The pulse health report - 2019 pulse disease seasonal update and National Variety Trial (NVT) disease ratings

Take home messages

• SARDI testing in 2019 found some Ascochyta fabae isolates aggressive on PBA Samira faba bean; potentially this is a third pathotype. However, the majority of reports of high levels of Ascochyta blight (AB) in PBA Samira were due to on-farm retained seed which has outcrossed in previous seasons. At this stage resistance ratings to AB for faba bean cultivars have not changed, but reactions on PBA Samira require ongoing monitoring.
• The new faba bean cultivar PBA Amberley has a high level of resistance to AB and has a provisional rating of moderately resistant (MR) to chocolate spot.
• Severe lentil AB infections were seen in PBA Hurricane XT crops and volunteer plants early in the 2019 season on Yorke Peninsula and in the Mid North region indicating that the moderately resistant -moderately susceptible (MRMS) rating in this cultivar may need to be downgraded in future seasons. The source of resistance in both PBA Hurricane XT and PBA Hallmark XT is now compromised, so monitor closely for infection and manage as if there is a potentially higher risk of AB.
• The new lentil cultivar PBA Highland XT has a high level of resistance to AB and is rated MRMS to botrytis grey mould (BGM).
• AB was common in chickpea crops despite the drier than average season. This confirms all chickpea crops must be protected against the disease early in the season using a thiram-based seed dressing and foliar fungicide sprays timed ahead of rain.
• The new chickpea cultivar PBA Royal has a provisional rating of moderately susceptible (MS) to AB.
• Cercospora leaf spot (CLS) was widespread across South Australia (SA) in faba bean crops early in the 2019 growing season. A trial at Bool Lagoon confirmed that a tebuconazole foliar spray timed with the grass spray is most effective at controlling CLS, even after the disease has established.
• Bacterial blight (BB) affected some field pea crops following severe frost in spring. There are no chemical treatments to control this disease. Avoid sowing field peas in frost prone paddocks, or, in these paddocks, sow PBA Oura, PBA Percy or PBA Butler which are less susceptible to BB. Consider removing stubble before sowing to reduce the frost risk.

2019 pulse disease seasonal update

The dry conditions in 2019 resulted in reduced disease levels in pulse crops although early observations of severe AB were seen on lentil and chickpea crops and volunteers. In addition, CLS was widespread in seedling faba bean crops across SA.

Chickpea

Ascochyta blight (AB)

In 2019, early reports of AB infection in Genesis090 chickpea crops, as well as volunteer plants, were received from the upper Yorke Peninsula and Lower North regions of SA. Despite the dry season, there were still reports of heavy infection occurring in some commercial crops and field trials in those regions following rain events, especially where planned fungicide sprays had been mistimed. This confirms the importance of monitoring crops for signs of infection and applying fungicides ahead of rainfall. A thiram-based seed dressing is also essential to prevent seed transmission of AB onto the emerging seedlings in 2020. All current commercial cultivars of chickpea are rated MS or susceptible (S), including PBA Royal which was released in 2019 with a provisional rating of MS to AB.

Lentil

Ascochyta blight (AB)

Early and severe reports of Ascochyta lentis infection in PBA Hurricane XT crops and volunteer plants were reported this season on the Yorke Peninsula and in the Mid North region indicating that its MRMS rating in SA is under threat.

SARDI’s annual testing has confirmed two pathotypes of A. lentis are present in SA; a Nipper-virulent type, and a Hurricane-virulent type. Forty isolates of A. lentis collected in 2018 from lentil field trials and commercial crops (35 from SA, 5 from Victoria (Vic)) were tested in controlled environment conditions in 2019 on a differential host set that included Nipper and PBA Hurricane XT (Table 1). Of the isolates tested, 27 of 40 (67.5%) were capable of infecting PBA Hurricane XT, an increase from 50% in 2018 and 28% in 2016 (Blake et al 2019a, Blake et al 2019b, Blake et al 2017). Indianhead is a source of resistance for the breeding program and the presumed source of resistance in PBA Hurricane XT, however it was infected by 25 of the 40 isolates (62.5%), an increase from 33% in 2018 and 5% in 2016 (Blake et al 2019a, Blake et al 2019b, Blake et al 2017). Hence this source of resistance is now compromised across SA lentil growing regions. The A. lentis pathogen population is naturally variable and these aggressive forms have been selected, over time, in intensive cropping systems.

Table 1. Forty Ascochyta lentis isolates collected in 2018 were inoculated onto a lentil host differential set in controlled environment conditions in 2019. Entries in the table are the number of isolates per category.

