Spot-type Net Blotch Research Articles

Increasing applications of potassium fertiliser to barley crops grown on deficient sandy soils increased grain yields while decreasing some foliar diseases

Most sandy soils used for cropping in south-western Australia (SWA) have now become potassium (K) deficient due to removal of K in hay and grain, so it is now profitable to apply K fertiliser to most barley (Hordeum vulgare L.) crops in the region. Leaf diseases of barley crops in the region have increased in recent years particularly in the in medium to high (350–600 mm annual average rainfall) areas of SWA. Seventeen field experiments were undertaken to determine the effect of applications of K fertiliser, either the chloride (KCl) or sulfate source (K2SO4), on grain yield increases and on the percentage leaf area diseased (%LAD) when diseases were controlled or not controlled by fungicide sprays. Maximum grain yield of barley was achieved where adequate K fertiliser (~8–22 kg K/ha) was applied and leaf diseases were controlled by fungicide. Applying increasing amounts of applied K fertiliser (0–120 kg K/ha) to barley decreased the %LAD by powdery mildew (Blumeria graminis f. sp. hordei Syn.) and spot-type net blotch (Pyrenophora teres f. maculata (Sacc.) Shoem.) and increased grain yield. By contrast, when leaf rust (Puccinia hordei G. Otth) was present the %LAD was unaffected by K application. When powdery mildew was the major disease, larger increases in grain yields and larger reductions in %LAD were obtained when KCl was used instead of K2SO4. About twice as much K fertiliser as K2SO4 was required for 90% maximum grain yield compared with KCl where powdery mildew was present. Applying larger amounts (>40 kg K/ha) of K fertiliser than required to achieve maximum grain yields did not further reduce %LAD by powdery mildew. There were no significant differences between the 2 sources of K fertiliser on the %LAD by spot-type net blotch. Generally, the percentage protein content and hectolitre weight of grain were unaffected by K fertiliser. Potassium fertiliser decreased the percentage grain < 2.5 mm (known locally as screenings) and control of the foliar leaf diseases by applications of fungicide resulted in a decrease in protein content and screenings and increased hectolitre weight of barley grain. The concentration of K in dried shoots that was related to 90% of the maximum shoot yield (critical diagnostic K) decreased as the plant matured, and was ~41 g/kg at Z22, ~30 g/kg at Z32, ~20 g/kg at Z40, and ~15 g/kg at Z59. The concentration of K in dried shoots which was related to 90% of the grain yield (critical prognostic K) decreased as plant matured, and was similar to critical diagnostic K values. Leaf disease had little effect on critical concentrations of K at early growth stages (Z22 and Z32).

Yield reduction in barley in relation to spot-type net blotch

To study the loss of grain yield associated with specific levels of spot-type net blotch of barley, experiments were conducted at three sites with between four and six different levels of application of the fungicide propiconazole or mixtures of propiconazole and iprodione applied to obtain a wide range of disease levels. Yield loss varied from 23 to 44%. There was a negative linear relationship between yield and the average disease severity on the top three leaves (flag, flag-1 and flag-2). The observed relationship was much stronger at the milk stage compared with early flag leaf emergence stage. On average, every 10% increase in disease severity on the top three leaves accounted for 0.4 t/ha yield loss. The yield response to disease was independent of locations and years. The disease affected grain quality, with grain protein and screenings consistently higher and grain size consistently lower than samples from undiseased barley.

Identification and chromosomal location of major genes for resistance toPyrenophorateresin a doubled-haploid barley population

Net blotch, caused by Pyrenophora teres, is one of the most economically important diseases of barley worldwide. Here, we used a barley doubled-haploid population derived from the lines SM89010 and Q21861 to identify major quantitative trait loci (QTLs) associated with seedling resistance to P. teres f. teres (net-type net blotch (NTNB)) and P. teres f. maculata (spot-type net blotch (STNB)). A map consisting of simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers was used to identify chromosome locations of resistance loci. Major QTLs for NTNB and STNB resistance were located on chromosomes 6H and 4H, respectively. The 6H locus (NTNB) accounted for as much as 89% of the disease variation, whereas the 4H locus (STNB resistance) accounted for 64%. The markers closely linked to the resistance gene loci will be useful for marker-assisted selection.

