SEED DISINFECTION METHOD

Abstract

The invention relates to a method for preparing disinfected seed, a use of a treatment composition, and an apparatus for disinfecting of seed. The method of the invention comprises contacting seed with a treatment composition comprising at least one disinfecting agent and/or a liquid component, and thereafter or at least partly simultaneously, exposing said seed to a treatment atmosphere for an exposure time of at least 1 second, wherein the treatment atmosphere has a relative humidity of at least 50% and a temperature of at least 40 C.

Claims

1. A method for preparing disinfected seed, comprising: contacting seed for an exposure time of at least 10 seconds with a liquid treatment composition comprising water, and one or more disinfecting agents selected from acetic acid, peroxyacetic acid, hydrogen peroxide, wherein any peroxide is present in an amount of less than 20% by weight of the treatment composition; and thereafter, exposing said seed to a treatment atmosphere for an exposure time of at least 1 second, wherein the treatment atmosphere has a relative humidity of at least 50% and a temperature of at least 40 C.

2. The method according to claim 1, wherein said treatment composition is supplied at a temperature of 15-40 C.

3. The method according to claim 1, wherein said treatment composition additionally comprises a surfactant.

4. The method according to claim 1, wherein said treatment atmosphere has a temperature of 50-100 C. and a relative humidity of at least 75%, and wherein said exposure time is up to 10 minutes.

5. The method according to claim 1, wherein said treatment composition has a pH of 6 or lower.

6. The method according to claim 1, comprising contacting seed with said treatment composition prior to said exposure, wherein said treatment composition comprises an aqueous solution comprising a surfactant, at least 0.10 wt. % of acetic acid and at least 0.10 wt. % of hydrogen peroxide, based on total weight of the treatment composition, and wherein said treatment atmosphere has a temperature of 50-100 C. and a relative humidity of at least 80%, and wherein said exposure time is from 30 seconds to 10 minutes.

7. The method according to claim 1, wherein the treatment composition is supplied to the seed in an amount of at least 0.1 g seed per kg treatment composition.

8. The method according to claim 1, wherein the treatment composition is supplied to the seed in an amount providing at least 100 g water per kg seed.

9. The method according to claim 1, wherein said seed is exposed to the treatment atmosphere 24 hours or less from having contacted the seed with the treatment composition.

10. The method according to claim 1, wherein the exposure to the treatment atmosphere is subsequent to contacting the seed with treatment composition, and wherein the method comprises removing at least part of the treatment composition from the seed prior to said exposing.

11. The method according to claim 1, wherein the seed is seed of an agricultural crop.

12. The method according to claim 1, comprising subsequent to said exposure to the treatment atmosphere, cooling and/or drying.

13. The method according to claim 1, comprising subsequent to said exposure to the treatment atmosphere, coating or pelleting the disinfected seed.

14. Use of a treatment composition comprising water for enhancing the bactericidal and/or bacteriostatic efficacy of a treatment atmosphere having a relative humidity of at least 50% and a temperature of at least 40 C. to which plant seed is exposed for at least 1 second.

15. A continuous process wherein seed is being transported through a first chamber in which first chamber the seed is contacted for an exposure time of at least 10 seconds with a liquid treatment composition comprising water, and one or more disinfecting agents selected from acetic acid, peroxyacetic acid, hydrogen peroxide, wherein any peroxide is present in an amount of less than 20% by weight of the treatment composition, and said seed is thereafter being transported through a second chamber in which second chamber the seed is exposed to a treatment atmosphere for an exposure time of at least 1 second, wherein the treatment atmosphere has a relative humidity of at least 50% and a temperature of at least 40 C.

16. The method according to claim 1, wherein said treatment composition is supplied at a temperature of 20-38 C.

17. The method according to claim 1, wherein said seed is exposed to the treatment atmosphere 1 hour or less from having contacted the seed with the treatment composition.

Description

EXAMPLES

[0094] As treatment composition, a commercial composition TC5 for horticultural disinfection was used which comprises an aqueous solution of peracetic acid (5%) combined with hydrogen peroxide (20%). Contacting the seed with treatment composition varies from 2 to 30 min depending on solution. In some cases the solution is removed or rinsed (1 to 5 min) with water to reduce toxicity after the exposure period. Then the seed can be centrifuged or can be directly subjected to the step of exposure to the treatment atmosphere. Thereafter, seeds are dried back to original moisture content as far as necessary.

