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Necrotic tipping and yellowing of leaves in wheat (cv. Diamondbird) in southern New South Wales in 2001

BJ Scott1, KJ Schulze2, GM Murray1, PJ Martin1 and KA Wratten1

1NSW Agriculture, Wagga Wagga Agricultural Institute, PMB, Wagga Wagga, NSW 2650, Australia. www.agric.nsw.gov.au Email brendan.scott@agric.nsw.gov.au ; gordon.murray@agric.nsw.gov.au , peter.martin@agric.nsw.gov.au , kerry.wratten@agric.nsw.gov.au
2
NSW Agriculture, Agricultural Research Station, PMB, Myall Vale, Narrabri, NSW 2390, Australia. www.agric.nsw.gov.au Email klara.schulze@agric.nsw.gov.au

Abstract

Diamondbird wheat showed extensive necrotic tipping and yellowing of leaves at many sites in southern New South Wales during spring of the 2001 season. No disease was identified on leaf or root material, so further leaf samples were collected from 32 sites and were analysed for a range of nutrient concentrations. Several possible nutritional problems were identified at various sites, but no deficiency or toxicity was universally associated with the symptoms. We suggest that in the 2001 season the yellowing and necrosis of leaf tips was a physiological symptom in response to moisture stress. Any possible role of the leaf rust gene Lr34 in the symptoms was unclear.

Key Words

disease, leaf rust, nutrition

Introduction

Diamondbird wheat is a cultivar well adapted to southern and central NSW. It has yielded well in field trials and commercial production over many seasons. Diamondbird is tolerant of the acidic soils which occur in the higher rainfall eastern area of the wheatbelt (1). In the 2001 growing season Diamondbird wheat showed extensive leaf tipping and yellowing in southern New South Wales (NSW) in late August and early September. While these symptoms had been observed in previous seasons, their occurrence in 2001 was more extensive; the symptoms were more intense and appeared earlier in the growing season.

Diamondbird is a selection from Pavon and consequently shows the genetic trait of yellowing of the leaf. It also contains the gene for leaf rust resistance Lr 34 (and the linked Yr18 gene), which cause death of the leaf tip (2). The leaf tipping characteristic associated with Lr34 is known to have a yield penalty of 6% in Mexico if no leaf rust is present or where leaf rust is controlled by chemical means (3). In southern NSW, these symptoms of yellowing and leaf tip necrosis are observed on Diamondbird wheat in most seasons.

However, in the 2001 season the symptoms were particularly severe and agronomists became concerned that a disease or general nutritional problem was the cause of the severe symptoms. Samples were collected and examined for possible diseases. In late spring of 2001 leaf samples were collected from 32 crops which showed symptoms and were analysed for concentration of a wide range of elements, seeking to identify any possible nutrient deficiency and toxicity problems in the crops.

Methods

Symptoms of leaf yellowing and necrosis were observed in many wheat crops throughout southern NSW from mid August in 2001. Samples of affected plants were collected from 15 crops that were representative of crops showing leaf chlorosis and necrosis in an area from Deniliquin to Albury in the south and to Barmedman and Cootamundra in the north. Most crops were at late stem elongation to flag leaf emergence. The samples were examined for symptoms and signs of disease associated with the condition. Necrotic leaves were examined by microscopy for fungal fruiting bodies and then incubated at 100% humidity at room temperature (20C) for 1–3 days before a second microscopic examination. Root systems were examined for their development and for lesions. Paddock histories including herbicide use were sought.

Further samples (Table 1) were collected for tissue analysis from Diamondbird crops that had chlorotic leaves with tip necrosis in late September when the crops were at the booting to heading stages of growth. The youngest emerged leaf blades (YEB) were collected by cutting with stainless steel scissors, handled with blue nitrile gloves that were free of powder and placed into kraft envelopes for dispatch to the analytical laboratory. The collections were made in September, 2001, and were analysed by Waite Analytical Services, Glen Osmond, South Australia for Fe, Mn, B, Cu, Zn, Ca, Mg, Na, K, P and S concentrations.

Results and Discussion

Symptoms occurred over an area of southern NSW bounded by Albury and Barham in the south, Hay and Hillston to the west, Condobolin in the north, and Cootamundra and Wagga in the east. The symptoms occurred mainly on the wheat cultivars ‘Diamondbird’ and ‘Dollarbird’, with fewer reports in ‘H45’. Both Dollarbird and Diamondbird carry the Lr34 gene, while H45 is likely to carry the gene (H Bariana, pers. comm.). Dollarbird and Diamondbird have over half their pedigree in common. H45 and Diamondbird share a common parent in cv Ciano.

