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ARS Home » Plains Area » Fargo, North Dakota » Edward T. Schafer Agricultural Research Center » Sunflower and Plant Biology Research » Research » Research Project #433145

Research Project: Improve Stalk Rot Phenotyping by Evaluation of Environment, Pathogen, and Host Factors for S. Sclerotiorum Infection in Sunflower Disease Nurseries

Location: Sunflower and Plant Biology Research

Project Number: 3060-21220-031-19-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Jul 1, 2017
End Date: Sep 30, 2019

Objective:
The objective of the proposed project is to evaluate environmental, pathogen isolate, and sunflower genotype factors to improve data quality in artificially inoculated S. sclerotiorum basal stalk rot screening nurseries. Assessment of factors that contribute to disease incidence following inoculation is crucial for improving methodology that will provide researchers with reliable and consistent phenotypic data. We will evaluate three factors that we hypothesize may influence the reliability of artificial inoculation for basal stalk rot: 1) Local environmental conditions of temperature and moisture upon introduction of artificial inoculum; 2) Relative aggressiveness of S. sclerotiorum isolate or mixture of isolates used as inoculum; 3) Genetic background and relative vigor of sunflower materials to be inoculated. Specifically objectives during the project period are: 1) Evaluate factors contributing to success of artificial inoculation for basal stalk rot at multiple locations that differ in climate, soil type, and management to ensure that quality phenotypic data is reproducible across different locations in random years. 2) Improve our understanding of S. sclerotiorum basal stalk rot infection of sunflower in the field and utilize this information to revise methodology for future disease screenings.

Approach:
We will conduct replicated evaluations across three years at two locations: Carrington, ND and Staples, MN. These locations differ in climate, soil type, and management. Carrington is a dryland site whereas the Staples site has available irrigation that can be used to supplement natural rainfall. Experiment and Treatment design: A split-split plot design will be utilized at each location, with whole-plots arranged as a randomized complete block design (three blocks). Whole-plot treatments will be a single S. sclerotiorum isolate (NEB-274), a mixture of 3 S. sclerotiorum isolates that show high virulence in greenhouse testing, and a mock control consisting of millet with no S. sclerotiorum mycelium. Subplot treatments will be three environment levels: 1) simulated no-till created by mulching the plots with small grain straw prior to inoculation; 2) vermiculite side-dressed with pathogen inoculum; and 3) standard environment with no mulch or vermiculite. Sub-subplot treatment levels will include seven sunflower genotypes that vary in genetic background, susceptibility to basal stalk rot infection and overall vigor (Table 1). These genotypes include susceptible and tolerant hybrid and inbred line materials, including public hybrid 894 and parental inbred lines HA 89 and RHA 274, for preliminary evaluation of the impact of plant vigor on inoculation success. These evaluations may provide useful information regarding the possibility of disease escape by less vigorous sunflower materials, such as interspecific hybrids with growth habits that differ from cultivated H. annuus. Plot Establishment and Disease inoculation: S. sclerotiorum inoculum will be prepared by growing isolates NEB-274, NEB-590, BN252, and BN293 (all collected in the Northern Plains region of the US) on autoclaved white proso millet. Millet infested with isolates NEB-590, BN252, and BN293 will be mixed in equal proportions prior to inoculation of plots. Single-row sunflower plots will be seeded using a row-crop planter using GPS-RTK guidance. Mycelial-infected millet inoculum and mock millet will be side-dressed in July, at about 4-5 weeks after planting, using no-till single-disk openers mounted on a toolbar along with a granular chemical applicator that allows for metering of inoculum into the furrow. Millet will be applied at a rate of 110g per 7.62 meter of plot row. GPS-RTK guidance will be used during inoculation to ensure uniform placement of inoculum next to plot rows. Data Collection: Disease incidence, determined by the number of plants expressing basal stalk rot symptoms, will be assessed 1 month and 2.5 months after inoculation. Assessing disease incidence twice will reveal if certain treatment combinations are more favorable for disease development. In particular, environment X isolate combinations that produce early and more consistent disease symptoms may prove to be useful for improving methodology. Daily temperature and precipitation data after inoculation will be recorded and may be useful in determining how weather may affect treatment responses at each location.