Linking yield loss from cereal foliar diseases with NVT resistance ratings

Take home messages

• Barley varieties differ in yield loss response to net form net blotch (NFNB) across resistance ratings.
• The most significant yield losses were incurred in varieties rated susceptible (S) to very susceptible (VS).
• Varieties at the susceptible end of the rating scale contribute to inoculum pressure and increase the risk of breakdown of resistance in other varieties.
• Results from yield response curve trials assist in validating National Variety Trial (NVT) disease resistance ratings by combining losses in yield and quality.

Background and aim

Australian barley (Hordeum vulgare) and wheat (Triticum aestivum) varieties are categorised into 9 resistance categories through the National Variety Trial (NVT) disease screening process. The resistance ratings are assigned by the pathologists’ working group collating data from national disease nurseries conducted annually. These categories range from resistant (R) to very susceptible (VS) and are communicated to industry via the NVT website, field days and industry presentations.

The aim of a GRDC funded project ‘Yield loss response curves for host resistance to leaf, crown and root diseases in wheat and barley‘ (DAW00245) is to determine yield losses in varieties with different levels of resistance under increasing levels of disease for a range of wheat and barley pathogens.

Yield response curve (YRC) experiments were conducted over a 4 year period (2014 to 2017) at the Hermitage Research Facility in Warwick, Queensland, to determine the yield and quality loss resulting from net form of net blotch (NFNB) (Pyrenophora teres f. teres) infection. Experiments consisted of 6 barley varieties with resistance levels ranging from moderately resistant to moderately susceptible (MRMS) to very susceptible (VS) to a specific pathotype of NFNB. Variety selection was based on resistance rating, maturity and ideally resistance to non-target diseases.

These varieties were evaluated for disease and quality losses at 5 different disease levels ranging between nil disease (fungicide protected) and an inoculated high disease treatment with no fungicide application. Across years, some varietal changes were made between experiments in an effort to minimise the impact of maturity on disease development and utilise varieties that best fit the resistance categories. Disease levels were manipulated by initial application of different levels of inoculum using diseased straw and fungicide applications when deemed necessary. Nil disease treatments received 3-4 fungicide applications, aimed at keeping these experimental plots disease free.

Results

For the purpose of this paper, only data from the trials conducted between 2014 and 2016 will be presented, with some reference to the 2017 trial; the reason being that 2017 was a particularly dry year in south-east Queensland, thus impacting the successful establishment of epidemics in the trials.

The main factors contributing to disease development in a variety are the inherent resistance/susceptibility of the variety, the severity and duration of the epidemic and environmental conditions in which the experiment was conducted. There were substantial differences in the environmental conditions between years in which these experiments were conducted, particularly in terms of rainfall, with the 2016 experiment receiving higher than average rainfall, particularly during the period conducive to disease development (Aug to Oct).

Three varieties, Compass, Fairview and Charger were included in all trials from 2014 to 2016. Yield losses were calculated as the difference between yield of the nil disease treatment (yield potential) and the individual disease treatments. The highest yield losses across treatments were recorded in the variety Charger (rated VS) (Figure 1).

Figure 1. Yield (t/ha) of barley varieties under different levels of infection by Pyrenophora teres f. teres (NFNB) between 2014 and 2016

The percentage yield loss in Charger between the nil disease and the high disease treatments ranged between 24.7% in 2015 and in excess of 40% in both 2014 and 2016. Yield losses of between 16.5% and 20.8% were observed in the variety Fairview (S), whereas in the variety Compass, the most resistant variety included in the experiments (rated MRMS), the yield losses measured were considerably less than those of the more susceptible varieties (14.9% (2014), 9.5% (2015) and 18.6% (2016)). Compass is resistant to the NFNB pathotype used in this study at the adult plant stage, but is rated VS at the seedling stage. Apart from yield loss resulting from early NFNB infection, yield losses observed in Compass could also be partially attributed to leaf rust infection (caused by Puccinia hordei), with the variety rated VS to the disease and suffering severe yield losses (28.8% and 45.6% as presented at the Dubbo GRDC Update 2017). In an attempt to limit the impact of non-target pathogens, especially leaf rust, on yield and quality, Compass was omitted from the 2017 experiment.

In general, disease had a lesser impact on the grain quality of varieties, with the biggest differences observed in the levels of seed retention (% of seed >2.5mm) (Figure 2). The limited differences in retention witnessed between disease levels in 2015 can be attributed to the lower epidemic levels established during the season. The largest differences were observed in Charger (VS) across years, whereas the different disease levels had almost no impact on retention in Compass (MRMS) across years.

Figure 2. Retention levels (% of seed >2.5mm) of barley varieties to different levels of infection by Pyrenophora teres f. teres (NFNB) between 2014 and 2016

The environment was less favourable for disease development in 2017 due to mostly dry and windy conditions. Supplementary sprinkler irrigation at dusk was used to promote epidemics in these experiments, however, disease development was slower than in previous years and did not reach the same levels of infection. Yield losses observed ranged between 19.7% and 28.3% with no significant interaction between variety and epidemic (Figure 3). Oxford (MS) suffered comparable yield losses to Topstart (SVS) and Charger (VS). This was contrary to results seen in 2015, where limited yield loss was observed in Oxford. Oxford is a later maturing variety, but this trait is not expected to have a big impact on disease development and should be investigated further.

Figure 3. Yield (t/ha) of barley varieties under different levels of infection by Pyrenophora teres f. teres (NFNB) in 2017

Discussion

Results from this set of experiments conducted across seasons indicate greater yield losses to NFNB in more susceptible varieties; particularly varieties rated VS compared to varieties on the resistant end of the rating scale. Varieties selected in 2017 were intentionally targeted at the susceptible end of the resistance spectrum. Results from the earlier experiments indicated that varieties with a low level of resistance (Moderately susceptible to susceptible; MSS) to NFNB did not appear to suffer much yield loss.

These experiments assist in the validation of NVT disease resistance ratings, by combining yield and quality loss information with disease severity data. In general, the yield losses observed for varieties were consistent with their resistance category.

By conducting yield response curve experiments across seasons, the impact of environmental variation of the yield and quality losses incurred by varieties under varying NFNB epidemics can be investigated. By exploring this environmental variation, industry is better equipped to make varietal selection and management decisions to maximise returns in the presence of NFNB.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the author would like to thank them for their continued support.

The authors would like to thank the technical - and farm staff at Hermitage and Leslie Research Facilities for their assistance.

Contact details

Lislé Snyman
DAF QLD
Hermitage Research Facility, 604 Yangan Rd, Warwick, Qld
(07) 4542 6761
lisle.snyman@daf.qld.gov.au

Greg Platz
DAF QLD
Hermitage Research Facility, 604 Yangan Rd, Warwick, Qld
(07) 4542 6733
greg.platz@daf.qld.gov.au

Clayton Forknall
DAF QLD
Leslie Research Facility, 13 Holberton St, Toowoomba, Qld
(07) 4529 1218
clayton.forknall@daf.qld.gov.au

Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994