Using a Hybrid Mapping Population to Identify Genomic Regions of Pyrenophora teres Associated With Virulence

Net blotches caused by Pyrenophora teres are important foliar fungal diseases of barley and result in significant yield losses of up to 40%. The two types of net blotch, net-form net blotch and spot-form net blotch, are caused by P. teres f. teres (Ptt) and P. teres f. maculata (Ptm), respectively. This study is the first to use a cross between Ptt and Ptm to identify quantitative trait loci (QTL) associated with virulence and leaf symptoms. A genetic map consisting of 1,965 Diversity Arrays Technology (DArT) markers was constructed using 351 progenies of the Ptt/Ptm cross. Eight barley cultivars showing differential reactions to the parental isolates were used to phenotype the hybrid progeny isolates. Five QTL associated with virulence and four QTL associated with leaf symptoms were identified across five linkage groups. Phenotypic variation explained by these QTL ranged from 6 to 16%. Further phenotyping of selected progeny isolates on 12 more barley cultivars revealed that three progeny isolates are moderately to highly virulent across these cultivars. The results of this study suggest that accumulation of QTL in hybrid isolates can result in enhanced virulence

Fungicide resistance management in Australian grain crops

Fungicide resistance is a serious and increasing problem in cropping systems worldwide. Fungicides are an important component of integrated disease management strategies for the protection of crops from the impacts of fungal diseases. However, as their use has increased, the effectiveness of some fungicides has been reduced by the development of fungicide resistant pathogen populations. Without intervention, more fungicides are likely to become ineffective

Stem rust outbreak in Queensland barley

Very dry conditions throughout much of eastern Australia in 2018 resulted in low overall disease incidence in cereal crops. At the time of writing, rust reports in cereals were limited to: wheat leaf rust in New South Wales, Victoria, Tasmania, South Australia and Western Australia; barley leaf rust in SA and WA; and oat crown rust in Queensland, NSW, Victoria and WA. Wheat stripe rust was reported in Victoria’s high-rainfall zone and NSW’s central west and south-west slopes, while single samples were also recorded in Tasmania’s Midlands region and SA’s Roseworthy. In view of the generally low 2018 disease incidence, it was surprising to see severe stem rust develop in several barley crops in south-east Queensland from October. Reports of stem rust-infected crops were received from Brigalow, Chinchilla, Dalby and Jandowae, Queensland

Using a Hybrid Mapping Population to Identify Genomic Regions of Pyrenophora teres Associated With Virulence

Net blotches caused by Pyrenophora teres are important foliar fungal diseases of barley and result in significant yield losses of up to 40%. The two types of net blotch, net-form net blotch and spot-form net blotch, are caused by P. teres f. teres (Ptt) and P. teres f. maculata (Ptm), respectively. This study is the first to use a cross between Ptt and Ptm to identify quantitative trait loci (QTL) associated with virulence and leaf symptoms. A genetic map consisting of 1,965 Diversity Arrays Technology (DArT) markers was constructed using 351 progenies of the Ptt/Ptm cross. Eight barley cultivars showing differential reactions to the parental isolates were used to phenotype the hybrid progeny isolates. Five QTL associated with virulence and four QTL associated with leaf symptoms were identified across five linkage groups. Phenotypic variation explained by these QTL ranged from 6 to 16%. Further phenotyping of selected progeny isolates on 12 more barley cultivars revealed that three progeny isolates are moderately to highly virulent across these cultivars. The results of this study suggest that accumulation of QTL in hybrid isolates can result in enhanced virulence

Genome-wide association mapping for seedling and adult resistance to powdery mildew in barley

