Effects of fungicide seed treatments on germination, population, and yield of maize grown from seed infected with fungal pathogens

Field Crops Research 122 (2011) 173–178

Contents lists available at ScienceDirect

Field Crops Research journal homepage: www.elsevier.com/locate/fcr

Effects of fungicide seed treatments on germination, population, and yield of maize grown from seed infected with fungal pathogens C.D. Solorzano a , D.K. Malvick b,∗ a b

Department of Crop Sciences, University of Illinois, Urbana, IL 61801, USA Department of Plant Pathology, University of Minnesota, St. Paul, MN 55108, USA

a r t i c l e

i n f o

Article history: Received 23 June 2010 Received in revised form 16 February 2011 Accepted 23 February 2011 Keywords: Stenocarpella Fusarium Seedborne Diplodia Fungi Corn

a b s t r a c t Seedborne fungi can reduce survival, growth, and yield of maize (Zea mays L.). Laboratory, field, and growth chamber experiments were conducted to determine the effects of the seed treatment fungicides fludioxonil, mefenoxam, and azoxystrobin on germination, plant population, and grain yield of maize grown from low-quality hybrid seed infected with seedborne fungal pathogens. Study I used seed of four hybrids infected at 0–54% incidence with Fusarium spp., Stenocarpella maydis, Penicillium spp., Rhizopus spp., and/or Aspergillus spp. Study II used three seed lots for each of two hybrids infected at 7–37% incidence with S. maydis. Warm and cold germination for untreated seed varied among hybrids in both studies. Warm germination of the seed lot with the highest incidence of S. maydis in study II treated with azoxystrobin and fludioxonil was significantly greater (+7%) than the nontreated control. Plant population in study I was significantly affected by seed treatment, hybrid, and their interactions. Populations were greater (≥9%) for fludioxonil, fludioxonil + mefenoxam, and fludioxonil + mefenoxam + azoxystrobin treatments compared to controls. In growth chamber experiments with pasteurized soil, emergence (≥5%) and plant dry weight (≥14%) were both greater than controls only with the triple seed treatment. Plant populations in study II for all seed treatments except mefenoxam and azoxystrobin alone were greater (≥4%) than controls. Yield in study I was significantly affected by hybrid and seed treatment. Yield for one hybrid was higher (≥20%) than the control with all seed treatments except fludioxonil, whereas yield with another hybrid was consistently greater (≥26%) only with the triple seed treatment. Yield in study II was significantly affected by hybrid, seed treatment, and their interactions. Yield was greater (≥8%) than the controls for all seed treatments with one hybrid and with all (≥5%) except azoxystrobin for the other hybrid. Highest yields occurred with the triple seed treatment. Results indicate that fludioxonil and azoxystrobin can increase germination, population, and yield of maize grown from seed infected by S. maydis and other fungi. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Maize (Zea mays L.) is a resilient crop that grows and yields well in many environments. Under some situations, however, seed and seedling diseases of maize can reduce plant survival, growth, and yield. These diseases are most common under conditions of environmental stress and when seed quality has been compromised (Agarwal and Sinclair, 1996). Symptoms include pre- and post-emergence damping-off, low seedling vigor, stunting; and discoloration and decomposition of roots and mesocotyl (Dodd and White, 1999). These symptoms can result from infection by several different fungal and Oomycete pathogens, including species of Aspergillus, Fusarium, Gibberella, Nigrospora, Penicillium, Pythium, Rhizoctonia, Stenocarpella, and Trichoderma (Agarwal and Sinclair,

∗ Corresponding author. Tel.: +1 612 625 5282; fax: +1 612 625 9728. E-mail address: [email protected] (D.K. Malvick). 0378-4290/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2011.02.011

1996; McGee, 1988). Many of these pathogens can be seed- or soilborne, but relatively little research has been done on the effects of seedborne fungal infection of maize and its management with fungicidal seed treatments. Fungal seedborne pathogens that are common and have different effects on maize include Fusarium spp., Stenocarpella maydis (Berk.) Sutton, and Penicillium oxalicum Currie & Thom (Kommedahl and Windels, 1981; McGee, 1988). For example, Fusarium proliferatum, Fusarium subglutinans, and Fusarium verticillioides can be seedor soilborne and cause seedling disease as well as root, ear, and stalk rot (Agarwal and Sinclair, 1996; Rao et al., 1978). Infected seed may lead to infection of seedlings as well as systemic infection of stalks and ears (Anderegg and Guthrie, 1981; Galperin et al., 2003). S. maydis (syn. Diplodia maydis) causes root rot, seedling blight, ear rot, and stalk rot of maize (Dodd and White, 1999; Koehler and Holbert, 1930). Seedborne infection by S. maydis may lead to infection of the plumule, seminal roots, and mesocotyl, resulting in stunting and death of seedlings (Koehler and Holbert, 1930). Seed- and soilborne

