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The influence of agronomic management on seed size attributes in kabuli chickpea.

Michael Lines1, Larn McMurray1, Jason Brand2 and Kristy Hobson2

1 South Australian Research and Development Institute (SARDI), PO Box 822, Clare, South Australia, 5453, Australia
2 Department of Primary Industries, Victoria, PB 260, Horsham, Victoria, 3401, Australia
Email: lines.michael@saugov.sa.gov.au web site: www.sardi.sa.gov.au

Abstract

Field experiments were undertaken at Kalkee, Dimboola and Turretfield in 2004, 2005 and 2007 to evaluate the effect of agronomic management practices on the seed size of kabuli chickpeas (cvs. Almaz and Genesis™090). Manipulation of seed size proved most effective through disease prevention and minimising weed competition. Under severe ascochyta blight disease pressure cultivars with intermediate disease resistance to ascochyta blight had 34% lower seed weights in treatments where disease was not controlled, than those where it was controlled. Experiments with varying weed competition showed chickpea seed weight decreased by up to 27% at the higher weed densities. Smaller increases in seed size were gained by lowering plant density and sowing earlier, although at some sites there was little or no difference between early and optimum sowing dates. Additional experiments comparing seed of specific seed size showed that while small (6mm) seeds produced a smaller seed size index than larger (8mm) seeds in Genesis 090, this was not substantial.

Key Words

Plant density, grain legume, pulse crop, seed weight, seed size index

Introduction

Chickpea (Cicer arietinum) is an important crop in Australian farming systems, as a beneficial rotational crop and as a cash crop in its own right. Currently 286,000 ha of desi and 35,000 ha of kabuli chickpeas are grown in Australia annually (Hawthorne et al. 2008). Production of kabuli chickpeas is increasing, particularly in southern Australia, due to the higher prices received for their grain compared to desi types and the availability of varieties with resistance to the foliar disease ascochyta blight (Ascochyta rabiei (Pass.) Labr.). Traditionally, Australia has grown kabuli varieties aimed at international markets for medium to large seeds (8-10mm), where maximising seed size is essential to optimise profitability and meet these small but high valued markets. The recent release of the small seeded kabuli cultivar Genesis™090, with wider adaptation and substantially higher grain yield than the larger seeded types, has enabled Australian growers to access the larger, lower valued world market for 7-8mm sized kabuli chickpeas. However, even in these markets there is still opportunity for growers to attract premium prices for larger sized seeds. Price differentials between seed size classifications can be 20% or more for each 1mm increase in size (P. Semmler, pers. comm).

Agronomic management strategies for chickpeas have generally been aimed at maximising grain yield with little regard to effects on grain seed size (Day et al, 2006; Carter, 1999). Furthermore, while kabuli chickpea breeding programs concentrate on breeding for larger seed size through traits such as flowering and maturity time, little is known as to whether seed size could also be increased by breeding for other traits such as competitiveness or early vigour.

This paper presents results of field research on the effect of agronomic management practices on seed weight and seed size of a medium to large seeded kabuli variety (Almaz) and a small seeded kabuli variety (Genesis 090). Almaz has intermediate resistance to ascochyta blight, and regularly attracts price premiums for its large seed size, while Genesis 090 is a small seeded kabuli with resistance to ascochyta (McMurray & Hobson, 2008). Management factors under assessment included sowing date, plant density, disease intensity (ascochyta blight), weed population (Wimmera rye grass) and sown seed size.

Method

Field experiments were conducted in South Australia and Victoria between 2004 & 2007:

