Single plant cells have amazing capacities for regenerating into entire plants. This property is known as ‘totipotency’ discovered in the 1920s. Linking this with increasing understanding of growth control by plant hormones resulted in the development of the sterile, in vitro, culture. Tiny groups of cells, explants, are cut from the rapidly growing tips of shoots in controlled environments and washed in sterilising agents. These are cultured sterile jars containing a layer of agar supplemented with nutrients and hormones.
Green plantlets growing on sterile agar
The process is known as ‘tissue culture’ or micropropagation. As the cells divide and multiply, they are transferred through a series of sterile conditions which encourage root formation.
Roots growing from newly developing plantlets
Ultimately numerous new whole plants are generated. At that point they are removed from sterile conditions and weaned by planting into clean compost in high humidity environments. High humidity is essential as these transplants lack the protective coating of leaf and stem waxes which prevent desiccation. Ultimately when fully weaned the plants are grown under normal nursery conditions into saleable products.
Why bother with this processes which requires expensive facilities and highly skilled staff? A prime advantage is that micropropagated plants have genotypes very closely similar to those of the original parent, essentially they are clones. As a result vast numbers of progeny can be generated from a few parents preserving their characteristics. That is particularly important as a means of bulking-up newly bred varieties of many ornamental and fruit producing plants which otherwise would be reproduced vegetatively from cuttings or by grafting and budding onto rootstocks. Micropropagation is therefore a means for safeguarding the intellectual property of plant breeding companies.
Explants cut from parent plants before culturing can be heat-treated as a means of removing virus infections. The resultant end-products of rooted plants are therefore disease-free or more accurately disease-tested. These plants are usually more vigorous and produce bigger yields of flowers and fruit. Orchids are one of the crops where the impact of micropropagation is most obvious in florists’ shops and supermarkets.
Orchids have benefitted greatly from micropropagation
Large numbers of highly attractive orchids are now readily available. Previously orchids were very expensive and available in sparse numbers.
The world is not perfect and there are disadvantages with micropropagation. Because the progeny are genetically similar they are uniformly susceptible to pests and pathogens. Crops of clonal plants can be and have been rapidly devasted by existing and new strains of insects and diseases to which they have no resistance.
Some plants such as lettuce require cool conditions for germination (<10 oC), a condition known as thermo-dormancy. This reflects the evolution of the wild parent species in cooler environments and growth cycles limited by higher summer temperatures. Transforming live but dormant seed into new healthy self-sufficient plants requires care and planning. The conditions in which seed is stored before use greatly affect the vigour and quality of plants post-germination. Seed which is stored too long or in unsuitable environments deteriorates resulting in unthrifty seedlings.
Seed is either sown directly into soil or into compost designed especially as an aid for germination. These composts contain carefully balanced nutrient formulae which provide larger proportions of potassium and phosphorus compounds which promote rooting and shoot growth. The amounts of nitrogen needed at and immediately post-germination are limited. Excess nitrogen immediately post-germination will cause over-rapid growth which is susceptible to pest and pathogen damage.
Minor nutrients will also be included in composts which ensures the establishment of efficient metabolic activities free from deficiency disorders. Composts require pH values at ~ 7.0 for the majority of seedlings unless they are of calicifuge (unsuited for calcareous soils) species where lime requirement is limited and the compost pH will be formulated at 6.0. Additionally, the pC will be carefully tuned ensuring correctly balanced ionic content avoiding root burning disorders. Finally, the compost should be water retentive but offering a rooting environment with at least 50 percent of the pore spaces filled with air. Active root respiration is essential while at the same time water is needed as the carrier for nutrient ions.
Seedlings encountering beneficial environments delivering suitable temperatures will germinate into healthy and productive plants.
Some plants such as lettuce require cool conditions for germination (<10 oC), a condition known as thermo-dormancy. This reflects the evolution of the wild parent species in cooler environments and growth cycles limited by higher summer temperatures.
Careful husbandry under protection such as in greenhouses provides plants which can be successfully transplanted into the garden. The soil receiving these should be carefully cultivated, providing an open crumb structure which permits swift and easy rooting into the new environment. It is essential that in the establishment phase plants are free from water stress. Measures which avoid predation from birds such as pigeons may also be required.
Netting or the placing of cotton threads above plants helps as a protection measure. Weeds must be removed otherwise competition will reduce crop growth and encourage pests and diseases, particularly slug browsing. Finally, the gardener will be rewarded for his/her work with a fruitful and enjoyable crop!
In the build up to our SCI Agri-Food Early Career Committee’s 2019 #agrifoodbecause Twitter competition, we are looking back over the best photos of the 2018 competition. Entrants were asked to take photos and explain why they loved their work, using the hashtag #agrifoodbecause on Twitter.