Incidence of Boron Toxicity in Spring Barley in Southwestern Australia

One hundred and four crops of spring barley (Hordeum vulgare L. cv. Stirling) grown throughout southwestern Australia (WA) were surveyed for symptoms of boron (B) toxicity. Symptoms were identified as B toxicity and not spot-type net blotch, a foliar disease, caused by the fungus Pyrenohora teres f. spp. maculata that produces similar leaf symptoms. Symptoms of B toxicity occurred in 43 crops (about 40% of the surveyed crops) that were widely distributed in the <350 to 450 mm annual average rainfall zones of WA, on duplex soils with alkaline and fine-textured subsoils that were non-saline but sodic. Concentrations of mannitol-extractable B in sub-soils varied widely between 0.7 and 130 mg B/kg soil. Soil B concentrations measured in either mannitol or hot CaCl2 increased with soil depth and were highest where soil pH values were >8 (1:5 soil:0.01 M CaCl2, w/v). Concentrations of B in whole shoots (WS) were positively correlated with concentrations of hot CaCl2-extractable and mannitol-extractable soil B. The positive linear relationship between B concentration in WS and extractable-B in either mannitol or hot CaCl2 improved (R 2 value increased) with increasing soil depth, particularly in the 50 to 80 cm layer. Concentrations of B in the WS of barley plants with symptoms of B toxicity were found to vary between 4 and 76 mg B/kg dried WS. An additional study showed that symptoms of B toxicity developed in the later stages of Stirling barley growth [boot stage (GS 40) to maturity (GS 70)] grown on duplex soils with high concentrations of mannitol-extractable B in the sub-soils >30 cm from the soil surface. As toxic concentration of B occurred at late stages of Stirling barley development, reductions in grain yield resulting from B toxicity were small (up to 10%).

First record of the teleomorph stage of Drechslera teres f. maculata in Australia

Pseudothecia carrying asci with mature ascospores of Drechslera teres f. maculata were isolated from barley stubble from the southern part of Western Australia. Inoculation experiments were able to produce typical spot-type net blotch symptoms on the barley cultivar Gairdner. This is the first confirmed report of this teleomorph in Australia.

Evaluation of fungicides in control of spot-type net blotch on barley

Ten fungicides ( pyraclostrobin, tebuconazole, flutriafol, epoxiconazole, propiconazole, triadimefon, azoxystrobin, trifloxystrobin, difenoconazole and a mixture of propiconazole with iprodione) were evaluated as single applications for control of spot-type net blotch of barley caused by Drechslera teres f. maculata at three locations during 1999 and 2000. Under moderate disease severity, yield losses ranged from 17–19 per cent depending on location and under high disease severity, yield losses reached 32 per cent. Pyraclostrobin, propiconazole and a mixture of propiconazole with iprodione were the most effective in controlling disease, improving yield and grain quality. These fungicides show most promise as commercial treatments when yield and quality are taken into account. Azoxystrobin, trifloxystrobin, difenoconazole and epoxiconazole also provided disease control.

DNA homology between Pyrenophora japonica and P. teres

Pyrenophora isolates associated with net- and spot-type net blotch of barley were compared with verified isolates of P. teres f. teres, P. teres f. maculata and P. japonica using total DNA banding patterns, morphology, symptomatology and mating studies. DNA of South African and overseas spot- and net-type isolates digested with Hae III and Msp I showed 74–100 % similarity. Furthermore, spot- and net-type isolates could be mated to produce viable progeny, indicating P. teres to have two-allele heterothallism. Single-ascospores inoculated on differential barley cultivars produced spot, net or mixed symptoms, suggesting that recombination has occurred. Based on the high degree of homology in DNA banding patterns between P. japonica and P. teres f. maculata , as well as similarities in symptom expression on differential cultivars and general morphology, P. japonica is proposed as synonym of P. teres .

