Virus in chickpea in northern NSW 2012

Andrew Verrell, NSW Department of Primary Industries, Tamworth Agricultural Institute, Tamworth NSW 2340

Take home message

  • Sow at optimal seeding rate - irrespective of sowing date, to ensure early canopy closure.
  • Plant on time – to suit your environment and minimise the impact of aphid flights.
  • Retain standing stubble – this deters aphids from landing on the crop.
  • Sow between standing cereal rows - use precision agriculture techniques to sow between the stubble rows. This assists generating a uniform crop canopy which makes the crop less attractive to aphids.
  • Ensure adequate nutrition – supplying adequate crop nutrition will assist in generating dense uniform canopies which deter aphids.

Introduction

There are over 14 species of virus that naturally infect chickpeas. These viruses are spread by airborne insects with aphids being the predominant vector.

The aphids that fly in to crops do not stay long and do not normally colonise plants. Typical virus symptoms are bunching, reddening, yellowing, death of shoot tips and early death of whole plants. However, it should be remembered that none of these are diagnostic for virus.

The occurrence of virus in chickpeas is episodic and changes dramatically from season to season and location. Clovers, medics, canola/mustard, weeds, and other pulses can host viruses that infect chickpea.

The best control strategies to reduce risk of viruses are agronomic. These include; retaining cereal stubble, sowing on time, establishing a uniform closed canopy and controlling weeds (Schwinghamer et al 2009). Seed and foliar insecticides are not recommended for chickpea viruses.

The 2012 season – assessment of virus in chickpea

A survey of 17 chickpea crops in northern NSW by Moore et al (2013) found a high incidence of Beet western yellows virus (BWYV) and lower incidences of Alfalfa mosaic virus (AMV) and Cucumber mosaic virus (CMV). Observations by Moore et al (2013) suggest 3 major infections with the 1st flight of aphids in the 1st week of September.

Chickpea trials at TAI had a high incidence of plants with virus symptoms. These trials were within 300m of lucerne and approximately 500m of canola paddocks. Three trials; sowing date, plant density and nutrient omission, were selected and plants exhibiting virus symptoms were counted on the 15th of October (see Table 1).

Table 1: Trial details for the three TAI trials assessed for virus in chickpeas

Trial

Varieties

Treatments

Sowing Date

Sowing Date

PBA BoundaryPBR logo, FlipperPBR logo, Genesis™ 090, Kalkee, Sonali, Cica-912

PBA HatTrickPBR logo 

30 plants/m2

7, 15, 30, 45 plants/m2

  7/5/2012

13/6/2012

  6/7/2012

  7/8/2012

Density

PBA BoundaryPBR logo, Cica-912, PBA HatTrickPBR logo, Genesis™ 090, KyabraPBR logo

 5, 10, 15, 20, 30, 45 plants/m2

31/5/2012

 

Nutrient omission

PBA HatTrickPBR logo (30 plants/m2)

All, 0, -N, -P, -K &

7 micro-nutrients

13/6/2012

All trials were sown at 40cm row spacing into standing wheat residue and chickpea rows were sown between the standing wheat stubble. Both the sowing date and density trials had 5.5 kg N/ha, 11 kg P/ha, 2 kg S/ha and 0.5 kg Zn/ha applied at sowing.

Plant density and virus

Varieties showed no significant difference in terms of plants with virus symptoms (%) but there was a highly significant effect with plant density (see Figure 1).

Figure 1: Plants exhibiting virus symptoms (%) related to plant density (plants/m2)

Very low plant density (5 plants/m2) exhibited the highest incidence of virus symptoms (62%) with the incidence declining in a curvilinear fashion as plant densities increased. There was no significant difference in the proportion of plants exhibiting virus symptoms for 20, 30 and 45 plant/m2 densities with virus symptom incidences of 13, 6 and 4 (%), respectively.

The relationship between the incidence of virus symptoms and plant density on grain yield was examined by plotting the number of plants with virus symptoms (plants/m2) against grain yield (kg/m2) (Table 2).

Table 2: Linear regression parameters for the number of plants with virus symptoms (plants/m2) versus grain yield (kg/m2).

Density

Intercept

Slope

R2

(plants/m2)

(kg/m2)

(kg grain/plant/m2)

(%)

  5

0.110

-0.010

23

10

0.139

-0.008

23

15

0.170

-0.005

11

20

0.217

-0.014

39

30

0.242

-0.014

23

45

0.257

-0.021

29

The number of plants/m2 showing virus symptoms accounted for 11%-39% of the variation in grain yield/m2. There was a general trend for yield loss to increase at higher densities with 20, 30 and 45 plants/m2 having yield declines of -14, -14 and -21 g of grain/plant/m2, respectively.

