Determining efficacy of Waste Lime in Managing Fusarium Root Rot of Field Peas

Project outcomes
The short term outcomes of this project include increase in awareness and knowledge among pea producers regarding alternatives to chemical control and efficacy of waste lime against root rot diseases. The findings are also expected to lead to changes in management decisions and recommendations, and adoption of this control measure. In the long term this method will provide cost effective, eco-friendly alternative to the use of chemical control measures, help reduce risk of losses due to root rot and other soil borne diseases and increase profitability and sustainability.
Context, Background, and Rationale
Dry Pea or field pea (Pisum sativum L.) is an important cool season legume crop grown in the United States. North Dakota, Montana and Washington are the leading dry edible pea producing states. The area under this crop has rapidly increased from 337,500 acres in 2003 to 847,500 acres planted to pea in 2007 nation wide and, from 166,000 acres to 515,000 acres during the above period in North Dakota (NAAS, 2008). Dry pea is susceptible to many root-rot pathogens including Aphanomyces, Fusarium, Pythium and Thielaviopsis. Among these, Fusarium root rot is a serious disease present in all pea producing areas in the United States (Kraft and Pfleger 2001), and has become a major constraint in dry pea production in the North Central region over the past years. Traditionally, Fusarium solani (Mart.) Sacc. f. sp. pisi (Jones) Snyder & Hans was considered to be the primary causal agent of this disease, but recent surveys conducted in North Dakota identified Fusarium avenaceum as being the most prevalent pathogen associated with pea root rot in this state (Mathew et al. 2008). There is a dearth of satisfactory methods to control this root rot and no cultivars with complete resistance to Fusarium root rot are currently available (Kraft and Pfleger 2001), seed treatments used are also limited in their efficacy (Sam Markell, personal communication). The importance of this crop to North Dakota and prevalence of the disease necessitates development of an integrated disease management program to reduce losses associated with Fusarium root rot in dry peas.
Waste lime or spent lime, a byproduct of sugar industry is used as soil pH amendment in Europe. It is reported to be effective in reducing the severity of root rot in sugar beet and spinach (Windels et al. 2004, and Ingemarsson 2004). The assumption is that this holds good for pea root rot disease too, because of the soil borne nature of the root rot pathogen and similar pH requirements. Preliminary studies conducted in our laboratory using several Fusarium species including those affecting peas have shown a significant reduction in fungal biomass even with an addition of waste lime equivalent to 2.5 tons/acre. This project aims at furthering this study and exploring the possibility of utilizing waste lime in managing root rot of field peas.
Further, lime also improves soil structure and tilth. Besides neutralizing pH, waste lime also contains nitrogen (0.6%), phosphorous (0.7%), potassium (0.05%), and magnesium (1.1%) and enriches the soil (Ingemarsson 2004). Waste lime has been successfully used in soils with a pH up to 8 (Windels et al. 2006) and the pH of most pea growing soils in North Dakota ranges from 5 to 8 (Mathew, 2006). Large quantities of waste lime is produced by sugar industries and available free of cost to growers, e.g. 500,000 tons of waste lime is produced annually by seven factories in the Red River Valley and Southern Minnesota. The only cost to be incurred by growers is that of transportation. The advantages of using waste lime in root rot management would be two fold, providing a cheaper method for controlling the disease, and as amendment that improve the soil chemical and physical conditions.
Literature review
Previous reports suggest that waste lime has been effective in reducing root rot and/or increases yield sugar beet grown in North Dakota and Minnesota (Windels et al. 2004). Waste lime when applied at 3t/ac or 10 t/ac reduced the Aphanomyces root rot of sugar beet from 93-100% to 62% compared to non limed plots (Windels et al. 2004). A reduction in Aphanomyces soil index values was recorded in sugar beet as a result of soil application of waste lime (Windels 2004). Application of lime has resulted in reduced root rot severity of sugar beet and caused increase in plant fresh weight in greenhouse studies in Sweden (Ingemarsson, 2004). Apart from these, lime has also been used to control club root of cabbage in US (Campbell and Greathead, 1989). A similar project, GW08-005 (characterization of soils properties associated with in spinach seed crops, and development of a quantitative molecular assay for Fusarium oxysporum f. sp. spinacae) was supported by SARE, aimed to assess the potential of hydrated lime application to suppress Fusarium wilt of spinach. But this proposed project aims at determining the efficacy of waste lime, which is a freely available byproduct from sugar industry in managing pea root rot.
