We describe the construction of a reference genetic linkage map for the Brassica A genome, which will form the backbone for anchoring sequence contigs for the Multinational Brassica rapa Genome Sequencing Project. Seventy-eight doubled haploid lines derived from anther culture of the F(1) of a cross between two diverse Chinese cabbage (B. rapa ssp. pekinensis) inbred lines, 'Chiifu-401-42' (C) and 'Kenshin-402-43' (K) were used to construct the map. The map comprises a total of 556 markers, including 278 AFLP, 235 SSR, 25 RAPD and 18 ESTP, STS and CAPS markers. Ten linkage groups were identified and designated as R1-R10 through alignment and orientation using SSR markers in common with existing B. napus reference linkage maps. The total length of the linkage map was 1,182 cM with an average interval of 2.83 cM between adjacent loci. The length of linkage groups ranged from 81 to 161 cM for R04 and R06, respectively. The use of 235 SSR markers allowed us to align the A-genome chromosomes of B. napus with those of B. rapa ssp. pekinensis. The development of this map is vital to the integration of genome sequence and genetic information and will enable the international research community to share resources and data for the improvement of B. rapa and other cultivated Brassica species.

Certain plant growth-promoting bacteria, such as Pseudomonas fluorescens 89B61 and Bacillus pumilus SE34, secreted high levels of indole-3-acetic acid (IAA) in tryptophan-amended medium in stationary phase as determined by chromogenic analysis and high-performance liquid chromatography. Two other growth-promoting strains, P. chlororaphis O6 and Serratia marcescens 90-166, did not produce these high levels of IAA. However, when the gacS mutant of P. chlororaphis O6 was grown in tryptophan-supplemented medium, IAA was detected in culture filtrates. IAA production by the gacS mutant in P. chlororaphis O6 was repressed in the tryptophan medium by complementation with the wild-type gacS gene. Thus, the global regulatory Gac system in P. chlororaphis O6 acts as a negative regulator of IAA production from trypophan.

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The objective of this study was to determine whether inoculation with Bacillus licheniformis MH48 as a plant growth-promoting rhizobacterium (PGPR) could promote nutrient uptake of seedlings of the ornamental plant Camellia japonica in the Saemangeum reclaimed coastal land in Korea. B. licheniformis MH48 inoculation increased total nitrogen and phosphorus content in soils by 2.2 and 20.0 fold, respectively, compared to those without bacterial inoculation. In addition, B. licheniformis MH48 produced auxin, which promoted the formation of lateral roots and root hairs, decreased production of growth-inhibiting ethylene, and alleviated salt stress. Total nitrogen and phosphorus uptake of seedlings subjected to bacterial inoculation was 2.3 and 3.6 fold higher, respectively, than the control. However, B. licheniformis MH48 inoculation had no significant effect on the growth of seedlings. Our results suggest that inoculation with B. licheniformis MH48 can be used as a PGPR bio-enhancer to stimulate fine root development, promote nutrient uptake and alleviate salt stress in ornamental plant seedlings grown in the high-salinity conditions of reclaimed coastal land.

This study was conducted to identify the chromosomal location and magnitude of effect of quantitative trait loci (QTL) controlling sweet corn (Zea mays L.) stand establishment and investigate the impact of dry kernel characteristics on seedling emergence under field conditions. Genetic and chemical analysis was performed on two F2:3 populations (one homozygous for su1 and segregating for se1, the other homozygous for sh2 endosperm carbohydrate mutations) derived from crosses between parental inbreds that differed in field emergence and kernel chemical composition. A series of restriction fragment-length polymorphism (RFLP) and phenotypic markers distributed throughout the sweet corn genome were used to construct a genetic linkage map for each population. F2:3 families from the two populations were evaluated for seedling emergence and growth rate at four locations. Mature dry kernels of each family were assayed for kernel chemical and physiological parameters. Composite interval analysis revealed significant QTL associations with emergence and kernel chemical and physiological variables. Improved emergence was positively correlated with lower seed leachate conductivity, greater embryo dry weight, and higher kernel starch content. QTL affecting both field emergence and kernel characteristics were detected in both populations. In the su1 se1 population genomic regions significantly influencing emergence across all four environments were found associated with the se1 gene on chromosome 2 and the RFLP loci php200020 on chromosome 7 and umc160 on chromosome 8. In the sh2 population the RFLP loci umc131 on chromosome 2 and bnl9.08 on chromosome 8 were linked to QTL significantly affecting emergence. Since seedling emergence and kernel sugar content have been shown to be negatively correlated, undesirable effects on sweet corn eating quality associated with each emergence QTL is discussed. Segregating QTL linked to RFLP loci in these populations that exert significant effects on the studied traits are candidates for molecular marker-assisted selection to improve sweet corn seed quality.