[0095] In all examples, GE is germination energy (%), Germ is final germination (%), TA is treatment atmosphere, and TC is treatment composition. The treatment compositions and surfactants used in the following examples are identified in table 13.

Example 1

[0096] General bacteria was determined by planting the seed over a semi-selective media (fungal growth suppressed) and incubated at 28 C. dark. Counts were done at day 4, 5 or 7 days and are presented as a % of bacteria infected seeds. A and B are comparative.

[0097] Table 1 shows the quality effect of the treatments on onion seed. The values are the average of two International Seed Testing Association standard tests and are given as % of germinated seed after 3 (GE) and 8 to 14 days (Final), both determined using 15 C. in dark with greenhouse test. Also shown is a value (% infected seed) for general superficial bacteria (Gen. Bact.) which was determined by planting the seed over a semi-selective media (fungal growth suppressed) and incubated at 28 C. dark. Counts were done at 5 and 7 days and presented as a % of bacteria infected seeds. Pre-treatment was with 5 wt. % TC5 (solution comprising 5 wt. % peracetic acid and 20 wt. % hydrogen peroxide, 20 times diluted). Sample C has fewer bacteria than comparative samples A and B.

TABLE-US-00001 TABLE 1 Avg. GE Avg. Final Gen. Bact. TC TA (%) Germ (%) (%) A (comparative) No No 60 87 100 B (comparative) No Yes 74 84 100 C TC5 Yes 40 87 13

Example 2

[0098] In example 2, Brassica seed was soaked for 2 min in 5% TC5, followed by 1 minute rinsing with water. The treatment atmosphere had 90% RH (relative humidity) and an exposure time of 2 minutes. Average results of 8 seed lots are shown in table 2. Herein, GE day 5 is the speed of emergence by day 5; GE final is final stand by day 7-8; Gen. Bact. general superficial bacteria, as in example 1 by day 5; CD-48 refers to the controlled deterioration or accelerated aging test for 48 hours evaluated by day 7-8; and Avg CFU: average Colony Forming Units of targeted pathogen per gram seed, evaluated after 5 days in selective media.

[0099] Sample C shows that with TC improved bacterial reduction effect was obtained compared with the TA alone. The combination results in a significant reduction of general bacteria and the specific pathogen (Xcc=Xanthomonas campestris pv. campestris) without significantly reducing the germination values or CD-values.

TABLE-US-00002 TABLE 2 GE day 5 GE final Gen. CD48 Avg Xcc Sample TC TA (%) Germ (%) Bact. (%) (%) (CFU/g) A* No No 93 95 92 72 3.66 10.sup.4 B* No Yes 96 88 73 70 1.5 10.sup.4 C TC5 Yes 86 86 33 60 2.77 10.sup.3

Example 3

[0100] In example 3, the method was applied to carrot cultivars. The results as given in table 3 demonstrate the reduction of bacteria by exposure to the treatment atmosphere (RH 90%, 2 min) in combination with contacting with a treatment composition (2 min soaking in TC5 (5%), rinse with water 1 min, 30 sec centrifuge). CFU Xhc (Xanthomonas hortorum pv. carotae) was measured similar to example 2.

TABLE-US-00003 TABLE 3 Avg. Carrot GE Avg. Final General Xhc Lot Cultivar TC TA (%) Germ (%) Bacteria (%) (CFU/g) 1 Var #1 TC5 No 21 89 100 6.10 10.sup.4 Yes 29 92 50 0 2 Var #2 No 46 63 100 2.10 10.sup.5 Yes 20 78 63 0 3 Var #3 No 56 66 100 2.40 10.sup.4 Yes 49 84 63 0

Example 4

[0101] In example 4, the method was applied to corn salad. The results are shown in table 4. A reduction of bacteria (in particular for foci of A. valerianellae) was obtained by contacting with a treatment composition (2 min soaking in TC5 5%), followed by rinsing with water 1 min and 30 sec centrifuge and subsequent 2 min exposure to 90% RH treatment atmosphere. Foci=number of Acidovorax valerianellae infested seedlings in a group, as measured according to ISTA 7-030.

