP markers SNP1G22 and SNPT10 (linked to Lr46 and Lr67), respectively, revealed the presence of Lr34, Lr46 and Lr67 in 11, 22 and 14 wheat lines, respectively. The identities of the APR in the remaining 22 lines are unknown, and potentially represent new resistance sources. Genetic analyses of these uncharacterized APR sources are underway to select single gene lines and allow fine mapping.