Powdery mildew caused by Podosphaera xanthii is an important foliar disease in melon. To find molecular markers for marker-assisted selection, we constructed a genetic linkage map of melon based on a population of 93 recombinant inbred lines derived from crosses between highly resistant AR 5 and susceptible 'Earl's Favourite (Harukei 3)'. The map spans 877 cM and consists of 167 markers, comprising 157 simple sequence repeats (SSRs), 7 sequence characterized amplified region/cleavage amplified polymorphic sequence markers and 3 phenotypic markers segregating into 20 linkage groups. Among them, 37 SSRs and 6 other markers were common to previous maps. Quantitative trait locus (QTL) analysis identified two loci for resistance to powdery mildew. The effects of these QTLs varied depending on strain and plant stage. The percentage of phenotypic variance explained for resistance to the pxA strain was similar between QTLs (R (2) = 22-28%). For resistance to pxB strain, the QTL on linkage group (LG) XII was responsible for much more of the variance (41-46%) than that on LG IIA (12-13%). The QTL on LG IIA was located between two SSR markers. Using an independent population, we demonstrated the effectiveness of these markers. This is the first report of universal and effective markers linked to a gene for powdery mildew resistance in melon.

Cucurbit chlorotic yellows virus (CCYV) causes chlorotic yellows on cucumber (Cucumis sativus) and melon (Cucumis melo) and is transmitted by Bemisia tabaci biotype B and Q whiteflies. To characterize the host range of CCYV, 21 cucurbitaceous and 12 other plant species were inoculated using whitefly vectors. All tested Cucumis spp. except Cucumis anguria and Cucumis zeyheri were systemically infected with CCYV, although infection rates varied among species. Citrullus lanatus, Cucurbita pepo, and Luffa cylindrica were susceptible to CCYV; however, the infection rates were low and symptoms were unclear. In addition to the cucurbitaceous plants, Beta vulgaris, Chenopodium amaranticolor, Chenopodium quinoa, Spinacia oleracea, Lactuca sativa, Datura stramonium, and Nicotiana benthamiana were also systemically infected by CCYV. Complete RNA1 and RNA2 were reverse-transcribed, cloned, and sequenced. CCYV RNA1 was found to be 8,607 nucleotides (nt) long and contained four open reading frames (ORFs). The first ORF spanned methyltransferase and RNA helicase domains followed by an RNA-dependent RNA polymerase domain, presumably translated by a +1 ribosomal frameshift. CCYV RNA2 was found to be 8,041 nt long and contained eight ORFs, including the hallmark gene array of the family Closteroviridae. Phylogenetic analysis demonstrated that CCYV was genetically close to Lettuce chlorosis virus, Bean yellow disorder virus, and Cucurbit yellow stunting disorder virus. Amino acid sequence similarities of representative proteins with these viruses indicated that CCYV should be classified as a distinct crinivirus species.

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A population of F7 recombinant inbred lines (RILs) was made from a cross between susceptible ('Santou') and resistant (PI197088-1) lines of cucumber in order to study powdery mildew resistance loci. Susceptibility to powdery mildew in the F7 RIL individuals showed a continuous distribution from susceptible to resistant, suggesting that powdery mildew resistance is controlled by quantitative trait loci (QTLs). A QTL analysis identified two and three loci for powdery mildew resistance under 26 and 20 degrees C conditions, respectively. One QTL was found in the same position under both temperature conditions. Therefore, it is more likely that one major QTL acts under both temperature conditions and that other QTLs are specific to the two temperature conditions. The above results suggest that the four QTLs are controlled in a different temperature manner, and that their combination played an important role in expressing a high level of resistance to powdery mildew in this cucumber population. Sequence-tagged site (STS) markers associated with each QTL were developed and would be useful for breeding a cucumber line with a high level of powdery mildew resistance.

Cyclamen persicum (cyclamen) is a commercially valuable, winter-blooming perennial plant. We cloned two cyclamen orthologues of AGAMOUS (AG), CpAG1 and CpAG2, which are mainly expressed in the stamen and carpel, respectively. Cyclamen flowers have 5 petals, but expression of a chimeric repressor of CpAG1 (CpAG1-SRDX) caused stamens to convert into petals, resulting in a flower with 10 petals. By contrast, CpAG2-SRDX only caused incomplete formation of stamens and carpels. Expression in Arabidopsis thaliana showed similar effects on flower organ specification. Simultaneous expression of CpAG1-SRDX and CpAG2-SRDX in cyclamen induced rose-like, multi-petal flowers, a potentially valuable trait in commercial ornamental varieties. Expression of CpAG2-SRDX in a cyclamen mutant lacking expression of CpAG1 more effectively produced multi-petal flowers. Here, we controlled the number of petals in cyclamen by simple genetic engineering with a chimeric repressor. This strategy may be applicable useful for other ornamental plants with two distinct AG orthologues.

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Fruit crispness is of great importance in cucumber as well as in other fruit vegetables, because it relates directly to the commercial value of the product. In breeding projects and pre-or postharvest studies of fruit texture, an effective quantification method has been desired to replace rough, qualitative evaluations of fruit texture based solely on human perceptions. We applied several analytical methods to the force-deformation curve to quantify cucumber fruit crispness and assessed the efficacy of these methods as candidate cucumber fruit crispness indicators for use in breeding or research. Texture parameters for the flesh and placenta of 12 cucumber cultivars, based on the crispness index, apparent fractal dimension, and power spectrum and peak analyses, were calculated from mechanical measurement results. There was a significant large genotypic (cultivar) effect on the texture parameter values and a lesser, but still significant, contribution from the environment. Furthermore, we found strong relationships between these texture parameters and sensory crispness. These results indicate that these methods for analyzing the force-deformation curve provide effective, quantitative indicators of fruit crispness, with considerable promise for application in scientific research and breeding programs.