Lentil research in progress including herbicide tolerance in the pipeline

Take home messages

• Diversification of lentil variety choice is imperative to reduce disease and reduce agronomic and marketing risks of lentil production under high intensity systems on the Yorke Peninsula.
• XT lentil varieties have improved tolerance to residues of Group B herbicides compared with conventional lentils but still incur yield loss in some situations. All existing product label rates, plant-back periods and directions for use must still be adhered to.
• New green lentil varieties provide growers with an opportunity to manage production and marketing risks but are a higher input lentil and therefore, production requires careful consideration.
• Innovative recent research in the development of novel herbicide tolerance is expected to provide further weed control options in pulses.

Background

The popularity of lentil as a cash and rotational crop in South Australia (SA) rose to record levels in 2014 principally on the back of high prices and the availability of recently released herbicide tolerant varieties. The area sown to lentils during 2014 was estimated at 106,000 Ha with over three quarters of this crop being sown on the Yorke Peninsula (YP) (PIRSA Crop and Pasture Report, July 2015). Lentil has now replaced field pea as the pulse crop occupying the largest area in the state. PIRSA estimates for 2015 suggest a further increase in lentil area with 115,000 Ha predicted including 85,000 Ha on the YP. Lentil is now the third largest crop on the YP at 17 per cent of the total cropping area, behind barley (33 per cent) and wheat (31 per cent). There are few regions in the world where lentil cropping intensity would be at this level. High intensity levels of any one crop in a region puts increased disease and weed pressures on the individual crop and on the sustainability of the system as a whole as seen with wheat/lupin rotations in Western Australia. Future advancements in breeding and agronomic research will help assist high intensity lentil production on the YP but diversity in variety choice, optimum agronomic and disease management practices and long term sustainable rotations are required by growers to avoid crop and system failures.

Breeding research and new varieties

Pulse Breeding Australia (PBA) has developed lentil varieties with improved yield and yield stability due to appropriate flowering and maturity times, as well as incorporating new traits including improvements in plant height and standability, disease and shattering resistance and tolerance to soil boron and salt. Six lentil varieties have been released in the last three years; two high yielding, broadly-adapted medium red lentils (PBA Ace and PBA Bolt), a higher yielding imidazolinone-tolerant small red lentil (PBA Hurricane XT), a new large red lentil (PBA Jumbo2), and two new green lentil varieties (PBA Greenfield and PBA Giant). Notes and characteristics on all recommended varieties for South Australia can be found in the 2015 SARDI Sowing Guide. Future breeding outputs from PBA aim to release varieties with a combination of the desired traits above.

New red lentil opportunity

The XT lentil varieties (PBA Herald XT and PBA Hurricane XT) have improved in-crop weed control options on the YP in recent years resulting in better weed management and increased lentil intensity. However where this technology is not essential or other management options are available careful consideration should be made to the yield and other trait benefits of conventional lentil varieties which may prove more profitable and marketable in many seasons.

The recently released variety, PBA Jumbo 2, continues to be the highest yielding Australian lentil after topping the SA NVT and PBA trials in 2014. In a performance not quite as impressive as in previous years it still finished 12 per cent above Nugget, two per cent above PBA Ace, three per cent above PBA Blitz and six per cent above PBA Flashacross all trials last year.

It also continues to out yield the XT varieties finishing nine per cent in front of PBA Hurricane XT and a massive 32 per cent above PBA Herald XT. PBA Jumbo2 has been released as a large seeded replacement for PBA Jumbo although seed size and colour are about the only features they share in common. It has improved agronomic characteristics over PBA Jumbo, including greater early vigour, and improved lodging, disease and shattering resistance. It is rated as resistant to both ascochyta blight (AB) and botrytis grey mould (BGM), resistance rating superior to almost all other varieties. As with other large seeded varieties, PBA Jumbo2 is well suited to the post-harvest removal of small broadleaf weeds seeds, however it does not have the XT herbicide technology.

PBA Jumbo2 has a large and vigorous plant type that aids in weed competition and sets up high yield potential, but it often has a lot of biomass to carry through dry finishes. However to date it appears to be able to do this better than other large varieties such as PBA Ace, Nugget and the green lentil varieties. Agronomic work is currently ongoing to investigate if seeding rate and sowing date manipulation are required to optimise its performance across a range of seasons and environments.

Green lentil opportunities

Australian lentil production is dominated by red lentils, however internationally there are significant green (yellow cotyledon) lentil markets. There is also a small domestic market for these types. Canada traditionally has produced more green lentils than red but in recent years has trended dramatically to greater production of the latter. The Australian green lentil industry is currently infantile but its existence may allow some growers to spread their production and marketing risks, particularly if production trends and seasonal forces combine in Canada to help produce large worldwide red lentil stocks.

Green lentils are generally sold and consumed whole with the seed coat intact and the markets prefer large uniform seed size with good green colour retention (lack of bleaching) and an absence of seed blemishes such as disease and wrinkled seed coat. There are also some smaller markets for medium and small sized green lentils. Achieving the combination of required characteristics above has traditionally been hard to achieve under Australian conditions, particularly as initial varieties were only medium in size and susceptible to disease. Recent breeding progress by PBA has resulted in the release of PBA Giant (large) and PBA Greenfield (medium) that will help growers produce a more marketable product.

Going green?

