Promising genome regions for improving cold tolerance of sorghum were identified on chromosomes SBI-01, SBI-03, SBI-07, and SBI-10. Chlorophyll fluorescence had no major effect on growth rates at low temperatures. Developing fast growing sorghum seedlings is an important breeding goal for temperate climates since low springtime temperatures are resulting in a prolonged juvenile development. The adaptation of sorghum to tropical and subtropical highlands gives hint for certain genetic variation. The goals of the present study were to detect marker-trait associations for leaf and dry matter growth rate and for chlorophyll fluorescence and content (SPAD) in relation to temperature. A diversity set comprising 194 genotypes was tested in eight controlled environments with temperatures ranging from 9.4 to 20.8 °C. Significant marker-trait associations (p < 0.05) were identified for each individual temperature regime and on the parameters of regression analyses describing the responses of growth or chlorophyll related traits to temperatures. The diversity set was fingerprinted with 171 diversity array technology (DArT) and 31 simple-sequence repeat (SSR) markers. SSRs were used to analyze the population structure while association studies were performed on DArT markers. Promising marker-trait associations for growth rates in relation to temperature were detected on chromosomes SBI-01, SBI-03, SBI-07, and SBI-10. Many promising loci were also significantly associated to the results obtained in individual low-temperature environments. Marker-trait associations for chlorophyll content and fluorescence did occasionally co-locate to those for growth during juvenile development but there was no evidence supporting our hypothesis that seedling growth at low temperatures is largely influenced by SPAD or fluorescence.
Downy mildew on garden cress caused by Perofascia lepidii has become prevalent in organic seed producing areas of Germany resulting in limited seed production and high yield losses. Downy mildew occurrence in young plants in fields that have never been cultivated with garden cress raised questions about infested seeds and soils as sources of the primary inoculum and the role of other members of the plant family Brassicaceae as hosts of P. lepidii. To address these questions 31 seed lots from nine garden cress fields were examined for contamination using P. lepidii species-specific PCR assays. DNA of P. lepidii was detected in 17 seed lots out of 31. In bioassays no disease was observed on plants grown from infested seed lots but in a few plants grown from seeds. The significance of soilborne inoculum was investigated by assessing disease incidence in plants grown in soil samples. Garden cress with downy mildew symptoms were recorded when plants were grown in pathogen infested soil samples. The results show that P. lepidii is able to survive in the soil and can be a primary inoculum source for downy mildew disease. Oospores formed in infected plants underpin the role of these survival structures that get incorporated into soil after harvesting. In a host specificity-test none of the tested species Brassica juncea; Brassica napus; Brassica rapa subsp. pekinensis; Brassica rapa silvestris; Raphanus sativus var. oleiformis; Raphanus sativus var. sativus; Sinapis alba; Sinapis nigra; Arabidopsis thaliana; Capsella bursa-pastoris; Cardamine pratense; Cardaria draba; Nasturtium officinale were infected by P. lepidii.
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