Search

Phytophthora root rot, caused by Phytophthora megasperma Drechs. f. sp. glycinea T. Kuan & D.C. Erwin, is one of the most serious diseases of soybean [Glycine max (L.) Merr.]. Six loci with alleles giving race-specific resistance of soybean to phytophthora have been reported. The first objective of this study was to map the phytophthora resistance (Rps) loci using restriction fragment length polymorphism (RFLP) markers. The second objective was to map the Rj2 locus for ineffective nodulation with RFLP markers, because of the linkage of Rj2 to Rps2. The mapping was conducted using a series of |Williams' near-isogenic lines (NILs) with each having one or two phytophthora resistance alleles. The NILs were screened with 141 mapped RFLP markers. At least one polymorphism was found between each NIL and the recurrent parent. Linkage tests among the polymorphic RFLP markers, Rps loci, and the Rj2 locus were conducted using [F.sub.2] populations. Linkage was found between RFLP markers and Rps1, Rps2, Rps3, Rps4, Rps5, and Rj2. Linkage was also found between Rps2 and Rj2., The six loci (Rps 1 to 6) responsible for soybean resistance to Phytophthoria root rot was mapped by restriction fragment length polymorphisms (RFLPs). DNA from near isogenic lines (NIL) were screened with 141 RFLP markers. Results showed at least one polymorphism between each NIL and the recurrent parent. Five (Rps 1 to 5) of the six loci were mapped within marker linkage groups. The locus for ineffective nodulation (Rj2) was also mapped by RFLP markers. This locus was found closely linked to Rps2.

Simple sequence repeat (SSR) markers with linkages to the Rps1, Rps2, Rps3, Rps4, Rps5, and Rps6 loci that govern soybean [Glycine max (L.) Merr.] resistance to Phytophthora root rot (caused by Phytophthora megasperma Drechs. f. sp. glycinea Kuan and Ervin) are desired. Near-isogenic lines (NILs) of Clark or Williams, homozygous resistant (RpsRps) at just one of those Rps loci, were mated to a NIL of Harosoy homozygous susceptible (rpsrps) at all six loci. From the 100 to 120 [F.sub.2:3] progenies per mating, 20 [F.sub.3] seedlings were evaluated for resistance (R) or susceptibility (S) following inoculation with the race of P. megasperma affected by the segregating Rps allele. About 15 RpsRps and 15 rpsrps [F.sub.2] individuals were used to construct contrasting DNA bulks. Presumptive linkage (i.e., SSR marker polymorphism between two bulks) was confirmed or refuted by SSR assay of 15 to 40 [F.sub.2] individuals within each homozygous class. Recombination values were maximum likelihood estimates from the SSR allelic segregation data of both classes, although the rpsrps class was less prone to phenotypic classification error. SSRs on linkage groups (LGs) N, J, F, and G were identified with linkages to Rps1, Rps2, Rps3, and Rps4, respectively. A skewed R:S segregation in the Rps5 population precluded detection of linked SSRs. The Rps6 locus, whose map position was heretofore unknown, was linked with three SSRs in a region of LG-G that contains Rps4 and Rps5. SSR-Rps linkages of P [is less than] 0.05 could only be identified for the Rps1 alleles because of a paucity of SSR markers and/or parental monomorphism in the genomic regions surrounding other Rps loci., PHYTOPHTHORA ROOT ROT can cause severe economic losses in soybean production (Diets et al., 1992). This root rot disease is favored by wet conditions, and tends to be prevalent in [...]