Our 2018 winner, Claire Dumenil from Rothamsted Research, won first prize for her visually striking image of a fruit fly on a raspberry. She received a free SCI student membership and an Amazon voucher.
#agrifoodbecause invasive pests threaten food production and food security, worldwide! #SWD #drosophilasuzukii #Rothamsted #cardiffuni – Claire Dumenil (@CnfDumenil)
#agrifoodbecause I work on reducing aphid infestations on wheat. From the lab to the field – Amma Simon (@amma_simon)
With their fluffy body bumblebees are fantastic pollinators! Work with them can improve crop pollination !! #agrifoodbecause – Sandrine Chaillout (@100chillout)
#agrifoodbecause I can develop drought tolerant wheat varieties – Samer Mohamed (@samer313)
#agrifoodbecause My Research looks at wild pollinators and how we can build a sustainable farming future with them and us in mind! – Laura James (@JamJamLaura)
#agrifoodbecause our improving understanding of the devastating pest, whitefly Bemisia tabaci s.l., will help farmers to increase yields and feed their children <3 – Sona Vyskocilova (@VyskocilovaS)
Plant breeders are increasingly using techniques to produce new varieties they say are indistinguishable from those developed through traditional breeding methods. New genome editing technologies can introduce new traits more quickly and precisely.
However, in July, 2018, the European Court of Justice decreed they alter the genetic material of an organism in a way that does not occur naturally, so they should fall under the GMO Directive. This went against the opinion of the Advocate General.
In October 2018, leading scientists representing 85 European research institutions endorsed a position paper warning that the ruling could lead to a de facto ban of innovative crop breeding.
The paper argues for an urgent review of European legislation, and, in the short term, for crops with small DNA adaptations obtained through genome editing to fall under the regulations for classically bred varieties.
‘As European leaders in the field of plant sciences […] we are hindered by an outdated regulatory framework that is not in line with recent scientific evidence,’ says one of the signatories, Dirk Inzé, Scientific Director at Life Sciences Institute VIB in Belgium.
In April, EU Members States voted for a near complete ban of the use of neonicotinoid insecticides – an extension to restrictions in place since 2013. The ban, which currently includes a usage ban for crops such as maize, wheat, barley, and oats, will be extended to include others like sugar beet. Use in greenhouses will not be affected.
Some studies have argued that neonicotinoids contribute to declining honeybee populations, while many other scientists and farmers argue that there is no significant field data to support this.
In response to the recent ban, SCI’s Pest Management Science journal has made a number of related papers free to access to better inform on the pros and cons of neonicotinoids.
Like to know more about neonicotinoids? Click the links below…
Robin Blake and Len Copping discuss the recent political actions on the use of neonicotinoids in agriculture, and the UK’s hazard-based approach following field research unsupportive of an outright ban on the insecticides.
Conflicting evidence on the effects of neonicotinoids on the honeybee population has beekeepers confused and has led to the increase in the use of older insecticides, reports one beekeeper.
Following the 2013 EU partial ban on neonicotinoids, experts called for good field data to fill knowledge gaps after questioning of the validity of the original laboratory research. To encourage future debate, realistic field data is essential to discouraging studies using overdoses that are not of environmental relevance.
This paper describes the consequences of the ban on neonicotinoid seed treatments on pest management in oilseed rape, including serious crop losses from cabbage stem flea beetles and aphids that have developed resistance to other insecticides.
The Research Articles
Particle size is one of the most important properties affecting the driftability and behaviour of dust particles scraped from pesticide dressed seeds during sowing. Different species showed variable dust particle size distribution and all three techniques were not able to describe the real-size distribution accurately.
Aside from particle size, drift of scraped seed particles during sowing is mainly affected by two other physical properties – particle shape and envelope density. The impact of these abraded seed particles on the environment is highly dependable on their active ingredient content. In this study, the envelope density and chemical content of dust abraded from seeds was determined as a function of particle size for six seed species.
Substantial honey bee colony losses have occurred periodically in the last decades, but the drivers for these losses are not fully understood. Under field conditions, bee colonies are not adversely affected by a long‐lasting exposure to sublethal concentrations of thiacloprid – a popular neonicotinoid. No indications were found that field‐realistic and higher doses exerted a biologically significant effect on colony performance.
Blue dye, in this cross-section of a maize cob, highlights the rice gene that controls T6P in the kernels’ phloem. Image: Rothamsted Research
Through the introduction of a rice gene, scientists have produced a maize plant that harvests more kernels per plant – even in periods of drought.
The rice gene expressed depresses levels of a natural chemical, trehalose 6 -phosphate (T6P), in the phloem of the transgenic maize plant. T6P is responsible for the distribution of sucrose in the plant.
Lowering levels of T6P in the phloem, an essential track in the plant’s transportation system, allows more sucrose to be channelled to the developing kernels of the plant. As a result of increased levels of sucrose in this area of the maize plant, more kernels are produced.
