The UK-grown onion sector shows strong potential for growth through new product development as consumers become increasingly aware of the health and dietary benefits of fresh onion consumption. Prospects for the production of new, more palatable sweet onions will be boosted by the development of improved grower diagnostics for flavour standardisation. Growers require simple-to-use on-farm diagnostics to assure flavour quality. The introduction of pungency tests has led to increased mild onion sales, however currently tests are out-sourced and as a result costly. Through this Defra- (Department for Agriculture Food and Rural Affairs) sponsored research project (HL0164), hand-held biosensor technology, adapted from the medical sector, has been developed for improved and lower cost pungency and sweetness analysis in onions. Cont/d.

The cultivation of tomato (Solanum lycopersicum) plants for their edible fruits is a worldwide industry that was valued at over $58.7B in 2011. Traditional breeding has predominantly focused on increasing fruit yield or the accumulated concentrations of health-promoting phytochemicals, such as the antioxidant Iycopene. As a result, tomato crops remain susceptible to a large number of potentially devastating diseases which cause significant economic losses to commercial producers. These diseases are incited by a diverse group of microorganisms including bacteria, fungi, nematodes and oomycetes. DNA microarrays are a rapid, sensitive and relatively low cost molecular tool. They can be used to simultaneously detect a large number of PCR-amplified target DNA fragments based on their hybridisation to pre-designed short (~30 bp) complementary oligonucleotide capture probes. Capture probes are commonly designed using barcode regions in the genome and rely on the presence of heterogeneous sequence. Several applications of microarrays have been proposed, including their use for detecting pathogen occurrence and monitoring environmental microbial populations. The ArrayTube platform consists of a 3 x 3 mm glass microprobe array biochip embedded within a modified 1.5 ml Eppendorf-style tube. It provides a discrete environment in which the entire hybridisation and enzyme-catalysed precipitation staining reactions can occur. Detection of hybridised probes is achieved by the acquisition of grey-value transmission data using a specialised ArrayTube Reader device.

The early stages of drought affect plant hormonal homeostasis, including root to shoot signalling. This thesis focuses on manipulating this signalling (to enhance plant drought tolerance) by adding bacterial inocula (Variovorax paradoxus 5C-2 or Bacillus subtilis IR15) to the rhizosphere of pea and lettuce plants. These bacteria can decrease plant ACC (ethylene) or increase cytokinin status, respectively. Firstly, characterising V. paradoxus 5C-2. indicated that it tolerates drought conditions, and colonises the roots of different plant species with different specificity. In the highly specific V. paradoxus 5C-2 / Pisum sativum interaction, bacterial genes of attraction (chemotaxis) are switched on. Secondly, V. paradoxus 5C-2 was applied to pea plants under field conditions and soil drying imposed. V. paradoxus 5C-2 did not alter rhizospheric microorganism community structure and activity, but pea biomass and nodule numbers increased, even in drying soil. Thirdly, root samples from the field were further studied using molecular biology techniques to find rhizobium candidate strains interacting with V. paradoxus 5C-2. The detection of specific RFLP patterns lead to the identification of a specific Rhizobium leguminosarum strain, which physically interacts with V. paradoxus 5C-2 as seen in LAMP-FISH (loop mediated isothermal amplification - fluorescence in situ hydridisation) by confocal microscopy. V. paradoxus 5C-2 increased rhizobium recruitment on root hairs by stimulating rhizobium expression of nodC genes needed for attachment to the roots. Finally, B. subtilis IR15 applied to the rhizosphere of lettuce plants increased foliar cytokinin concentration, and shoot biomass of plants grown in drying soil. Since cytokinins can inhibit root elongation, B. subtilis IR15 was transformed to express the ACC deaminase gene of V. paradoxus 5C-2: ~This increased root elongaljon of lettuce seedlings in in vitro experiments. Further studies to allow the practical transfer of these inocula to farming systems were discussed.

