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Using a recombinant luminescent Nitrosomonas europaea assay to quantify biological nitrification inhibition (BNI), we found that a wild relative of wheat (Leymus racemosus (Lam.) Tzvelev) had a high BNI capacity and releases about 20 times more BNI compounds (about 30 ATU g −1 root dry weight 24 h −1 ) than Triticum aestivum L. (cultivated wheat). The root exudate from cultivated wheat has no inhibitory effect on nitrification when applied to soil; however, the root exudate from L. racemous suppressed NO À 3 formation and kept more than 90% of the soil's inorganic-N in the NH þ 4 -form for 60 days. The high-BNI capacity of L. racemosus is mostly associated with chromosome Lr#n. Two other chromosomes Lr#J, and Lr#I also have an influence on BNI production. Tolerance of L. racemosus to NH þ 4 is controlled by chromosome 7Lr#1-1. Sustained release of BNI compounds occurred only in the presence of Plant Soil (2007) 299:55-64

We have characterized a so-called D genome specific repetitive DNA sequence (pAs1) of Aegilops squarrosa L. (2n = 14, genome DD) with respect to its DNA sequence and its distribution among Triticeae species. The clone consisted of three units of a repetitive DNA sequence of 336 or 337 base pairs, and was AT rich (65.2%). DNA analyses revealed the presence of the pAs1-like sequences in other genomes of Triticeae species, although the repetition was greatly (as much as 100-fold) variable among the genomes. The repetitive sequences from 10 diploid species were amplified using PCR with specific primers, and the sequential variability was analyzed by the digestion pattern obtained with five restriction enzymes. Since the AfaI site was the most conservatively present in the unit of the repetitive sequences, we named them "Afa family." The analysis clearly displayed the variation of the repetitive sequences regardless of the uniformity of the size of the amplified product. These results indicated that plural amplification events of these repetitive sequences happened independently in the genome evolution of Triticeae.

Wide crossing is one of a number of practical methods that can be used to expand genetic variation in common wheat (Triticum aestivum). However, in crosses between wheat and distantly related species such as maize (Zea mays) and pearl millet (Pennisetum glaucum), non-wheat chromosomes are often eliminated from the hybrid during embryogenesis. In this study, we used pearl millet pollen to pollinate the pistils of a range of plants in the tribe Triticeae, as well as oat. Seven days after pollination, the dynamics of the pearl millet chromosomes in the embryos were observed using in situ hybridization, probing both the pearl millet genomic DNA and its centromere-specific repeats. In embryos from the crosses with oat, all seven of the pearl millet chromosomes were retained. However, in hybrids with the Triticeae species, chromosome elimination occurred during embryogenesis. Pearl millet chromosome showed chromosome rearrangements and non-disjunction together with micronuclei. These rearranged chromosomes and micronuclei derived from the breakage of bridges and retention of acentric fragments in anaphase, respectively. The cause of the chromosome elimination of wheat-pearl millet hybrid is not malfunction of the kinetochores binding to the spindles but the malfunction of the sister chromatids segregation at anaphase especially of chromosome arm.