TABLE-US-00004 TABLE 4 Corn salad Final General Lot Cultivar TC TA Avg. GE Germ Bacteria Foci 1 Var #1 TC5 No 92 92 100 11 Yes 84 97 60 2 2 Var #1 No 72 75 100 12 Yes 61 76 100 0 3 Var #1 No 80 81 100 29 Yes 41 80 85 0 4 Var #2 No 95 94 100 7 Yes 96 97 100 0 5 Var #3 No 95 93 100 31 Yes 93 91 78 0

Example 5

[0102] In example 5, the method was applied to water melon cultivars. The results as given in table 5 demonstrate a reduction of bacteria, obtained by 2 min soaking in TC5 5%, rinse with water 1 min, 30 sec centrifuge and subsequent 2 min exposure to a 90% RH treatment atmosphere. In particular good results are obtained for the number of plants infected with Acidovorax citrulli.

TABLE-US-00005 TABLE 5 Watermelon Final General Infected Lot Cultivar TC TA Germ Bacteria plants (a) 1 A TC5 No 80 80 49 Yes 84 38 0 2 C No 92 90 (b) Yes 89 50 (a) # Infected plants A. citrulli; (b) Inconclusive

Example 6

[0103] In example 6, the method was applied to carrot seed infested with Xanthomonas spp. The results as given in table 6 demonstrate effective seed disinfection in combination with good germination properties. In particular, use of water (tap water) as treatment composition provides for disinfection in combination with advantageous germination properties.

[0104] In all examples, N.d. indicates that a measurement was carried out but that the number of CFU detected was below minimum value or the detection limit of 100 CFU. The skilled person understands that log CFU/10 000 seeds refers in all examples to the common logarithm (base 10), such that a decrease with 1 indicates a 10 fold reduction in CFU.

TABLE-US-00006 TABLE 6 Lot 1 Lot 2 Lot 3 TC TA X spp. Germ X spp. Germ X spp. Germ None None 3.6 89.7 4.5 96.0 0.6 90.3 None Yes n.d. 87 0.1 91.7 n.d. 91.3 TC6 for 2 min Yes n.d. 89.3 n.d. 94.0 n.d. 90.7 TC1 for 1 min Yes n.d. 89.3 n.d. n.d. 93 TC1 for 3 min Yes n.d. 87.3 n.d. n.d. 89.7 TC7 for 2 min Yes n.d. 78 n.d. n.d. 87.7 X spp: Xanthomonas spp. log CFU/10 000 seeds; Germ.: germination percentage (%) after 2 weeks. *: comparative

Example 7

[0105] In example 7, the method was applied to Brassica seeds infested with Xanthomonas spp. and Alternaria. The results as given in table 7 demonstrate effective disinfection in combination good germination properties. In particular good results were obtained for Xcc load in lot 2, when comparing treatment with and without treatment composition.

TABLE-US-00007 TABLE 7 ET Tmp RH Alt. (%) Xcc Lot Tr (s) ( C.) (%) TC GE GC infest. Log CFU 1 U* 0 0 0 None 88 90 46 4 A* 120 65 90 None 89 93 0 n.d. B 120 65 90 TC8, 5 min 51 66 0 n.d. C 120 65 90 TC6, 2 min 76 87 0 n.d. D 120 65 90 TC6, 5 min 78 91 0 n.d. E* 120 71 90 None 86 90 0 n.d. 2 U* 0 None 83 85 40 4.3 A* 300 64 90 None 88 91 0.5 5 B 300 64 90 TC8, 5 min 20 24 0 n.d. C 300 64 90 TC6, 2 min 85 89 0 n.d. D 300 64 90 TC6, 5 min 73 77 0 n.d. E* 300 70 90 None 84 86 0 4 Tr.: treatment used; ET: exposure time (s), Tmp: exposure temperature ( C.); RH: relative humidity (%), all for the treatment atmosphere; GE: germination energy; GC: germination capacity; Alt. inf.: seed infected with Alt.brassicicola (%); Xcc: log CFU Xcc detected in 10 000 seeds. *comparative, n.d.: not detected

Example 8

[0106] In example 8, the method was applied to Brassica seeds infested with Xanthomonas spp. Contact time with treatment composition was 20 or 30 min, as indicated in tables 8 and 9, using the formulations and process conditions as shown in table 10. The treatment atmosphere temperature was kept the same for all samples (0.5 C.) at a temperature above 50 C.

