2012 Annual Report
1a.Objectives (from AD-416):
(1) Screen soybean lines for resistance to Phomopsis Seed Decay (PSD).
(2) Breed high-yielding resistant cultivars and germplasm lines for North Central and Southern U.S. soybean production regions by incorporating new resistance genes and alleles.
(3) Develop new and rapid screening tools that are correlated with the field screening method for the measurement of plant resistance.
1b.Approach (from AD-416):
Phomopsis seed decay (PSD) of soybean is a major cause of poor quality and poor germination of soybean seeds in the United States, especially in the mid-southern U.S. This research will be focus on two sides of the disease equation:.
1)screening untapped (not yet tested for PSD resistance) 123 MG 3-5 germplasm lines collected from 28 countries, and.
2)breeding lines and cultivars from southern U.S. with resistance to PSD. This research will provide tools and potential new resistance genes to increase breeding efficiency for high-yield PSD resistant lines.
In 2009, 123 PI (plant introduction) lines were screened for Phomopsis seed infection in a naturally infested field at the Vegetable Research Station, Kibler, AR. Seed infection ranged from 5 to 28% for the maturity group (MG)-3 PI’s, 6 to 37% for the MG-4 PI’s, and 7 to 30% for the MG-5 PI’s. A total of 42 MG3-5 PI lines were selected from the 2009 tests for further analysis in 2010 and 2011. Most of these lines were selected because they had low levels of Phomopsis seed decay (PSD) at two or more of the test sites. Several in each maturity group were also selected because they had high levels of PSD. These lines will serve as controls. The 42 lines were screened in a naturally infested field at the Vegetable Research Station, Kibler, AR, in 2010 and 2011. Lines were grouped by maturity into three separate tests each in a randomized complete block design with four replications. There were two tests in each maturity group: an uninoculated test and a test inoculated with an isolate of Phomopsis (P.) longicolla (the primary cause of PSD) collected from previous year’s infected seed. Seed from each plot were visually rated for quality, tested for germination, and plated for fungal infection. Average seed infection of PI’s by P. longicolla ranged from 4 to 19% for MG 3, 1 to 21% for MG 4 and 0 to 10% for MG 5 in 2010. In 2011, dry weather in September resulted in very low seed infection by P. longicolla. Infection by P. longicolla was negatively correlated to germination and visual seed quality. Inoculation with P. longicolla did not significantly affect the level of seed infection by this fungus.
The effects of cultivar, foliar fungicide application, and delayed harvest were determined at the Vegetable Research Station in a naturally infested field. Seven soybean lines were planted: MD/PSD-0259 and PI 80837 (Phomopsis resistant), AP350 and AG 4403 (Phomopsis susceptible), UA4805 and Osage (Purple Seed Stain Resistant), and Sweon 97 (Purple Seed Stain susceptible). At reproductive stage R5, half of the plots were sprayed with the foliar fungicide quadris. Delays in harvest increased seed infection, especially in years with heavy rainfall in the fall. When seed infection was high, an application of fungicide reduced seed infection. There were significant differences between soybean lines in the amount of seed infection by P. longicolla and by Cercospora (C.) kikuchii, the purple seed stain pathogen. Increased seed infection by P. longicolla decreased germination and seed vigor, but seed infection by C. kikuchii did not.
In the effort of breeding for PSD resistance, we have selected four advanced early-maturing lines with PSD resistance derived from PI 80837 and PI 360841 in 2009. These lines showed some levels of seed shattering in the field but good seed quality and PSD resistance. These lines were evaluated for adaptation and yield in 2010. They showed early maturity, excellent seed quality, but relatively low yields and some seed shattering. The scientists discontinued these lines for yield testing but used them as parents for crossing in the next cycle of breeding. We constructed five breeding populations to pyramid different PSD resistance genes from PI 91113, PI 360841, PI 417479, PI 235346, and PI 371611. This effort is on-going and will continue in 2012. The scientists have also developed nine other breeding populations to incorporate PSD resistance from different sources (PI 417479, PI 417050, PI 424324B, PI 594858A, PI 458130, PI 567635, and PI 235335) into high yielding MG4-5 cultivars/lines adapted to the mid-south. These breeding populations are being advanced and pure lines will be derived for yield and PSD tests.