174

C.D. Solorzano, D.K. Malvick / Field Crops Research 122 (2011) 173–178

P. oxalicum can cause damping-off and seedling blight of seedlings (Callan et al., 1996; Halfon-Meiri and Solel, 1990). The damaging effects of maize seed and seedling diseases may be minimized with proper seed handling, cultural practices, and seed-applied fungicides (McGee, 1981; Munkvold, 2009). Maize seed severely infected with fungal pathogens is typically removed in the seed cleaning process, but seed with low or moderate levels of infection may not be removed before it is planted (Dodd and White, 1999). Good cultural practices, especially sowing seed in soil that is warm, dry, and free of chemical stressors, can reduce seed and seedling disease (McGee, 1981). Maize seed in often treated with fungicides to reduce seed and seedling diseases (Agarwal and Sinclair, 1996; McGee, 1981; Munkvold, 2009). Captan was widely used, but newer products have largely replaced it (Pedersen et al., 1986; Munkvold, 2009). Most maize seed in the U.S.A. is treated with mefenoxam or metalaxyl and a fungicide such as fludioxonil and/or a strobilurin product. One example is the commonly used product Maxim® XL that is consists of mefenoxam and fludioxonil. Fludioxonil is a phenylpyrrole fungicide that inhibits energy production by disrupting respiration in many different fungi (Leadbeater et al., 1990). Mefenoxam and metalaxyl are acetanilide fungicides that inhibit ribosomal RNA synthesis in Oomycetes (Cohen and Coffey, 1986). More recently, strobilurin fungicides such as azoxystrobin, trifloxystrobin, and pyraclostrobin are used to treat maize seed (Munkvold, 2009). Strobilurins inhibit mitochondrial respiration by binding at the Qo site of cytochrome b in many fungal and Oomycete pathogens (Bartlett et al., 2002; Thomson, 2000). Most studies of fungicidal maize seed treatments have focused on soilborne pathogens (Baird et al., 1994; Pedersen et al., 1986; Rodriguez-Brljevich et al., 2010). For example, seed treated with Captan and planted in several Midwestern U.S. states resulted in about 10% greater stands and yields than nontreated controls (Pedersen et al., 1986). In another study focused on seedling blight and root rot caused soilborne Fusarium graminearum, treatment of seed with Captan, fludioxonil, imazalil, and triticonazole did not improve plant population or yield of maize (Du Toit, 1995). In a growth chamber study with soilborne Fusarium spp., seed treatment with fludioxonil, Captan, and difenoconazole improved shoot and root length and root health (Munkvold and O’Mara, 2002). Although a few studies have suggested that some seed treatments may be effective against seedborne Fusarium spp. (Galperin et al., 2003; Munkvold and O’Mara, 2002), little is known about the effects of seed treatments on growth and yield of maize grown from seed infected by seedborne fungal pathogens, especially genera other than Fusarium. The objective of this research was to determine the effects of the seed-applied fungicides azoxystrobin, fludioxonil, and mefenoxam on germination, plant population, and yield of maize grown from seed infected with S. maydis and other seedborne fungal pathogens.

of the four hybrids FR-A (FR 3310LL × FR 2980), FR-F (FR 3361 × LH 283), FR-G (FR 1064), and W-B (W 5541 MP OT 9230) was used. For study II, seed from hybrids H1 (FR 4341 × FR 3912) and H2 (FR 6942 × FR 3912) was used, each with three seed lots containing several levels of infection by S. maydis. This seed for study II was produced in University of Illinois plots near Urbana. The kind and incidence of seedborne infection were determined by disinfesting 100 seeds with 0.5% aqueous NaOCl solution for 1 min, rinsing with sterile H2 O, placing on potato dextrose agar (Beckton Dickinson, Sparks, MD) amended with 0.3 ml/l of lactic acid (APDA), and then incubating at 25 ± 2 ◦ C with a 10 h photoperiod for 6 days. Fungi that grew from the seed were identified based on morphological characteristics (Barnett and Hunter, 1998; Booth, 1971; Murphy et al., 1974; Nelson et al., 1983). This procedure was conducted two times at different times for all seed. Incidence of seed infection by fungal pathogens ranged from low to high for the hybrids and seed lots in studies I and II (Table 1). In study I, Fusarium and Aspergillus were the only genera detected in seed of all hybrids. Fusarium spp. and S. maydis were detected at the highest levels of infection, e.g., as high as 47% (hybrid FR-F) and 54% (hybrid FR-G), respectively. Other fungi detected at levels above 15% were Aspergillus niger, Penicillium spp., and Rhizopus sp. The hybrid W-B had been selected as a high quality seed lot for study I, and the low level of fungal infection along with the higher plant populations and yields indicate it was higher quality than the other hybrids. In study II, S. maydis was detected at rates from 7 to 37% in hybrids and seed lots, and the incidence of other fungi was 0–7% (Table 1). Hybrid H1-B was considered as the relatively high quality hybrid for study II. Seed for both studies was treated with several combinations of fludioxonil, mefenoxam, and azoxystrobin, in the form of the commercial products Maxim® , ApronXL® , and Dynasty® , respectively (Syngenta Crop Protection, Greensboro, NC), using a slurry-type treater. Four seed treatments were used in study I, in rates of g a.i./100 kg of seed), fludioxonil 2.5 g + mefenoxam 1.0 g, azoxystrobin 1.0 g, fludioxonil 2.5 g + mefenoxam 1.0 g + azoxystrobin 1.0 g, and fludioxonil 2.5 g. In study II, the five seed treatments were fludioxonil 2.5 g + mefenoxam 2.0 g, fludioxonil 2.5 g + mefenoxam 2.0 g + azoxystrobin 1.0 g, fludioxonil 2.5 g, mefenoxam 1.0 g, and azoxystrobin 1.0 g. Nontreated seed was used as controls. Standard germination tests (warm) and tray cold seed germination tests were conducted by SGS Mid-West Seed Services, Inc. (Brookings, SD) using methods from the “International Rules for Seed Testing” published by the International Seed Testing Association (ISTA). Seed was incubated for 7 days at 25 ◦ C for the warm test, and 7 days at 10 ◦ C followed by 7 days at 25 ◦ C for the cold test. Two replicates of 100 untreated control seeds only were used for study I, and two replicates of 100 control and treated seeds were used for study II. 2.2. Field and growth chamber studies

