2010 Annual Report
1a.Objectives (from AD-416)
Broaden soybean germplasm for genetic resistance to new and emerging nematode populations; identify shifts in genetic profiles and virulence of soybean cyst nematode; and measure effects of cultural practices and diseases on soybean cyst nematode reproduction.
1b.Approach (from AD-416)
Evaluate accessions of Glycine max and Glycine soja for resistance to multiple populations of soybean cyst nematode (SCN), particularly those capable of reproducing on cultivars utilizing PI 88788 as resistance source. Characterize new sources for unique resistance genes and develop molecular markers associated with resistance. Pyramid resistance genes into elite backgrounds of maturity groups III, IV, and V in combination with resistance to predominant fungal pathogens to develop improved germplasm/ cultivars. Characterize SCN field populations to determine effectiveness of current sources of resistance. Predict stability and changes in SCN populations by accelerated selection pressure in greenhouse tests. Determine rhizosphere factors that influence SCN reproduction under different tillage and cropping schemes. Evaluate effects of concomitant infection of charcoal rot and other diseases on SCN reproduction.
Populations developed from genetically diverse plant introductions with broad-based resistance to soybean cyst nematode (SCN), that were crossed to elite soybean cultivars, continued to be progeny tested for release. An advanced line, JTN-5109, with SCN resistance derived from a new source, PI 567516C in maturity V group was evaluated in USDA Uniform Tests. A manuscript on mapping for resistance was prepared and submitted to a refereed journal for consideration of its publication. JTN-5203, a selection with resistance to multiple nematode populations combined with resistance to predominant fungal pathogens in maturity V group ranked number one in Tennessee State Variety Tests for yield. A release notice is under preparation for its approval. Multi-location evaluation tests for maturity IV group included 12 selected progenies for SCN resistance and the sources of resistance include PI507354, Columbia (PI 22897), PI438489B and Hartwig. Sixteen selections are evaluated in maturity V group with sources of resistance derived from PI507471, PI437655, ‘Hartwig’ and ‘Fowler’. Nearly 200 germplasm lines were screened in the greenhouse for their reaction to nematode.
As expected, the characterization of SCN populations varied with length of exposure to soybean resistance. Variation in SCN characterization also decreased as length of exposure to plant resistance increased. Natural infections did not allow for field evaluations of soybean rust. Greenhouse testing found no SCN resistance in Mid South Area soybean rust resistant lines. Growth chamber testing was conducted in 2010 on co-infected plants with inconclusive results. Data continues to be collected for sub-objective 2B; however, we have noted that certain populations drift in their characterization more rapidly than others despite lack of host selection pressure. This stresses the need for controls to monitor SCN population characterization when used in germplasm testing. Data collection is ongoing for sub-objective 3A with part of the data in manuscript draft status. Data collection is continuing for sub-objective 3B.
Soybean Cyst Nematode Adaptation to the Most Common Soybean Resistance. Soybean cyst nematode is one of the major yield limiting pests in soybean production world-wide. Management of the nematode has been accomplished with a combination of resistant varieties and non-host crops. Recently non host crops are not economically profitable and this practice has been discontinued. Management has solely relied on resistant varieties. In the USA approximately 95% of the resistant soybean varieties are derived from one source of resistance, PI88788, despite more than 120 sources of resistance have been identified. Linkage to undesirable traits can limit the use of other sources of resistance soybean cyst nematodes but continued use of the same source of resistance selects for those individuals which can reproduce on this source of resistance. Geographic adaptation of soybean cyst nematodes to soybean resistance based on time of exposure to soybean resistance has been documented in a study characterizing field populations in Tennessee, Illinois, Indiana, and Ontario, Canada. As expected, the characterization of soybean cyst nematode populations varied with length of exposure to soybean resistance. Tennessee, where resistant varieties have been used since 1978, had the largest number of populations which could reproduce on resistant cultivars. The other locations started using resistant soybean lines from 1980 to 1989 and had much lower numbers of populations which reproduced on resistant lines. Variation in soybean cyst nematode characterization also decreased as length of exposure to plant resistance increased. This information will be useful for developing management strategies.
Identification of Additional Sources of Resistance to Soybean Cyst Nematode (SCN) in USDA Soybean Germplasm Collection: Soybean cyst nematode is consistently the leading limiting root parasite affecting soybean yields worldwide. Resistant cultivars have reduced yield losses in soybean; however, continuous use of soybean cultivars with resistance primarily derived from a single resistance source has caused shifts in nematode populations over a period of time, rendering the resistant cultivars susceptible. Additional sources of resistance to SCN in soybean are needed for the development of new germplasms with broad resistance to be used by public and private sector scientists in the U.S. and abroad. An ARS researcher at Jackson, TN, worksite has screened, in the greenhouse, new soybean germplasm lines that were recently introduced from China whose reaction to SCN populations was unknown and has identified five new soybean lines (PIs 567734, 567739A, 567749A, 567762A and, 567774A) with various levels of SCN resistance. The potential impact of this research could be that the newly identified soybean lines will be used to develop soybean source materials with broad and improved resistance to SCN with DNA markers associated to resistance genes to assist in selection of resistant lines.
Kazi, S., Schultz, J., Bond, J., Arelli, P.R., Hashmi, R., Lightfoot, D.A. 2009. Iso-lines and Inbred-lines Confirmed Loci that Underlie Resistance from Cultivar ‘Hartwig” to Three Soybean Cyst Nematode Populations. Theoretical and Applied Genetics. 120:633-644.