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Inoculation with ArbuscularMycorrhizal Fungi Increases theYield of Potatoes in a High PSoilDavid D. Douds Jr.a, Gerald Nagahashia, CarolynReiderb & Paul R. Hepperlyb

a U.S. Department of Agriculture, AgriculturalResearch Service, Eastern Regional Research Center,600 East Mermaid Lane, Wyndmoor, PA 19038, U.S.A.b The Rodale Institute, 611 Siegfriedale Road,Kutztown, PA 19530Published online: 15 May 2014.

To cite this article: David D. Douds Jr., Gerald Nagahashi, Carolyn Reider &Paul R. Hepperly (2007) Inoculation with Arbuscular Mycorrhizal Fungi Increasesthe Yield of Potatoes in a High P Soil, Biological Agriculture & Horticulture:An International Journal for Sustainable Production Systems, 25:1, 67-78, DOI:10.1080/01448765.2007.10823209

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Biolo[?ical Agricullllre and Horticulture, 2007, Vol. 25, pp. 67-78 0144-8765/07 $10 © 2007 A B Academic Publishers P1inted in Great Britain

Inoculation with Arbuscular Mycorrhizal Fungi Increases the Yield of Potatoes in a High P Soil

David D. Douds1··, Jr., Gerald Nagahashi\

Carolyn Reider2·# and Paul R. Hepperly2

1 U.S. Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038, U.S.A. 2 The Rodale Institute, 611 Siegfriedale Road, Kutztown, PA 19530

ABSTRACT

Arbuscular mycorrhizal (AM) fungi are potentially important tools in agricultural systems that reduce or eliminate chemical inputs common in modem ag1iculture. We tested the response of potato (Solanum tuberosum L. cv. Superior) to inoculation with AM fungi in a field with very high available P (375 J.Ig g-1 soil) in two growing seasons. Inoculation treatments included a commercially available inoculum containing Glomus intraradices, mixed species inocula produced on-farm in mixtures of compost and vermiculite, and a control treatment consisting of a freshly prepared compost and vermiculite mixture. In addition, two farming systems were imposed: conventional chemical fe1tilizers or dairy manure composted with leaves were applied to meet recommended nutrient requirements. Yields of tubers on a fresh weight basis in the first year were significantly increased by AM fungus inoculum, 33% under conventional fertilizer application and 45% with compost addition vs. controls in each system. The response to inoculation the second year was less; however yields of inoculated plants were I 0 to 20% greater than controls. There was a significant positive treatment effect of inoculation upon production of larger sized potatoes in the second year. Neither year saw a marked difference in yield response among AM fungus inocula. These results demonstrate the potential yield benefits of inoculation of potatoes with AM fungi produced on the farm.

INTRODUCTION

Arbuscular mycoiThizal (AM) fungi are soil fungi that form a symbiosis with the majority of crop and horticultural plants. Among the benefits to the host plant ascribed to the symbiosis are enhanced uptake of immobile mineral nutrients,

*Con·esponding author: david.douds@ars.usda.gov Present address: 103 Lutz Rd., Boyertown, PA 19512, U.S.A.

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68 DAVID D. DOUDS JR. AND OTHERS

enhanced water relations, and increased resistance to pathogens (Smith & Read, 1997). In addition, AM fungi have been shown to produce a glycoprotein, glomalin, that is believed to play a key role in stabilizing soil aggregates (Wright & Upadhyaya, 1996, 1998). Therefore, AM fungi potentially play important roles in sustainable plant production systems that reduce or eliminate synthetic chemical inputs.

Inocula of these fungi are currently commercially available. Another option for agronomists and horticulturists is to produce their own inoculum of AM fungi on the farm (Douds et at., 2005). The first methods for the on-farm production of AM fungus inoculum were developed in Colombia and India (Sieverding, 1991; Gaur, 1997). Generally, these methods entailed tilling and fumigating a small plot or bed of soil and then inoculating with a selected AM fungus or mixture of AM fungi. A selected host plant or rotation of host plants is then grown on the plot for 4 months to 3 years, after which the soil is harvested and used as inoculum. Modifications omit the use of fumigants and therefore propagate indigenous AM fungi (Gaur et at., 2000; Gaur & Adholeya, 2002). These methods are amenable to labour intensive agriculture in which, for example, the inoculum can be applied by hand to planting holes. Utilization of inoculum of Glomus manihotis produced in the on-farm system stimulated a 20% increase in yield of cassava (Manihot esculenta) in Colombia (Sieverding, 1991).