Drought is an increasing problem in countries such as Uganda. Image: Hannah Longhole
‘These structures are particularly sensitive to drought – female kernels will abort,’ said Matthew Paul, team leader and plant biochemist at Rothamsted Research, UK. ‘Keeping sucrose flowing within the structures prevents this abortion.’
The transatlantic team, from Rothamsted and biotechnology company Syngenta in the US, built on field tests published three years ago that demonstrated increased productivity of the same genetically-modified maize.
‘This is a first-in-its-kind study that shows the technology operating effectively both in the field and in the laboratory,’ said Paul.
Maize growing on world’s oldest experiment, Broadbalk field at Rothamsted Research. Image: Rothamsted Research
Drought is becoming an increasing problem for developing countries, where the economic and social impacts are most evident.
Maize, also known as corn, and other cereals are relied on heavily across these nations due to their low cost and high nutritional value, with rice, maize, and wheat used for 60% of the global food energy intake.
The results of these trials are promising, and the team believe this work could be transferred to wheat and rice plants, as well as other cereals, said Paul.
On average, 10% of all crop production is lost annually to drought and extreme heat, with the situation getting worse year on year. Heat stress happens over short-time periods, but drought happens over longer timescales and is linked to drier soils. Maize and wheat are especially hard hit, with yields falling by up to 50% if drought hits.
On the High Plains, the largest US wheat-growing region, drought is a possibility every season. ‘Drought stress can be a key concern, especially in dry lands, but even in irrigated areas we can’t expect the same levels of water in future and farmers face restrictions,’ says Chris Souder at Monsanto.
So, this is not simply a developing world problem. Pedram Rowhani, University of Sussex, UK, found cereals in more technically developed agricultural systems of North America, Europe, and Australia suffered most from droughts. Yield losses due to drought were 19.9% in the US compared to almost no effect in Latin America.
Crop breeders in the past paid a great deal of attention to yield, but not enough to resilience to extreme events such as drought, Rowhani says, but this is changing. Growers increasingly want built-in drought resilience and plant scientists are looking for novel solutions. New, unconventional approaches based on novel insights from basic science might be necessary.
Hundreds of genes and proteins are involved in the complex trait of drought resistance. Plants avoid drought stress by shortening their life cycle with accelerated flowering, or cut down water loss by closing leaf pores called stomata. One approach by breeders is to target specific traits by crossing individual plants that perform best under drought conditions.
Stomata are found of the underside of leaves and are used for gas exchange. Image: Pixabay
‘About 97% of plant water loss occurs through the stomata. If you want to regulate the amount of water a plant uses, regulate the stomata,’ says Julie Gray, University of Sheffield, UK. Gray has been genetically tweaking wheat, barley, and rice plants so they have fewer of these pores.
She believes rising CO2 levels in the atmosphere means that they do not suffer from less carbon dioxide from opening their stomata. ‘CO2 levels have gone up 40% over the last 200 years. It’s quite possible they are producing more stomata than they need,’ says Gray.
Power plant in Tihange, Belgium. CO2emissions continue to increase. Image: Hullie@Wikimedia Commons
Gray reports that plants grown at 450ppm CO2 with reduced stomatal density, but increased stomatal size, had larger biomass and increased growth tolerance when water was limited. ‘Plants can operate with perhaps half as many stomata before you see significant effects on photosynthesis, so you can definitely reduce water loss this way,’ says Gray.
Root of the issue
At the other end of the plant plumbing system are roots. Susannah Tringe, Joint Genome Institute, UK, is seeking microbes that can gift stress-tolerance to their plant hosts. ‘The microbes associated with plants are likely to be just as important for plant growth and health as the microbiome of humans,’ says Tringe.
Though a lot of work has focused on finding the ‘magic microbe,’ Tringe believes whole communities will be necessary in real field conditions, whereas a single strain could be out-muscled by competitors.
Regular bouts of drought are leading to famine in developing countries. Video: Food and Agriculture Organization of the United Nations
Sugar and drought
‘Drought is probably the most widespread abiotic stress that limits food production worldwide. There is always need to improve drought tolerance,’ says Matthew Paul, Rothamsted Research Institute, UK.
‘Sucrose is produced in photosynthesis,’ Paul explains. ‘During drought conditions, plants will withhold sucrose from the grain, as a survival mechanism’. This can terminate reproductive structures and abort seed formation, even if drought is short-lived, greatly compromising yield.
A plant scientist studying rice plants. Image: IRRI Photos@Flickr
Rothamsted researchers have looked at modifying plants so sugar keeps flowing. ‘If you can get more sugar going to where you want it […] then this could improve yields and yield resilience,’ enthuses Paul. Field studies show that GM maize improved yields from 31 to 123% under severe drought, when compared with non-transgenic maize plants.