Key message Two new major QTL were identified for powdery mildew resistance. We confirmed that the QTL on 7HS contributed mainly to the adult-plant resistance, while another one on chromosome arm 1HS made a significant contribution to the seedling resistance. Abstract Powdery mildew (PM), caused by Blumeria hordei, can occur at all post emergent stages of barley and constantly threatens crop production. To identify more genes for efective resistance to powdery mildew for use in breeding programs, 696 barley accessions collected from diferent regions of the world were evaluated for PM resistance at seedling and adult growth stages in three diferent states of Australia. These barley accessions were genotyped using DArTSeq with over 18,000 markers for a genome-wide association study (GWAS). Using the FarmCPU model, 54 markers showed signifcant associations with PM resistance scored at the seedling and adult-plant stages in diferent states of Australia. Another 40 markers showed tentative associations (LOD>4.0) with resistance. These markers are distributed across all seven barley chromosomes. Most of them were grouped into eleven QTL regions, coinciding with the locations of most of the reported resistance genes. Two major MTAs were identifed on chromosome arms 3HS and 5HL, with one on 3HS contributing to adult plant resistance and the one on 5HL to both seedling and adult plant resistance. An MTA on 7HS contributed mainly to the adult-plant resistance, while another one on chromosome arm 1HS made a signifcant contribution to the seedling resistance

Genome-wide association mapping analysis to identify genomic regions associated with virulence in Pyrenophora teres f. teres

Net form of net blotch, caused by the fungal pathogen, Pyrenophora teres f. teres (Ptt), is an important foliar disease present in all barley (Hordeum vulgare) producing regions of the world. This fungus is a heterothallic haploid ascomycete and reproduces both sexually and asexually. Sexual recombination in Ptt can produce new combinations of pathogen virulences and lead to changes in disease expression in the host. Changes in virulence can be devastating to the barley industry especially if a limited number of barley varieties with common resistances are grown. Knowledge of the genetic structure and genes involved in virulence is vital to researchers and breeders to increase the durability of Ptt resistance in barley varieties. We have used a genome-wide association mapping approach to characterise genomic regions associated with virulence in Australian barley varieties. One hundred and eighty-seven Ptt isolates collected from five Australian states were genotyped using DArTseq (Diversity Arrays Technology Pty Ltd) markers and phenotyped across ten different barley genotypes. Association mapping analysis identified eleven unique genomic regions associated with virulence. The majority of these genomic regions were located on Ptt chromosomes 3 and 5. Four of the regions identified were confirmed via bi-parental quantitative trait loci mapping analysis in two different Ptt/Ptt populations. Knowledge of the virulence genes present in the Australian Ptt pathogen population will provide barley breeding programs with valuable information for future breeding of Ptt resistant barley varieties

Advances in understanding the epidemiology, molecular biology and control of net blotch and the net blotch barley interaction

Net blotches are the most widely distributed foliar diseases of barley worldwide, causing significant losses in grain yield. They occur as net form net blotch, caused by Pyrenophora teres f. teres and spot form net blotch caused by P. teres f. maculata. Both sexual and asexual reproduction play a role in the P. teres disease cycles leading to changes in genetic variation of populations. Breeding programs have to keep pace with pathogenic changes and ensure different sources of resistance are present in current barley cultivars. Knowledge of the genetic architecture and genes involved in virulence is thus vital to increase the durability of net blotch resistance in barley cultivars. This chapter explores the molecular biology, life-cycle and epidemiology of the net blotch fungi and discusses the key challenges we are facing in managing the net blotches using both fungicide resistance and breeding strategies to achieve durable disease resistance in barley

Advances in understanding the epidemiology, molecular biology and control of net blotch and the net blotch barley interaction

Net blotches are the most widely distributed foliar diseases of barley worldwide, causing significant losses in grain yield. They occur as net form net blotch, caused by Pyrenophora teres f. teres and spot form net blotch caused by P. teres f. maculata. Both sexual and asexual reproduction play a role in the P. teres disease cycles leading to changes in genetic variation of populations. Breeding programs have to keep pace with pathogenic changes and ensure different sources of resistance are present in current barley cultivars. Knowledge of the genetic architecture and genes involved in virulence is thus vital to increase the durability of net blotch resistance in barley cultivars. This chapter explores the molecular biology, life-cycle and epidemiology of the net blotch fungi and discusses the key challenges we are facing in managing the net blotches using both fungicide resistance and breeding strategies to achieve durable disease resistance in barley