Another method for the on-farm production of AM fungus inoculum has been developed for farmers in temperate climates (Douds et at., 2006). Bahiagrass (Paspalum notatum Flugge) seedlings colonized by AM fungi are transplanted into raised bed enclosures filled with compost diluted with vermiculite. The enclosures are weeded and watered as needed for one growing season, during which the roots and AM fungi spread throughout the media. The bahiagrass is later frost killed and the AM fungi over winter naturally in situ. The compost and vermiculite mixture is then ready for use as inoculum the following spring. Propagule densities in yard clippings compost and vermiculite mixtures ranged from 42 to 500 propagules cm-3 depending on the vermiculite dilution. The inoculum is most readily used as an amendment to horticultural potting media for vegetable seedling production prior to transplant to the field.

Phosphorus is the soil nutrient which plays the greatest role in the AM symbiosis. The extraradical mycelium of AM fungi effectively extend the volume of soil explored for available P from the root hair zone of a nonmycorrhizal root to a distance up to 15 em from the colonized root (George, 2000). This enhanced P uptake can result in increased growth of mycorrhizal plants over nonmycorrhizal controls in low P soils. Phosphorus also has a negative effect on the symbiosis, however. Plants grown in high P soils limit colonization of their roots by AM fungi (Mosse, 1973; Menge et at., 1978), presumably as a way to limit the carbon cost of the symbiosis in situations where the benefit may be minimal (Hayman, 1983). Therefore,

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MYCORRHIZAL FUNGI AND POTATO YIELDS IN HIGH P SOIL 69

positive growth responses to inoculation with AM fungi do not occur typically in high P soils, and indeed negative responses have been seen (Mosse, 1973; Peng et al., 1993). However, research has shown that even in the absence of a growth or P uptake enhancement relative to nonmycorrhizal plants, the majority of P uptake can be attributed to the fungus (Smith et al., 2004; Li et al., 2006).

Experiments were conducted in 2002 and 2003 to determine the effect of inoculation with AM fungi upon growth and yield of potatoes in a field with high available P. Two types of inocula were compared: a commercially available inoculum containing Glomus intraradices Schenck and Smith in a vermiculite and peat based mixture and a multi-species inoculum produced on-farm in compost and vermiculite mixtures.

MATERIALS AND METHODS

AM fungus inocula

There were three inoculation treatments in Experiment I (2002). One inoculation treatment was 15 cm3 of the commercially available inoculant Myke® (Premier Tech Biotechnologies, Riviere-du-Loup, Quebec G5R 6Cl Canada). This inoculant contained 30 propagules of G. intraradices, as guaranteed by the manufacturer. The second AM fungus treatment was 15 cm3

of a 1:9 [ v/v] mixture of yard clippings compost and vermiculite containing Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe, Glomus etunicatum Becker & Gerdemann, Glomus claroideum Schenck & Smith, and Gigaspora gigantea (Nicol. & Gerd.) Gerdemann & Trappe produced in 2001 on-farm at the Stoneleigh Estate (Villanova, PA) (Douds et al., 2006) and stored 5 months at 4°C. This volume of inoculum was estimated via MPN bioassay (Alexander, 1965) at the time of planting to contain 3225 propagules of AM fungi, present as spores, infective hyphae, and colonized pieces of P. notatum roots. The third inoculation treatment was the control, which consisted of 15 cm3 of a l :9 [v/v] freshly prepared mixture of yard clippings compost and vermiculite. This was included to provide the nutrients and background microorganisms present in the inoculum produced on the farm.

There were four inoculation treatments in Experiment II (2003). One was 15 cm3 of a new batch of the same commercial inoculum used in Experiment I. The second was 15 cm3 of a 1:4 [v/v] mixture of yard clippings compost and vermiculite in which G. mosseae, G. etunicatum, and Glomus geosporum (Nicol. & Gerd.) Walker were grown in 2002 at the Stoneleigh Estate. This inoculum contained an estimated 1800 propagules, determined also by MPN bioassay, after over wintering naturally outdoors in the production enclosures (Douds et al., 2006), as a farmer would utilize the inoculum produced on-farm.

