Effect of fungicide seed treatments on Fusarium virguliforme infection of soybean and development of sudden death syndrome

Figures & data

Table 1. The seed treatments and rates used in field and greenhouse experiments.

Active ingredient^a	Rate (g a.i. per 100 kg seed)
Non-treated	0
Mefenoxam	3.75
Fludioxonil + mefenoxam	5 + 3.75
Azoxystrobin + mefenoxam	3 + 3.75
Fludioxonil + azoxystobin + mefenoxam	5 + 3 + 3.75
Trifloxystrobin + metalaxyl	5 + 4
Prothioconazole + metalaxyl	5 + 4
Prothioconazole + trifloxystrobin + metalaxyl	2.5 + 2.5 + 4
Prothioconazole + trifloxystrobin + metalaxyl + Bacillus pumilus	5 + 5 + 4 + 6 × 10^10 CFU^b
Thiophanate-methyl + mefenoxam	354 + 3.75
Pyraclostrobin + thiophanate-methyl + metalaxyl	5 + 45 + 3.75
Thiophanate-methyl + azoxystrobin + Bacillus pumilus + prothioconazole + fludioxonil + mefenoxam	354 + 3 + 6 × 10^10 CFU^b + 5 + 5 + 3.75

^aThe fungicides tested were: mefenoxam (Apron XL, Syngenta Crop Protection, Greensboro, NC); metalaxyl (Allegiance FL, Bayer CropScience, Research Triangle Park, NC); fludioxonil (Maxim 4 FS, Syngenta Crop Protection); azoxystrobin (Dynasty, Syngenta Crop Protection); trifloxystrobin + metalaxyl (Trilex AL, Bayer CropScience); prothioconazole (Redigo, Bayer CropScience); Bacillus pumilus GB34 (Yield Shield, Bayer CropScience); thiophanate-methyl (Topsin 4.5 FL, United Phosphorus Inc., King of Prussia, PA); and pyraclostrobin + thiophanate-methyl (BAS 580, BASF Corporation, Research Triangle Park, NC).

^bActive ingredient is a bacterium, and the rate is expressed in colony forming units (CFU) per 100 kg seed.

Table 2. Summary of main effects and interactions on soybean stand count, Fusarium virguliforme DNA concentration in roots, sudden death syndrome (SDS) area under disease progress curve (AUDPC), yield, root length, root average diameter, and number of root tips for roots collected at growth stages V4, V7 and V12 at Valmeyer, IL in 2008.

Source	df	Plant stand	Fv DNA^a	SDS^b	Yield	Root length			Root average diameter			Number of root tips
						V4	V7	V12	V4	V7	V12	V4	V7	V12
Cultivar (C)	1	<0.0001^c	0.5674	<0.0001	<0.0001	0.0242	0.0062	0.2687	0.2095	0.0393	0.2657	0.9617	0.3151	0.5836
Seed Treatment (S)	11	0.0002	0.4670	0.0025	0.1913	0.5184	0.8607	0.2835	0.8914	0.0451	0.3751	0.9428	0.0052	0.2660
C × S	11	0.2562	0.9865	0.2577	0.7787	0.0489	0.7781	0.9187	0.6921	0.0133	0.8026	0.1756	0.0130	0.6849

^aNatural log transformations of [values × 10] were used to meet assumptions of normality and homogeneity of variance for analysis.

^bAUDPC calculated by: , in which X_i = the disease index per cent rating at the ith observation, t_i = time (days between ratings), and n = total number of observations.

^cNumbers are the P > F values, alpha = 0.05.

Table 3. Effects of cultivars and seed treatments on root length at the V4 developmental stage, and root diameter and number of root tips at the V7 developmental stage at Valmeyer, IL in 2008.

Seed treatment	Root length at V4 (cm)		Root diameter at V7 (mm)		Root tips at V7 (no.)
	FS 4456^a	Pioneer 94M30^a	FS 4456	Pioneer 94M30	FS 4456	Pioneer 94M30
Non-treated	112 cde	150 ab	0.90 abcdefgh^b	0.98 a	848 cdefg	648 efg
Mefenoxam	103 cde	133 abcde	0.93 abcde	0.96 ab	910 bcdef	693 defg
Mefenoxam + fludioxonil	114 cde	113 cde	0.95 abc	0.89 abcdefgh	566 g	607 fg
Mefenoxam + azoxystrobin	125 bcde	132 abcde	0.89 abcdefgh	0.86 defghi	700 defg	857 cdefg
Mefenoxam + fludioxonil + azoxystrobin	98 e	137 abc	0.84 ghi	0.89 bcdefgh	1,072 abc	668 efg
Trifloxystrobin + metalaxyl	121 bcde	133 abcde	0.85 efghi	0.88 bcdefghi	824 cdefg	818 cdefg
Metalaxyl + prothioconazole	106 cde	163 a	0.87 cdefghi	0.86 defghi	850 cdefg	839 cdefg
Metalaxyl + prothioconazole + trifloxystrobin	120 bcde	113 cde	0.89 bcdefgh	0.87 cdefghi	934 bcde	994 abcd
Prothioconazole + trifloxystrobin + metalaxyl + B. pumilus	110 cde	114 cde	0.94 abcd	0.80 i	874 cdefg	1,286 a
Mefenoxam + thiophanate-methyl	108 cde	110 cde	0.92 abcdefg	0.85 fghi	822 cdefg	1,213 ab
Metalaxyl + pyraclostrobin + thiophanate-methyl	134 abcd	124 bcde	0.92 abcdefgh	0.84 hi	674 efg	941 bcde
Mefenoxam + thiophanate-methyl + azoxystrobin + B. pumilus + prothioconazole + fludioxonil	131 abcde	101 de	0.92 abcdef	0.84 ghi	780 cdefg	841 cdefg