2. Materials and methods 2.1. Seed selection and fungal infection, seed treatments, and germination tests Two studies (I and II) were conducted with hybrid maize seed produced in Illinois. The hybrids were not known to have resistance to seedborne or seedling diseases. Specific hybrid seed lots from Illinois Foundation Seeds (IFS) production fields were selected for study I per recommendations from representatives of IFS and Dr. Don White from the University of Illinois (Table 1). The seed lots were chosen based on apparent fungal seedborne infection and poor quality detected by visual assessment. Only conditioned seed without visible external fungal growth was used. For study I, seed

Field studies were conducted in field plots near Urbana, IL. In study I, three replications of each seed treatment by hybrid combination were established in 2003 and 2004 in a randomized complete block design in a split plot arrangement, with hybrids as main plots and seed treatments as subplots. Seed was sown in a Drummer silty clay loam soil (fine-silty, mixed, superactive, mesic Typic Endoaquoll) on May 19, 2003 and on April 27, 2004. Soybean (Glycine max (L.) Merr.) was the preceding crop, conventional tillage was used, and target planting density was 59.55 × 103 seeds/ha for all plots. Experimental units consisted of two rows, 5.3 m long, with 0.8 m spacing between rows. The insecticide cyfluthrin (Aztec® 2.1%; Bayer CropScience, RTP, NC) at 8.4 kg/ha was applied preplant in 2003, but not in 2004. Severe root damage and lodging due to corn rootworm occurred in 2004 only. The herbicides ace-

C.D. Solorzano, D.K. Malvick / Field Crops Research 122 (2011) 173–178

175

Table 1 Incidence (%) of fungi detected in seed of four nontreated maize hybrids used in study I and for three seed lots of each of two nontreated maize hybrids used in study II; and germination (%) of seed from each hybrid and seed lot under warm and cold laboratory assay conditions. Maize Hybrid Study Ia

Fusarium spp. Stenocarpella maydis Aspergillus niger Aspergillus flavus Penicillium spp. Rhizopus spp. Trichoderma spp. Warm germinationc Cold germinationc a b c

Study IIa

FR-A

FR-F

FR-G

W-B

42 1 11 2 17 2 0 93 95

47 0 23 0 0 20 0 98 87

15 54 1 0 3 0 0 66 60

3 0 2 0 9 1 0 96 91

H1b

H2b

A

B

C

A

B

C

2 37 0 2 0 0 2 74 74

3 7 0 7 0 3 0 87 86

0 12 0 2 0 0 0 94 91

2 27 0 3 0 0 0 88 84

0 17 3 5 0 2 0 82 83

0 25 2 2 0 0 0 92 90

Mean incidence (%) of fungi are based on two replications of 100 seeds each. Three seed lots (A, B, and C) per hybrid. Germination rates did not differ significantly (P = 0.05) for the different hybrids and seed lots of the nontreated seed used in each study.

