Developing non-peat growing media with microbial amendments

Background
Governmental directives state that because of the unsustainable and destructive nature of peat extraction, suitable alternatives for use in the horticultural industry need to be found. Much research has examined alternatives to peat, but plants grown in non-peat media can grow poorly, and are often smaller and more varied in size compared to those grown in peat. Over the last four years, Royal Holloway and the RHS have collaborated on a BBSRC project to examine how soil microbes, specifically beneficial symbiotic fungi (termed ‘mycorrhizas’) can help to overcome the shortcomings of non-peat media. We have found that some non-peat media show much promise if inoculated with the fungi. This successful project has laid the foundations for a detailed examination of non-peat media in an industry that is currently heavily reliant on peat and where plant quality is critical – that of pot-grown herbs. The largest market in the UK is for basil and coriander and we will focus on these crops. In addition to mycorrhizas, we have been trialling the use of and soil-borne plant growth-promoting rhizobacteria (PGPR) and have found that adding these to soil can have synergistic effects on mycorrhizal growth and plant yield.

Aim
The overall aim of project is to examine how mycorrhizal fungi and PGPR can be incorporated into various non-peat media for the production of high-quality pot-grown herbs, specifically basil and coriander.

Objectives
1. To determine which mycorrhizal fungal species grow best in non-peat media and what effects they have on herb growth and disease resistance.
2. To determine which PGPR species interact with mycorrhizal fungi and what the ‘optimum’ species combination is for plant health and increased yield.
3. To determine how the microbes affect culinary value, specifically volatile production, and to compare this with plants grown in peat.
4. To determine how these microbes affect nutrient and water relations of plants and to examine the addition of water-holding gels to the media.
5. To determine optimum inoculation methods for the microbes, by trialling direct to the medium or as a seed coat addition.
6. To determine how shelf life of plants grown in non-peat media with our optimum microbial species compares to that grown conventionally in peat.

Outline of work programme
In conjunction with a major herb producer, we will first trial a number of different mycorrhizal fungi, and PGPR species, supplied by a plant biotechnology company. Using molecular techniques, we will determine which bacteria and fungi colonize the root systems and which provide the greatest benefits to plants, in terms of growth and volatile content. Mycorrhizas can increase disease resistance in plants and we will study how resistance to diseases such as downy mildews in basil can be enhanced. We know that different mycorrhizas have differential abilities to help plants take up mineral nutrients from the soil and to tolerate drought. Both of these parameters are critical in herb production and we will measure nutrient uptake and water use efficiency of plants with different fungi and PGPR. We will add different water-holding gels to the media to examine whether these and mycorrhizas together can make plants more drought tolerant and ultimately prolong shelf life. These studies will address objectives 1, 2, 3 and 4.

When a species or mixture of species of fungi has been found that produces optimal plants, we will investigate how to inoculate it into pots in a commercial setting, trialling methods of inoculation to the media and to the seed coat. This addresses objective 5.
Ultimately, the quality of the pot herbs purchased depends on the growing conditions and the ability to tolerate transport and shelving in a shop. RHUL has a lot of experience with shelf life problems and we will examine how plants with our optimum fungal inoculants compare with peat-grown specimens in shop conditions. This addresses objective 6.

The project will provide a multidisciplinary training experience in soil microbiology, biotechnology, and food science and nutrition while also providing skills in marketing and business development.