Hyaloperonospora parasitica, phylum Oomycota, is a biotrophic plant pathogen that causes downy mildew on its cruciferous host plants. Naturally-infected plants show disease resistance visible as a hypersensitive response (HR).. This response results from the interaction of pathogen effectors with receptors and signalling molecules in the plant cell, causing localised necrosis killing the infected host cell. H parasitica isolates that are host-specific on the model plant Arabidopsis have been used to identify such pathogen effector genes. In this work I attempted to use this information to identify similar genes in isolates host specific to the crop plant Brassica oleracea. Potential effector molecules, encoding amino-terminal signal peptides, produced by Arabidopsis isolates ofH parasitica were sequenced in up to . 16 isolates and analysed for selection pressure, using population genetic methods. Highly variable genes were categorised as candidate virulence factors that might be involved in molecular interactions with the host detection machinery. Since they exhibit high amino acid variability, they are likely to be under positive selection pressure for change. The most diverse gene (ATR13) was cloned and expressed in planta to test for HR. This group of genes were then used to determine if they were under similar levels of selection in B. oleracea isolates of H parasitica. To search for the homologues in this related H parasitica subspecies a genomic library and an expressed sequence tag (EST) library were produced, as direct methods of gene isolation and were generally unsuccessful. The two main strategies employed were the use of microsyntenies to localise effector regions in the genome and a random sequencing approach to search for genes that encode signal peptides and effector motifs, such as the predicted targeting motifs RXLR and DEER, which are important to the delivery of oomycete effectors into host cells. While it was possible to find the regions of ATR13 and ATRl in the genome, it was not possible to find the orthologues of these avirulence factors. Using the EST approach many new candidate effectors were identified. It is clear from the data produced in this project that although the H parasitica isolates from B. oleracea and Arabidopsis both infect Brassicacae, they are very distantly related. So far no highly variable genes were found in the crop pathogen, although many interesting new candidates for secreted virulence factors were identified and work on a potential locus of avirulence factors has been initiated.

No description available.

No description available.

No description available.

No description available.

No description available.

The impact of TAL Pro-long and certain other sucrose ester coatings on the development of six common post-harvest fungal rots of pome fruit was investigated. The preparations were not observed to be fungistatic but TAL Pro-long did diminish the incidence of fungal infections on conference pears held in cold storage. At higher temperatures, depending on the nature of the disease, the coatings were able to modify the spatial distribution and reduce the rate of spread of the lesions within apples (cvs 'Chiver's Delight', 'Cox's Orange Pippin' and 'Granny Smith's') and pears (predominantly cv. 'Conference'). In comparison to the rate of decay in non-coated fruit, TAL Pro-long had a greater effect on those rots caused by <i>Botrytis cinerea</i> Fr., <i>Monilinia fructigena</i> (Aberh. & Ruhl.) Honey and <i>Rhizopus nigricans</i> Lind. than those of <i>Alternaria alternata</i> Fr., <i>M. laxa</i> (Aberh. & Ruhl.) Honey and <i>Penicillium expansum</i> Link em. Thom. The efficacy of the treatments was attendant on the ability of the surface coatings to ameliorate the rate of fruit ripening and was much influenced by the composition and concentration of the preparations, the variety of the fruit, the timing of the applications (relative to the onset of ripening and the climacteric rise in ethylene), and the temperature to which the produce was subsequently exposed. Studies indicated that, in Conference pears, the profile of simple sugars and the activity of certain extracellular enzymes produced by <i>M. fructigena</i> and <i>P. expansum</i> were modified by TAL Pro-long. The changes in enzyme activity were not obviously correlated with the development of the rots but there was an apparent association between coating and the reduced availability of monosacharides and sucrose in the tissues of the host. The sucrose ester coatings accentuated the differential permeability of the fruit skin to gases leading to a rapid decline in oxygen and a rise in carbon dioxide. Experiments indicated that such modified gas environments were unlikely to prevent the growth of pathogens but that they did effect the production and action of ethylene. It is suggested that the internal gas atmospheres established within the fruit delayed the inactivation of hormonal 'senescence retardants' and thereby diminished the sensitivity of the tissues to ethylene with the result that the rate of ripening was reduced and the innate resistance mechanisms of the fruit were retained for an extended period.