tochlor (DegreeTM 42%; Monsanto, St. Louis, MO) at 4.8 kg/ha and atrazine (Aatrex® 42.6%; Syngenta) at 4.5 kg/ha were applied preplant in both years. Plant population was determined by counting all of the plants in each plot at the V3 growth stage. Grain yield was obtained using a plot combine and yield was adjusted to 15.5% moisture. Rainfall in 2003 and 2004 from May through September was 60.8 cm and 52.1 cm, respectively, and soil temperature at a depth of 10.2 cm at 10 days after planting was 14.9 ◦ C in 2003 and 15.5 ◦ C in 2004 (Illinois State Climatologist, Champaign, IL). A portion of study I was also conducted in a growth chamber using soil from the same field that was pasteurized to reduce potential confounding effects by soilborne pathogens; and the same hybrids, seed treatments, and experimental design were used as in the field. Soil samples were collected in September to a depth of 15 cm from 10 arbitrarily selected locations in the field plot area, combined, and mixed to form one bulk sample. The soil was mixed 1:1 with sand, steamed at 82 ◦ C for 30 min, and placed into 10 cm pots. Five seeds sown per pot were considered a single replicate, and each seed treatment by hybrid combination was replicated three times. Pots were maintained at 16 ± 2 ◦ C with a 12 h photoperiod, and light intensity of 80 ␮mol/m2 /s. The pots were watered daily and emergence was determined 15 days after planting (DAP). Whole plants were collected at 21 DAP, washed, dried at 50 ◦ C for 24 h, and weighed. This study was repeated once. Study II utilized a randomized complete block design and a split–split plot arrangement in field experiments, with hybrid as main plots, seed lot with several incidence levels of S. maydis as subplots, and seed treatment as sub-subplots. Each seed treatment by seed lot combination was replicated three times. Seed was sown on April 14 and 27, 2004 at two sites near Urbana, IL, one with Elburn silt loam soil (fine-silty, mixed, superactive, mesic Aquic Argiudoll) and the other with Drummer silty clay loam. Field preparation, agronomic, and experimental factors were the same as in study I, and the insecticide cyfluthrin was applied preplant at 8.4 kg/ha in both experimental sites. 2.3. Statistical analysis Analysis of variance was performed using PROC MIXED in SAS version 9.1 (SAS Institute Inc., Cary, NC) for all data unless noted otherwise. For study I, replicates and the interaction of replicates by hybrids were used as random effects, and hybrids, seed treatments, and the interaction between seed treatments and hybrids were used as fixed effects. Data from each year of study I were analyzed separately due to severe root damage and lodging from

corn rootworm in one year but not the other. The same fixed and random effects were used for analysis of the data from the growth chamber experiments, and replication was included as a random effect that was nested within hybrid and seed treatment. For study II, hybrids, fungicides, seed treatments, and their interactions were used as fixed effects; and replications, locations, and replications by hybrids and by fungicides nested within hybrids were considered as random effects. Location had no significant affect in study II and the data for both locations were combined for analysis and presentation. The main and interaction effects were compared with Fisher’s LSD and considered significant at P ≤ 0.10 for all field and growth chamber experiments. Linear regression analysis was conducted using SAS to determine if mean fungal infection rate and germination were correlated. For the laboratory germination study, differences in effects were considered significant at P ≤ 0.05.

3. Results 3.1. Germination rates for untreated and treated seed Warm and cold germination rates did not differ significantly among the hybrids and lots of nontreated seed in studies I and II (Table 1). In study I, the mean warm germination was above 65% and cold germination was above 59% for all of the nontreated control seed. The mean germination rate was lowest for hybrid FR-G, which had a high incidence of S. maydis infection. In study II, warm and cold germination rates for control seed ranged from 74% to 94% for the hybrids and seed lots with several levels of infection by S. maydis (Table 1). The correlations between infection rate and germination were −0.68 and −0.63 for cold and warm germination, respectively. Cold and warm germination rates for treated differed significantly (P = 0.05), based on infection level, hybrid by infection level, and hybrid by infection level by seed treatment only for seed lots A and B of hybrid 1 in study II. Warm germination of seed lot A was significantly greater for the fludioxonil (81%) and azoxystrobin (81%) treatments compared to the control (74%), however, cold germination was not significantly increased by these seed treatments (additional data not shown). For seed lot B of hybrid 1, warm (92%) and cold (90%) germination of seed treated with azoxystrobin was significantly greater than the warm (87%) and cold (85%) nontreated controls. Other seed treatments had no significant effect on germination for the other seed lots of hybrid 1, and no seed treatments significantly increased germination for hybrid 2 (additional data not shown).

176

C.D. Solorzano, D.K. Malvick / Field Crops Research 122 (2011) 173–178

Table 2 Plant population and grain yield for maize hybrids FR-A, FR-F, FR-G, and W-B treated with four fungicidal seed treatments in field study I conducted over two years. Yeara

2003

2004

a b c d e

Seed treatmentb

Nontreated Fludioxonil + mefenoxam Azoxystrobin Fludioxonil + mefenoxam + azoxystrobin Fludioxonil Nontreated Fludioxonil + mefenoxam Azoxystrobin Fludioxonil + mefenoxam + azoxystrobin Fludioxonil

FR-A

FR-F

FR-G

W-B

pl/hac , d

Mg/hae

pl/hac

Mg/ha

pl/hac

Mg/ha

pl/hac

Mg/ha

52.49 b 56.00 a 55.77 ab 55.36 ab 56.18 ab 45.52 b 54.54 a 53.72 a 54.54 a 52.49 a