^a Cultivar FS 4456 and Pioneer 94M30 are considered moderately susceptible and moderately resistant to sudden death syndrome, respectively.

^b Mean separation in PROC MIXED were used to identify differences among seed treatments across cultivars at alpha = 0.05. Values followed by the same letter within a root measurement are not significantly different from each other.

Table 4. Effects of seed treatments on plant stand and sudden death syndrome (SDS) area under disease progress curve (AUDPC) at Valmeyer, IL in 2008.

Active ingredient	Plant stand (plants m^−2)	SDS (AUDPC)^a
Non-treated	26.8 d^b	252 a
Mefenoxam	28.1 cd	201 bc
Mefenoxam + fludioxonil	32.4 a	169 bcd
Mefenoxam + azoxystrobin	31.0 ab	149 d
Mefenoxam + fludioxonil + azoxystrobin	31.3 ab	194 bcd
Trifloxystrobin + metalaxyl	31.1 ab	198 bcd
Metalaxyl + prothioconazole	30.6 ab	152 cd
Metalaxyl + prothioconazole + trifloxystrobin	30.6 ab	217 ab
Prothioconazole + trifloxystrobin + metalaxyl + B. pumilus	29.9 bc	159 cd
Mefenoxam + thiophanate-methyl	30.9 ab	163 cd
Metalaxyl + pyraclostrobin + thiophanate-methyl	31.5 ab	175 bcd
Mefenoxam + thiophanate-methyl + azoxystrobin + B. pumilus + prothioconazole + fludioxonil	27.8 cd	174 bcd

^aAUDPC calculated by: , in which X_i = the disease index per cent rating at the ith observation, t_i = time (days between ratings), and n = total number of observations.

^bMean separation in PROC MIXED were used to identify differences between seed treatments at alpha = 0.05, values followed by the same letter within a column are not significantly different from each other.

Table 5. Summary of fixed-effects and interactions on soybean plant stand, Fusarium virguliforme (Fv) DNA concentration in roots, 2009 sudden death syndrome (SDS) area under disease progress curve (AUDPC), yield, root length, root average diameter and number of root tips from roots collected at growth stages V1, V3 and V6 at Urbana, IL in 2008 and 2009.

Source	df	Plant stand	Fv DNA^a	SDS^bc	Yield	Root length			Root average diameter			Number of root tips
						V1	V3	V6^d	V1^a	V3^a	V6	V1	V3^e	V6^e
Cultivar (C)	1	0.9968^f	0.5989	<0.0001	0.4780	<0.0001	0.2917	<0.0001	0.0505	0.2524	<0.0001	<0.0001	<0.0001	0.0750
Seed Treatment (S)	11	0.1019	0.4666	0.1224	0.2375	0.1419	0.7450	0.2806	0.0671	0.2194	0.1747	0.5992	0.1680	0.5934
C × S	11	0.9561	0.1908	0.4528	0.8252	0.4143	0.8939	0.9353	0.0853	0.4197	0.1069	0.8324	0.6693	0.4564

^aNatural log transformations of [values × 10] were used to meet assumption of normality and homogeneity of variance for analysis.

^bSudden death syndrome foliar symptoms were only present in 2009 for disease rating and analysis.

^cAUDPC calculated by: , in which X_i = the disease index per cent rating at the ith observation, t_i = time (days between ratings), and n = total number of observations.

^dSquare root transformations of values were used to meet assumption of normality and homogeneity variance for analysis.

^eNature log transformations of values were used to meet assumption of normality and homogeneity of variance for analysis.

^fNumbers are the P > F values, alpha = 0.05.

Table 6. Summary of fixed-effects and interactions on soybean stand count, Fusarium virguliforme (Fv) DNA concentration in roots, sudden death syndrome (SDS) area under disease progress curve (AUDPC), root length, root average diameter and number of root tips for roots collected from greenhouse trials.

