Variations for some quantitative traits and molecular markers in some ancestors and cultivars of soybean, and evaluation of yield increase by breeding in the southern U.S.

Author

Ali Ustun

Date of Award

8-1999

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

Fred L. Allen

Committee Members

Peter M. Gresshoff, Arnold M. Saxton, Burton C. English, Dennis W. West.

Abstract

Formal soybean breeding programs in the U.S. started in the 1930's and extensive research changed the plant from a forage crop to a seed crop. Soybean has become one of the five crops commercially important. Soybean breeders have made selection mostly for yield, protein and oil content, lodging, and disease and pest resistance. Genetic progress in these traits might have caused decline in genetic variability. On the other hand, different soybean breeding lines have been crossed in the southern and northern U.S. This study was aimed to (1) estimate the yield increase in the southern U. S. by genetic improvement, (2) show genetic variability of agronomic traits and find molecular marker diversity in soybeans from ancestral lines to modem cultivars, and (3) demonstrate the genetic variability by heritabilities and Quantitative Trait Loci (QTL) in eight crosses made between southern x southern and northern x southern ancestral lines or cultivars representing different eras in soybean breeding.

A total of 10 yield trials were conducted in two years in four locations in Tennessee with eight ancestral lines and cultivars from different eras. Soybean yield in the southern U.S. has increased 14 kg ha^-1yr ^-1.This increase was linear which implies that there is still remaining variation in the southern soybean gene pool to make genetic progress for yield.

Genetic diversity among eight southern and four northern cultivars was determined by microsatellite (SSR) and DNA Amplification Fingerprinting (DAF) molecular markers. Also, data from eight F₂populations and parents were collected. SSR and DAF marker polymorphisms, and heritabilities for yield and oil content showed a declining trend over generations in the southern breeding lines. Correlations among genetic similarities from SSR, DAF, CP (Coefficient of parentage) and agronomic traits were significant. Although SSR similarity was correlated with yield, it should be retested with a larger sample size. It is concluded that the markers which have QTL associations with agronomic traits may provide very useful information to decide parents for crosses.

F_2:3 lines derived from individual 250 F₂plants in each cross were tested in the field for agronomic traits. With the exception of Lee x Ogden (first generation cultivars) cross, other southern x southern crosses did not reveal a significant heritability for yield from parent-offspring regression. Northern x southern crosses had considerably higher heritability for yield, but their population mean was lower than southern x southern crosses. It is suggested that the elite lines from Lee x Ogden and from recurrent selections in northern x southern crosses can increase variability for yield in the southern gene pool.

One cross of southern ancestral lines and one cross of fifth generation cultivars were also evaluated for SSR marker QTL associations with agronomic traits. In the cross between ancestral lines, SSR markers Satt022, SattlSO and Satt353 were associated with yield in F₂ but Satt022 was not confirmed in F_2:3 lines. There were QTLs for other traits which were either significant or near to significant level either in F₂ or in F₃. In the cross between fifth generation cultivars, Satt022 was associated with yield and Satt353 was associated with oil content and plant height. The change in the QTL relationships from ancestral lines to the fifth generation cultivars implies that some QTLs may not be detected, but different QTLs were developed over time in southern breeding lines. The variability for yield, which was not detected by heritabilities as found by SSR marker QTLs. This indicates that QTLs can be a reliable way to demonstrate genetic variability.

Recommended Citation

Ustun, Ali, "Variations for some quantitative traits and molecular markers in some ancestors and cultivars of soybean, and evaluation of yield increase by breeding in the southern U.S.. " PhD diss., University of Tennessee, 1999.
https://trace.tennessee.edu/utk_graddiss/7483