11.15 a 11.27 a 10.56 a 11.52 a 11.34 a 6.66 a 7.80 a 6.41 a 7.41 a 7.51 a

36.49 d 58.64 a 43.47 c 58.64 a 47.98 b 13.94 d 55.36 a 43.47 b 53.72 a 34.03 c

9.34 c 14.12 a 11.21 b 13.41 a 11.47 b 2.13 c 7.40 a 5.10 b 7.44 a 2.83 c

22.14 c 28.30 b 31.57 ab 32.80 a 32.39 ab 28.29 ab 32.39 a 29.54 ab 28.70 ab 26.65 b

5.10 b 5.34 b 5.56 ab 6.41 a 5.22 b 2.91 a 2.25 a 3.36 a 2.15 a 2.51 a

52.08 c 52.90 bc 56.59 ab 56.60 ab 59.05 a 36.08 d 56.18 ab 47.57 c 56.00 a 51.67 bc

12.55 a 12.78 a 12.83 a 13.11 a 13.51 a 6.36 b 7.73 ab 7.86 ab 8.79 a 8.39 a

Data for the two years of this study were analyzed separately due to severe corn rootworm root damage and lodging in 2004 but not in 2003. Rates for seed treatments per 100 kg of seed were 2.5 g (a.i.) for fludioxonil, 2.0 g (a.i.) for mefenoxam, and 1.0 g (a.i.) for azoxystrobin. Plant population measured as plants/hectare (pl/ha) × 103 . Mean values for population and yield within columns and year having the same letter are not significantly different at P ≤ 0.10. Corn grain yield measured as Mg/ha.

3.2. Effects of seed treatments and fungal infestation levels on plant populations Maize plant population was significantly influenced by seed treatment in both studies. Although four fungal species were above 10% incidence in one or more hybrids (Table 1), S. maydis was the most intensively studied seedborne pathogen at 54% incidence in hybrid FR-G in study I and 7–37% incidence in study II. Seed treatment, hybrid, and their interactions significantly affected plant population in study I. The plant populations for one or more seed treatments were significantly greater than the nontreated control for all hybrids in both years except for hybrid FR-G in 2004 (Table 2). This was also the year for this study that severe damage from corn rootworm developed. The most consistent response for significant and highest plant populations were obtained with the double treatment containing fludioxonil and mefenoxam and the triple treatment containing fludioxonil plus mefenoxam and azoxystrobin in both years. The greatest increase in population of treated compared to nontreated seed was with hybrid FR-G, which had the high level of S. maydis infection compared to the other hybrids that had undetectable levels of this fungus. However, some hybrids infected with other fungi also benefited from seed treatment, e.g., especially large increases were seen with hybrid FR-F that was infected with high levels of Fusarium spp. and A. niger. In study II, seed treatment, hybrid, and hybrid by seed treatment were significant sources of variation for plant population (Table 3). The interaction of hybrid by treated seed lot (with various levels of infection) and the location were not significant for plant population and the data were combined for presentation across locations and seed lots for each hybrid. In study

II, the benefits to plant populations for seed infected with several levels of S. maydis was documented with different hybrids and seed lots. The nontreated seed of hybrid 2, which had the higher mean rate of infection by S. maydis, had the lowest plant population (Tables 1 and 3). This negative relationship between infection and population extended to all nontreated seed lots. Populations for nontreated seed lots A, B, and C of hybrid 1 were 47.03 × 103 , 54.55 × 103 , and 54.74 × 103 plants/ha, with B and C being significantly greater than A, but not different than each other. Populations for nontreated seed lots A, B, and C of hybrid 2 were 48.86 × 103 , 49.01 × 103 , and 54.62 × 103 plants/ha, with A and B being significantly lower than C, but not different than each other (additional data not shown). Populations of both hybrids were significantly greater for treated than nontreated seed for all seed treatments except mefenoxam alone (Table 3). The population was numerically highest with the triple seed treatment for both hybrids.

3.3. Effects of seed treatments on emergence and growth in growth chamber studies The hybrid by seed treatment interaction that was observed in the field experiments of study I was not significant in the growth chamber experiment with pasteurized field soil, so data for the four hybrids were combined for presentation. Only the triple seed treatment significantly increased both emergence and dry weight of plants compared to the nontreated control (Table 4).

Table 3 Plant population and yield of two maize hybrids treated with fungicidal seed treatments at two field locations in study II.a Seed treatmentb

Hybrid 1c

Hybrid 2d e,f

Population Nontreated Fludioxonil + mefenoxam Fludioxonil + mefenoxam + azoxystrobin Fludioxonil Mefenoxam Azoxystrobin

52.47 c 55.16 ab 55.86 a 54.35 b 51.62 cd 50.88 d

(pl/ha)

Yield (Mg/ha)

Populatione (pl/ha)

Yield (Mg/ha)

12.24 b 13.24 a 13.31 a 12.88 a 12.83 a 12.07 b

48.15 b 52.19 a 52.55 a 51.74 a 47.70 b 52.15 a

11.95 c 13.22 ab 13.67 a 13.39 ab 12.86 b 13.43 a

a Neither location nor seed lot had a significant effect on plant population or yield, so the data from two locations were combined for analysis as were three seed lots per hybrid. b Rates for seed treatments per 100 kg of seed were 2.5 g (a.i.) for fludioxonil, 2.0 g (a.i.) for mefenoxam, and 1.0 g (a.i.) for azoxystrobin. c Mean S. maydis infection for hybrid 1 = 19%. d Mean S. maydis infection for hybrid 2 = 23%. e Plant population measured as plants/hectare (pl/ha) × 103 . f Mean values for population and yield within columns having the same letter are not significantly different at P ≤ 0.10.

