New medics for Mallee farming

By BCG Staff and Contributors
Views

TAKE HOME MESSAGES

  • Six new strand medics have been shortlisted as having improved dry matter production and seed yield over Herald, Angel and Jaguar. They also have powdery mildew resistance, sulfonylurea herbicide tolerance and larger seeds.
  • Powdery mildew resistant strand medics exhibited lower levels of the phytoestrogen coumestrol (which can effect ovulation in sheep) in the presence of powdery mildew and Phoma black stem at Minnipa in 2013.
  • New evidence gained by the previous South Australian Grains Industry Trust (SAGIT) project confirms that medics are correctly classified as moderately resistant (MR) to Pratylenchus neglectus.

BACKGROUND

From 2010-12 SARDI evaluated the agronomic performance of 27 strand medic hybrids possessing various combinations of new traits. Six new lines were identified as having powdery mildew resistance (PM), sulfonylurea residue (SU) tolerance, aphid resistance and larger seeds. From these, five lines were selected and included in Grain & Graze 2 medic evaluation trials at Hopetoun and Nhill in 2013. The standout performer for dry matter production was Sultan-SU – a newly released barrel medic with tolerance to Group B, SU herbicide residues (See 2013 BCG Season Research Results , pp. 196-202).

A further season was needed to validate Sultan-SU’s better performance against other released varieties in the Wimmera and Mallee area. In addition, given SultanSU’s tolerance to Group B-SU residues, its further tolerance to the residues of another group B herbicide group, imidazolinones, was also of interest. Relevant South Australian medic variety development research is presented here, because of the poor seasonal conditions experienced by this trial.

AIMS

To compare the performance of Sultan-SU medic with released cultivars in the southern Mallee for another season and to assess its tolerance to Group B imidazolinone residues.

To assess the potential of six multi-trait advanced breeders’ lines for commercial cultivar development.

TRIAL DETAILS

Location:                       Beulah

Soil type:                       Clay loam with sub-soil constraints

Annual rainfall:             162mm

GSR (Arp-Oct):             126mm

Crop types:                   Medic varieties – Sultan-SU, Caliph, Cavalier, Herald, Angel

Sowing date:                 24 April

Seeding equipment:     Knife points, press wheels, 30cm row spacing

Sowing rate:                  10kg/ha

Treatments:                   Imidazolinone residue was applied pre-sowing as Intervix @ 20% residue (150 mL/ha) and 40% residue                                                         (300mL/ha) to soil sown to plots of Sultan-SU and Caliph

Fertiliser:                       Granulock Supreme Z @ 50kg/ha

Weeds and pests were controlled to best practice commercial standards.

METHOD

A replicated field trial was sown using a randomised block trial design. Normalised Differential Vegetation Index (NDVI) was used to assess early biomass differences on 21 July. Biomass cuts were planned, but the trial was terminated by dry seasonal conditions.

RESULTS AND INTERPRETATION

There were no early biomass differences determined by NDVI in response to medic variety or imidazolinone residues. The lack of response by the Group B intolerant cultivars, Caliph, Cavalier and Herald, may have been due to the dry seasonal conditions after sowing, which caused imidazolinones to adsorb onto soil particles, preventing breakdown and plant uptake or that medics in general are not very sensitive to imidazolinone residues.

Medic plants were stressed by dry conditions and numerous frosts and failed to grow to their full potential. They did, however, manage to flower and set seed. Grain & Graze 3 will monitor regeneration of medic varieties in 2015, and repeat the imidazolinone residue trial.

Other SARDI research

2013

Large plots (10m x 3m, intended for grazing in 2014) of medic varieties were sown at Rudall, Karoonda and Netherton in 2013, and assessed for agronomic performance (dry matter, seed yield).

Despite an initially promising start to the season, the harsh spring finish in 2013 provided a rigorous test of the medics’ ability to produce seed and persist. None of the trials suffered significant PM damage and the best performing check cultivar, Angel, performed very well.

Breeders were encouraged that despite the general absence of PM infection, three short-listed lines performed as well as Angel (or slightly better) for overall average dry matter and seed yield at the three sites. The group of short listed lines generally performed well for seed yield despite the harsh spring. Rudall (range 450-600kg/ha), Netherton (550-680kg/ha) and Karoonda (420-480kg/ ha) were on a par with Angel (average 580kg/ha).

2014

Trials at Rudall and Karoonda* were allowed to regenerate for further dry matter assessments. Data had not yet been analysed at the time of writing.

The Netherton site was sown to Kord CL Plus wheat and sprayed with Intervix® in order to monitor the ability of the entries to regenerate in the presence of imidazolinone residues. Depending on seasonal conditions post Intervix® application, we are interested in finding out whether Angel and the PM lines (SU tolerant) have an advantage over the intolerant varieties (such as Jaguar and Tornafield) in 2015.

New evidence gained by the previous SAGIT project confirms that medics are correctly classified as moderately resistant (MR) to Pratylenchus neglectus .