Approach, activities, methods, and inputs
The laboratory experiments will be conducted to study the effect of waste lime on mycelial growth and sporulation of different Fusarium species (e.g. F. avenaceum, F. solani, F. oxysporum, F. acuminatum, and F. graminearum) isolated from pea roots at concentrations equal to those applied under field conditions. Radial growth and sporulation will be studied using solid media and changes in fungal biomass will be evaluated using liquid culture. Calculated amounts of waste lime will be added to potato dextrose agar (PDA) to give a concentration of 1, 2.5, 5, and 10g of waste lime per petri plate containing 20ml of media which is equal to 1, 2.5, 5, and 10 t/ac of waste lime. PDA plates without any waste lime will serve as control. These petri plates will be inoculated with 5mm discs of actively growing culture and incubated at room temperature. Observations on radial growth will be collected from 2 days after inoculation (DAI) to 6 DAI. Sporulation or number of conidia produced at 6 DAI will be counted using a haemocytometer. Ability of waste lime to inhibit spore germination will be studied at the above concentrations on solid media. Conical flasks containing 50ml of potato dextrose broth will be prepared and calculated amounts of waste lime will be added to each flask to give a concentration of 0, 1, 2.5, 5, and 10 of waste lime per flask. These flasks will be inoculated with 5mm discs of actively growing culture and will be incubated at room temperature on a rotary shaker at 120 rpm for 6 days. After 6 days the mycelium will be harvested and dried in a hot air oven at 70ºC for 24h and the dry mycelial weight will be recorded. The experiment will be laid out in a completely randomized design and each treatment will be replicated three times and the experiment will be repeated three times.
Greenhouse studies will be conducted to assess the efficacy of waste lime in controlling the Fusarium spp. under controlled conditions. This study will involve planting seeds in pots filled with autoclaved soil to which a standard amount of inoculum of F. avenaceum and F. solani, the major known root rot pathogens in peas will be added. Different rates of waste lime equivalent to 0, 1, 2.5, 5, and 10t/ac will be added to pots. The amount of waste lime to be added in this study will be calculated based on the amount available to each plant under field conditions according to the number of plants per acre. Treatments with pots containing inoculum but no waste lime and only autoclaved soil will serve as controls. Each treatment will be applied on 10 seeds. The experiment will be set up as randomized complete block design with four replicates and experiment will be repeated three times. The roots will be rated for symptoms on 0-5 scale (Kraft 1975).
Field studies will be conducted in two different locations viz. research plots of NDSU at Fargo or Carrington and a grower’s field with known history of root rot. Two cultivars, one resistant and one susceptible cultivar, will be selected depending on the results of ongoing varietal screening. Fungal population present in the soil will be assessed prior to the application of waste lime. Lime will be applied at the rates of 0 (untreated control), 1, 2.5, 5, and 10t/ac of wet weight to the experimental plot. This will be done by spreading and incorporating waste lime shipped in from nearby sugar mills into the soil with a chisel plough in the fall of the year before starting the study. Each treatment will be replicated four times. The experiment will be laid out as randomized complete block design. Roots will be rated on 0-5 scale two to three weeks after emergence by destructive sampling of 10 plants from each replication. Stand counts and yield will be recorded at the end of crop season. This will be repeated in two growing seasons.
Statistical analyses for the above studies will be performed using SAS version 9.1 (SAS Institute Inc. 2002-2003). Data will be analyzed using the Proc GLM procedure. Mean comparisons will be performed using Fisher’s protected least significant difference (LSD) test.
Time-line: 2009- Application of waste lime in fall before the ground freezes and conducting greenhouse and laboratory experiments; 2010- field trails first rep and finishing up green house experiments; 2011- field trials second rep, data analysis and publication
Outputs
Findings from this project will be made available to pea growers through extension bulletins and websites. The results will be presented at grower meetings and seminars at local and national level. The findings will result in scientific publications.
Evaluation plan
The success of waste lime as a potential control measure will be assessed through experimental results obtained at each stage of the project.
Stage1: Lab experiments: changes in fungal growth and sporulation and spore germination in the lab, extent of reduction in radial growth, spore production, spore germination, and biomass at different waste lime concentrations will determine initial efficacy of this amendment against various species of Fusarium.
Stage 2: in the greenhouse changes in root rot lesion length and root mass will ascertain efficacy of waste lime.
Stage 3: in the field disease incidence, severity, stand count, and yield will determine efficacy of waste lime.