Note: R = resistant, MR=moderately resistant, MRMS = moderately resistant-moderately susceptible, MS = moderately susceptible; S = susceptible

In light of the observed reactions on PBA Hurricane XT, growers should regularly inspect both PBA Hurricane XT and PBA Hallmark XT lentil crops to determine if AB infection is severe enough to directly affect yield. PBA Hallmark XT is presumed to have the same source of resistance to AB as PBA Hurricane XT and tests at SARDI (as CIPAL1422) have found that the former is able to be infected by recently collected Hurricane-virulent isolates at a moderate level.

The newly released lentil cultivar, PBA Highland XT, has a provisional rating of MR to foliar AB in SA with resistance to both the Nipper-virulent and Hurricane-virulent AB pathotypes. However this rating may be subject to change when more data becomes available. Growers should monitor for AB and if infection is present, plan to spray ahead of rain fronts at podding to protect the developing seed. The cultivar also has a provisional BGM rating of MRMS, similar to PBA Hurricane XT, PBA Ace and PBA Flash.

Faba bean

Ascochyta blight (AB)

There were numerous reports of mild AB leaf infection in faba bean crops in 2019 that did not cause major problems, as the cool (5-15°C) and wet conditions did not persist in most growing regions. There are no changes to disease ratings for faba bean cultivars for 2020. However, the two pathotypes of A. fabae are found in all the faba bean growing regions in SA and the more aggressive pathotype 2 is now widespread in the South East and on the Eyre Peninsula. Farah is rated S to pathotype 2, while PBA Rana, PBA Zahra and PBA Marne are MRMS to this pathotype. PBA Samira, Nura, the Group B herbicide tolerant PBA Bendoc, and the new release PBA Amberley (tested as AF11023) are all resistant-moderately resistant (RMR) to both pathotypes.

During the 2019 season, reports were received of higher than expected levels of AB on PBA Samira in commercial crops. However in all of these reports, crops had been sown with on-farm retained seed and in many of these cases, the seed crop had been grown next to a faba bean cultivar that is susceptible to pathotype 2 of A. fabae, such as PBA Rana or Farah. Faba beans are open pollinated and this can lead to mixing of genetic material from grower retained seed. These genetic mixtures can lead to perceived changes in the resistance of a cultivar. To minimise the risk of cross-pollination, growers should ensure seed kept for future plantings are isolated from other cultivars by a minimum of 200m.

In 2019, forty isolates of A. fabae collected in 2018 from faba bean field trials and commercial crops (23 from SA, 17 from Vic) were tested in controlled environment conditions on a differential faba bean host set. This host set includes the commercial cultivars PBA Rana and PBA Zahra as well as three Ascochyta resistant (AR) selections viz. Farah AR, Samira AR and Nura AR, which were fixed for AB resistance within the breeding program and known not to be outcrossed. For the first time, results suggest the presence of a possible third pathotype emerging in the A. fabae population that is aggressive on PBA Samira. This is demonstrated by 4 of 40 (10%) isolates that caused a MRMS reaction on Samira AR (Table 2). Continued monitoring will be critical to confirm this shift in the pathogen population.

Table 2. Forty Ascochyta fabae isolates collected in 2018 were inoculated onto a faba bean host differential set in controlled environment conditions in 2019. Entries in the table are the number of isolates per category. AR lines are Ascochyta resistant selections fixed within the breeding program.

Note: R = resistant, MR=moderately resistant, MRMS = moderately resistant-moderately susceptible, MS = moderately susceptible; S = susceptible

Chocolate spot (CS)

PBA Amberley was released in late 2019 with a provisional MR rating to CS making it more resistant than all other current commercial varieties, which are rated MS or S to CS. There were only a few reports of CS in faba and broad bean crops in SA during 2019 mostly in the South East region, late in the season. This included a disease management trial at Bool Lagoon that became infected in late November. This replicated plot trial was sown with the faba bean cultivars, PBA Amberley (tested as AF11023) and PBA Bendoc, and the broad bean cultivar PBA Kareema. Plots received one of four fungicide regimes: (1) ‘nil’, (2) tebuconazole at 145ml/ha (430g/L a.i., Genfarm Blast® 430 Fungicide) with grass spray then carbendazim at 500mL/ha (500g/L a.i., Adama Howzat® SC) at canopy closure and early podding (‘standard’), (3) tebuconazole with grass spray (‘minimum’), or (4) tebuconazole at grass spray and at canopy closure (‘low cost’). PBA Amberley had significantly less disease on pods and leaves compared to PBA Bendoc and PBA Kareema (Table 3a). This infection occurred eight weeks after the last foliar fungicide spray and so the treatments were ineffective except for slightly less disease on pods in the standard treatment compared to untreated plots (Table 3b). It is unlikely that there will be any effect on yield as the infection occurred late in the season.

