G. Valè

An integrated physical and genetic map represent a prerequisite for DNA sequence assembly of wheat chromosome 5A. About 95,000 BAC clones for 5A were fingerprinted using SnaPshot method and the useful fingerprints were assembled into contigs using both FPC and LTC software. Two minimal tiling paths (MTPs), were defined: FPC-MTP consisting of 4,201 for 5AS and 6,560 for 5AL overlapping BAC clones and LTC-MTP made of 5,412 for 5AS and 8,709 for 5AL overlapping BACs. Both MTPs were organized in three dimensional (3D) pools, to increase the efficiency of further anchoring, that was performed using two different strategies. The anchoring of FPC-MTP was done through screening with several classes of molecular markers mapped on four segregating populations, including SSRs (simple sequence repeat) and based on transposable element-junctions obtained either from literature or by in silico screening of 454-derived 2x coverage of 5A flow sorted DNA. To anchor the LTC-MTP an Agilent 15K specifi...

ABSTRACT In this study, an isolate of Magnaporthe oryzae expressing the green fluorescent protein gene (gfp) was used to monitor early events in the interaction of M. oryzae with resistant rice cultivars harbouring a blast resistance (R) gene. In the resistant cultivars Saber and TeQing (Pib gene), M. oryzae spores germinated normally on the leaf surface but produced morphologically abnormal germ tubes. Germling growth and development were markedly and adversely affected in leaves of these resistant cultivars. Penetration of host cells was never seen, supporting the idea that disruption of germling development on the leaf surface might be one of the resistance mechanisms associated with Pib function. Thus, this particular R gene appeared to function in the absence of host penetration by the fungal pathogen. Confocal laser scanning microscopy of M. oryzae‐infected susceptible rice cultivars showed the dimorphic growth pattern that is typically observed during the biotrophic and necrotrophic stages of leaf colonization in susceptible cultivars. The suitability of the gfp‐expressing M. oryzae isolate for further research on R‐gene function and identification of resistant genotypes in rice germplasm collections is discussed.

Cultivated European rice germplasm is generally characterized by moderate to high sensitivity to blast, and blast resistance is therefore one of the most important traits to improve in rice breeding. We collected a panel of 25 rice genotypes containing 13 broad range rice resistance genes that are commonly used in breeding programs around the world: Pi1, Pi2, Pi5, Pi7, Pi9, Pi33, Pib, Pik, Pik-p, Pita, Pita 2 , Piz and Piz-t. The efficiency of the selected Pi genes towards Italian blast pathotypes was tested via artificial inoculation and under natural field infection conditions. To characterize haplotypes present in the chromosomal regions of the blast resistance genes, a polymorphism search was conducted in the sequence regions adjacent to the blast resistance by examining DNA from the Pi gene donors with a panel of 5–7 potential receivers (cultivated European rice genotypes). Seven InDel and 8 presence/absence polymorphisms were directly detected by gel analysis after DNA amplification, while sequencing of 12.870 bp through 32 loci in different genotypes revealed 85 SNP (one SNP every 151 bp). Seven SSRs were additionally tested revealing 5 polymorphic markers between donors and receivers. Polymorphisms were used to develop 35 PCR-based molecular markers suitable for introgressing of Pi genes into a set of the European rice germplasm. For this last purpose, allelic molecular marker variation was evaluated within a representative collection of about 95 rice genotypes. Polymorphic combinations allowing introgression of the broad spectrum resistance genes into a susceptible genetic background have been identified, thus confirming the potential of the identified markers for molecular-assisted breeding.