Sclerotinia stem rot [caused by Sclerotinia sclerotiorum (Lib.) de Bary] is considered the second most important cause of yield loss in soybean [Glycine max (L.) Merr]. Soybean cultivars show variability in susceptibility, but no complete resistance to the disease has been reported and little information on the genetics of resistance is available. The objective of this study was to identify putative quantitative trait loci (QTLs) associated with Sclerotinia stem rot resistance in soybean. Recombinant inbred lines (RILs) from five populations were developed by crossing Williams 82, a susceptible cultivar, with five cultivars exhibiting partial resistance: Corsoy 79, Dassel, DSR173, S19‐90, and Vinton 81. The F2 to F5 generations were advanced by single seed descent. Parental polymorphism was tested with 507 simple sequence repeat (SSR) primers from the integrated linkage map of soybean, and primers were selected for progeny screening in the five populations on the basis of polymorphism and distribution in the genome. Five hundred RILs, consisting of 100 F5:6 lines from each population, were evaluated for resistance to Sclerotinia sclerotiorum isolate 143 by a detached leaf method in the laboratory to measure lesion area on leaves inoculated with mycelium plugs. Single degree‐of‐freedom contrasts in PROC MIXED and interval analysis were used to detect putative QTLs. Twenty‐eight putative QTLs for resistance to Sclerotinia stem rot of soybeans were identified on 15 different linkage groups in five RIL populations by single degree‐of‐freedom contrasts. Alleles involved in reduction of lesion size came from both the resistant and susceptible parents, and transgressive segregates were identified in two populations. The amount of phenotypic variation explained by individual QTLs ranged from 4 to 10%. Seven QTLs on seven different linkage groups were identified in multiple populations with some QTL regions corresponding with mapped resistance genes and resistance gene analogs. The results suggest that several genes control resistance to Sclerotinia stem rot and that markers could facilitate an initial screen of segregating breeding populations.

Soybean (Glycine max Merr.) production is reduced under iron-limiting calcareous soils throughout the upper Midwest regions of the US. Like other dicotyledonous plants, soybean responds to iron-limiting environments by induction of an active proton pump, a ferric iron reductase and an iron transporter. Here we demonstrate that heterologous expression of the Arabidopsis thaliana ferric chelate reductase gene, FRO2, in transgenic soybean significantly enhances Fe(+3) reduction in roots and leaves. Root ferric reductase activity was up to tenfold higher in transgenic plants and was not subjected to post-transcriptional regulation. In leaves, reductase activity was threefold higher in the transgenic plants when compared to control. The enhanced ferric reductase activity led to reduced chlorosis, increased chlorophyll concentration and a lessening in biomass loss in the transgenic events between Fe treatments as compared to control plants grown under hydroponics that mimicked Fe-sufficient and Fe-deficient soil environments. However, the data indicate that constitutive FRO2 expression under non-iron stress conditions may lead to a decrease in plant productivity as reflected by reduced biomass accumulation in the transgenic events under non-iron stress conditions. When grown at Fe(III)-EDDHA levels greater than 10 microM, iron concentration in the shoots of transgenic plants was significantly higher than control. The same observation was found in the roots in plants grown at iron levels higher than 32 microM Fe(III)-EDDHA. These results suggest that heterologous expression of an iron chelate reductase in soybean can provide a route to alleviate iron deficiency chlorosis.

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Naranjilla (Solanum quitoense Lam.) is an Andean fruit crop with great economic prospects in global export markets. The conservation and improvement of this crop greatly depend on the quantification of its genetic variability and on finding alternative sources of diversity in the Lasiocarpa section. The main objective of this study was to evaluate the extent to which SSR primer pairs specifically designed for Solanum tuberosum L. could be used in genetic diversity and phenetic studies of S. quitoense and its wild relatives from the Lasiocarpa section. Thirteen nuclear SSR primer pairs, out of 48 tested, were successfully transferred. Seven of these primers produced a total of 25 alleles and an average polymorphic information content (PIC) value of 0.4030. The genetic similarity index (Jaccard) between all accessions analyzed was 0.46 (0.54 dissimilarity), a value expected to increase with a greater sample population and a greater array of SSR primer pairs. Our preliminary UPGMA cluster analysis displayed seven major clusters and reinforces previous claims regarding the phenetic relations of section Lasiocarpa. The most important similarities between our results and the results of previous studies lie in the potential exclusion of S. stagnale from this section and the close genetic relationship that exists between S. candidum and the Asian members of this plant group. Our findings open the possibility for the exploitation of cross‐species amplification as a source of SSR markers for this plant group; thus contributing toward current developments aimed at improving and preserving S. quitoense, a crop of great importance to the Andean region.

Estudio preliminar de la diversidad genética de Ilex guayusa ecuatoriana mediante marcadores inter simple sequence repeat (ISSR) ResumenEvaluamos el grado de diversidad genética de Ilex guayusa, una especie de importancia etnobotánica y comercial para las comunidades indígenas de la Amazonía ecuatoriana. Caracterizamos genéticamente a 157 individuos, provenientes de chacras ubicadas a lo largo de seis provincias, con nueve marcadores ISSR (Inter Simple Sequence Repeats). Se detectó en total 91 bandas polimórficas, pero el índice de heterocigosidad estimada (H e =0.19) de la población reveló un nivel reducido de variabilidad genética para la especie. Los índices de distancias genéticas de Nei (0.013 ≤ Ds ≤ 0.086) revelaron un nivel reducido de divergencia genética entre individuos provenientes de provincias diferentes. De manera similar, el análisis de varianza molecular (AMOVA) demostró que solamente el 18% de la variación observada para I. guayusa ocurre entre poblaciones. El bajo grado de diversidad genética encontrado para I.guayusa puede ser atribuido al hecho de que esta especie es cultivada exclusivamente mediante propagación clonal; una actividad cultural que probablemente ha homogenizado el acervo genético de la especie a lo largo de su rango geográfico de cultivo. El análisis de coordenadas principales (PCoA) demostró que el germoplasma colectado puede estructurarse en tres grupos distintos caracterizados por un leve contraste genético en gradiente direccional, de norte a sur. La inclusión de un mayor número de muestras de provincias sub-representadas (ej. Sucumbíos) y poblaciones silvestres, si existen, ayudaría a esclarecer el nivel de diversidad genética y estructura poblacional de la especie, y la historia de su cultivo en la región.Palabras Clave. Aquifoliaceae, Guayusa, propagación clonal, baja diversidad genética. AbstractWe assessed the degree of genetic diversity of llex guayusa, a species of ethnobotanic and commercial relevance for indigenous communities of the Ecuadorian Amazon. We characterized 157 individuals, from small cultivation sites across six provinces, using nine Inter Simple Sequence Repeat (ISSR) markers. A total of 91 polymorphic bands were detected in, but estimated heterozygosity (He = 0.19) revealed a reduced level of genetic variability. Pairwise-Nei genetic distance indices (0.013 ≤ Ds ≤ 0.086) implied a reduced level of genetic divergence between individuals from different provinces. Accordingly, partitioning of genetic diversity (AMOVA) indicated that only 18% of variation observed for I. guayusa occurred between populations. The low degree of genetic diversity found for I. guayusa could be ascribed to the fact that the species is exclusively cultivated via clonal propagation; a cultural activity which has probably homogenized the species' genetic pool across its geographic range of cultivation. However, PCoA analysis resolved collected germplasm into three distinct groups displaying a subtle genetic contrast in a directional gradient, from north to south. The inclusion o...