Plant symptoms and presence of biotic and abiotic pathogens

Affected crops first showed a distinct yellowing over the whole crop. The yellowing began at the tips of the upper leaves and progressed to affect the whole leaf. Necrosis followed yellowing, beginning at the leaf tip of the upper leaf and sometimes progressing to the whole leaf (Fig 1). The leaf yellowing symptoms were initially similar to those caused by barley yellow dwarf virus (4). However, the rapid development of leaf necrosis and the uniform development of symptoms within the crop were not consistent with this viral disease.

No fruiting bodies of fungal pathogens were observed on fresh leaves or on leaves incubated at high humidity. The saprophytic fungus Alternaria sp. fruited abundantly on incubated dead leaves. Roots of affected plants appeared normal, with no lesions from root rotting fungi or pathogenic nematodes.

Paddock history showed no consistent association of the symptoms with any herbicide use. Although the herbicide Logran was used on most affected crops, it was also widely used on many other crops that did not show symptoms.

Figure 1 General crop symptoms and individual leaf symptoms in Diamondbird wheat, (photos, K Condon)

Nutritional analysis

No abnormal concentrations of nutrients were universally associated with the symptoms (Table 1). Some sites in the western areas (lower average annual rainfall) appeared to have low K concentrations (Barham and Griffith; Table 1; <23000 mg/kg in the YEB; cited by Reuter and Robinson, 5). In the high rainfall wheatbelt (Cootamundra, Albury) plant Mg concentration was low (<1200 mg/kg), but was probably not deficient; deficiency is probably at <1000 mg/kg. Low Mg in cereals has been observed over many seasons on the acidic soils of the eastern higher rainfall wheatbelt. Both low K and Mg could potentially give a yellowing of the older leaves and so may exacerbate the general yellowing symptom in Diamondbird but the symptoms of interest to us were on the younger upper leaves. Low Zn concentrations (<14 mg/kg) also occurred at Griffith, Lockhart and Cootamundra. The lowest values at Lockhart (<10 mg/g) may well be deficient. Sulphur concentrations were in the range 2100 to 4900 mg/kg and unlikely to be deficient.

The data set also contains some low P concentrations (critical 2100 to 2300 mg/kg) at Condobolin and Griffith, and marginal Ca concentrations (<1800 mg/kg) at Cootamundra. N deficiency is the most obvious candidate to induce yellowing of older leaves. Unfortunately, there were no analyses for N. Presumably, most farm advisers who collected these samples believed that the N fertiliser application to the crops we examined was adequate.

Interestingly there is also low B in the high rainfall wheatbelt (adequate, 3 – 25 mg/kg). This deficiency would affect the young leaves. Boron deficiency has been recorded on some soils of the tablelands and slopes of NSW in subterranean clover and lucerne. In subterranean clover, B deficiency reduced seed set far more than dry matter production (6).

The samples had Fe, Mn and Na concentrations with the ranges 51 to 153, 54 to 171 and 12 to 210 mg/kg respectively. In these samples Na was not toxic (< 5000 mg/kg) and in our experience Mn is adequate (19 mg/kg) and not toxic; concentrations > 300 mg/kg can cause toxicity in varieties sensitive to Mn toxicity. Fe has been has been quoted as adequate at 10 mg/kg and toxic when >300 mg/kg

Table 1. The concentrations (mg/kg) in youngest emerged leaves of Diamondbird wheat collected in September 2001 in southern NSW. The location of the nearest township and its long term average annual rainfall are shown.

District

Rainfall annua(annual)

