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United States Department of Agriculture

Agricultural Research Service

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Location: Horticultural Crops Research

2012 Annual Report

1a. Objectives (from AD-416):
1) Validate a quantitative PCR (qPCR)-based assay for P. rubi evaluations from raspberry roots and soil. 2) Continue evaluations of solarization and Brassicacaceous seed meal amendments as preplant treatments for raspberry. 3) Establish trials to determine whether bed fumigation and alleyway management methods sufficiently delay pathogen entry into planting beds to permit successful plant establishment.

1b. Approach (from AD-416):
First, we will validate a quantitative molecular assay to improve our ability to evaluate treatment effects on P. rubi. The bioassay we currently use is very sensitive to small amounts of P. rubi but not distinguish moderately effective treatments from non-treated controls. A truly quantitative assay will give us a more realistic assessment of the efficacy of treatments. A quantitative real-time PCR (qPCR) assay for P. rubi is already in development in our lab. We verified that we can amplify and detect the correct region of P. rubi DNA, and propose to validate the test across multiple P. rubi isolates, and validate that it is accurate using DNA recovered from soil or raspberry roots. In preliminary experiments, we found that soils amended with Brassica juncea or Sinapis alba seed meal suppressed P. penetrans; Agrobacterium tumefasciens was also suppressed in B. juncea-amended soils. Solarization is another non-chemical pretreatment option, which has been shown to prevent root rot for 2-3 years in western Washington fields.

3. Progress Report:
Cane height of plants in bed fumigated plots was identical to that of plants in broadcast fumigated plots in four of the five trials. At one trial, (Burlington), canes in bed fumigated plots were significantly taller than those in broadcast fumigated or non-fumigated plots. In general, there was no difference in root rot severity between bed fumigated and broadcast fumigated treatments. However, in Lynden Trial 3, root rot symptoms were less in samples from bed fumigated plots than in the broadcast fumigated plots. P. penetrans were found in roots from four of the five trials. Among these, there was no difference between bed and broadcast treatments in two trials. In the remaining two trials, there were fewer P. penetrans in the bed fumigated plots. Taken together, these results show that in each trial, bed fumigation provided suppression of Phytophthora and P. penetrans that was at least as good as that of broadcast fumigation. In some cases, bed fumigation was superior to broadcast fumigation. Similarly, plants in bed-fumigated plots grew as well as, or better than their counterparts in broadcast fumigated plots. This research was conducted in support of objective 1A of the parent project.

4. Accomplishments

Last Modified: 2/23/2016
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