Source	df	Plant stand	Fv DNA^a	SDS^b	Root length^a	Root average diameter^c	Number of root tips^a
Cultivar (C)	2	0.6562^d	0.4604	0.6562	0.0005	0.5698	0.0025
Seed Treatment (S)	11	0.1585	<0.0001	0.1347	0.9781	0.7967	0.8254
C × S	22	0.7084	0.5366	0.6491	0.1087	0.6187	0.4504

^aSquare root transformations of values were used to meet assumption of normality and homogeneity variance for analysis.

^bAUDPC calculated by: , in which X_i = the disease index per cent rating at the ith observation, t_i = time (days between ratings), and n = total number of observations.

^cNatural log transformations of [values × 100] were used to meet assumptions of normality and homogeneity of variance for analysis.

^dNumbers are the P > F values, alpha = 0.05.

Table 7. Effect of seed treatments on Fusarium virguliforme (Fv) DNA concentration in roots from greenhouse based studies.

Seed treatment	Fv DNA^a (pg mg^−1 root)
Non-treated	47,489 ab
Mefenoxam	51,702 a
Mefenoxam + fludioxonil	43,281 abc
Mefenoxam + azoxystrobin	46,156 ab
Mefenoxam + fludioxonil + azoxystrobin	44,146 abc
Trifloxystrobin + metalaxyl	40,272 bc
Metalaxyl + prothioconazole	39,018 bc
Metalaxyl + prothioconazole + trifloxystrobin	43,928 abc
Prothioconazole + trifloxystrobin + metalaxyl + B. pumilus	47,830 ab
Mefenoxam + thiophanate-methyl	34,425 ab
Metalaxyl + pyraclostrobin + thiophanate-methyl	43,222 abc
Mefenoxam + thiophanate-methyl + azoxystrobin + B. pumilus + prothioconazole + fludioxonil	26,673 d

^aSquare Root transformation of values were used to meet assumptions of normality and homogeneity of variance for analysis. De-transformed least-square means are displayed.

^bMean separation in PROC MIXED was used to identify differences between seed treatments at alpha = 0.05, values followed by the same letter are not significantly different from each other.

Table 8. Effect of seed treatments on seed germination, plant length, lesion length and disease severity of Fusarium virguliforme-inoculated seeds in the rolled-towel laboratory assay.

Seed treatment	Seed germination (%)^a	Plant length (cm)	lesion length (cm)^bc	Disease severity (%)^bd
Non-treated/non-inoculated^e	95 ab^g	26.45 abc	1.74 abcde	9.3 bcd
NaOCl^f/non-inoculated^e	93 abc	30.65 a	0.89 bcde	1.9 de
Non-treated	89 abc	23.40 abcd	2.52 ab	22.6 abc
NaOCl^f	94 abc	25.56 abc	3.89 a	22.2 abc
Mefenoxam	87 abc	19.95 bcd	2.66 ab	29.1 ab
Azoxystrobin	88 abc	25.78 abc	2.54 ab	15.2 abc
B. pumilus	57 d	10.20 e	2.41 abc	50.6 a
Fludioxonil	97 a	27.58 ab	0.69 cde	5.4 cde
Prothioconazole	93 abc	16.76 de	3.09 a	31.0 ab
Pyraclostrobin	78 cd	19.56 cd	2.23 abcd	31.1 ab
Pyraclostrobin + thiophanate-methyl	91 abc	21.75 bcd	0.39 e	11.5 bc
Thiophanate-methyl	79 bcd	20.25 bcd	0.65 de	12.9 abc
Trifloxystrobin	81 bcd	16.58 de	2.72 ab	34.0 ab
Azoxystrobin + B. pumilus + fludioxonil + mefenoxam + prothioconazole + thiophanate-methyl	82 bcd	27.63 ab	0.55 e	1.0 e

^aSquare root transformations of values were used to meet assumptions of normality and homogeneity of variance for analysis. De-transformed least-square means are displayed.

^bNatural log transformations of [values × 10] were used to meet assumptions of normality and homogeneity of variance for analysis. De-transformed least-square means are displayed.

^cLength of lesions observed on lower stems and roots measured in cm.

^dPer cent disease severity calculated by: [lesion length/plant length] × 100.

^eSeeds were not inoculated with 100 µL of 2.5 × 10⁵ Fv conidial solution, while all other seed treatments were inoculated.

^fBefore the experiment, NaOCl (0.5%) was used to rinse seeds for 90 seconds. Then, seeds were rinsed twice with distilled water to remove NaOCl.

^gMean separation in PROC MIXED were used to identify differences between seed treatments at alpha = 0.05, values followed by the same letter are not significantly different from each other.