(n.b. Use of tebuconazole on faba bean crops is covered by permit PER13752)

Table 3a. Chocolate spot assessed as per cent area diseased per plot on pods and leaves in each cultivar of faba and broad bean at Bool Lagoon in 2019. Different letters represent significant difference between varieties.

*tested as AF11023; L.s.d. = least significant difference.

Table 3b. Percentage of chocolate spot disease symptoms (per cent area diseased per treatment) on pods of faba and broad bean in disease management trial at Bool Lagoon in 2019. Different letters represent significant difference between treatments.

Nil = no spray; Minimum = tebuconazole at grass spray; Low cost = tebuconazole at grass spray and at canopy closure (27 August); Standard = tebuconazole at grass spray, carbendazim at canopy closure (27 August) and 20 September; L.s.d. = least significant difference.

CS is favoured by mild temperatures (15-25°C) and high humidity (>70%) extending over 4-5 days during flowering and after canopy closure. Areas that receive good rain through August and early spring are at higher risk of CS developing and spreading. This includes the South East of SA and Lower Eyre Peninsula regions. Growers are encouraged to be proactive in controlling CS by applying pre-emptive fungicide sprays at early-mid flowering before symptoms appear. Follow up sprays may be required in high rainfall regions and high biomass crops (especially where there was high seeding and/or early sowing) as humidity is retained in the canopy which is an ideal environment for CS to proliferate. Areas around trees and under power lines can become hot spots for the disease if spray planes are unable to reach those areas of the crop. Thick canopies from early sowing or high seeding rates can produce warm humid conditions under the canopy which is ideal for disease development and spread. CS can be easily distinguished from other faba bean leaf diseases as it also infects flowers unlike the other faba bean diseases.

Cercospora leaf spot (CLS)

All current commercial cultivars of faba beans are susceptible to CLS and there were early reports of widespread disease across the state in 2019.

In 2019, a replicated plot trial at Bool Lagoon was conducted to assess the effectiveness of including two different pre-sowing fungicide treatments (a seed treatment and an in-furrow treatment, both currently unregistered for use in faba bean) applied at sowing to control CLS however neither treatment gave effective control of the disease.

CLS appears early in the season on the bottom leaves as the pathogen survives on faba bean debris and in soil. The spores are spread through wind and rain splash to plants and the disease moves further up the plant through the season, which can cause extensive defoliation if not well controlled. Short rotation intervals between faba bean crops leads to increased disease carryover and higher infection levels. Paddocks regularly cropped to faba beans benefit from an early fungicide spray (for example; tebuconazole) to prevent infection and spread of CLS. Where CLS has already infected crops, later sprays of carbendazim for CS will also restrict further spread of CLS.

A helpful guide for growers and agronomists to identify common faba bean diseases can be found at: Spot the Difference - Identifying faba bean Diseases - GRDC Communities . Correct identification is important as different fungicides are used to manage different fungal disease.

Field pea

Bacterial blight (BB)

Severe BB was reported across SA in late August and early September. BB is typically reported after frost events as occurred in 2018 and 2019; frosted cells provide an entry point for the Pseudomonas bacteria to infect. However, there is no treatment for the disease, so the only management strategy is to avoid entering the paddock to prevent further spread via wheels or boots. The preferred field pea varieties to grow in frost prone areas are PBA Percy, PBA Butler or PBA Oura as these are less susceptible to BB than other varieties.

This foliar disease begins as fan shaped lesions at the base of the leaf where it is attached to the stem and it spreads up and down the stem. Infection can start in one spot in a paddock then spread over a wide area; including being transported through or between paddocks on shoes or tyres. At harvest, prevent crop residue from infecting grain of clean crops by harvesting infected crops last in the pulse harvesting program. Do not retain grain from infected crops as there is a high chance of seed infection. If only a small area of crop has been infected, then it is possible to harvest a clean area for seed. There is no risk to stock of infected crops being baled for hay but do not spread the hay onto paddocks intended for field pea for the 2020 season. Feed lotting the hay would be the preferred option or it could be used on a property that doesn't grow field pea. During transportation it would be best if the hay was tarped to prevent spread into roadside paddocks.