Ca

Mg

K

B

Cu

Zn

P

Albury

769

2300

1220

29000

3.2

5.7

18.7

3300

Albury

769

2400

1100

32000

3.3

4.4

16.9

3300

Albury

769

2200

1140

36000

3.5

5.5

21.0

3600

Albury

769

2100

1160

32000

4.2

4.2

18.5

3300

Cootamundra

629

2100

1200

39000

2.7

5.0

17.2

4200

Cootamundra

629

1640

1160

31000

3.8

4.2

15.2

3600

Cootamundra

629

1970

1090

31000

3.3

4.8

13.1

3700

Temora

535

4800

1960

26000

5.7

4.8

18.2

2200

Temora

535

4100

1690

24000

4.9

5.6

15.8

2800

Temora

535

4100

2900

17800

14.0

6.8

15.7

2400

Temora

535

3600

2600

18000

15.5

6.0

14.5

2200

Lockhart

491

5000

1970

20000

6.1

3.6

11.9

2300

Lockhart

491

4000

2100

21000

5.7

3.8

9.8

2200

Lockhart

491

4400

2400

20000

15.8

5.1

12.1

2800

Lockhart

491

4100

1280

17600

3.5

2.6

11.4

1870

Lockhart

491

3100

1090

13100

3.4

2.8

9.5

1540

Lockhart

491

4600

1740

16200

4.2

3.9

14.1

1990

Lockhart

491

3800

1700

24000

6.2

2.3

12.4

2400

Condobolin

473

2700

1510

36000

6.1

6.2

16.2

2300

Condobolin

473

2700

1400

24000

6.6

6.3

17.0

2700

Barham

408

3400

2000

24000

15.8

5.5

15.1

2600

Barham

408

3400

2100

23000

15.6

5.5

14.8

2800

Barham

408

3600

2400

21000

19.1

5.5

15.7

2600

Griffith

406

3600

1910

23000

7.3

3.3

12.5

2100

Griffith

406

4600

2400

20000

9.5

4.4

17.4

2900

Yanco

394

3300

1570

30000

5.4

5.4

22

3200

Yanco

394

2400

1580

28000

6.2

3.9

22

3000

Yanco

394

3100

1840

28000

8.2

5.1

22

3100

Hillston

367

2900

1610

37000

5.9

7.2

30

3700

Hillston

367

2000

1470

39000

7.6

6.0

26

3600

Hillston

367

2400

1410

45000

4.5

5.7

26

3600

Hay

366

2600

2200

22000

12.8

5.3

13.1

2600

Adequate range from (5)

n.a.

>2000

>1000

>23000

3 – 25

1.7 – 25

10 – 70

2100–5000

Performance of Diamondbird wheat

Diamondbird is well adapted to southern NSW and has given good yields in field trials and commercial production over many seasons. The yields of Diamondbird have been higher by 5% than the yields of Janz in 136 late stage variety evaluation experiments throughout the seasons 1992 to 2001 in south eastern NSW and equal in 127 experiments in western NSW (Table 2). Janz has significantly out yielded Diamondbird in 1997 in western NSW. The role of the symptoms we report in lowering of grain yield in Diamondbird in 2001 is unclear but did not decrease yield significantly compared to Janz in that season. In the southeast, the 5% yield advantage of Diamondbird was not apparent in 2001.

Table 2. Yield of cv. Diamondbird wheat relative to cv Janz (%), and the grain yield (t/ha in parentheses) of cv Janz in the seasons 1995 to 2001 and in the longer term (1992–2001) in late stage variety evaluation trials in the southern area of New South Wales.

       

Season

       

Area

1995

1996

1997

1998

1999

2000

2001

1992-2001

South east

113%*
(4.76)

99% n.s.
(5.63)

97% n.s.
(4.01)

109%***
(5.34)

102%*
(6.01)

113%***
(5.58)

98% n.s.
(5.25)

105%***
(4.95)

South west

110%**
(3.25)

99%n.s.
(2.84)

93%*
(3.32)

99% n.s.
(3.83)

103% n.s.
(4.37)

110%**
(4.12)

97% n.s.
(4.91)

102% n.s.
(3.86)

*, P ≤0.05; **, P ≤ 0.01; ***, P ≤ 0.001; n.s., not significant

Conclusion

There is no evidence that the symptoms of the yellowing and tipping seen in Diamondbird in the 2001 were caused by disease or a single nutritional problem. However, various possible deficiencies may have contributed to the intensity of the symptoms in some paddocks. Nitrogen deficiency has not been eliminated as a factor.

More generally, the symptoms that occurred in 2001 are known to occur in Diamondbird in most seasons with some yellowing and death of the leaf tip shortly after flowering. In addition, there is a characteristic yellowing of leaf tips in varieties related to the wheat Pavon and this includes Diamondbird. However in 2001 season these symptoms have occurred earlier in the season and were more severe. The effect was quite widespread across southern NSW and occurred on a wide range of soil types making a single nutrient deficiency or toxicity an unlikely general cause. It is possible that the symptom reported here is a response to the dry August of 2001. Any contribution of the Lr34 rust resistance gene, and the linked Yr18 gene, to the symptom is unclear as other varieties with these genes (eg. Janz) did not display the symptoms reported here.

References

(1) Anon. 2002. Winter Crop Sowing Guide 2002. NSW Agriculture, Orange, NSW.

(2) Singh, R.P. 1992. Association between gene Lr34 for leaf rust and leaf tip necrosis in wheat. Crop Sci. 32: 874–878.

(3) Singh, R.P., Huerta-Espino 1997. Effect of leaf rust resistance gene Lr34 on grain yield and agronomic traits of spring wheat. Crop Sci. 37: 390–395.

(4) Wallwork, H. 2000. Cereal Leaf and Stem Diseases. Grains Research and Development Corporation: Kingston, ACT, Australia.

(5) Reuter, D.J., Robinson J.B. 1997. Plant analysis: an interpretation manual. CSIRO, Collingwood, Victoria.

(6) Dear B. S. and Lipsett, J. (1987). The effect of boron supply on the growth and seed production of subterranean clover (Trifolium subterraneum L.). Aust. J. Agric. Res. 38: 537-46

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