Before considering green lentil production, growers need to consider a number of production, storage and marketing issues with green lentils, including:

• Visual appearance of seed is very important, therefore good disease and insect control and timely harvest is required. Production in environments where there is a lower risk of climatic events affecting seed quality issues such as wrinkled seed coat, bleaching or delayed harvest will also aid in producing a marketable product.
• Production is small and new in Australia, and therefore, it is important to understand marketing opportunities prior to deciding to grow them and also to have the capability for on farm storage.
• Larger plant type with increased early vigour and often later maturity than reds, this combination leads to a plant type that reaches earlier canopy closure, is more prone to lodging and more prone to early onset of BGM. Consider a slight delay in sowing time and reduction in seeding rate if sowing in favourable production environments.
• No green lentil has the XT herbicide technology, but there larger plant size is more competitive with weeds and larger seed size is well suited to the post harvest removal of smaller weed seeds.

Update in lentil disease research

Recent research has indicated the presence of a virulent strain of Ascochyta lentis which is able to infect the previously resistant cultivar Nipper. It is now widespread across SA and Victoria. Isolates have been collected from numerous naturally infected lentil field trials in SA and Victoria from 2010 to 2014 and tested across a number of varieties in controlled environment conditions by SARDI. Infection levels on the cultivar Nipper have become increasingly more common and aggressive in recent years. Of the 21 isolates collected in 2013, the four most aggressive were from Hart, Riverton, Melton and Kulpara and of the remaining 17 isolates a further nine were from the YP. In 2014 an isolate virulent and an isolate avirulent on Nipper along with an old control isolate (Kewell) were tested against a range of commercial lentil varieties (Table 1). Results showed a stronger correlation between the virulent isolate and disease assessments from the PBA breeding trials at Mallala (2013) and Horsham (2014) than between the avirulent isolate and the field trials (Table 1). There was also a high level of correlation between the results from the two PBA sites. These results indicate the widespread nature of the Nipper virulent form of A. lentis in southern Australia. This work is funded by the South Australian Grains Industry Trust (SAGIT).

Table 1: Comparison of AB infection levels on lentils inoculated with three separate isolates of Ascochyta lentis under controlled environment conditions in 2014 and natural infection levels in PBA field trials, Mallala 2013 & Horsham 2014. Results in isolate tests show the % plant disease on two week old seedlings averaged for four plants by four replicates. Results for PBA field trials are averaged for three replicates.

The increased presence of A. lentis isolates aggressive to Nipper in lentil crops may be due to a selective response due to the wide spread growing of this cultivar since 2006. It highlights the importance of an integrated disease management strategy including the use of seed treatments and selection of varieties with different sources of disease resistance.

Improved weed control in lentil

Research by the Southern Region Pulse Agronomy (SPA) program and PBA has focused on improving Group B herbicide tolerance in lentil. Group B herbicides (including Imidazolinone (Imi) and Sulfonyl Ureas (SU)) applied in cereal phases of the crop rotation can aid weed control across the whole farming system due to their residual activity. However, their use can also reduce subsequent pulse production, particularly on alkaline, high pH, light textured soils where their residual life is often extended. Two lentil varieties, PBA Herald XT and PBA Hurricane XT are now commercially available with a permit allowing the post-emergent use of Imazethapyr. Research by SPA during 2013 and 2014 in lentil producing regions of SA and Victoria aimed to confirm this in-crop tolerance as well as exploring benefits from potential improved residual tolerance. Trials were set up at various locations to simulate residual Group B herbicide carry-over through the application of treatments at either very low rates post sowing pre-emergent (PSPE) (Figure 1) or commercial rates pre-sowing in autumn.

Key findings from the agronomic herbicide trials:

• Response of lentils to herbicide treatment s varied with seasonal conditions, method of herbicide incorporation, stubble coverage, soil texture and fertility.
• Treatments that showed high plant damage generally incurred high yield losses, however low levels of chlorosulfuron plant damage still resulted in significant yield loss in some trials.
• XT lentil varieties showed improved tolerance compared to conventional lentil varieties to all treatments, however they still incurred yield loss to some chemistries under certain conditions, indicating low safety margins to these chemistries (Figure 1).
• Chlorsulfuron and triasulfuron were the most damaging treatments in the trials. Metsulfuron was found to be the safest of the sulfonylurea chemistries tested.
• It is important to note that all existing product label rates, plant-back periods and directions for use must still be adhered to. Further research is required to identify if sufficient crop safety exists in XT lentils to seek changes to label recommendations for other Group B herbicides.

Figure 1: Effect of various Group B chemistries applied PSPE at four application rates on the grain yield of PBA Hurricane XT and Nipper lentils, Pinery, 2013. Solid horizontal line indicates untreated variety yield, with shading showing associated error.

Bright future for weed control in pulses

Building on the success of the lentil research, the SARDI pre-breeding project ‘Improving weed management in pulses through herbicide tolerance’ has developed Group B tolerant faba bean and Group C tolerant lentil germplasm. Agronomic field trials in SA in 2014 confirmed faba bean lines with tolerance to a range of Imi chemistries and early generation PBA yield trials have identified lines with good adaptation to southern Australia. Preliminary field validation trials also confirmed a very high level of metribuzin tolerance in lentil germplasm. This material has now been ‘crossed’ with the Group B tolerant lines with the aim of developing dual herbicide tolerant (Group B+C) varieties. The project is now expanding into the development of novel herbicide tolerance in both kabuli and desi chickpea with some recent exciting findings currently being validated.

Contact details

Larn McMurray
SARDI Clare, 9 Old North Road, Clare, SA, 5453
08 8842 6265
larn.mcmurray@sa.gov.au