NIAB - National Institute of Agricultural Botany

Orson's Oracle

Is plant resistance a free lunch?

Posted on 16/06/2017 by Jim Orson

There is often a perception that plant resistance to pests or diseases is a bit of a free lunch. Instead of paying for a pesticide the plant will look after itself. In general, this is not true. The presence of resistance genes can result in a yield drag either in the absence of a challenge from an insect pest/disease and/or when challenged by an insect/disease.

This issue became clearer at the turn of the century because of advances in genomics and NIAB TAG had quite an internal debate in 2004 on the cost of plant resistance. In that year, there were very high numbers of orange wheat blossom midge which resulted in responses to insecticides in trials of up to 2.75 t/ha in susceptible wheat varieties. Counts in the unsprayed plots showed that the resistant varieties were almost clean of larvae and yet they still had significant responses to insecticides of around 1.25 t/ha. There were very low levels of aphids in that year and so it was postulated that the response of the resistant varieties could have been due to the insecticides reducing the energy expended by the crop in fighting off the very high numbers of blossom midge larvae.

Recent research partly funded by the AHDB shows that there are yield penalties associated with septoria, yellow rust and brown rust resistance genes in wheat. Losses from an individual resistance gene to an individual disease could amount to 0.3 to 1.0 t/ha in the absence of disease challenge. The researchers muse that total losses could be higher where a number of resistance genes are introduced to provide resistance to a range of diseases but do not offer any proof that this may happen. Reassuringly, stacking of individual genes against septoria does not significantly increase yield losses and not all rust resistance genes exhibit a yield cost in the absence of disease. The latter provides plant breeders with some options of incorporating genes without detriment to yield.

Is there any way forward or will disease or pest resistance in crops always be associated with yield losses? A letter to a recent edition of the Nature magazine suggests that there may be a way out of this conundrum, at least for disease resistance. It seems that researchers have identified a genetic approach whereby a resistance gene is ‘switched on’ only when the plant is under challenge from disease. They have managed to engineer this for both the laboratory test plant of thale cress (Arabidopsis thaliana) and rice. So there may be a free lunch after all.

I have used the word ‘engineer’ and whether such an approach can be achieved by more conventional means is beyond my area of understanding. However, the title of the letter ‘uORF-mediated translation allows engineered plant disease resistance without fitness costs’ suggests that some form of genetic engineering may be key. This is another example where the green blob’s built-in objection to any form of genetic engineering may come back to bite them. Surely, if such a process meets realistic registration requirements then only a fool would object?

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Science under pressure

Posted on 02/06/2017 by Jim Orson

My wife and I regularly go to the British Library. It is close to Kings Cross railway station and is a delightful way of starting a day out in London. There is always a small exhibition in its main vestibule and the subjects change on a regular basis. Last time we visited, it was on Victorian entertainment. It is clear that science lectures were then considered a good night out and the populace was very willing to pay for the experience.

Not a lot of people know this but the popularity of scientific lectures in the early 19th century resulted in Albemarle Street in Piccadilly becoming the first one-way street in the world in order to improve traffic flow. The decision was taken after a series of lectures by Humphry Davy (of miners’ safety lamp fame) at the Royal Institution caused horrendous queues of horse-drawn carriages bringing in the eager audience.

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The Royal Institution in one-way Albemarle Street, Piccadilly

Science was certainly making great strides and each discovery was celebrated. There was a less well known lecturer, Professor E V Gardner, who appears to have been very popular in the late 19th century. I have tried to find out more about him but there is little on the internet other than that he had his own college and he also worked for another institution. Outside his lectures he was drawn into a debate about using aluminium compounds to whiten bread. In 1873 he wrote a letter to the press stating “It is curious to observe how, in hurried exercise of judgement, even technical journalists are capable of publishing most gross mistakes”. Unfortunately this is still a familiar theme. By the way, aluminium compounds as bread additives were banned in 1875.

Science remained a subject over which the populace enthused for another century. Last autumn the harvest festival at our local church included a hymn written in 1968 with the following lines; “Praise God for harvest of science and skill, the urge to discover, create and fulfil: for dreams and invention that promise to gain a future more hopeful, a world more humane”. It was written in the early days of the green revolution which has resulted in a more humane world, with the numbers of undernourished people in the world steadily falling since the early 1990s.