Brown stem rot (BSR) causes vascular and foliar damage in soybean [Glycine max (L.) Merr.]. Identification of plants resistant to BSR by inoculation with Phialophora gregata (Allington & W.W. Chamberlain) W. Gams is laborious and unreliable because of low heritabillty. Molecular markers linked to the resistance gene could be used to screen for resistant individuals and hasten the development of BSR resistant genotypes. The objective of this study was to develop molecular markers for efficient identification of BSR resistant plants in a breeding program. Seventeen resistant and 29 susceptible cultivars and plant introductions as well as recombinant inbred lines derived from a cross between BSR 101 and PI 437.654 were assayed by PCR-based markers derived from RFLPs K375I-1 and RGA2V-1, Satt244, or developed from bacterial artificial chromosome (BAC) sequences. The DNA markers that were developed tag the BSR locus and are informative in a diverse range of soybean germplasm. Markers detected different banding patterns between resistant and susceptible genotypes. The PCR-based markers will most likely be useful in screening for BSR resistance and allow soybean breeders to transfer rapidly resistance derived from [Rbs.sub.3] to improved cultivars or soybean lines. The markers are relatively easy-to-use, inexpensive, and highly informative. Soybean breeding efforts can now be designed to incorporate the use of marker information when parental genotypes possess contrasting banding patterns., BROWN STEM ROT is a devastating fungal disease of soybean (Glycine max) caused by Phialophora gregata, a soil-borne fungus. The pathogen infects host plants through the roots and causes vascular [...]

Increases in the seed protein concentration of soybean [Glycine max (L.) Mere.] would improve the value of the crop. Two major quantitative trait locus (QTL) alleles from Glycine soja Sieb. and Zucc. that increased seed protein concentration were identified previously. The first objective of our study was to test the two G. soja QTL alleles in a population developed through backcrossing the alleles into a soybean background. The second objective was to evaluate the effect of one of the G. soja QTL alleles in three genetic backgrounds. A backcross three (BC3) population was developed and evaluated in the field across two locations over 2 yr. To test the allele in different backgrounds, a line from the backcross population was crossed to three soybean genotypes. Populations developed from these crosses were then evaluated in three field environments. In the backcross population, genetic market alleles linked to the QTL allele from G. soja on linkage group (LG) I were significantly (P [is less than] 0.05) associated with greater protein and less oil concentration, reduced yield, smaller seeds, taller plants, and earlier maturity than the G. max alleles. Markers linked to the second G. soja QTL allele on LG E were not significantly associated with seed or agronomic traits. In the genetic background tests, markers linked to the G. soja QTL allele on LG I were associated with an increase in protein concentration in two of the three crosses. These results show that seed component traits can be successfully modified through genetic mapping coupled with marker assisted selection., SOYBEAN IS PRODUCED primarily for its seed protein and oil. Increases in the seed protein concentration of soybean would enhance the value of the crop and a number of researchers [...]

A number of molecular genetic maps of the soybean [Glycine max (L.) Merr.] have been developed over the past 10 yr. These maps are primarily based on restriction fragment length polymorphism (RFLP) markers. Parental surveys have shown that most RFLP loci have only two known alleles. However, because the soybean is an ancient polypioid, RFLP probes typically hybridize and map to more than one position in the genome. Thus, the polymorphic potential of an RFLP probe is primarily a function of the frequency of the two alleles at each locus the probe detects. In contrast, simple sequence repeat (SSR) markers are single locus markers with multiple alleles. The polymorphic potential of an SSR marker is dependent on the number of alleles and their frequencies. Single locus markers provide an unambiguous means of defining linkage group homology across mapping populations. The objective of the work reported here was to develop and map a large set of SSR markers. A total of 606 SSR loci were mapped in one or more of three populations: the USDA/Iowa State G. max x G. soja [F.sub.2] population, the Univ. of Utah Minsoy x Noir 1 recombinant inbred population, and the Univ. of Nebraska Clark x Harosoy [F.sub.2] population. Each SSR mapped to a single locus in the genome, with a map order that was essentially identical in all three populations. Many SSR loci were segregating in two or all three populations. Thus, it was relatively simple to align the 20+ linkage groups derived from each of the three populations into a consensus set of 20 homologous linkage groups presumed to correspond to the 20 pairs of soybean chromosomes. On the basis of in situ segregation or linkage reports in the literature all but one of the classical linkage groups can now be assigned to a corresponding molecular linkage group., GENETIC LINKAGE MAPS serve the plant geneticist in a number of ways, from marker assisted selection in plant improvement to map-based cloning in molecular genetic research. Thus, in a widely [...]