Title: Methodology for creating alloplasmic soybean lines by using Glycine tomentella as a maternal parent Authors
Submitted to: Plant Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 9, 2014
Publication Date: June 25, 2014
Citation: Singh, R.J., Nelson, R.L. 2014. Methodology for creating alloplasmic soybean lines by using Glycine tomentella as a maternal parent. Plant Breeding. DOI:10.1111/pbr.12196. Interpretive Summary: Wild relatives of crop plants are an important source of genetic diversity and this is especially true for soybean. Soybean is one of the least diverse crop species and only one wild relative can be easily crossed with soybean. For the first time, we developed and implemented procedures for producing fertile plants from crosses between soybean and a very distant, perennial relative, Glycine tomentella, using G. tomentella as the maternal parent. Using the G. tomentella as the maternal parent not only allows for the transfer of the typical complement of genes but the resulting progeny also have the cytoplasm of the wild relative, which can affect the plant. Although we can make the crosses between these two species in the traditional manner, extraordinary procedures are needed to rescue the developing seeds and eventually produce fertile soybean plants. Most of the plants produced have 40 chromosomes like soybean but unlike G. tomentella that has 78 chromosomes. Most of these plants with 40 chromosomes are fertile but some are sterile. We are increasing seeds of the fertile plants for evaluation to determine what has been transferred from G. tomentella to soybean. Some fertile plants have as many as 5 extra chromosomes from G. tomentella but they are not cytogenetically stable. Fertile plants with 41 chromosomes have been identified and are being used to develop plants with an extra pair of G. tomentella chromosomes which can be stable. The genetically stable, fertile lines that we produce will be of interest to all soybean scientists interested in genetic diversity.
Technical Abstract: Soybean breeders have not exploited the diversity of the 26 wild perennial species of the subgenus Glycine Willd. that are distantly related to soybean [G. max (L.) Merr.]. The objectives of this study were to introgress cytoplasmic and genetic diversity from G. tomentella PI 441001 (2n=78) into the cultivated soybean, to isolate and identify cytologically and morphologically monosomic alien addition lines (MAALs; 2n=41) and disomic alien addition lines (DAALs; 2n=42) from G. tomentella PI 441001 (2n=78) x G. max cv. Dwight (2n=40). We have hybridized and produced fertile soybean lines using G. tomentella (2n=78; PI 441001) using male and female parent with soybean cv. Dwight (2n=40). In this study, we describe a methodology for producing alloplasmic fertile soybean plants from PI 441001 x Dwight. Immature seeds (19-21 days post-pollination) were excised and cultured to produce F1 plants (2n=59). The F1 plants resembled PI 441001more than Dwight and were sterile. Mitotic metaphase chromosomes of PI 441001 and Dwight were indistinguishable. Meiosis in F1 plants was irregular with mostly univalents at diakinesis and metaphase I. At pachynema, completely synapsed bivalents were observed. Amphidiploid (2n=118) plants, induced by colchicine treatment, were vigorous and produced mature pods and seeds after backcrossing with Dwight. The BC1 plants (2n=79) produced dark green curved leaves with short petioles, however, they produced mature pods and seeds in crosses with Dwight. Chromosome numbers in BC2F1 plants ranged from 2n=41-50. From BC2 F2 to BC3F1, number of plants in parenthesis with 2n=40 (275), 2n=41 (208), 2n=42 (80), 2n=43 (27), 2n=44 (12), and 2n=45 (3) were identified. We expected to isolate 39 MAALs (2n=41) and 39 DAALs (2n=42). From greenhouse- grown plants, we were able to identify five morphologically distinct MAALs. One MAAL was for chromosome 13 (satellite chromosome). Fertile lines from 2n=40 (225 plants), 2n=41 (150 plants), 2n=42 (84 plants), 2n=43 (14 plants, 2n=44 (2 plants), and 2n=45 (1 plant) were grown in the field during 2012 and 2013. A very low frequency of plants with 2n=40 chromosome were sterile (pods elongated 1-2cm without seeds-vestigial pods). This is the first report of creating new alloplasmic soybean lines with cytoplasm from G. tomentella. These are unique germplasm for broadening the cytoplasmic and genetic base of soybean.