Now science, in relation to agricultural progress, is viewed in a different light. There is a widespread cynicism; witness the row over the safety of glyphosate. So when did it go wrong? Autumn 1997 was a watershed. A letter to Nature was published saying that BSE in cattle could be transmitted to other species. This was following on from well intentioned denials by politicians that such a thing could not happen. It was in fact a misinterpretation of the scientific advice at the time, which was that transmission across species was unlikely but could not be completely ruled out.

This event seemed to break the popular belief in the UK that scientific endeavour was necessarily a force for good in order to meet the future challenges for food production. Ever since, science in relation to food safety and production has been under intense scrutiny.

There is a need to improve the credibility of science, particularly so-called popular science . One essential element is to make the peer review system more robust. This present weakness has been targeted by the green blob who have funded ‘popular research’ and published it in ‘peer reviewed’ journals. Many of these papers, when subject to wider scrutiny, have been torn to shreds and some have had to be withdrawn.

A way forward is to do something that was suggested at the Cambridge Science Festival a few years back. Papers are peer reviewed and the resulting drafts are published on the internet for at least a few months for wider scrutiny. Only after such an exercise should a final version of the paper be published. Such a process should also be adopted for project reports funded by public and levy money, which generally have a less rigorous review process. The internet opens up the possibility for more stringent review systems and we should use it.

There also needs to be better scientific communication with the public. I have just been leafing through the details of those appearing in this year’s Latitude festival in Suffolk. In addition to singers and groups that I have or have not heard of, there was a list of scientists who will be appearing but not singing! This Wellcome Trust initiative has been part of the festival for the last few years and, according to independent analysis, has been effective and well received. We need more of this. Remarkably, it is a return to the Victorian age when people paid to hear the latest in scientific progress. Why not? The science being done today, particularly in the biosciences, is no less exciting or transformative.

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Spray drift and pesticide legislation

Posted on 19/05/2017 by Jim Orson

A couple of blogs ago I discussed some of the issues around aquatic buffer zones. I promised to mention spray application in a future blog. Well, the future starts here.

One issue that spray specialists keep banging on about is boom height. Lifting the boom so that nozzle tips are 20 cm above the typical recommended height of 50 cm can double spray drift. Why is spray drift so sensitive to boom height?

Drift from all types of nozzles can be minimised by ensuring that the tips of the nozzles are as low as possible above the target to provide good spray coverage. This is 50 cm for 110 degree nozzles at a half metre spacing. In addition, spray pressures should not be above around 3 bar for conventional flat fan nozzles.

Data produced from experiments in the wind tunnel of the Silsoe Spray Application Unit emphasise the considerable influence on spray drift of the height of the tip of the nozzle. Increasing it by 20 cm (8 inches) can double the drift from a conventional standard flat fan nozzle and the increase from extended range/variable pressure flat fan nozzles is even greater. These latter nozzles produce higher levels of drift than conventional flat fan nozzles when operating at 3 bar.

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The question frequently posed is why such a small increase in the height of the tip of the nozzle can increase drift risk so dramatically? The answer is clearly demonstrated in the photograph taken at the Silsoe Spray Application Unit. This shows that drift largely emanates from a zone a distance below the nozzle.

The actual distances involved will depend on many variables, such as nozzle type and size, wind speed, forward speed and spray pressure. However, in simple terms, where the tips of the nozzles are 50 cm above the target and the zone where most of the drift originates is 20 cm above the target, then increasing the height of tip of the nozzle by 20 cm can more than double the size of this zone.

There is a simple explanation as to why drift largely emanates from spray fan nozzles at a distance from the tip of the nozzle: the spray liquid leaves the nozzle under pressure and at a high velocity and entrains (draws in) air as it travels.

The influences of both spray pressure and air entrainment fade as the spray droplets move away from the flat fan nozzle and eventually the droplets fall solely by gravity if the boom is far too high. By the time they get to just above the target, the droplets are moving slower and are the most vulnerable to drift. Smaller droplets lose their momentum more quickly and so not only is the ‘driftable zone’ wider for fine quality sprays from flat fan nozzles but also the smaller droplets are more ‘driftable’.