  • 1. Sowing time: RCBD trials were located at Kalkee in the Wimmera (annual rainfall (AR) - 450mm) in 2004 and 2005, and Dimboola (AR - 450mm) in 2007. Three sowing times were compared in each experiment: early (mid May), optimum (mid June) and late (mid July). The sowing rate in each case was 30 plants/m2sqm. Each trial consisted of four varieties, all including Genesis 090, and Almaz at Dimboola. Ascochyta blight was controlled with foliar fungicides. Whole plots were harvested at maturity and measurements included grain yield, seed weight and seed size (not presented). Seed weight was determined by counting out and weighing 100 seeds.
  • 2. Plant density: RCB designed trials were located at Kalkee in 2004 and 2005, and Dimboola in 2007. Five plant densities were compared: 15, 30, 45, 60 and 90 plants/m2. Measurements included emergence, grain yield, seed weight and seed size (not presented). Ascochyta blight was controlled with foliar fungicides.
  • 3. Disease intensity: a RCB designed trial located at Turretfield in 2005 (light clay over medium clay; AR - 456mm) compared the effect of different fungicide regimes on ascochyta blight foliar symptoms. Five fungicide regimes were compared, but only three included in this paper: Nil (no foliar fungicide sprays), Standard treatment of chlorothalonil (1440 g ai/ha applied six weeks after sowing, at flowering and at podding) and fortnightly applications of chlorothalonil (1440 g ai/ha applied every fourteen days from six weeks after sowing till end of podding (nine sprays). Disease was initiated in all plots by sowing an inoculated susceptible plant between plots, which induced a severe level of ascochyta blight pressure in untreated plots of susceptible varieties.
  • 4. Weed populations: a RCB designed trial comparing the competitiveness of eight chickpea varieties was sown at Turretfield in 2007. Three levels of competition were compared, using annual ryegrass (Lolium rigidum, cv Wimmera) as the source: Nil (no ryegrass sown), Low (ryegrass at 40 plants m-2) and High (ryegrass at 400 plants m-2). Measurements included grain yield and seed weight. Ascochyta blight was not present in this experiment.
  • 5. Sown seed size: a RCB designed trial at Dimboola in 2007 compared the effect of sowing seed of specific seed size on subsequent harvested seed size. Seed was allocated into four size treatments: 7mm, 8mm, 9mm and composite (random seed allocation). Measurements included grain yield, seed weight, seed size index and seed size distributions. Seed size index was determined by the sum of the products of the sieve diameters and the percentage of the seeds not passing through that sieve all divided by 100. Seed size was measured by sieving and weighing the proportions of each size bracket. Ascochyta blight was controlled with foliar fungicides.

Results and Discussion

Sowing time

Seed weights were influenced by sowing date at Dimboola (2007) and Kalkee in 2005, but not at Kalkee in 2004 which was severely moisture stressed and low yielding (Figure 1). At Dimboola in 2007 seed weights were reduced by 17% (Almaz) and 8 % (Genesis 090) when sowing was delayed until July (Figure 1). Similarly, Genesis 090 at Kalkee in 2005 displayed a 4% reduction in seed weight. Similar trends were shown in grain yields, with reductions of 95% for Almaz and 54% for Genesis 090, when sowing was delayed from May to July at Dimboola in 2007. These results closely reflect seasonal conditions, particularly at grain fill. During the dry year in 2004 plants were under severe moisture stress, and all sowing times were very low yielding, while the late and wet finish to 2005 was more favourable for later sown chickpea and only a low reduction in grain yield and seed weight occurred. However, the dry, harsh finish to 2007 greatly reduced seed weights and grain yield at the later sowing time by suppressing grain fill.

Figure 1: Effect of sowing time on seed weight (g/100 seeds) of Almaz and Genesis 090 at Dimboola (2007) and Genesis 090 at Kalkee (2004 and 2005). Kalkee 2004 was not significant

Plant density

Plant density had no effect on seed weight of Almaz or Genesis 090 at Dimboola (2007) or at Kalkee in 2005 (Figure 2). However, at the severely drought stressed Kalkee site in 2004, Genesis 090 showed a 20% reduction in seed weight (Figure 2), and a 70% reduction in grain yield (data not presented) when plant density increased from 15 to 90plants/m2. This outcome reflects the competition between plants for water, particularly toward grain fill, resulting in lower seed weights and yields where competition was greater. These results indicate that only in situations of severe moisture stress did plant density have any significant effect on seed weight.

Figure 2: Seed weight (g/100 seeds) of Almaz and Genesis 090 at Dimboola (2007) and Genesis 090 at Kalkee (2004 and 2005) in response to plant density.

Disease intensity

Grain yields and seed weights increased with disease control (Figure 3). The larger seeded kabuli, Almaz, showed a 34% increase in seed size from nil to fortnightly disease control. By contrast Genesis 090, which is resistant to ascochyta blight, showed no significant increase in seed weight. Grain yields also benefited from fortnightly control, with 95% (Almaz) and 35% (Genesis 090) yield increases compared to unsprayed plots (Figure 3). These results reflect the loss of leaves, branches and stems through disease infection, delaying the reproductive phase and seed formation (Haware, 1998). Furthermore, infection during the podding phase of development led to reduced pod fill and in some cases pod abortion. This suggests that disease control, either genetically or agronomically, is important in maximising seed weight. Results from disease intensity experiments at Turretfield 2004 and Kalkee 2005 (data not included) supported these findings.

Figure 3: Seed weight (g/100 seeds) and grain yield (t/ha) of Almaz and Genesis 090 with and without disease control at Turretfield, 2005.