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70 DAVID D. DOUDS JR. AND OTHERS

The third inoculation treatment consisted of 15 cm3 of a I: 12 [ v/v] mixture of dairy manure/leaf compost mixed with vermiculite in which the same three AM fungi were propagated at The Rodale Institute (Kutztown, PA) in 2002. This inoculum also over wintered naturally in situ in the production enclosures and contained 322 propagules at the time of planting. The final treatment was the control application of 15 cm3 of a 1:4 [ v/v] freshly prepared mixture of yard clippings compost and vermiculite.

Planting and experimental design

The experiments were conducted in the Compost Utilization Trial at The Rodale Institute in Kutztown, PA (Reider et at., 2000). The impacts of compost utilization and crop rotation upon the indigenous AM fungus community at this site were reported earlier (Douds et at., 1997). The soil at the experimental site was predominately a Berks shaley loam (Typic Dystrochept). Soil pH across the field ranged from 6.4 to 6.9 (in water), available P from 713 to 787 kg Pp

5 ha-1 (HCI and NH

4F extractable), and exchangeable K from 219 to 277 kg

Kp ha-1 (NH4

OAc extraction). The previous crop on the experimental plots in both years was maize. There were two nutrient management treatments, each imposed upon separate 6.1 x 21.3 m plots within four blocks. These included: (1) conventional chemical fertilizers and (2) dairy manure and leaf compost added to supply sufficient N for crop growth. Nutrient additions to all plots in Experiment I began with a maintenance application of 186 kg K ha-1

(as K2SO) on 11 March 2002. Conventionally managed plots also received

168 kg N ha-1 and 56 kg P ha-1 on 2 April, as well as an additional sidedress of N on 10 June (84 kg N ha-1

). Other plots received a dairy manure + leaf compost on 2 April (12105 kg ha-1 dry wt basis). This supplied 325 kg N, 91 kg P, and 184 kg K ha-1

• The compost was produced on site from a 1 :4 [ v/v] mixture of dairy cow manure and leaves, respectively. The manure component included straw and newspaper bedding. Application of compost N exceeded that of conventional chemical fertilizers because only 40-50% of the N in manures and composts is considered immediately available to plants (Penn State Agronomy Guide 1991-1992, 1991; Reider et at., 1992).

Seed potatoes (Solanum tuberosum L. cv. Superior) were planted at 25 em spacings in rows 91 em apart and manually inoculated on 19 April 2002 for Experiment I. Ten seed potatoes were inoculated for each treatment in each of the four blocks by placing the inoculum directly beneath the seed potato. Treatments were imposed sequentially on individual seed potatoes progressing down the row (e.g. ABCABC ... ). Weeds were controlled mechanically on all plots with two rotary hoe applications and three cultivations. Rainfall at the site was above average for the months the plants were grown (April through July: 46.6 em in 2002 vs. 39.6 em average). However, the total for July was

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MYCORRHIZAL FUNGI AND POTATO YIELDS IN HIGH P SOIL 7 I

4.25 em less than average, and supplemental irrigation was applied twice (26 June and 11 July, 2.5 em each).

The experimental design was changed in Experiment II. Potatoes ( cv. Superior) were planted on I May 2003 in two 6.1 x 21.3 m plots. One plot received conventional chemical fertilizers ( 168 kg N ha-1 and 56 kg P ha-1

before planting followed by a sidedress of 84 kg N ha-1 as urea and NH4N0

3)

and the other received dairy manure and leaf compost as in Experiment I. This experimental design precluded comparisons of nutrient management systems in Experiment II, but that was not the focus of the experiment. Each of the middle four rows of the plots received five replicates of each inoculation treatment, each replicate was a unit of four consecutive seed potatoes. Therefore, each of the four inoculation treatments was replicated in 20 units of four potatoes each in each plot. Plots were cultivated twice. Rainfall was again above average for this period (May through August: 59.5 em vs. 41.6 em). Nonetheless, plots required irrigation on 3 and 15 July (2.5 em each).

