Improving yield and quality in leafy vegetables and tomatoes through manipulation of soil mycorrhizae

Baby leaf vegetables and herbs are harvested within a few weeks of sowing in sterile or flame-treated fields, other salad crops (eg tomatoes) are grown hydroponically. In these crops, establishing beneficial symbiotic relationships with natural soil fungi or bacteria are unlikely and this may seriously limit yield. There are reports of enhanced productivity when arbuscular mycorrhizal fungi (AMF) are added, but these studies rarely look for benefits relevant to crops with a short growth cycle. Fewer studies have considered the effects on crop quality, however, food quality, diet and health are important issues for the food industry. The presence of AMF has been shown to partially ameliorate the effects of salinity and/or drought stress in a number of crop species (ZhongQun, 2007; Kohler, 2008) where the effects of stress are thought to be reduced because the symbiotic relationships induce higher levels of antioxidants (AO). If this is so then such plants would also have increased nutritive value in human diets. This project will address applied aspects of adding AMF and provide fundamental knowledge of how fungal and/or bacterial symbionts affect metabolic processes within the plant. The project will answer 4 important questions 1. Do mycorrhizal associations differ between commercially grown crops with a short growth cycle and similar field grown crops? 2. Could increased AMF colonization provide greater opportunities for carbon storage in the soil via the biosynthesis of glomalin or other glycoproteins? 3. Is growth enhanced in crops with a short growth cycle by addition of AMF? Does the presence of AMF reduce the effects of mild stress? 4. Does the presence of AMF (and/or stress) alter the nutritional quality of the crop? 1. Using PFLA techniques we will characterise the microbial communities that establish in the rhizosphere of leafy vegetables and determine if bacteria or fungi predominate in our crops. Light microscopy will be used to record AMF colonization. Comparisons will be made between field- and glasshouse pot-grown material sourced from collaborating growers. Crops will include lettuce and other salad leaves, tomato and selected herbs. 2. We will quantify soil glomalin levels. Such glycoproteins may represent significant opportunities as a carbon sink, especially in Mediterranean climates and future UK climates following global change (Persiani et al, 2008). These proteins may also chelate toxic heavy metals. 3. Using glasshouse grown crops we will quantify the effect of adding different AMF on yield. Experiments will use organic and non-organically grown leafy vegetables, and hydroponically grown tomatoes. 4. We will assess the nutritional quality of plant material grown in the presence or absence of AMF. We have shown that AO content in coriander increases 3-fold when grown at lower temperatures but takes 4 weeks longer to reach maturity and that organically-grown coriander has a lower AO content than non-organic material (Stead, commercial trial). Soil grown lettuce had 2x the total AO content at harvest compared to hydroponically grown plants (Wagstaff, commercial trial). In rocket increasing light intensity almost doubled total AO content (Wagstaff, in prep). We will now study other indicators of quality (eg phenolics, sugars) that can influence human health in our chosen crops in order to improve and optimise food quality by manipulating the symbiotic relationships between the crop plant and AMF. This study will help UK Growers improve yields and crop quality thus improving UK food security and sustainability whilst contributing to an improved dietary intake by consumers. The project is forward looking as consideration will be given to the consequences of climate change (reduced water availability, possible accumulation of heavy metals). The project will provide a student with laboratory skills and industry-related training in an area where there is a shortage of trained staff.