Weed population

Both chickpea cultivars showed a reduction in seed weight when in competition with ryegrass (Figure 4). Genesis 090 showed no significant reduction in seed weight between nil and low ryegrass densities, but a 12% drop in seed weight from nil to high ryegrass densities. Almaz showed more sensitivity to competition than Genesis 090, yielding consistently smaller seeds as ryegrass density increased, and showing a 27% reduction in seed size from nil to high ryegrass densities. As with plant density, these results show the effect of competition between plants for water, resulting in lower seed weights and yields where competition was greater. Furthermore, it is likely that the extra sensitivity of Almaz arises due to its later maturity compared to Genesis 090, making it more susceptible to moisture stress.

Sown seed size

Grain yields from 6mm Genesis 090 seeds were 71% lower than those of 8mm seeds, with a reduction in seed size index (a weighted mean of the seed sizes) of 0.2mm (Table 1). The smallest Almaz seed size showed a reduction in seed weight, with 7mm seeds 6% lighter than both 8 and 9mm seeds. This most likely results from poor germination and slower establishment of smaller seeds, resulting in smaller grain and lower yields (Carter, 1999). However, grain yields and seed size index measurements in both varieties showed that the composite

Figure 4: Effect of ryegrass density on seed weight (g/100 seeds) of Almaz and Genesis 090 at Turretfield, 2007.

treatment (containing seeds of all size allocations) performed similarly to the largest size seeds. In neither variety was there any significant correlation between seed size index and seed weight, however this may be confounded by the dry seasonal finishing conditions, resulting in low grain yields. Sown seed size had a greater effect on yield and seed size index of the earlier-maturing Genesis 090 than Almaz. This is likely due to Genesis 090’s wider flowering window compared to Almaz, allowing seed formation to occur over a longer period.

Table 1: Grain yield, seed weight, and seed size comparisons of two kabuli chickpea varieties sown with seed of different size at Dimboola, 2007.

 

Sown seed size

Grain Yield
(t/ha)

Seed weight (g/100 seeds)

Seed Size Index (mm)

Seed Size (%/mm bracket)

9mm

8mm

7mm

<7mm

Almaz

7mm

0.27

37.9

8.18

38

46

13

3

8mm

0.35

40.4

8.21

36

51

11

2

9mm

0.39

40.3

8.23

38

48

13

1

Composite

0.39

38.7

8.22

39

47

12

3

Genesis 090

6mm

0.45

30.4

7.35

4

35

53

8

7mm

0.58

31.0

7.47

4

45

45

6

8mm

0.77

31.5

7.55

4

52

40

4

Composite

0.80

31.5

7.59

4

56

37

4

 

LSD (P<0.05)

0.19

1.7

0.12

5.4

8.9

7.1

2.1

Conclusion

While all five strategies were effective in enhancing seed size to some extent, the largest and most consistent improvements were achieved by providing optimum disease management and weed control. Plant density, sowing time and sown seed size contributed only slightly to maximising seed size, and therefore management of these strategies should be more aimed at maximising yield than seed size. Plant breeding strategies aimed at developing varieties with greater ascochyta blight resistance and good weed competitiveness will aid growers in producing kabuli varieties with maximum seed size.

References

Carter, J (1999). Chickpea Growers Guide: a guide to the production of chickpea. Eds D Robey and M Raynes. Agriculture Victoria

Day T, Day H, Hawthorne W, Mayfield A, McMurray L, Rethus G and Turner C (2006). Grain Legume Handbook. Eds J Lamb and A Poddar. pp 1:10-18, The Grain Legume Handbook Committee, Riverton, SA

Haware MP (1998) Diseases of chickpea, In eds. Allen DJ and Lenne JM, The pathology of food and pasture legumes, CAB International and ICRISAT; Wallingford, UK. pp 473-562

Hawthorne W, Bray T, Cumming G and Meldrum A (2008). Pulse Australia Crop Forecast - April 2008. Online, accessed 21 May 2008. www.pulseaus.com.au/statistics_and_market_overview/market_overview/535/ Pulse%20Australia%20Crop%20Forecast%20April%202008.pdf

McMurray L and Hobson K (2008). Chickpea variety sowing guide – 2008. Online, accessed 19 May 2008. www.pir.sa.gov.au/data/assets/pdf_file/0003/37713/08chickpfs.pdf

Semmler P (2008). Personal Communication. fansem@optrusnet.com.au. Australian Milling Group, Horsham

Whish JPM, Sindel BM, Jessop RS and Felton WL (2002). The effect of row spacing and weed density on yield loss of chickpea. Australian Journal of Agricultural Research 53 1335 – 1340

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