Anecdotal evidence identified a change in the reaction of the resistant lentil cv Nipper to ascochyta blight in South Australia in 2010 and subsequent seasons, leading to infection. This study investigated field reactions of lentil cultivars against Ascochyta lentis and the pathogenic variability of the A. lentis population in southern Australia on commonly grown cultivars and on parental germplasm used in the Australian lentil breeding program. Disease data recorded in agronomic and plant breeder field trials from 2005 to 2014 in southern Australia confirmed the change in reaction on the foliage of the previously resistant cvs Nipper and Northfield. Cultivar responses to seed staining from A. lentis did not change. The change in foliar response was confirmed in a series of controlled environment experiments using single, conidium-derived, isolates of A. lentis collected over different years and inoculated onto differential host sets. Specific isolate/cultivar interactions produced a significant range of disease reactions from high to low aggressiveness with a greater percentage of isolates more aggressive on cvs Nipper, Northfield and PBA Flash than previously detected. Specific isolates were tested against Australian lentil cultivars and breeding lines in controlled conditions, again verifying the aggressiveness on cv Nipper. A small percentage of isolates collected prior to the commercial release of cv Nipper were also able to infect this cultivar indicating a natural variability of the A. lentis population which subsequently may have been selected in response to high cropping intensity of cv Nipper. Spore release studies from naturally infested lentil stubbles collected from commercial crops also resulted in a high percentage of infection on the previously resistant cvs Nipper and Northfield. Less than 10% of the lesions developed on the resistant differentials ILL7537 and cv Indianhead. Pathogenic variation within the seasonal populations was not affected by the cultivar from which the stubble was sourced, further indicating a natural variability in aggressiveness. The impact of dominant cultivars in cropping systems and loss of effective disease resistance is discussed. Future studies are needed to determine if levels of aggressiveness among A. lentis isolates are increasing against a range of elite cultivars.
Yield loss caused by root lesion nematodes (Pratylenchus neglectus and P. thornei) was measured using the nematicide aldicarb (Temik 150GTM) or by correlating yield with initial or final nematode densities. In 1996, rotation trials (1 P. neglectus and 1 P. thornei) were established with susceptible and moderately resistant wheat varieties and resistant barley and triticale varieties. An intolerant oat variety (cv. Echidna) was planted over all plots in 1997. Nematode densities were 90% (P. neglectus) or 95% (P. thornei) lower in oat plots following the resistant triticale (cv. Tahara) relative to the susceptible wheat (cv. Machete). In 1997, a significant, negative correlation between both initial and final nematode density and yield was obtained. In wheat variety trials (3 sites) in 1997, a significant, negative correlation was also obtained between mean variety yield and mean final P. neglectus density or mean P. neglectus multiplication rate. Yield loss of up to 20% was calculated from the regression. In all trials, cereal varieties that were more resistant were also more tolerant. In 1996, aldicarb rate trials (1 P. neglectus and 1 P. thornei) were established to assess the affect of rate and timing of aldicarb application on yield of 2 susceptible/intolerant wheat varieties (cvv. Machete and Janz). Lower rates of aldicarb (≤1.5 kg a.i./ha) gave inconsistent nematode control and did not significantly increase yield. Rates ≥2.5 kg a.i./ha reduced nematode densities by 70–90%, resulting in up to 23% greater yield for Machete. The magnitude of yield loss caused by P. neglectus or P. thornei determined with or without nematicide was similar between trials.
Proceedings of the Institution of Civil EngineersCivil Engineering 169 February 2016 Issue CE1 Pages 25-33 http://dx.doi.org/10.1680/jcien.15.00027 Paper 1500027 Received 24
Ascochyta fabae Speg. is a serious foliar fungal disease of faba bean and a constraint to production worldwide. This study investigated the phenotypic and genotypic diversity of the A. fabae pathogen population in southern Australia and the pathogenic variability of the population was examined on a differential set of faba bean cultivars. The host set was inoculated with 154 A. fabae isolates collected from 2015 to 2018 and a range of disease reactions from high to low aggressiveness was observed. Eighty percent of isolates collected from 2015 to 2018 were categorized as pathogenicity group (PG) PG-2 (pathogenic on Farah) and were detected in every region in each year of collection. Four percent of isolates were non-pathogenic on Farah and designated as PG-1. A small group of isolates (16%) were pathogenic on the most resistant differential cultivars, PBA Samira or Nura, and these isolates were designated PG-3. Mating types of 311 isolates collected between 1991 and 2018 were determined and showed an equal ratio of MAT1–1 and MAT1–2 in the southern Australian population. The genetic diversity and population structure of 305 isolates were examined using DArTseq genotyping, and results suggest no association of genotype with any of the population descriptors viz.: collection year, region, host cultivar, mating type, or PG. A Genome-Wide Association Study (GWAS) was performed to assess genetic association with pathogenicity traits and a significant trait-associated genomic locus for disease in Farah AR and PBA Zahra, and PG was revealed. The high frequency of mating of A. fabae indicated by the wide distribution of the two mating types means changes to virulence genes would be quickly distributed to other genotypes. Continued monitoring of the A. fabae pathogen population through pathogenicity testing will be important to identify any increases in aggressiveness or emergence of novel PGs. GWAS and future genetic studies using biparental mating populations could be useful for identifying virulence genes responsible for the observed changes in pathogenicity.
We report the incidence of anthracnose caused by Colletotrichum trifolii on Cullen australasicum, a native Australian legume. Natural infection was observed on plants grown in a genetic resources characterisation experiment at Waite Research Precinct, Adelaide. The affected plants showed wilting of the branches and light brown lesions on the leaves. The characteristic symptom was a bluish black discolouration on the infected leaves and stems. In some plants, the infection spread from the leaves and stems across the entire plant leading to the death of the plant. Fig. 1. Wilting of stems observed on Cullen australasicum plants at the
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