C.D. Solorzano, D.K. Malvick / Field Crops Research 122 (2011) 173–178 Table 4 Emergence and dry weight of four maize hybrids (FR-A, FR-F, FR-G, and W-B)a treated with fungicide seed treatments in growth chamber studies with pasteurized field soil. Seed treatmentb

Emergence (%)c

Dry weight (g)

Nontreated Fludioxonil + mefenoxam Azoxystrobin Fludioxonil + mefenoxam + azoxystrobin Fludioxonil

79.6 c 85.4 ab 89.6 a 84.6 b 83.6 bc

0.93 b 0.98 b 0.99 ab 1.06 a 0.99 ab

a The hybrid by seed treatment interaction was not significant and the data represent the mean from the four hybrids combined. b Rates for seed treatments per 100 kg of seed were 2.5 g (a.i.) for fludioxonil, 2.0 g (a.i.) for mefenoxam, and 1.0 g (a.i.) for azoxystrobin. c Mean values for emergence and dry weight within columns having the same letter are not significantly different at P ≤ 0.10.

3.4. Effects of seed treatments and fungal infection on yield Yield of maize grown from the poor-quality seed lots selected for these studies was significantly greater for one or more seed treatments than the nontreated controls in both studies I and II (Tables 2 and 3). In study I, hybrid, seed treatment, and their interaction were significant for yield in 2003, and hybrid and seed treatment were significant in 2004 (Table 2). Yield for one or more seed treatments were significantly greater than the nontreated control for hybrids FR-F and FR-G in 2003, which had relatively high levels of infection by S. maydis, Fusarium, or Aspergillus, and for FR-F and W-B in 2004. For example, yield for hybrid FR-F was significantly higher for all seed treatments than the nontreated control in 2003, and for all seed treatments except fludioxonil alone in 2004. The largest increase in yield of treated vs. nontreated seed was measured with hybrid FR-G, which had a high level of S. maydis infection relative to other hybrids. With hybrid FR-G in 2003, only the triple seed treatment resulted in a yield significantly greater than the nontreated control. In 2004, the triple seed treatment significantly increased yield compared to the nontreated controls for hybrids FR-F and W-B, and yield was most often greatest with the triple treatment (Table 2). Seed infected with S. maydis was not the only seed to respond to seed treatments, since some hybrids infected with the other fungi also had significantly increased yield after seed treatment. For example, the greatest difference in yield between treated and untreated seed was measured with hybrid FR-F, which had relatively high levels of infection by A. niger and Fusarium spp. In study II, hybrid, seed treatment, and their interactions significantly affected yield (Table 3). The interactions of hybrid by seed lot and location were not significant for yield, so the data were combined across locations and seed lots for each hybrid for presentation. Yields were significantly greater than the nontreated control with all seed treatments except azoxystrobin alone for hybrid 1, and for all seed treatments for hybrid 2. Yield benefits following treatment of seed that was infected with several levels of S. maydis was shown with different hybrids and seed lots. Yields were numerically highest and significantly greater that the nontreated control with the triple treatment for both hybrids, but generally not significantly different than the other seed treatments. 4. Discussion Hybrid maize seed sold in the U.S.A. is usually treated with fungicides before planting, and the types of fungicides used are changing as new products are developed. Most efficacy studies on maize seed treatment fungicides have been conducted with good quality seed and have focused on soilborne pathogens. This study demonstrates that treatment of maize seed with azoxystrobin and fludioxonil can significantly improve germination, growth, plant population, and