There are calls for CRD to adopt four star nozzles in order that aquatic buffer strips can be reduced in width. The current three star nozzles reduce drift by 75% compared to a standard 11003 nozzle working at 3 bar pressure. Some ‘smaller droplet’ air induction nozzles meet this target but often at slow forward speeds and pressures which may mean some compromises in efficacy. Even when working at 3 bar they have a few issues with efficacy e.g. small weeds with foliage applied herbicides and, anecdotally, on potato blight. One way of reducing spray drift by 90% or even 95% is to use even coarser nozzles but this will result in further compromises with efficacy because of poor spray retention on leaves and/or spray distribution, particularly on small targets and even, perhaps, on the soil surface.

There are ways in which such drift reduction is possible and which largely or completely retain efficacy but it may require a radical overhaul of the vast majority of sprayers currently on farms. Air assistance is one option. With conventional boom sprayers, achieving a 90% drift reduction and the good and uniform spray distribution necessary for some targets may mean a reduction in boom height. Some sprayer manufacturers now offer 25 cm nozzle spacings as an option aimed at drift control with the recommendation that the boom is operated 25 cm above the target. Boom suspension then needs to be very good with effective height sensors and probably some articulation.

There is a long way to go on the issue of aquatic buffer zones and spray application. This topic deserves to be higher up on the agenda of the future of farming in the UK.

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What do plants do at night?

Posted on 05/05/2017 by Jim Orson

 

Early March is the time for the Cambridge Science Festival. This is a great event and this year I attended 11 lectures over the fortnight. One was on how plants detect the time of the day and the season. It was fascinating but I do not think that I am sufficiently competent to report accurately the current scientific understanding.

Much of the research is done on the weed Arabidopsis thaliana (thale cress). It was the first plant to have its genome sequenced and is a popular tool for understanding the molecular biology of many plant traits, including flower development and light sensing. The lecturer showed a time graph of the growth of Arabidopsis and, to my complete surprise, it only grew in the dark.

I discussed this with my wife and she came to the conclusion that there are similarities between Arabidopsis and me. We both respire all the time but can do only one other task. In the case of the plant it is to photosynthesise during daylight hours and to grow at night.

After reading a few papers it seems that many broad-leaved plants largely or only grow at nights, something that both Charles Darwin and I have noted! The opposite may be mainly true for cereals and many grasses. I have to highlight that this is a complicated issue and there are no absolutes and, also, much depends on issues such as moisture supply and ambient temperatures.

I think we have to be careful about what is meant by growth. It is, in the context of this blog, an increase in the physical size of the plant. However, it should be noted that growth starts with cell division at the shoot apex and ends with a change in the physical size of the plant.

The explanation for why warm nights are good for growth may be because they enable more plant respiration which provides the materials required for this process. However, the more I thought about the subject the more uncomfortable I became with the claim by some crop physiologists that warm nights during grain-fill of wheat encourage too much respiration of the plant’s reserves and therefore lower yields. I have unthinkingly repeated this statement in previous blogs, hence my decision to investigate further.

It seems the opposite is true and that warmer nights can encourage a faster rate of grain-fill. However, and it is a big however, in field experiments on both wheat and barley, the plots warmed only at night had lower yields because of reduced grain-fill i.e. smaller grains. This is because duration of grain-filling is determined principally by accumulated temperature (thermal time). In these experiments, any increase in the rate of grain-filling due to warmer nights was more than offset by the negative effects of the shorter grain-fill duration

I have tested this explanation with a few simplistic models of grain-filling and typical day and night temperatures experienced in the UK in June. I used an average daily maximum of 22 C and an average daily minimum of 10 C. Just raising the daily minimum to 11 C reduced the duration of grain-fill by between 3 and 7% according to which model I used. The possible increase in rate of grain-fill from the warmer nights quoted in the literature suggests that this will not compensate for its shorter duration.

However, real life situations are more complicated. The same daily average temperature, which drives the duration of grain-fill, can be achieved by two contrasting weather patterns; warm sunny days with cool nights or cooler cloudy days with warmer nights. Of these two contrasting conditions, warm sunny days with cooler nights will provide higher yields due to more solar radiation being intercepted by the crop because, if the average temperatures are the same, the duration of grain-fill will be unaffected. This is providing that the crop has sufficient moisture and nutrients.

Field experiments again where field plots are only heated at night, suggest that warmer nights between the third node stage and mid-anthesis of wheat and barley have more impact on final yield than during grain-fill. In this case the lower yields were due to a reduction in the number of grains at harvest. Again, the duration of this critical period of the crop’s development is largely driven by thermal time.

