Field evaluation and genetic variation of some novel soybean cyst nematode resistance sources
Authors:
J. R. Gelin1 and P.R. Arelli2
Abstract:
The soybean cultivars currently used in the US have very low genetic diversity because they derived from a limited number of plant introductions (PI) (Lorrenzen and Shoemaker, 1994; Shoemaker, 1994). Soybean PIs come from Asia, and have historically been used either directly as varieties after evaluation or as sources of desirable genes for soybean breeding programs (Caviness, 1992). They have also been used in the US as sources of resistance to important diseases including Soybean Cyst Nematode (SCN), caused by Heterodera glycines Ichinohe, and Soybean Sudden Death Syndrome (SDS), caused by Fusarium solani (Mart.) Sacc. f. sp. phaseoli (Burk.) Snyd. & Hans., type A (Fehr, 1993; Palmer et al., 1996; Rao-Arelli, 1994; Rao-Arelli et al., 1992). These two infectious diseases often occur jointly in the field, resulting in important yield losses. Generally, the PIs used in soybean breeding programs as sources of resistance against SCN have a black seed coat, poor agronomic performance, and are also very susceptible to SDS in the field (Gibson et al., 1994; Gelin, 1996). Breeders are in search for new sources of SCN resistance in order to expand the genetic diversity of SCN resistance and at the same time to develop cultivars with combined resistance to both diseases. In this research, 31 new SCN-3 resistant plant introductions (P. R. Arelli, personal communication) were evaluated at two different locations in Southern Illinois in 1995, along with 11 previously used SCN resistance sources and 40 cultivars used as controls. The objectives of the study were: (i) to evaluate the agronomic performance of the new PI lines for flower color, flowering date, harvest maturity, yield and seed quality; (ii) to estimate their SDS response in the field; and (iii) to assess their genetic variation with the use of two simple sequence repeats (SSR) DNA markers.
Assignment of the E4 locus to Soybean Classical Linkage Group 4
Authors:
J. Abe1, O. K. Han2, K. Komatsu1, and Y. Shimamoto1
Abstract:
Most soybean cultivars have a short-day requirement for floral induction, in which flowering is normally suppressed under long daylength conditions. Insensitivity of flowering to long daylength is thus an important character in order to develop cultivars adapted to the long daylength of high latitude regions. The present study was conducted to identify and map the maturity gene controlling insensitivity of flowering to incandescent long daylength (ILD) found in an early-maturing cultivar from Hokkaido, Japan. A cross was made between the ILDinsensitive cultivar, 'Ohyachi 2' (e3e3e4e4), and the ILD-sensitive line, 'Harosoy-e3' (e3e3E4E4). F2 segregation data indicated an involvement of a single recessive gene (e4) in the ILD insensitivity of 'Ohyachi 2', and a recombination value of 14.9 ± 3.1 % was estimated between the gene and Enp endopeptidase isozyme) located on linkage group 4. The present study thus confirmed that the maturity gene for the ILD insensitivity of 'Ohyachi 2' is a recessive allele (e4) at the E4 locus, which is located on classical linkage group 4. The order is E4, Enp, Ln (narrow leaflet).