Colour differentiation of high-lycopene tomato fruit through the addition of the colourless-epidermis (y) mutation

High-lycopene tomatoes (Solanum lycopersicum) are characterised by an intense red flesh-colour, due to an elevated concentration of the carotenoid, lycopene. However, this characteristic is only visible once fruit are cut open, making it impossible to differentiate intact high-lycopene fruit from standard tomato fruit, a clear market disadvantage. The reason that fruit colour of both high-lycopene and standard fruit looks almost identical from the outside is because tomato fruit normally contain the yellow flavonoid 'naringenin chalcone' in a thin layer of epidermal cells. It is this combination of naringenin chalcone and the underlying lycopene in the flesh that gives tomatoes their characteristic orange-red colour. By incorporation of the recessive colourless epidermis mutant allele 'y' (which prevents naringenin chalcone accumulation) into high-lycopene fruit, we have been able to create high-lycopene tomatoes (hp1.ogc.y) exhibiting a deep-pink colour visible from the outside. Hue angle of the skin of the high-lycopene 'y' mutant and a regular highlycopene tomato (hp1.ogc.Y) was 30 and 38°, respectively, while flesh values were similar at 31 and 32°, respectively. Removal of naringenin chalcone from the epidermis appeared to improve the visibility of underlying lycopene, such that fruit outer colour became a subsequent indicator of underlying flesh colour. The removal of epidermal pigmentation means that high-lycopene fruit can now be differentiated from standard tomato fruit in the market place without the need to cut fruit open.

Comparison of host range and pathogenicity of isolates of Pythium myriotylum and Pythium zingiberis

Apart from morphology and genetic characteristics, species status of Pythium zingiberis and P. myriotylum may also be confirmed based on their pathogenicity and host range. An Australian putative P. zingiberis isolate and imported type isolates of P. myriotylum and P. zingiberis were subject to both in vitro and in vivo pathogenicity tests. In vitro tests were carried out on excised carrot, ginger, potato, radish, and sweet potato tuber/root sections, and on seeds and seedlings of cucumber, cauliflower, millet, rye, sweet corn, tomato, and wheat. In all assays conducted, the Australian isolate was found to be the most pathogenic, followed by type specimen of P. zingiberis (UOP 275), and then the type specimen P. myriotylum (CBS 254.70). An in vivo experiment on ginger plants at 35°C (with 10 h day light) in quarantine conditions showed that the ginger plants inoculated with the Australian isolate and also the type specimen of P. zingiberis died at 21 days after inoculation, whereas those inoculated with P. myriotylum CBS 254.70 were still green and healthy. Along with cardinal growth rate, the Australian isolate was confirmed to be closely related to P. zingiberis. This is also the first direct comparison in pathogenicity of P. zingiberis and P. myriotylum.

Transcriptome Analysis of Capsicum Chlorosis Virus-Induced Hypersensitive Resistance Response in Bell Capsicum

Background Capsicum chlorosis virus (CaCV) is an emerging pathogen of capsicum, tomato and peanut crops in Australia and South-East Asia. Commercial capsicum cultivars with CaCV resistance are not yet available, but CaCV resistance identified in Capsicum chinense is being introgressed into commercial Bell capsicum. However, our knowledge of the molecular mechanisms leading to the resistance response to CaCV infection is limited. Therefore, transcriptome and expression profiling data provide an important resource to better understand CaCV resistance mechanisms. Methodology/Principal Findings We assembled capsicum transcriptomes and analysed gene expression using Illumina HiSeq platform combined with a tag-based digital gene expression system. Total RNA extracted from CaCV/mock inoculated CaCV resistant (R) and susceptible (S) capsicum at the time point when R line showed a strong hypersensitive response to CaCV infection was used in transcriptome assembly. Gene expression profiles of R and S capsicum in CaCV- and buffer-inoculated conditions were compared. None of the genes were differentially expressed (DE) between R and S cultivars when mock-inoculated, while 2484 genes were DE when inoculated with CaCV. Functional classification revealed that the most highly up-regulated DE genes in R capsicum included pathogenesis-related genes, cell death-associated genes, genes associated with hormone-mediated signalling pathways and genes encoding enzymes involved in synthesis of defense-related secondary metabolites. We selected 15 genes to confirm DE expression levels by real-time quantitative PCR. Conclusion/Significance DE transcript profiling data provided comprehensive gene expression information to gain an understanding of the underlying CaCV resistance mechanisms. Further, we identified candidate CaCV resistance genes in the CaCV-resistant C. annuum x C. chinense breeding line. This knowledge will be useful in future for fine mapping of the CaCV resistance locus and potential genetic engineering of resistance into CaCV-susceptible crops.