In the absence of virus (intercept), yields ranged from 1.1 t/ha (5 plants/m2) up to 2.57 t/ha (45 plants/m2) (see Table 2). Comparing the intercepts to actual plot yields gave yield declines due to virus for 5, 10, 15, 20, 30 and 45 plants/m2 of 29, 17, 9, 18, 11 and 12 %, respectively.

Sowing date and virus

Seven varieties were sown (30 plants/m2) across 4 sowing dates along with PBA HatTrickPBR logo  at 4 plant densities (see Table 1). The proportion of plants with virus symptoms was highly significant for sowing date, variety and sowing date x variety (Fig. 2).

In Figure 2, varieties are listed in order of average proportion of plants with virus symptoms across the 4 sowing dates. The order of varieties is consistent with current published virus ratings (Hawthorne, 2008) with FlipperPBR logo rated as MS-MR, PBA HatTrickPBR logo MS and Sonali VS.

The 2nd and 3rd sowing dates had the highest incidence of virus with average values of, 2, 12, 14 and 5 (%) for the 1st, 2nd, 3rd and 4th sowing dates, respectively. By the time of the first reported aphid flights the 1st sowing date had developed tall dense uniform canopies with complete row closure (1st flower range, 21/8-7/9). The 2nd and 3rd sowing dates were behind in terms of growth and development (1st flower range, 7/9-24/9, 24/9-4/10, respectively). The 4th sowing date was still in vegetative mode, very short with the cereal stubble still visible and standing above the chickpea plants (1st flower range, 9/10-13/10). Optimum sowing time in this environment is in the last week of May.

This trial also allowed the effect of sowing date x density to be examined in PBA HatTrickPBR logo (see Table 1 and Fig. 3). Similar trends in the effect of sowing date on virus symptoms were

evident, with the 2nd and 3rd sowing dates having the highest incidence. Importantly, across all 4 sowing dates, the trend for plant density is the same with the proportion of plants with virus symptoms declining as plant density increases.

Figure 2: Proportion of plants with virus symptoms (%) for sowing date by variety

Figure 3: Proportion of plants with virus symptoms (%) for sowing date by plant density for PBA HatTrickPBR logo

Nutrition and virus

A Normalized Difference Vegetation Index (NDVI) was generated for the nutrient omission trial on the 5th of September when there were NO virus symptoms present (Fig. 4). The NDVI is prepared from spectral data in the visible and near infrared regions of the electromagnetic spectrum. It can be used to measure and monitor plant growth (vigour), vegetation cover, and biomass production from multispectral data.

Figure 4:NDVI date for selected nutrient treatments recorded on the 5th Sep. 2012

The zero, -N and –P treatments had lower NDVI values compared to the All nutrients treatment which suggest lower biomass and a more sparse canopy where nutrients were omitted. The incidence of virus symptoms for these same treatments is presented in Fig. 5. The nutrient omission treatments had significantly higher levels of plants with virus symptoms compared to plants with adequate nutrition (All nutrients treatment).

Figure 5: Proportion of plants with virus symptoms (%) for selected nutrient omission and All nutrient treatments

Conclusion

  • Sow at the optimal seeding rate - irrespective of sowing date, to ensure early canopy closure to reduce aphid attraction to plants next to bare soil.
  • Plant on time – to suit your environment and minimise the impact of aphid flights.
  • Retain standing stubble – this deters aphids from landing on the crop.
  • Sow between standing cereal rows - use precision agriculture techniques to sow between the stubble rows. This assists generating a uniform crop canopy which makes the crop less attractive to aphids.
  • Ensure adequate nutrition – supplying adequate crop nutrition will assist in generating dense uniform canopies which deter aphids.

Acknowledgements

Thanks to Michael Nowland and Paul Nash for their assistance in the trial program.

Contact details

Dr Andrew Verrell
NSW Department Primary Industries
Ph: 0429 422 150
Email: andrew.verrell@dpi.nsw.gov.au

References

  1. Hawthorne W (2008) Revised chickpea variety disease resistance and controls. Australian Pulse Bulletin PA 2008 #21
  2. Schwinghamer M, Knights T, Moore K (2009) Virus control in chickpea--special considerations. Australian Pulse Bulletin PA 2009 #10
  3. Kevin Moore, Malcolm Ryley, Murray Sharman and Joop van Leur (2013) Chickpeas! Varietal performance, wet feet and root rot, virus and salinity effects in 2012, Ascochyta management, seed quality, issues in central Queensland and effects of desiccating too early with glyphosate on seed germination.  Proceedings 2013 GRDC Grains Research Update, Goondiwindi

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