Sampling and analysis

Mid-growing season samplings were conducted in each experiment. Three plants from each nutrient management x block x inoculation treatment combination were unearthed from Experiment I on 18 June 2002. This yielded 12 plants from each nutrient management x inoculation combination. The first plant from each unit of four in Experiment II was unearthed on 19 June 2003, to yield 20 plants for each inoculation treatment per nutrient management regime. Shoot dry weights were measured after oven drying at 80°C for 72 h. Shoot N (Wall & Gehrke, 1975) and P (Murphy & Riley, 1962) concentrations were determined after digestion with H

2S0

4 and Hp2• Shoot N was not measured

in Experiment II. A sample of fine roots (total root length at least 200 em) was analyzed for percentage root length colonized by AM fungi after clearing and staining (Phillips & Hayman, 1970) via the gridline intersect method (Newman, 1966).

A final sampling to measure yield of tubers was conducted on 1 August 2002 for Experiment I and 19 August 2003 for Experiment II. Tubers were unearthed by hand with shovels, graded by size, and weighed. Size categories were: (1) 2.5-4.4 em, (2) 4.4-6.4 em, (3) 6.4-8.3 em, (4) 8.3-10.2, and (5) larger than I 0.2 em. Yield data for Experiment I were expressed on a per plant basis while those for Experiment II were expressed per three plant sampling unit.

Data were analysed using analysis of variance using block-interaction mean squares for tests of main effects and interactions in Experiment I (Anderson & McLean, 1974). Separate data sets for each fertility regime in Experiment II were analysed using ANOVA according to a completely randomized

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72 DAVID D. DOUDS JR. AND OTHERS

design. Measurements for which significant treatment effects were found were characterized further using Tukey's method of multiple comparisons. Data for percentage root length colonized by AM fungi were analysed after arc sin transformation.

RESULTS

Experiment I

Inoculation with AM fungi had no effect upon the shoot dry weights or shoot N and P concentrations at the midseason sampling (Table 1 ). Inoculation significantly affected the colonization of roots by AM fungi at the mid-growing season sample, increasing mycorrhiza formation compared to controls in the conventionally managed plots. The significant nutrient treatment X inoculation interaction indicated a greater response of colonization to inoculation in the conventional vs. the compost fertility regime. Plants grown in compost amended plots had significantly higher shoot P concentrations than those receiving conventional fertilizers.

Inoculation with AM fungi significantly increased the total fresh weight yield of tubers (p < 0.01). The two AM fungus treatments had total yields averaging 45 and 33% greater than controls in plots receiving compost and conventional

TABLE I

Physical parameters of potato plants sampled on 18 June, 2002 (Expeliment I).'

AM fungus Shoot dry Shoot P Shoot N Colonization inoculation weight (g) (% root length)

(%dry wt.)

Compost fettility regime Control 18.6 ± 2.0 0.52 ± 0.02 4.02 ± 0.20 8.7 ± 1.6 MYKE 16.3 ± 2.5 0.53 ±0.02 4.04 ± 0.15 9.1 ±2.1 On-farm 19.8 ± 2.2 0.52 ± 0.02 3.82±0.16 11.4 ± 1.5

Conventional fertility regime Control 19.7 ± 3.5 0.42 ± 0.02 3.99 ± 0.18 10.4 ± 2.1 MYKE 16.7 ± 3.0 0.42 ± 0.02 3.86 ± 0.21 17.3 ± 2.1 On-farm 16.3 ± 2.0 0.41 ± 0.01 3.90±0.17 20.0 ± 1.8

ANOVA Nuttient treatment ns *** ns ns Inoculation ns ns ns ** NT xi ns ns ns *

'Means of 12 plants± SEM. ns,*,**,*** =Not significant or significant at p :S 0.05, 0.01, or 0.001, respectively. AM fungus inoculation treatments: MYKE® (commercially available from Premier Tech Biotechnologies, Riviere-du-Loup, Quebec G5R 6Cl Canada), on-farm (a mixed species inoculum produced in a yard clippings compost and vermiculite mixture with Paspa/um notatum as host), and control (a freshly prepared mixture of compost and vermiculite).