Assessment of resistance in barley to Pyrenophora teres and Pyrenophora japonica

Nine barley cultivars (cvs) were evaluated for their reactions to two leaf spot fungi, Pyrenophora teres and Pyrenophora japonica. The type of lesions occurring on headed plants after inoculation was a reliable indicator of susceptibility or resistance of cvs to net blotch and spot-type net blotch in the field. Adult-plant resistance to isolates of P. teres occurred in some Australian, European and American cvs used for malt production. No lesions or only small spots without chlorotic halos developed on headed plants of resistant cvs. Cultivars susceptible to P. teres showed typical net-blotch lesions, having dark-brown striations extending both longitudinally and transversely within the lesions. In the case of spot-type net blotch, lesions varied from dark-brown spots to solid stripes, spreading longitudinally between leaf veins. Most cvs showed an intermediary reaction to P. japonica, and only one cv. was very susceptible to this fungus.

Effect of propiconazole on necrotrophic fungi and yield of barley genotypes differing in susceptibility to Rhynchosporium secalis

Propiconazole was applied to various barley genotypes in field experiments conducted in the barley-growing areas of the Western Cape Province in South Africa during 1989 and 1990. Rhynchosporium secalis was the pathogen noticed most frequently in both years, reaching infection levels of > 60% at the late milk grain stage in unsprayed plots of Clipper and Stirling. In 1989 leaf blotch was reduced and yield was increased significantly in Stirling with one spray of propiconazole at flag-leaf emergence. In 1990 yield increased significantly in both cultivars when two sprays were applied, one at formation of the first node on the main tiller and the second one at flag-leaf emergence. The yield components affected by R. secalis were kernel weight and kernel size. In 1989 spray treatments also increased yields in one genotype resistant to leaf blotch, but susceptible to spot-type net blotch. Common net blotch could be controlled with one spray and spot-type net blotch with two sprays, but control of these two diseases was not clearly related to yield responses in Rhynchosporium-resistant genotypes. Other factors associated with yield increases caused by propiconazole in the absence of recognized foliar diseases are discussed.

EFFECT OF TILT ON SEVERITY OF SPOT-TYPE NET BLOTCH, GRAIN YIELD AND YIELD COMPONENTS IN BARLEY

Spot-type net blotch, incited by Pyrenophora teres f. maculata has become widespread in Saskatchewan. This study was conducted to evaluate the effect of the fungicide Tilt (propiconazole) on the severity of spot-type net blotch, grain yield and yield components in spring barley. The susceptible cultivar Elrose was subjected to five schedules of foliar application of Tilt at Medstead, Shellbrook and Saskatoon, Saskatchewan in 1985 and 1986. The moderately susceptible cultivar Argyle was included in the experiments conducted in 1986. Results show that Tilt controlled spot-type net blotch in Elrose. However, the effective period was limited. A single application did not control spot-type net blotch in cases with rapid disease development. Application of Tilt at Zadoks growth stages 31 and 49 would be required to provide reliable control in a susceptible cultivar. Control of spot-type net blotch increased grain yield. A single application of Tilt increased grain yield up to 23% over the untreated control. In most cases, a double application of Tilt did not increase grain yield over a timely single application. Increased grain yield was associated with increased kernel weight. The correlation coefficient between grain yield and kernel weight ranged from 0.82 to 0.88. Tilt had no effect on a healthy crop of Elrose and the moderately susceptible cultivar Argyle.Key words: Pyrenophora teres f. maculata, Hordeum vulgare L., propiconazole, barley

Effect of spot-type net blotch (Drechslera teres (Sacc.) Shoem) infection on barley yield in short season environment of northern cereal belt of Western Australia

The effect of spot-type net blotch (Drechslera teres (Sacc.) Shoem.) on yield was studied in fourteen field experiments located at two sites over seven years in the area where the disease occurs; the northern cereal belt of south-west Western Australia. An overall reduction of 26% in grain yield occurred associated with spot-type net blotch infection. The yield losses varied depending upon season, date of sowing and cultivar. Disease was found to reduce 100 grain weight and number of ears/m2, but number of grains/ear were not affected. Regression analysis supported the above negative effect of disease on yield in general, but in a few cases disease and yield were positively correlated. The Area Under Curve (AUC) model was considered most appropriate and percentage yield loss (L) was estimated as L = 0.0233 AUC. Using this relationship, potential losses in yields of cvv. Beeeher and O'Connor were estimated to be 34% and 29%, respectively. The application of this relationship is suggested to be limited to short season environments similar to the northern cereal belt of Western Australia. A need to understand factors which modify the yield response to this disease is highlighted.