177

yield of maize grown from seed of poor quality due to seedborne infection by S. maydis, A. niger, Fusarium and Rhizopus sp., and other fungi. It had been known that seedborne pathogens can decrease maize germination and growth, however, management of seedborne fungal pathogens of maize has not been well understood (McGee, 1988; Munkvold and O’Mara, 2002). In one of very few published studies of the effects of fungicide seed treatments on seedborne pathogens of maize, Galperin et al. (2003) reported that treatment of seed with the fungicide prochloraz reduced seed-toseed to transmission and subsequent seedling blight caused by Fusarium moniliforme. Munkvold and O’Mara (2002) suggested that difenoconazole, fludioxonil, and Captan may suppress seedborne fungi in maize. Wall et al. (1983) reported improved emergence and yield from Phomopsis-infected soybean seed following treatment with fungicides. The potential benefits of several combinations of seed treatment fungicides on population and yield of maize grown from seed infected with high levels and multiple types of seedborne fungi was demonstrated in replicated field and growth chamber studies. Plant population was a key response variable because it is influenced by seedborne diseases and maize does not compensate well for reductions in plant population. Significant increases in plant population were measured more often than significant increases in yield for treated vs. nontreated seed. Baird et al. (1994) reported that combinations of protectant seed treatment fungicides can reduce soilborne seedling disease damage and increase maize populations. Results from the present study demonstrate that both plant population and yield of maize can increase with fungicidal seed treatments applied to poor quality seed. Plant population and yield increases from the seed treatments were related to the incidence and types of seedborne fungal infection, especially S. maydis, which was at high levels in one hybrid in study I and at low to high levels in seed lots in study II. The putative role of seedborne pathogen suppression by seed treatments in increasing emergence and plant growth was supported in growth chamber studies where the potential effects of soilborne pathogens were reduced or eliminated by soil pasteurization. The seed-applied fungicides fludioxonil, mefenoxam, and azoxystrobin had different effects on plant population and yield of maize grown from the poor quality seed. The triple treatment usually resulted in the numerically highest plant population and yield, however, this treatment was often not significantly different than the fludioxonil + mefenoxam treatment. Fludioxonil and azoxystrobin appeared to have similar suppressive effects on seedborne S. maydis, although additional benefits were also observed where azoxystrobin was added to fludioxonil. These fungicides often had the greatest effects on increasing plant population and yield when applied to seed with relatively high levels of seedborne fungal infection, indicating that they can suppress S. maydis and other seedborne fungi. The effects of these two fungicides on seed with high levels of seedborne Fusarium and Rhizopus varied between years of the field studies. In contrast, treatment with mefenoxam alone generally resulted in lower plant stands and yields than when it was combined with azoxystrobin and/or fludioxonil. This was expected because the primary activity of mefenoxam is against infection of maize by Pythium, which had no apparent activity in the well-drained field sites in this study. Growth chamber studies with pasteurized field soil focused the evaluation of seed treatments on seedborne fungi by reducing or eliminating the potentially confounding effects of soilborne pathogens. Only the triple seed treatment significantly increased emergence and dry weight compared to the control in the studies with pasteurized soil. The results from the growth chamber support the role that the seed treatments may play in reducing damaging activity of seedborne pathogens in the likely absence of high levels

178

C.D. Solorzano, D.K. Malvick / Field Crops Research 122 (2011) 173–178

of soilborne pathogens, whereas seed treatments in the field studies may have affected soilborne as well as the seedborne pathogens. The germination tests also exclusively evaluated the effects of seed treatments on seedborne pathogens, especially S. maydis with minimal potential for external sources of inoculum. The warm and cold germination rates were negatively correlated with the level of seedborne S. maydis, indicating that seedborne infection by this pathogen can reduce seed germination. The influence of fungicidal seed treatments on the germination of seed infected by S. maydis was positive but was also inconsistent. Although germination of treated seed of two seed lots of hybrid 1 infected with S. maydis was significantly greater than untreated seed for some seed treatments, there was no significant benefit in germination from any seed treatment for the other seed lots in study II under cool or warm conditions. Strobilurin fungicides, which include azoxystrobin, trifloxystrobin, and pyraclostrobin, have only recently been used widely as seed treatments for maize (Munkvold, 2009). Azoxystrobin was one of the first, and was added to fludioxonil + mefenoxam as a seed treatment. Few studies on its use as a seed treatment on maize have been published, and none to our knowledge on its effect on seedborne pathogens including S. maydis. A recent study of maize seed treated with fludioxonil + mefenoxam + azoxystrobin + thiamethoxam reported that this treatment combination reduced Fusarium disease severity and increased chlorophyll fluorescence; however, its effect on plant population and yield were not measured (RodriguezBrljevich et al., 2010). Although the present study used different methods and focused on different plant response data, it also indicates that seed treatments containing azoxystrobin can reduce detrimental effects of fungal infection on seedling growth and performance. In summary, this study demonstrates that fungicide seed treatments containing fludioxonil and azoxystrobin can improve germination, plant population, growth, and yield of maize grown from seed containing moderate to high levels of seedborne fungi. These benefits were most clearly documented with seedborne S. maydis. The benefits of seed treatments appeared to be related to the type and level of seedborne fungal infection. Additional work is needed to clarify the environmental conditions and the type of infection that result in optimal efficacy of these and other fungicides for improving performance of maize grown from seed of poor quality due to fungal infection. Acknowledgements We thank D. White, W. Pedersen, and J. Pataky for support and assistance with this project, Syngenta Crop Protection for partial financial support, and E. Grunden for expert technical assistance. This research was conducted in partial fulfillment of the requirements for an M.S degree for the first author in the Department of Crop Sciences at the University of Illinois.