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MYCORRHIZAL FUNGI AND POTATO YIELDS IN HIGH P SOIL 73

FIGURE 1. Yield of potato tubers grown under two fertility regimes as influenced by inoculation of seed potato with a commercially available AM fungus inoculum (MYKE®, Premier Tech Biotech­nologies), inoculum produced on-farm in a mixture of yard clippings compost and vermiculite, and a control mixture of fresh compost and vermiculite. Means of 28 plants ± SEM.

fertilizers, respectively (Figure I). Plots receiving compost yielded significantly more than conventional fertilizer treated plots (508 vs. 323 g tubers plant-1)

(p < 0.05). Mycorrhizal treatment however did not affect the distribution of weight of tubers across the size categories (data not shown).

Experiment II

Plants in Experiment II were smaller than those of Experiment I at the midseason sampling likely due to their later planting date (Table 2). Inoculation had no sig­nificant effect on shoot dry weight or overall mycorrhizal fungus colonization of roots at the time of sampling. Shoot P levels of plants inoculated with the on-farm inoculum produced at the Stoneleigh Estate were lower than those of other plants. This was likely a dilution effect since these plants tended to be larger, particularly in the conventionally managed plot.

The response of yield to inoculation with AM fungi in Experiment II was less than in Experiment I (Figure 2). Total yields of inoculated plants were 16-20% greater than controls under conventional fertility and I 0-11% greater when fertilized with dairy manure plus leaf compost, though these differences were not significant (p > F = 0.2306 for conventional and 0.3970 for compost). Inoculated plants produced more of the larger tubers. Inoculation main effects were significant for both fertility regimes for size 4 potatoes (8-10 em, p > F = 0.0338 and 0.0007 for compost and conventional, respectively). Plants

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-Ill c ca i5.. M ... 8.

DAVID D. DOUDS JR. AND OTHERS

Control MYKE OF-YCC OF-DMLC

FIGURE 2. Yield of potato tubers grown under two fertility regimes as influenced by inoculation of seed potato with a commercially available AM fungus inoculum (MYKE®, Premier Tech Bio­technologies), inocula produced on-farm in a mixture of yard clippings compost and vermiculite (OF-YCC) or dairy manure + leaf compost and vermiculite (OF-DMLCJ, and a control mixture of fresh compost and vermiculite. Means of 20 three plant sampling units ± SEM.

TABLE 2

Physical parameters of potato plants sampled on 19 June, 2003 (Experiment II).'

AM fungus Shoot dry Shoot P Colonization inoculation weight (g) (%dry wt.) (%root length)

Compost fertility regime Control 7.1 ±0.7 0.58 ± 0.02 11.2±0.9 MYKE 8.4 ± 1.3 0.54 ± 0.01 15.9 ± 1.6 On-farm 8.7 ± 0.7 0.47 ± 0.01 9.8 ± 1.2 On-farm (TRI) 7.3 ±0.9 0.55 ± 0.02 12.2 ± 1.4

A NOVA ns *** ns Conventional fertility regime

Control 12.9±1.3 0.53 ± 0.01 11.0 ± 1.1 MYKE 11.3 ± 1.4 0.53 ± 0.01 11.7 ± 1.1 On-farm 17.7 ± 3.0 0.46 ± 0.02 14.4 ± 1.2 On-farm (TRI) 13.8±1.3 0.49 ± 0.01 13.8 ± 1.3

AN OVA ns *** ns

'Means of20 plants± SEM. ns,*** =Not significant or significant at p <::: 0.001. AM fungus inocula as in Table I, with the addition of on-farm (TRI), a mixed species inoculum produced in a mixture of dairy manure plus leaf compost and vermiculite at The Rodale Institute.

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MYCORRHIZAL FUNGI AND POTATO YIELDS IN HIGH P SOIL 75

inoculated with the inoculum produced at the Stoneleigh Estate in a 1:4 [v/v] mixture of yard clippings compost and vermiculite had significantly more tubers of this size than did controls (228 g per three plant harvest unit vs. 49 g, respectively) when grown with conventional fertilizers. Plants inoculated with the commercially-available inoculum tended to produce more small tubers, sizes I and 2 (2.5-6.4 em; 580 g per three plant harvest unit vs. an average of 448 g for the other treatments with compost addition and 506 g vs. 420 g with conventional fertilizers).