[0107] The results as given in tables 8 and 9 demonstrate effective disinfection in combination with good germination properties.

[0108] Untreated sample 1 had severe infestation. Sample 2 shows a reduction of bacteria by soaking in water followed by 2 min exposure to the treatment atmosphere. Sample 3 with 3 min exposure time provided even better reduction of Xcc. Treatment compositions comprising a surfactant provided for lower general bacteria. The amount of general bacteria was particularly low for samples 10 and 11 with a treatment composition comprising 0.2% H.sub.2O.sub.2 and acetic acid with 0.01% Rhamnolipids. Table 9 shows that contacting the seed with treatment composition for 30 minutes provides for good reduction of Xcc CFU with a various treatment compositions.

TABLE-US-00008 TABLE 8 TC contact TA exposure Germination General Sample Surfactant TC (min) time (min) (%) Bacteria Xcc (CFU) 1 None 0 91 100 1.00 10.sup.5 2 TC1 20 2 83 33 1.33 10.sup.4 3 20 3 82 38 1.89 10.sup.2 4 S1 20 2 84 15 2.77 10.sup.3 5 20 3 84 23 *N.d. 6 S2 20 2 82 3 2.20 10.sup.4 7 20 3 83 3 2.53 10.sup.3 8 S1 TC2 20 2 83 5 5.72 10.sup.3 9 20 3 71 8 1.82 10.sup.3 10 S2 TC4 20 2 81 1 N.d. 11 20 3 83 1 7.22 10.sup.2 *N.d. = not detected

TABLE-US-00009 TABLE 9 TC TA Germi- contact exposure nation Xcc Sample Surfactant (min) time (min) (%) (CFU) 12 0 0 93 1.00 10.sup.5 13 TC1 30 3 80 N.d. 14 S1 TC2 30 3 90 N.d. 15 30 3 75 N.d. 16 30 3 71 96 17 TC3 30 3 81 N.d. 18 S2 TC2 30 3 75 100 19 TC3 30 3 77 N.d. *N.d. = not detected

Example 9

[0109] In example 9, rice seed was soaked for 30 min in TC1 and TC2, followed by 30 s centrifuge. The treatment atmosphere had 90% RH (relative humidity) and an exposure time of 2.5 min. The results are shown in Table 10.

TABLE-US-00010 TABLE 10 Final Avg Aa Surfactant TC TA GE (%) Germ (%) (CFU/g) No No 98 75 4.54 10.sup.6 No TC1 Yes 93 88 9.75 10.sup.2 S2 TC2 Yes 88 78 5.00 10.sup.1

Example 10

[0110] In example 10, Brassica seed was soaked for 30 min in TC1 and TC2, followed by 30 s centrifuge. The treatment atmosphere had 90% RH (relative humidity) and an exposure time of 2.5 min. The results are shown in Table 11.

TABLE-US-00011 TABLE 11 Final Xcc Surfactant TC TA GE (%) Germ (%) (CFU/g) No No 94 92 2.3 10.sup.6 TC1 Yes 90 87 1.5 10.sup.1 S2 TC2 Yes 88 82 1.0 10.sup.0

Example 11

[0111] In example 11, Brassica seed was soaked for 30 min in TC1, followed by 30 s centrifuge. The treatment atmosphere had 90% RH (relative humidity) and an exposure time of 2.5 min. The average results of 19 lots of Brassica are shown in Table 12.

TABLE-US-00012 TABLE 12 GE Final Xcc TC TA (%) Germ (%) (CFU/g) No No 88 87 1.4 10.sup.5 TC1 Yes 86 83 0

TABLE-US-00013 TABLE 13 Code Description Surfactant S1 DMSO 0.01% S2 Rhamnolipids 0.01% Treatment TC1 Water composition TC2 (H.sub.2O.sub.2 + Peracetic acid) @ 0.2% TC3 (H.sub.2O.sub.2 + Peracetic acid) @ 1.0% TC4 (H.sub.2O.sub.2 + Acetic acid) @ 0.2% TC5 (H.sub.2O.sub.2 + Peracetic acid) @ 5% TC6 H.sub.2O.sub.2 @ 3% TC7 H.sub.2O.sub.2 @ 10% TC8 H.sub.2O.sub.2 @ 30%