References Agarwal, V.K., Sinclair, J.B., 1996. Principles of Seed Pathology, second ed. CRC Press Inc., Boca Raton, FL. Anderegg, J., Guthrie, J.W., 1981. Seed-borne Fusarium moniliforme and seedling infection in hybrid sweet corn. Phytopathology 71, 1196–1198. Baird, R.E., Nankam, C., Fallah Moghaddam, P., Pataky, J.K., 1994. Evaluation of seed treatments on shrunken-2 sweet corn. Plant Dis. 78, 817–821. Barnett, H.L., Hunter, B.B., 1998. Illustrated Genera of Imperfect Fungi. APS Press, St. Paul, MN. Bartlett, D.W., Clough, J.M., Godwin, J.R., Hall, A.A., Hamer, M., Parr-Dobrzanski, B., 2002. Review: the strobilurin fungicides. Pest Manage. Sci. 58, 649–662. Booth, C., 1971. The Genus Fusarium, second ed. Commonwealth Mycology Institute, Kew, Surrey. Callan, N.W., Miller, J.B., Mathre, D.E., Mohan, S.K., 1996. Soil moisture and temperature effects on shrunken-2 sweet corn seed decay and seedling blight caused by Penicillium oxalicum. J. Am. Soc. Hortic. Sci. 121, 83–90. Cohen, Y., Coffey, M.D., 1986. Systemic fungicides and the control of Oomycetes. Annu. Rev. Phytopathol. 24, 311–338. Dodd, J.L., White, D.G., 1999. Seed rot, seedling blight, and damping-off. In: White, D.G. (Ed.), Compendium of Corn Diseases. APS Press, St. Paul, MN. Du Toit, L.J., 1995. Field and greenhouse studies of Fusarium graminearum seedling blight of maize. M.S. Thesis. University of Illinois at Urbana-Champaign, Urbana, Illinois. Galperin, M., Graf, S., Kenigsbuch, D., 2003. Seed treatment prevents vertical transmission of Fusarium moniliforme, making a significant contribution to disease control. Phytoparasitica 31, 344–352. Halfon-Meiri, A., Solel, Z., 1990. Factors affecting seedling blight of sweet corn caused by seed-borne Penicillium oxalicum. Plant Dis. 74, 36–39. Koehler, B., Holbert, J.R., 1930. Corn Diseases in Illinois. University of Illinois, Agricultural Experiment Station, Urbana, IL. Kommedahl, T., Windels, C.E., 1981. Root-, stalk-, and ear-infecting Fusarium species on corn in the USA. In: Nelson, P.E., Toussoun, T.A., Cook, R.J. (Eds.), Fusarium Diseases, Biology and Taxonomy. Pennsylvania State University Press, University Park and London. Leadbeater, A.J., Nevill, D.J., Steck, B., Nordmeyer, D., 1990. CGA: a novel fungicide for seed treatment. In: Brighton Crop Protection Conference – Pests and Diseases, vol. 3 , pp. 825–830. McGee, D.C., 1981. Seed pathology: its place in modern seed production. Plant Dis. 65, 638–641. McGee, D.C., 1988. Maize Diseases. A Reference Source for Seed Technologists. APS Press, St. Paul, MN. Munkvold, G.P., O’Mara, J.K., 2002. Laboratory and growth chamber evaluation of fungicidal seed treatments for maize seedling blight caused by Fusarium species. Plant Dis. 86, 143–150. Munkvold, G.P., 2009. Seed pathology progress in academia and industry. Annu. Rev. Phytopathol. 47, 285–311. Murphy, J.A., Campbell, L.L., Pappelis, A.J., 1974. Morphological observations of Diplodia maydis on synthetic and natural substrates as revealed by scanning electron microscopy. Appl. Microbiol. 27, 232–250. Nelson, P.E., Toussoun, T.A., Marasas, W.F.O., 1983. Fusarium Species: An Illustrated Manual for Identification. Pennsylvania State University Press, University Park, Pennsylvania. Pedersen, W.L., Perkins, J.M., White, D.G., 1986. Evaluation of captan as a seed treatment for corn. Plant Dis. 70, 45–49. Rao, B., Schmitthenner, A.F., Caldwell, R., Ellet, C.W., 1978. Prevalence and virulence of Pythium species associated with root rot of corn in poorly drained soil. Phytopathology 68, 1557–1563. Rodriguez-Brljevich, C., Kanobe, C., Shanahan, J.F., Robertson, A.E., 2010. Seed treatments enhance photosynthesis in maize seedlings by reducing infection with Fusarium spp. and consequent disease development in maize. Eur. J. Plant Pathol. 126, 343–347. SAS, Institute Inc., 2004. SAS/STAT 9.1 User’s Guide. SAS Institute Inc., Cary, NC. Thomson, W.T., 2000. Agricultural Chemicals: Fungicides/2000: Book IV. Thomson Publications, CA. Wall, M.T., McGee, D.C., Burris, J.S., 1983. Emergence and yield of fungicide-treated soybean seed differing in quality. Agron. J. 75, 969–973.