The branched-chain amino acid aminotransferase TaBCAT1 modulates amino acid metabolism and positively regulates wheat rust susceptibility

Plant pathogens suppress defense responses to evade recognition and promote successful colonization. Although identifying the genes essential for pathogen ingress has traditionally relied on screening mutant populations, the post-genomic era provides an opportunity to develop novel approaches that accelerate identification. Here, RNA-seq analysis of 68 pathogen-infected bread wheat (Triticum aestivum) varieties, including three (Oakley, Solstice and Santiago) with variable levels of susceptibility, uncovered a branched-chain amino acid aminotransferase (termed TaBCAT1) as a positive regulator of wheat rust susceptibility. We show that TaBCAT1 is required for yellow and stem rust infection and likely functions in branched-chain amino acid (BCAA) metabolism, as TaBCAT1 disruption mutants had elevated BCAA levels. TaBCAT1 mutants also exhibited increased levels of salicylic acid (SA) and enhanced expression of associated defense genes, indicating that BCAA regulation, via TaBCAT1, has a key role in SA-dependent defense activation. We also identified an association between the levels of BCAAs and resistance to yellow rust infection in wheat. These findings provide insight into SA-mediated defense responses in wheat and highlight the role of BCAA metabolism in the defense response. Furthermore, TaBCAT1 could be manipulated to potentially provide resistance to two of the most economically damaging diseases of wheat worldwide.

Preserving Spring Oat Yields in New York Through Varietal Resistance to Crown Rust

Crown rust is the principal disease of spring oat in New York. Management with resistance genes is effective but contingent on understanding varietal responses to local pathogen populations. Field studies were conducted from 2015 to 2018 to assess the crown rust susceptibility of commercial cultivars and public breeding lines under natural conditions in New York. Three of the 10 commercial varieties trialed were determined to be resistant, and breeding lines from five different states also exhibited resistance. On average, yield was reduced by 34.56 kg/ha for every 1% increase in crown rust severity, whereas the impact on test weight was negligible. A race differential panel was deployed in 2018 at a central screening nursery to determine the range of pathogen virulence present. Susceptible interactions were observed on only five crown rust differentials, and virulence on all five has been recorded at high levels across the country. Crown rust may be a limiting factor to oat production in New York, but yield potential and crop value can be preserved by planting an appropriately resistant variety.

Susceptibility of Winter Wheat and Triticale to Yellow Rust Influenced by Complex Interactions between Vernalisation, Temperature, Plant Growth Stage and Pathogen Race

Environmental factors influence the disease susceptibility of crop plants. In this study, we established an experimental system to investigate the effects of vernalisation, temperature and plant growth stage on the susceptibility of winter wheat and winter triticale to Puccinia striiformis, the causal agent of yellow (stripe) rust. Two temperature regimes: standard (18 °C day/12 °C night) and low (12 °C day/6 °C night), vernalised and non-vernalised seedlings, vernalised adult plants and two pathogen races were investigated. At low temperatures, vernalisation reduced the susceptibility of seedlings exposed to the ‘Warrior’ race, while this was only the case for five out of eight varieties exposed to the ‘Kranich’ race. Changing from standard to low temperature resulted in increased susceptibility of non-vernalised seedlings of seven varieties inoculated with the ‘Warrior’ race and five varieties inoculated with the ‘Kranich’ race. Increased susceptibility at low temperature was also detected for several varieties at the adult plant growth stage. Comparisons between vernalised seedlings and adult plants revealed an effect of plant growth stage on disease susceptibility (e.g., Adult Plant Resistance) in five varieties at standard temperature for the ‘Warrior’ race and in five and four varieties at standard and low temperature respectively, for the ‘Kranich’ race. The complex and unpredictable interactions between environment and pathogen influencing yellow rust susceptibility of individual varieties stress the importance of phenotyping for disease resistance under different environmental conditions and pathogen populations. The environmental impact on rust susceptibility should also be taken into account in early-warning systems targeting wheat and triticale breeding programmes and growers.

Variability in leaf rust susceptibility among peach cultivars

The aim of this work was to estimate the susceptibility of thirty-six peach cultivars to leaf rust caused by Tranzschelia discolor f. sp. persica. The incidence and severity of the disease as well as defoliation in peach trees of an experimental orchard of Parana Federal University of Technology, Campus Dois Vizinhos were evaluated on the growing seasons 2004/2005 and 2005/2006. Immunity to this disease was not observed in the studied cultivars. There was difference in leaf rust intensity depending on the growing season conditions. Cultivars 'Pilcha', 'Sinuelo', 'Chirua', 'Sulina', 'Eldorado' and 'Pampeano' showed tolerance to leaf rust, whereas cultivars 'Vila Nova', 'Fla 1372', 'Coral 2', 'Chimarrita', 'Della Nona', 'BR-1 ' and 'Guaiaca' showed high susceptibility.