It is important to identify which strain of Pseudomonas bacteria (pv. syringae or pv. pisi) is causing the outbreaks so the correct isolates are used in resistance screening. Please forward infected samples for research purposes to Dr Pragya Kant, AgVictoria CropSafe Isolate Collection, Reply Paid 69952, Horsham, Vic 3400.

Pulse disease National Variety Trial (NVT) program

Through an expansion of GRDC’s NVT program, independent disease ratings of pulses will now be available. This new project provides robust disease ratings using processes adapted from those that were established for wheat and barley. The crops and diseases included are shown in Table 4.

As part of this new project, the definitions for each disease rating category were updated (Table 5). Due to this update, there will be some changes to the current pulse disease ratings with better alignment between crops and diseases.

Within this new project there are a total of 49 disease screens conducted annually, drawing on the plant pathology expertise across Australia. The disease screens are conducted in either field and/or glasshouse conditions designed to maximise disease development.

At the end of the season, data collected nationally are collated and disease ratings assigned by experts for each disease. The disease ratings are updated annually and made available in state-based disease guides and on the NVT web site (NVT Online).

Table 4. The crops and diseases included in the new National Variety Trial screening that commenced during 2019, and the states where they will be screened.

Table 5. The updated pulse disease ratings used in the National Variety Trials which will be implemented in pulse ratings released during 2020 and onwards.

Disease samples of ascochyta blight and sclerotinia sought

Diseased samples of pulses with ascochyta blight or sclerotinia are sought by SARDI for GRDC-investment projects monitoring pathogen populations and changes in cultivar resistance. If you can help, please contact Sara Blake (email: sara.blake@sa.gov.au ) for a collection kit that includes sample envelopes and a return Express Post envelope.

Diagnostic pulse plant samples

can be sent by Express Post to Jenny Davidson SARDI, Locked Bag 100, Glen Osmond, 5064. Dig up whole symptomatic and asymptomatic plants and send with roots wrapped in damp (not wet) paper towel. Send at the beginning of the week, so the parcel does not get held up in the post. Send an email to jenny.davidison@sa.gov.au to notify that the plants are coming.

Crop protection products

There are often changes to permits for the use of fungicides in pulse crops. See Pulse Australia’s website (Pulse Australia) or the APVMA website for current information on crop protection products including Minor Use Permits.

Acknowledgements

The research undertaken here is made possible by the significant contributions of growers and agronomists through both trial cooperation and provision of diseased plant materials for the isolate collection as well as the support of the GRDC, the authors would like to thank them for their continued support.

This work is supported by investment from GRDC through GRDC Projects DAS1807-006BLX (Improved disease management in South Australian field crops through surveillance, diagnostics and epidemiology knowledge), DAV00150 (Southern Pulse Agronomy), UA00163 (Pulse Breeding: Faba bean breeding), and CUR00023 (Ascochyta blight of pulses). Pulse disease screening for the National Variety Trials in South Australia are supported by investment from GRDC through GRDC Project DAS1905-013SAX. The authors also acknowledge Dr Jeffrey Paull, University of Adelaide, faba bean breeder, for his review of this paper.

Useful resources

Subscribe to CropWatch e-newsletter: Crop Watch - PIRSA

ExtensionAus website: Field Crop Diseases - GRDC Communities

Disease management of pulses grown in low to medium rainfall zones - GRDC

2020 SA crop sowing guide - GRDC

New pulse variety releases:

PBA Royal chickpea: PBA Royal - Seednet

PBA Highland XT lentil: PBA Highland XT lentil

PBA Amberley faba bean: PBA Amberley - Seednet

References

Blake S, Kimber R, Day S, McMurray L, Brand J, Paull J, and Davidson J. (2017) Pulse diseases 2016. GRDC Update, Adelaide, 7-8 February 2017. pp89-95 Pulse Diseases 2016 - GRDC

Blake S, Farqharson L, Walela C, Hobson K, Kimber R, Davidson J (2019a) Ascochyta blight in intensive cropping of pulses, GRDC Update, Adelaide, 12-13 February 2019 Ascochyta blight in intensive cropping of pulses -  GRDC

Blake S, Rose J, Roberts P, Day S, Hobson K, Davidson J, (2019b) In-Season Pulse Disease Update, Hart Field Day Guide, 17 September 2019, p70-78.

Contact details

Sara Blake
GPO Box 397, Adelaide SA 5001
08 8429 2248
sara.blake@sa.gov.au
@Sara_N_Blake