Effect of seed treatment with acetic acids in control of seed borne diseases

Anders Borgen⁽¹⁾

Holmemosevej 7, 4780 Stege, Denmark, email:anders@ecoweb.dk

Bent Nielsen

DJF-Flakkebjerg, 4200 Slagelse, Denmark, email:Bent.Nielsen@agrsci.dk

ABSTRACT

In field trials, seed treatment with acetic acid has reduced common bunt (Tilletia tritici) in winter wheat by 91.5-96.2% and by 83% in spring wheat without negative effects on germination vigour of the seeds. Leaf stripe (Pyrenophora graminea) in spring barley was reduced by 93,4%. Acetic acid is a cheap and environmental friendly fungicide with a possible scope of application especially in organic agriculture, where conventional pesticides are prohibited.

INTRODUCTION

Lime has been used as a seed treatment against common bunt since the 1700th century (Olsen 1792). The effect of lime as a seed treatment against common bunt is likely to be an effect of water-reaction (pH) since lime is a strong base. The opposite effect of a very low pH has never been studied as a seed treatment, but already Hahne (1925) showed that acetic acid has a strong effect on bunt-spore germination. However, the use of acetic acid as a seed treatment against common bunt must relay on a combination of the effect on the pathogen and the side-effect especially on seed germination. The effect of lime against common bunt is not complete, and the use has been limited since the development of more effective seed treatments like copper (Kühn 1866) and hot water treatment (Jensen 1888a, 1888b). Since the development of organic mercury seed treatment (Riehm 1913) common bunt has been controlled almost exclusively by synthetic pesticides in the industrialised world.

In the past decades, increasing focus has been put on the environmental side-effects of the synthetic pesticides and a wish to reduce the amount of pesticides used, or to replace them with naturally occurring substances (Nielsen et al. 1998). In organic agriculture normal pesticides are not used, and here seed borne diseases has become a severe problem. The aim of this study is to investigate whether seed borne diseases can be controlled by seed treatment with acetic acid.

MATERIALS AND METHODS

Field trials were conducted at three sites on Zealand, Denmark: Common bunt at Højbakkegård in 1997 and '98, leaf stripe in barley at Flakkebjerg in 1999 and both leaf stripe and common bunt at Mørdrupgård in year 2000.

The effect of different doses and concentrations of acetic acid was tested by applying increasing doses to seeds of wheat and barley. For the test of the effect on common bunt (Tilletia tritici syn. T.caries) at Højbakkegård in 1997 and '98 the winter wheat variety 'Pepital' was used and at Mørdrupgård in 2000 the spring wheat variety Dragon was used. The spring wheat seed used had a very low germination ability in order to increase the possibility to get a high infection in the field and to detect possible side effects on germination from the seed treatment. The seeds were contaminated with 5 g spores per kg seeds, which resulted in a contamination between 1.7 to 2.0 mill spores per gram seeds when tested by the ISDA haemocytometer method (Keitreiber 1984).

Test for the effect on leaf stripe (Pyrenophora graminea syn. Dreschlera graminea) were in both years done in seed lots of the variety Alexis which by a blotter test was tested to be heavily infected.

In 1997 and '98 normal fermented 5% vinegar for household use was used (FDB Lagereddike). In 1999 and 2000 the different concentrations were made by adding increasing volumes of inert water into concentrated acetic acid (99.9%). After treatment the seeds were stored at 5 Cº. Samples were taken out for field test 2-6 days after seed treatment. Germination tests were conducted 1-3 month later at Højbakkegård and Mørdrupgård. At Flakkebjerg the effect on germination were tested by the number of emerging plants in the field.

Germination tests in lab were done as a cold sand test in plastic plates containing 1.5 kg sand with water (65ml H₂O/kg quartz sand). Sowing depth was 1.5 cm and temperature was 10 Cº. The emergent number of seedlings were counted every day for 5 days after first emergence. The number of replicates were 3-4.

In the field trials at Højbakkegård and Mørdrupgård, treatments were sown in rows of each 1.25 m in 8 or 10 replicates. Total number of diagnosed plants in these trials was 1-2000 on average in each treatment. Trial at Flakkebjerg were sown in rows of 4 meter with 100 seeds pr. meter in 4 replicates After heading the ratio of infected ears (common bunt) or plants (leaf stribe) were counted based on visible macro-symptoms.

Table 1: Effect of different combinations of acetic acid as a seed treatment. Percent reduction in disease frequency of spring wheat infected by common bunt (Tilletia tritici) tested against treatments with inert water. Grey cells indicating treatments with a significant reduction in germination vigour. Experimental year 2000 at Mørdrupgård. Average infection in control plots was 8.0%.
	Dose of acetic acid, ml/kg
		5	10	20	30	40	50
	5%	20 n.s.	49	79	62 n.s.	54 n.s.	63
	10%	35	59 n.s.	83	70	63	70
	20%	4	39	75	54	45	55 n.s.
	30%	30	55	30 n.s.	67	60 n.s.	67 n.s.
	99.9%	46	66	86 n.s.	74	69 n.s.	75 n.s.

