Developing an Effective Strategy for Management of Internal Discoloration of Horseradish Root

Developing an Effective Strategy for Management of Internal Discoloration of Horseradish Root

Summary

This study is being conducted to develop an effective method for management of internal discoloration of horseradish roots. Internal discoloration of horseradish is a disease complex caused by at least three fungi, Verticillium dahliae, V. longisporum, and Fusarium solani. These fungi are carried in the propagating roots (set-borne inoculum) and also survive in the soil (soil-borne inoculum). The first step for management of the disease was to develop a reliable method to eradicate set-borne inoculum of the pathogenS. This was achieved by treating the sets in hot water. The most effective treatment for eradication of set-borne inoculum, without adversely effecting set germination or plant vigor, was determined to be hot-water treatment of horseradish sets at 47ºC for 20 min. The Second step for management of the disease was protecting plants against soil-borne inoculum in the fields. This goal is being fulfilled by set treatment with the fungicide fludioxonil (Maxim 4FS or Maxim Potato WP)or biocontrol agent Trichoderma virens (SoilGard 12G) prior to planting sets.

Objectives/Performance Targets

This is a two-year project to develop an effective strategy for management of the internal discoloration of horseradish roots. The specific objectives of this research project are:
(i) to evaluate and demonstrate the effectiveness of thermo-therapy for control of set-borne inoculum of the internal root discoloration;
(ii) to demonstrate the effectiveness of the biofungicides for control of the internal root discoloration;
(iii) to demonstrate effectiveness of an IPM approach to solve the complex internal discoloration disease of horseradish root; and
(iv) to establish a sustainable horseradish production system.

Accomplishments/Milestones

Set culturing. The percentage of the sets with fungal colonies decreased as the hot-water treatment temperature was raised and duration of treatment increased. The percentage of untreated sets (control) with Fusarium was significantly higher than percentage of heat-treated sets with Fusarium. There was a negative linear response of percentage of sets with Fusarium to temperature.

In the hot-water treatment experiment with cultivar 1590, Fusarium was detected only when the sets were heat-treated at 44°C for 10, or 30 min; 46°C for 10; min and in untreated sets. No Fusarium or Verticillium was detected when the sets were heat-treated at 46°C for 30 min; 48°C for 10 or 30 min; and 50°C for 10 or 30 min. Verticillium was detected when the sets were heat-treated at 44°C for 10 or 30 min; and also in untreated sets.

In cultivar 1573, no Fusarium or Verticillium was detected when sets were heat-treated at greater than 47°C. In cultivar 1722, no Fusarium was detected when sets were heat-treated at temperatures above 46°C for 20 min. In cultivars 1573 and 1722, percentage of sets with Verticillium was significantly higher for control treatment as compared to other treatments but not 46°C for 10 min.

In cultivar Victor-7, when the sets were cultures 5 days after treatment, the percentage of sets with Fusarium was significantly higher for untreated control as compared to treatments at 46°C for 10 min. When the sets of same size were cultured 3 months after heat treatment, percentage of sets with Fusarium was significantly higher for untreated control when compared to other treatments. No Fusarium was detected in any of the sets treated at temperatures above 46°C for 30 min.

The percentage of sets with Fusarium was significantly higher in the sets of cultivars 15K and BTW that received no heat treatment as compared to those that were treated at 47°C for 20 min. For cultivars 1573 and BTW, no Fusarium was detected when the sets were treated at 47°C for 20 min. No Verticillium was detected in any of the sets treated at 47°C for 20 min.

Set germination and plant vigor. The greenhouse study showed that germination of sets of both 15K and 1573 was not significantly affected when they were treated at temperatures of 46, 47, 48, or 49°C for 10, 20, or 30 min and at 50°C for 10, and 20 min. The treatment at 50°C for 30 min, however, significantly reduced the percentage of germinated sets. The vigor and foliage weight of plants grown from untreated sets were lower than those of heat-treated sets.

Both fungicides (Maxim 4FS and Maxim Potato) and biocontrol agents SoilGard and G-41 protected plants against the pathogens causing internal discoloration of roots in the fields without any adverse effects on set germination or plant vigor. Serenade MAX reduced germination of sets when applied onto hot-water treated sets. Disease incidence (percentage of roots affected) and disease severity (percentage of root surface area discolored at the cross section) were 68.75 and 7.51%, respectively, in plants grown from non-heat treated and non-fungicide/biocontrol-agent treated sets compared to 13.75 and 0.87% of the plants grown from hot-water treated and G-41 treated sets, and 20.0 and 1.06% of the plants grown from hot-water treated and Maxim Potato treated sets in Wisconsin trials. In Illinois, disease incidence and severity of plants grown from non-heat treated and non-fungicide/biocontrol-agent treated sets were 57.5 and 3.17%, respectively, compared to 4.17 and 0.21% of plants grown from sets treated with hot-water treated and G-41, and 7.50 and 0.46% of the plants grown from sets grown with hot-water and Maxim Potato.

Impacts and Contributions/Outcomes

The research is expected to help to establish a sustainable horseradish production in Illinois, as well as in the US. The strategy developed in this research will be rapidly implemented because:
(i) there is no effective method for control of internal discoloration of horseradish roots is available,
(ii) the proposed strategy can easily be implemented by the growers,
(iii) the method is very cost/effective (about 2% of farm-gate value of the cop),
(iv) the management approach is environmentally safe and can be used in organic horseradish production, and
(v) all materials used in implementing the strategy are commercially available.

Collaborators: