Association Analysis and Identification of SNP Markers for Stemphylium Leaf Spot (Stemphylium botryosum f. sp. spinacia) Resistance in Spinach (Spinacia oleracea)

Stemphylium leaf spot, caused by Stemphylium botryosum f. sp. spinacia, is an important fungal disease of spinach (Spinacia oleracea L.). The aim of this study was to conduct association analysis to identify single nucleotide polymorphism (SNP) markers associated with Stemphylium leaf spot resistance in spinach. A total of 273 spinach genotypes, including 265 accessions from the USDA spinach germplasm collection and eight commercial cultivars, were used in this study. Phenotyping for Stemphylium leaf spot resistance was evaluated in greenhouse;genotyping was conducted using genotyping by sequencing (GBS) with 787 SNPs;and single marker regression, general linear model, and mixed linear model were used for association analysis of Stemphylium leaf spot. Spinach genotypes showed a skewed distribution for Stemphylium leaf spot resistance, with a range from 0.2% to 23.5% disease severity, suggesting that Stemphylium leaf spot resistance in spinach is a complex, quantitative trait. Association analysis indicated that eight SNP markers, AYZV02052595_115, AYZV02052595_122, AYZV02057770_10404, AYZV02129827_205, AYZV0-2152692_182, AYZV02180153_337, AYZV02225889_197, and AYZV02258563_213 were strongly associated with Stemphylium leaf spot resistance, with a Log of the Odds (LOD) of 2.5 or above. The SNP markers may provide a tool to select for Stemphylium leaf spot resistance in spinach breeding programs through marker-assisted selection (MAS).

Genetic dissection of maize seedling root system architecture traits using an ultra-high density bin-map and a recombinant inbred line population

Maize（Zea mays） root system architecture（RSA）mediates the key functions of plant anchorage and acquisition of nutrients and water. In this study,a set of 204 recombinant inbred lines（RILs） was derived from the widely adapted Chinese hybrid ZD958（Zheng58 Chang7-2）,genotyped by sequencing（GBS） and evaluated as seedlings for 24 RSA related traits divided into primary,seminal and total root classes. Signi ficant differences between the means of the parental phenotypes were detected for 18 traits,and extensive transgressive segregation in the RIL population was observed for all traits. Moderate to strong relationships among the traits were discovered. A total of 62 quantitative trait loci（QTL） were identi fied that individually explained from1.6% to 11.6%（total root dry weight/total seedling shoot dry weight） of the phenotypic variation. Eighteen,24 and 20 QTL were identi fied for primary,seminal and total root classes of traits,respectively. We found hotspots of 5,3,4 and 12 QTL in maize chromosome bins 2.06,3.02-03,9.02-04,and 9.05-06,respectively,implicating the presence of root gene clusters or pleiotropic effects. These results characterized the phenotypic variation and genetic architecture of seedling RSA in a population derived from a successful maize hybrid.

Population isolation shapes plant genetics, phenotype and germination in naturally patchy ecosystems

Aims Habitat connectivity is important in conservation since isolation can diminish the potential of a population for adaptation and increase its risk of extinction.However,conservation of naturally patchy ecosystems such as peatlands has mainly focused on preserving specific sites with exceptional characteristics,neglecting the poten-tial interconnectivity between patches.In order to better under-stand plant dynamics within a peatland network,we assessed the effect of population isolation on genetic distinctiveness,phenotypic variations and germination rates using the peatland-obligate white-fringed orchid(Platanthera blephariglottis).Methods Fifteen phenotypic traits were measured for 24 individuals per pop-ulation(20 distinct populations,Quebec,Canada)and germination rates of nearly 20000 seeds were assessed.Genetic distinctiveness was quantified for 26 populations using single nucleotide polymor-phism markers obtained via a pooled genotyping-by-sequencing approach.Geographic isolation was measured as the distance to the nearest population and as the number of populations occurring in concentric buffer zones(within a radius of 2,5 and 10 km)around the studied populations.Important Findings All phenotypic traits showed significant differences among popu-lations.Genetic results also indicated a pattern of isolation-by-distance,which suggests that seed and/or pollen exchange is restricted geographically.Finally,all phenotypic traits,as well as a reduced germination rate,were correlated with either geographic isolation or genetic distance.We conclude that geographic iso-lation likely restricts gene flow,which in turn may affect germi-nation.Consequently,it is imperative that conservation programs take into account the patchy nature of such ecosystems,rather than targeting a few specific sites with exceptional character for preservation.