For a comprehensive survey of the structure and dynamics of the Dutch Phytophthora infestans population, 652 P. infestans isolates were collected from commercial potato fields in the Netherlands during the 10-year period 2000–2009. Genotyping was performed using 12 highly informative microsatellite markers and mitochondrial haplotypes. In addition, for each isolate, the mating type was determined. STRUCTURE analysis grouped the 322 identified genotypes in three clusters. Cluster 1 consists of a single clonal lineage NL-001, known as “Blue_13”; all isolates in this cluster have the A2 mating type and the Ia mitochondrial haplotype. Clusters 2 and 3 display a more elaborate substructure containing many unique genotypes. In Cluster 3, several distinct clonal lineages were also identified. This survey witnesses that the Dutch population underwent dramatic changes in the 10 years under study. The most notable change was the emergence and spread of A2 mating type strain NL-001 (or “Blue_13”). The results emphasize the importance of the sexual cycle in generating genetic diversity and the importance of the asexual cycle as the propagation and dispersal mechanism for successful genotypes. Isolates were also screened for absence of the Avrblb1/ipiO class I gene, which is indicative for virulence on Rpi-blb1. This is also the first report of Rpi-blb1 breakers in the Netherlands. Superimposing the virulence screening on the SSR genetic backbone indicates that lack the Avrblb1/ipiO class I gene only occurred in sexual progeny. So far, the asexual spread of the virulent isolates identified has been limited.

Four hundred and seventy-eight microsatellite markers derived from expressed sequence tags (EST-SSRs) were screened among three mapping populations (W-7984xOpata 85, WOpop; LumaixHanxuan, LHpop; WenmaixShanhongmai, WSpop). The number of polymorphic EST-SSR primer pairs found in WOpop, LHpop and WSpop was 92, 58 and 29 respectively. A total of 101 EST-SSR loci amplified from 88 primer sets were distributed over the 20 chromosomes of the reference maps (no markers were located on chromosome 4B). These 101 mapped EST-SSR markers add to the existing 450 microsatellite loci previously mapped in bread wheat. Seventy-four of the 101 loci showed significant similarities to known genes, including 24 genes involved in metabolism, 4 in cellular structures, 9 in stress resistance, 12 in transcription, 2 in development, 2 transporters and 21 storage proteins. Besides gliadin and glutenin, most of the 53 genes with putative functions were mapped for the first time by EST-SSR markers in bread wheat. Sequence alignment of the mapped wheat EST-SSR loci allowed tentative assignment of functionality to the other members of grasses family. Colinearity combined with homology information offers an attractive approach to comparative genomics.

A major QTL affecting root traits and leaf ABA concentration was identified in maize (Zea mays L.) and named root-ABA1. For this QTL, back-cross-derived lines (BDLs) homozygous either for the (+) or for the (-) allele increasing or decreasing, respectively, root size and leaf ABA concentration, were developed. This study was conducted to evaluate the QTL effects in various genetic backgrounds and at different water regimes. The (+/+) and (-/-) BDLs were crossed with five or 13 inbred tester lines of different origin, thus producing two sets of test-crosses that were evaluated in Italy and China, respectively. Testing was conducted under both well-watered and water-stressed conditions. In Italy, the test-crosses derived from (+/+) BDLs, as compared with those derived from (-/-) BDLs, showed, across both water regimes, higher leaf ABA concentration (on average 384 versus 351 ng g(-1) DW) and lower root lodging (28.0 versus 52.5%), and lower grain yield under water-stressed conditions (4.88 versus 6.27 Mg ha(-1)). In China, where root lodging did not occur, the test-crosses derived from (+/+) BDLs were less productive at both water regimes (on average, 6.83 versus 7.49 Mg ha(-1)). The lower grain yield of the test-crosses derived from (+/+) BDLs was due to a lower number of ears per plant and to lower kernel weight. The results indicate that the (+) root-ABA1 allele confers not only a consistently lower susceptibility to root lodging but also a lower grain yield, especially when root lodging does not occur.

Setaria viridis (green foxtail) is a common weed and is the putative ancestor of foxtail millet (Setaria italica). Population densities of S. viridis and its effect on foxtail millet yield were studied for 4 years in two locations, with three cultivars, under monoculture and no use of selective herbicide. Each year the density of S. viridis plants increased in all fields at a population growth rate k = 1.13. The stability of the k estimate in monoculture could serve as a reference value to predict the fate of a weed population in multi-year demographic models, using corrective factors to account for specific effects of given crop rotation and cropping practices. The low k value was due to a very low reproduction rate, around 6 10 )4 adults per seed, which suggests high dormancy and seed predation. The yield of millet decreased linearly as the infestation increased, with the same slope whatever the cultivars. The yield loss was 0.58 tonne ha )1 for each additional plant m )2 , indicating high sensitivity to competition from the wild relative. The close relationship between the weed and the crop, which could lead to similar biological responses to environmental conditions, could explain these results.

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