DISCUSSION

Inocula of AM fungi, whether commercially available or produced via the on-farm system in compost and vermiculite, had similar positive effects on potato yield in Experiment I. This result agrees with most previous studies. Inoculation of microplants of potato cv. Golden Wonder with a commercially available AM fungus inoculum containing three species increased the tuber yield when grown in the greenhouse in sand containing slow release fertilizer (Ryan et al., 2003). In another greenhouse experiment, AM fungus inoculation of prenuclear minitubers of Peruvian potato increased yield an average of 85% over controls at low P availability (Davies et a/., 2005). Results of other inoculation studies with potato have shown that results depend upon the potato cultivar or AM fungus isolate (Vos:itka & Gryndler, 2000) used and/or the tuber size category of interest. Graham et at. ( 1976) found that inoculation of potato with Glomus fasciculatum increased yield while inoculation with G. mosseae did not. Duffy & Cassells (2000) found that inoculation with two commercially available inocula, each containing a mixture of AM fungus species, increased the growth and production of seed grade tubers (2.5-3.5 em diameter) by cv. Golden Wonder, but inoculation with G. intraradices alone did not. Further, none of the inocula increased the overall yield of tubers. Niemira et a/. (1995) also found that a commercial inoculum containing G. intraradices significantly increased the production of minitubers of potato cv. Atlantic.

The variable response of potato to inoculation with AM fungi cited by other researchers using different cultivars and inocula, and in this report over different growing seasons, may be due to a number of factors, some of which may not be controllable in the field. The variable efficacy of different isolates of AM fungi is likely due to the functional diversity of AM fungi (Smith et al., 2000; Stampe & Daehler, 2003). Further, differences in mycorrhizal dependency of cultivars within a crop species have been shown, for example with wheat (Hetrick eta/., 1993, 1996) and white clover (Eason et al., 2001). Another biotic factor that affects the response to inoculation with AM fungi

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76 DAVID D. DOUDS JR. AND OTHERS

is the size and activity of the indigenous AM fungus community. Response to inoculation decreases with increasing background levels of indigenous AM fungi (Sieverding, 1991; Hamel et at., 1997).

Abiotic factors also affect a plant's response to inoculation with AM fungi. The most important of these is the level of available P in the soil. Generally, as soil P increases, the potential for a mycorrhiza-mediated growth benefit decreases (Allison & Goldberg, 2002; Lekberg & Koide, 2005). This has been demonstrated for potato (Black & Tinker, 1977). Cutoti values of soil P above which an inoculation response is unlikely vary for soil type and crop, and range from 50 to 140 11g extractable P g-1 soil (Amijee et at., 1989; Thingstrup et at., 1998). Here, a strong yield response in the presence of very high levels of P (approx. 375 11g g-1 soil) was seen. This demonstrates the potential benefit of early root contact with a concentration of AM fungus propagules while soil temperatures are cool and limit P uptake (Bravo & Uribe, 1981 ). Also, the response of green pepper to inoculation at this site indicated the benefits to yield from outplanting seedlings already colonized by AM fungi (Douds & Reider, 2003). Other abiotic factors, such as soil temperature and moisture level, also atJect response to AM fungi (Andersen et at., 1987; Karasawa et at., 2000).

This study has shown that inocula of AM fungi produced on-farm m compost and vermiculite mixtures can increase the yield of potato tubers m the field. More efficient, mechanical means of delivery of the inoculum to the planting site in the field would make application of the inoculum more economically feasible for row crops.

ACKNOWLEDGEMENTS

We thank Neil Wijetunga and Stephanie Campbell for technical assistance and John and Chara Haas for generously providing facilities at the Stoneleigh Estate. This work was supported in part by USDA-CSREES Northeast Sustainable Agri­culture Research and Education grant LNE03-179.

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MYCORRHIZAL FUNGI AND POTATO YIELDS IN HIGH P SOIL 77

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(Received 7 November 2006; accepted 7 May 2007)

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