Powdery mildew

Minnipa Agricultural Centre (MAC) monitored the performance of three early generation powdery mildew (PM) strand medic selections sown as demonstration plots in 2012 and allowed to regenerate in 2013 and 2014. An early PM infection was observed and scored on a visual basis. Dry matter cuts were taken on 7 July 2014.

While this was not a replicated trial, a sound correlation was found between the PM rating and dry matter yield with the three PM lines producing an average 40 per cent more dry matter yield in the presence of PM infection (Figure 1).

Background Harbinger (susceptible) probably contributed to what little PM infection was scored in the resistant plots. This result was significant because it was the first opportunity to correlate an advantage in dry matter yield with PM resistance (in addition to the increase in seed yield shown at Netherton in 2011).

Frischke_1_2014
Figure 1. Dry matter response (kg/ha) to powdery mildew infection (0 = no infection, 10 = 100% infection).

Phytoestrogens

Some foliar fungal diseases can induce production of the phytoestrogen ‘coumestrol’ in medics, which can affect ovulation rates in sheep at concentrations as low as 25ppm. While a direct link between PM, high coumestrol levels and poor sheep fertility has not been established, it is something to keep in mind if ewes are grazing mildew affected medic. This possibility is supported by data from Netherton (2011) in which susceptible cultivars affected by PM alone had coumestrol levels of up to 370ppm, whereas three unaffected PM resistant lines had levels below detection.

At Minnipa in 2013, there were clear differences in PM infection between the PM resistant lines and the three susceptible strand medic cultivars (Herald, Angel and Jaguar). These un-grazed plots were very bulky and by September also had quite high levels of Phoma `spring black stem’ infection (which has been implicated in increased coumestrol levels).

In the presence of both PM and Phoma, high levels of coumestrol were found in all three cultivars, whereas in the presence of mostly Phoma only, the coumestrol levels were much lower in the PM lines (Figure 2). Arguably, the combination of both Phoma and PM in the 2013 MAC plots was the cause of the significantly elevated levels of coumestrol in affected plants.

Frischke_2_2014

Figure 2. Coumestrol levels isolated from cultivars/entries in the presence of the foliar pathogens Phoma spring black stem and powdery mildew.

Sultan-SU

Launched at the 2014 GRDC Update in Adelaide, Sultan-SU is a new barrel medic bred by crossing SU tolerant Angel strand medic with Caliph barrel medic and then back-crossing to Caliph four times.

Key features of Sultan-SU:

  • First barrel medic with tolerance to sulfonylurea (SU) herbicide residues
  • Early maturing (~70-90 days to flowering), similar to Caliph and Angel
  • A Caliph replacement with improved regeneration; less hard-seeded than Caliph (~85% cf 95%), similar to Jester
  • Good aphid resistance (bluegreen and spotted alfalfa aphid)
  • Boron tolerant
  • Improved flexibility in rotations after use of SU herbicides

Like typical barrel medics, Sultan-SU is well suited to mildly acidic to alkaline (pHCa >5.5) soils, with textures ranging from loams to clays. It is also useful in a pasture mix to accommodate variable soil types/textures within a paddock (eg. sow Sultan-SU with Angel strand medic in a dune/swale system). Seed of Sultan-SU is available from Heritage Seeds.

COMMERCIAL PRACTICE

SARDI medic breeding and development programs are producing new varieties with new traits to help improve early vigour, dry matter and seed production in the presence of constraints such as herbicide residues and disease. This translates to greater feed value for livestock, increased biological nitrogen fixation, improved pasture legume persistence and competitiveness in mixed farming operations.

Including new varieties in pasture mixes with traits such as powdery mildew resistance, aphid resistance, larger seeds, tolerance to herbicide residues and boron tolerance will help medic pastures to achieve their full potential when constraints could potentially limit production.

ON-FARM PROFITABILITY

Apart from direct production benefits for livestock value and the system benefits for cropping, a resilient medic that persists through cropping sequences offers pasture systems a fodder option that is effectively free and has reduced financial risk; machinery, labour and seed expenses are avoided, as well as disturbance of the soil from a sowing pass.

REFERENCES

For more information on other varieties and the SARDI Pastures Group

ACKNOWLEDGEMENTS

This research was funded by GRDC through the Grain & Graze 3 program, SFS00028
South Australian Grains Industry Trust, Development of a strand medic cultivar resistant to powdery mildew, S1213.

This article also includes extracts from the Minnipa Agricultural Center field day booklet article, ‘New Medics for the EP and Mallee’ by Jake Howie, Ross Ballard, David Peck & Jeff Hill, SARDI, Waite Campus.

Back to top

Become a BCG Member

BCG exists for its members. Research and extension activities are designed to provide members with information and resources that will help them improve the productivity, profitability and sustainability of their farm businesses.

Improve your profitability

Receive the latest research, extension and event news direct to your inbox! For a limited time, receive a free technical bulletin when you subscribe.