2013 Annual Report
1a.Objectives (from AD-416):
1. Develop breeding/mapping populations and select high-yield resistant breeding lines from the new sources of resistance identified in the first phase of this project.
2. Determine the genetics of resistance of these new sources of resistance and develop molecular markers for these traits.
3. Determine pathogen diversity with emphasis on how this affects the expression of resistance to PSD in soybean.
1b.Approach (from AD-416):
Field screening and laboratory assays will be conducted to determine:.
1)The resistance of soybean lines to PSD; and.
2)The genetic and pathogenic diversity of PSD isolates collected and purified from different genotypes of soybean in different geographic origins.
During this reporting period, 10 soybean Phomopsis seed decay (PSD) - resistant germplasm lines that were identified from our previous studies, along with six susceptible lines, were planted in Kibler, Arkansas, on June 7, 2013. Three experiments (for maturity groups III, IV and V) were set up in four replications of a split-plot design in which the inoculation treatments (inoculated or non-inoculated) are the main units and soybean lines within each maturity group are the sub-unit. Two harvest times, at the R8 and the R8+2weeks stages (normal vs. delayed), will serve as repeated measures. The inoculated plots will be sprayed with Phomopsis spores at the R5 to R6 growth stage. There are 256 plots planted in each location. Overhead irrigation will be used to increase seed infection.
Isolates of Phomopsis longicolla were collected from lower stems of soybean plants grown in two fields in Arkansas. Stem sections were collected from 100 locations in each field using a 20 X 20 m grid. Hundreds of isolates have thus far been collected. Efforts have been made to purify and single-spore those isolates. Selected isolates have been sequenced at internal transcribed spacer (ITS) region to confirm the pathogen identity.
For breeding and genetics purposes, the following plant populations are being advanced in Fayetteville, AR, for breeding/mapping purposes:
5002T x PI 417479
5002T x PI 417050
R03-984 x PI 417050
R07-R07-10244 x PI 424324B
R04-1268RR x PI 594858A
R07-10231 x PI 235335
PI 567635 x R01-976
PI 506647 x R05-3239
PI 567381B x Osage
PI 567635 x UA 5612
In addition, 41 new lines were selected from sudden death syndrone crosses (12 from 5002T x PI 417050, 12 from 5002T x PI 417479, and 16 from R03-984 x PI 417050). These lines are being evaluated for yield and PSD in Stuttgart, AR.