The effect of endophyte on the performance of irrigated perennial ryegrasses in subtropical Australia

The effect of fungal endophyte (Neotyphodium lolii) infection on the performance of perennial ryegrass (Lolium perenne) growing under irrigation in a subtropical environment was investigated. Seed of 4 cultivars, infected with standard (common toxic or wild-type) endophyte or the novel endophyte AR1, or free of endophyte (Nil), was sown in pure swards, which were fertilised with 50 kg N/ha.month. Seasonal and total yield, persistence, and rust susceptibility were assessed over 3 years, along with details of the presence of endophyte and alkaloids in plant shoots. Endophyte occurrence in tillers in both the standard and AR1 treatments was above 95% for Bronsyn and Impact throughout and rose to that level in Samson by the end of the second year. Meridian AR1 only reached 93% while, in the standard treatment, the endophyte had mostly died before sowing. Nil endophyte treatments carried an average of ~0.6% infection throughout. Infection of the standard endophyte was associated with increased dry matter (DM) yields in all 3 years compared with no endophyte. AR1 also significantly increased yields in the second and third years. Over the full 3 years, standard and AR1 increased yields by 18% and 11%, respectively. Infection with both endophytes was associated with increased yields in all 4 seasons, the effects increasing in intensity over time. There was 27% better persistence in standard infected plants compared with Nil at the end of the first year, increasing to 198% by the end of the experiment, while for AR1 the improvements were 20 and 134%, respectively. The effect of endophyte on crown rust (Puccinia coronata) infection was inconsistent, with endophyte increasing rust damage on one occasion and reducing it on another. Cultivar differences in rust infection were greater than endophyte effects. Plants infected with the AR1 endophyte had no detectable ergovaline or lolitrem B in leaf, pseudostem, or dead tissue. In standard infected plants, ergovaline and lolitrem B were highest in pseudostem and considerably lower in leaf. Dead tissue had very low or no detectable ergovaline but high lolitrem B concentrations. Peramine concentration was high and at similar levels in leaf and pseudostem, but not detectable in dead material. Concentration was similar in both AR1 and standard infected plants. Endophyte presence appeared to have a similar effect in the subtropics as has been demonstrated in temperate areas, in terms of improving yields and persistence and increasing tolerance of plants to stress factors.

Susceptibility of Pinus contorta - Pinus banksiana complex to Endocronartium harknessii: host-pathogen interactions

Lodgepole (Pinus contorta Dougl. ex Lound.) and jack (Pinus banksiana Lamb.) pines occur sympatrically and hybridize in central and northwestern Alberta, providing opportunities for studying unique ecological and evolutionary interactions. We conducted a greenhouse inoculation experiment to investigate interactions between 40 populations of lodgepole and jack pines and their putative hybrids across this hybrid zone and two sources of the western gall rust fungus, Endocronartium harknessii (J.P. Moore) Y. Hiratsuka, one from lodgepole pine and the other from jack pine. Rust susceptibility and height were assessed when the seedlings were 6 months and 1 year old. Lodgepole pine and the hybrids were significantly more susceptible to the rust infection than jack pine. Jack pine grew significantly faster than the hybrids and lodgepole pine. In addition, the seedlings infected with spores from lodgepole pine grew significantly slower than those with spores from jack pine. While the overall rust scores indicated that spores from lodgepole pine was more virulent to the hosts than those from jack pine, both spore sources were better adapted to their own host species, causing significant spore source × host group interactions. However, such host specificity in the western gall rust is far from stabilized (equilibrium) because of continued gene exchanges among the two parental species and their hybrids.Key words: Pinus contorta - Pinus banksiana complex, western gall rust, natural hybridization, coevolutionary genetics.

Perennial ryegrass endophytes in Galicia, Northwest Spain

Fifty-six half-sib families of perennial ryegrass (Lolium perenne), derived from wild populations in Galicia, were examined for the presence of perennial ryegrass endophytes; 28 were endophyte-infected (E+) and 28 were endophyte-free (E−). All families were established in spaced-plant nurseries and trial plots at two locations in Galicia, in 1992. E+ families had a significantly (P<0·05) higher first cut, spring and total yield than E− families at one location in the third year after planting. At this location, water deficit was about 75% higher than at the other location in all three years of study. Endophyte did not affect crown rust susceptibility or forage quality (crude protein, water-soluble carbohydrate and in vitro digestibility). Ergovaline alkaloid concentration in the 28 E+ families varied from 0 to 0·55 μg/g dry matter (DM) (mean 0·15), with 14 families containing levels of ergovaline >0·1 μg/g DM. Thus endophyte infection may benefit the host in drought-prone areas of Galicia, with an increased chance of E+ plants being favoured by either natural or artificial selection.