Search

ENORMOUS GENOMIC RESOURCES have been developed for model plants such as Arabidopsis thaliana (L.) Heynh. and rice (Oryza sativa L.), including detailed genetic maps (Harushima et al., 1998), huge numbers [...]

Hybrid onion (Allium cepa) seed is produced using cytoplasmic male sterility (CMS). For the most commonly used source of onion CMS, male fertile plants possess male sterile (S) cytoplasm and dominant allele(s) at one nuclear male fertility locus (Ms). Because male fertility restoration is not necessary for bulb production, it is desirable to purge dominant alleles at Ms from populations and breeding lines to facilitate the development of male sterile inbreds for hybrid production. In this research, we used molecular markers to establish the cytoplasms and genotypes at Ms in progenies from testcrosses of male sterile lines with plants from three populations [B2354, Ailsa Craig (AC), and Sapporo-Ki (Ski)] possessing the dominant Ms allele. We scored male fertility of testcross progenies by visual examination of flowers and acetocarmine staining of pollen. Different sources of the dominant Ms allele showed significantly different amounts of male fertility restoration and proportions of stainable pollen, complicating visual selection against the dominant Ms allele. For AC and Ski, molecular markers correctly predicted male sterility vs. male fertility of progenies in the greenhouse and field. However, for B2354, male fertility restoration was less clear and especially difficult to score under field conditions, consistent with reduced penetrance of male fertility restoration for this source of the dominant Ms allele. These results will be of interest to onion breeders selecting S-cytoplasmic male sterile lines for hybrid onion development. [ABSTRACT FROM AUTHOR]

Closely related cucurbit species possess eightfold differences in the sizes of their mitochondrial genomes. We cloned mitochondrial DNA (mtDNA) fragments showing strong hybridization signals to cucumber mtDNA and little or no signal to watermelon mtDNA. The cucumber mtDNA clones carried short (30-53 bp), repetitive DNA motifs that were often degenerate, overlapping, and showed no homology to any sequences currently in the databases. On the basis of dot-blot hybridizations, seven repetitive DNA motifs accounted for [is greater than] 13% (194 kb) of the cucumber mitochondrial genome, equaling [is greater than] 50% of the size of the Arabidopsis mitochondrial genome. Sequence analysis of 136 kb of cucumber mtDNA revealed only 11.2% with significant homology to previously characterized mitochondrial sequences, 2.4% to chloroplast DNA, and 15% to the seven repetitive DNA motifs. The remaining 71.4% of the sequence was unique to the cucumber mitochondrial genome. There was [is less than] 4% sequence colinearity surrounding the watermelon and cucumber atp9 coding regions, and the much smaller watermelon mitochondrial genome possessed no significant amounts of cucumber repetitive DNAs. Our results demonstrate that the expanded cucumber mitochondrial genome is in part due to extensive duplication of short repetitive sequences, possibly by recombination and/or replication slippage.

Taxonomy Iris yellow spot virus ( IYSV) is in the genus Tospovirus, family Bunyaviridae, with a single-stranded, tri-segmented RNA genome with an ambisense genome organization. Members of the other genera in the family infect predominantly vertebrates and insects. Geographical distribution IYSV is present in most Allium-growing regions of the world. Physical properties Virions are pleomorphic particles of 80-120 nm in size. The particle consists of RNA, protein, glycoprotein and lipids. Genome IYSV shares the genomic features of other tospoviruses: a segmented RNA genome of three RNAs, referred to as large ( L), medium ( M) and small ( S). The L RNA codes for the RNA-dependent RNA polymerase ( RdRp) in negative sense. The M RNA uses an ambisense coding strategy and codes for the precursor for the GN/ GC glycoprotein in the viral complementary (vc) sense and a non-structural protein ( NSm) in the viral (v) sense. The S RNA also uses an ambisense coding strategy with the coat protein ( N) in vc sense and a non-structural protein ( NSs) in the v sense. Transmission The virus is transmitted by Thrips tabaci Lindeman (Order: Thysanoptera; Family: Thripidae; onion thrips) and with less efficiency by Frankliniella fusca Hinds (tobacco thrips). Host IYSV has a relatively broad host range, including cultivated and wild onions, garlic, chives, leeks and several ornamentals. Some weeds are naturally infected by IYSV and may serve as alternative hosts for the virus. Symptoms IYSV symptoms in Allium spp. are yellow- to straw-coloured, diamond-shaped lesions on leaves and flowering scapes. Diamond-shaped lesions are particularly pronounced on scapes. As the disease progresses, the lesions coalesce, leading to lodging of the scapes. In seed crops, this could lead to a reduction in yield and quality. Early to mid-season infection in bulb crops results in reduced vigour and bulb size. Control Resistant varieties are not available, but a limited number of accessions with field tolerance have been identified. Integrated disease management tactics, including sanitation, crop rotation, thrips management, maintenance of optimal plant vigour, soil fertility, irrigation and physical separation of bulb and seed crops, can mitigate the effect of the disease. Virus code: 00.011.0.85.009 Useful link: [ABSTRACT FROM AUTHOR]