Please accept that this is a rather simplistic description of some very complicated plant processes.

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Where are the dead fish?

Posted on 21/04/2017 by Jim Orson

I recently attended a workshop on aquatic buffer zones. Some contributions indicated that they may not yet be sufficiently wide. There are two possible reasons for this. Firstly, it was suggested that spray drift could be far higher than that indicated by the models currently used in EU registration systems. Secondly, there were suggestions that higher levels of protection of aquatic ecosystems from pesticides may be necessary. I must admit that I was shaken by these statements because we already have aquatic buffer zones of up to 18 metres wide. The widest buffer zones are usually for insecticides but, rather ominously, one black-grass herbicide product (so far) also has an 18 metre buffer zone.

The obvious question was posed. Is there evidence that there is a problem from spray drift? More succinctly, where are the dead fish? Fish welfare is only one aspect of the health of aquatic ecosystems but the point is well made.

The Environment Agency publishes annually its analysis of the environmental health of the main water bodies in England. In 2015 only one of the 4,678 main water bodies in England contained a pesticide in current agricultural use at a level that was above the Environmental Quality Standard set by the Agency and others. The other nine water bodies failing to meet the Environmental Quality Standards for pesticides had active substances that have been withdrawn from agricultural or industrial use. Hence, on a grand scale there does not appear to be much of a problem from current agricultural use.

There are of course countless smaller water bodies and streams where environmental health is not regularly monitored and we do not know the extent of the impact of pesticide drift on their ecosystems. However, it has to be noted that the ecosystems, particularly of some smaller watercourses, are affected by other factors. Some ditches, particularly close to major roads, appear lifeless because of factors other than pesticides. Soil contamination and other pollutants have a major impact on many of our small watercourses.

Jim Orson NIAB TAG blog watercourse  Where do we go from here and how do we reduce unnecessary restrictions on agricultural productivity due to ever increasing aquatic buffer zones? Personally, I think that we need to start with the definition of a watercourse. The definition used by many authorities, including our Chemicals Regulation Division (CRD) of HSE, goes something along the lines of ‘a natural or artificial channel through which water flows’. Does this mean that we should really be trying to maintain the health of water ecosystems in ditches which are dry for most of the year? I am not so sure because as such ditches dry they contain a series of stagnant puddles which are not conducive to some of the aquatic organisms that the pesticide regulations are designed to protect.

It is interesting to note that the guidance document on protecting water ecosystems for the pesticide registration authorities of the EU member states uses a different definition of a watercourse. On page 40 it says that the guidance document ‘predominantly addresses the risk for organisms occurring in permanent edge-of field water bodies, that is, water bodies that contain water throughout the year’. That is, in my opinion, a more realistic definition of what should be protected.

In France only watercourses that are marked blue on a 1:25,000 scale map need to be protected by an aquatic buffer strip in order to avoid spray drift affecting aquatic ecosystems. I have found an UK government data site that has watercourses marked blue on a 1:10,000 scale. Using my experience of some farms, this site could be used to prioritise which farm ditches are worth protecting with aquatic buffer zones. Prioritising could offer the means of improving the protection of recognised watercourses on this map, not only from spray drift but also from other pollutants.

I offer this as a way forward but also would like to say that the ditches not appearing on this map may need some minimal level of protection, even when dry. This is particularly true of ditches at the bottom of slopes in drinking water catchments in order to reduce the risk of pesticides entering raw drinking water through run-off. However, as a general statement, not to spray within 18 metres of a puddly ditch is perhaps not the ideal way to address an overall improvement in water health.

It has long been argued that people are more likely to adopt improved practices if they can be provided with a hopeful vision. The vision on aquatic buffer zones as it stands is not that hopeful but prioritising watercourses may convince farmers that there is a practical and realistic way forward. It could be that prioritising the protection of recognised watercourses is also something that the UK government can still afford to support after Brexit by generously funding realistic sized permanent and floristic buffer zones which are easy to police. I mention the need for floristic buffer zones in order to support biodiversity too. Surrounding recognised water courses with such vegetation will provide the connectivity for biodiversity that many argue is necessary.

Of course, reducing spray drift will also help to lessen the area devoted to buffer strips. The concern is that methods of reducing drift beyond the 75% achieved by the small droplet flat-fan air induction nozzles may well mean poorer efficacy of many pesticide products. This issue will be the subject of another blog in the near future.

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