In 1998 at Højbakkegård (Figure 2), the application of a 5% solution of acetic acid reduced the frequency of common bunt by more than 91,5% at a dose of 20 ml/kg or higher. The negative effect on seed vigour seems to be proportional to the dose applied (Figure 3). When more than 40 ml/kg was applied, the effect was statistical significant according to the contrast test.

Even low vitality seeds were used in a very susceptible spring wheat variety Dragon at Mørdrupgård in year 2000, the bunt frequency was very low in all plots. The use of low vigour seeds resulted in a low field germination in both treated and untreated plots. The average number of ears were only 37 per plot. As it is appears in Table 1, the effect of many treatments were statistical insignificant because of a low number of plants, especially infected plants. However, the same optimal dose can be found to be about 20 ml/kg in a concentration between 5% and 20%.

Barley leaf stripe

At Flakkebjerg 1999, the infection of barley leaf stripe was significantly reduced proportional to the dose of 5% acetic acid applied (Figure 4). However, at the highest dose of 50 ml/kg the number of emergent seedlings in the field was significantly reduced (p<0.0001). The highest reduction recorded without significantly reduction in germination was at the dose of 40 ml/kg, where leaf stripe was reduced by 55,9%.

In spring barley at Mørdrupgård the infection of leaf stripe was reduced by 93,4% at the dose of 20 ml/kg of concentrated acetic acid with no significant effect on field emergence (Table 2).

Table 2: Effect of different combinations of acetic acid as a seed treatment in barley. Percent reduction in disease frequency of barley leaf stripe (Pyranophora graminea) tested against untreated control. Grey cells indicating treatments with a significant reduction in germination vigour. Experimental year 2000 at Mørdrupgård. Average infection in control plots was 17.4%.
	Dose of acetic acid, ml/kg
		5	10	20	30	40	50
	0%	28,6 n.s.	4,2 n.s.	6,4 n.s.	8,3 n.s.	-1,6 n.s.	7,2 n.s.
	5%	-7,8 n.s.	10,4 n.s.	26,9 n.s.	32,9 n.s.	54,5	84,8
	10%	-6,2 n.s.	12,7 n.s.	67,8	82,4	95,8	84,5
	20%	8,1 n.s.	26,7 n.s.	84,3	96,1	93,3	50,6 n.s.
	30%	29,2 n.s.	36.0 n.s.	90,3	91	99,5 n.s.	48,8 n.s.
	99.9%	12,7 n.s.	68,5	93,4	99,7 n.s.	99,7 n.s.	94,4

DISCUSSION AND CONCLUSION

Acetic acid is a natural occurring substance with a high biodegradability and a very low oral toxicity to humans, game birds and others who normally come in contact with seeds treated with fungicides. However, acetic acid is an acid and evaporates from the seeds during seed treatment. Precautions should therefore be takes to insure human health and safety at work. Substituting conventional fungicides with acetic acid is believed to reduce general environmental impact of seed treatments. Seed treatment with acetic acid would be cost effective, since it is a cheap substance and unsold treated seeds could be used for feeding, while seeds treated with more eco-toxic fungicides most be incinerated under controlled conditions.

In the winter wheat experiments, the infection of common bunt was high as was the reduction of infection by 91.5-96.2% when treated with 20 ml/kg of acetic acid with out affection the germination vigour of the seeds. In spring wheat the infection was lower and a reduction of only 75-83% was recorded. The differences in effect between the experiments in winter wheat and spring wheat can not be concluded from these experiments. It may be caused by the differences in crop, in differences in infection level or the fact that the spring wheat was grown from very low vitality seed which may have made the seeds more sensitive to the treatment.

The experiments with spring barley shows that barley leaf stripe can be effectively controlled by a high concentration of acetic acid in a dose of 20 ml/kg. In the first experiment only a low concentration of 5% was tested and in this concentration the results are equivalent with the second experiment.

Common bunt is a very devastating plant disease since only a few plants can give the hole crop an odour of rotten fish. The sum of treatments must therefore have a very high effect against this disease (Borgen 2000a). Even the effect of 91.5-96.2% as shown in this experiments are not adequate in cases with a high spore load in susceptible varieties as used in these experiments. Seed treatments with acetic acid can therefore not stand alone, but must be combined with other measures in an integrated strategy. This could be physical removal of spores or only used according to thresholds depended on the susceptibility of the varieties (Borgen 2000a).

Barley leaf stripe is an important seed borne disease, but the effect of the disease is only significant to the yield. The need for effective control is therefore less than for common bunt in wheat. A control effect of 93.4% as achieved in this experiment is therefore believed to be sufficient in most cases.

In resent years, soil borne infection of common bunt has been of increasing importance in wheat production (Borgen 2000b). Some systemic pesticides are effective also against soil borne infection, and has a higher effectivity also against seed borne infection of near to 100%. In organic agriculture, conventional fungicides are prohibited and acetic acid could therefore be an interesting alternative to the current practice of discarding all infected seed lots or to be used in combination with other treatments (Spie 2000).

REFERENCES

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