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Physiology in the production and improvement of cereals

RESEARCH REVIEW 18

Physiology in the production and improvement of cereals

by
R. Sylvester-Bradley & R.K. Scott with C.E. Wright as technical secretary

January 1990

ABSTRACT

This report focuses on the context in which decisions are taken during cereal production, and analyses the part that physiology can play in influencing those decisions. Using this approach we have identified the aspects of physiology on which more study has a good chance of improving production.

Before writing the report we took evidence, particularly about the views of the end users, and an initial working group of cereal physiologists was augmented with expertise on specific issues where necessary.

At the start, we set out the points of physiology on which there was general agreement and which could be seen as pertinent to the production of cereals (Chapter 2). Thus we begin by summarising the physiology relating to roots, leaves, tillers, ears and grains, but only identifying the points on which choices may turn in practice.

The most crucial element in the interpretation of cereal physiology is that aging (development) and growth should be perceived as independent processes.
In analysing the potential for cereal production (Section 3.9, page 92), the extent to which potential is achieved clearly reveals much scope for improvement. The ranges in wheat performance from 6.4 to 8.6 t/ha over seasons in the 1980s and 6.2 to 8.2 t/ha between experimental husbandry farms of ADAS demonstrates the huge influence that environment has over performance. The exceptional performances at all sites in 1984 and over all seasons at Rosemaund EHF can both be attributed at least in part to slow development with fast growth. Hence, in making decisions crop by crop we can assert that growers should set their sights on both speeding growth and prolonging development.

Unfortunately the current disposition of institutions researching on crops too often allows their scientists to ignore that good decision-making must depend upon the combined forces of deduction and experience; the laboratory-based physiologist assumes that decisions must all be made by deduction whilst the field-based agronomist takes it for granted that all he can do is 'suck it and see'.

Our concern in the body of the report has therefore been to juxtapose the approaches of the physiologist and agronomist, so that the agronomist is reminded of the relevant physiology and the physiologist can see the relevant agronomy (Chapter 3). We contend that to provide for profitable decision-taking both influences should be harnessed; agronomic experience sets the limits within which a practice can sensibly be altered and, when relevant agronomic experience is deficient, physiological knowledge provides the means to reason how adjustments should be made.

Paradoxically, agronomic experience is becoming increasingly deficient. This is because of the ever more complex constraints under which growers have to work with the ever shrinking support for work on new developments. Thus, the industry will increasingly rely upon knowledge of crop function to decide what course to take at each stage in the production process.

Having consulted physiologists worldwide we have considered the requirements of breeders and biotechnologists (Section 3.10, page 103; Section 3.11, page 110) and identified opportunities for research in their support. However, we deliberately avoid saying that new funding of physiology should concentrate on preparing the ground for the genetic manipulator; the excitement that the new prospects have engendered guarantees investment without the assistance of levy funds.

That choice of variety (Section 3.2, page 28) is of consuming interest to growers is understandable; that this interest finds vent in so many uncoordinated trials is not. There is clear scope for coordinating official and private trials of varieties and amalgamating their results in order to improve the precision of the tests being made and the chance of fitting varieties to circumstances. Inclusion of meaningful agronomic characters when distinguishing varieties would also help towards this end (Section 4.4.1, page 118).

The normal compromises struck in date and rate of sowing (Section 3.3, page 34) appear to leave unrealised much potential for growth and yield. With economic and other restrictions on the use of nutrients and pesticides the need is to fully harness any environmental strengths. We see some scope to explore and overcome the physiological obstacles which negate the benefit from intercepting extra light energy and nitrogen through early sowing and denser stands (Section 4.4.2, page 123).

With weed control (Section 3.5, page 57), stringent use of herbicides is the crucial object. To this end we endorse existing and new work on predicting the weed seed burden, determining weed thresholds for crop loss, determining how either crop or weed may tolerate chemical sprays, and determining the principles governing spray application techniques.

Looking in the same way at current strategies for disease control (Section 3.6, page 65) there appears scope for improvement through research into disease effects at different stages of crop development, especially on the main yield-forming leaves (Section 4.4.4, page 130), and direct effects of fungicides on crop growth.

Environmental repercussions of nitrogen (Section 3.4, page 44) now mean that, without the support of industry, more attention will be paid to the nitrogen left behind by cereals than to nitrogen forming the grain. Our view is that, given adequate techniques, cereals could be fertilised more effectively if the aim were to optimise canopy development rather than to supply a 'requirement' guessed at an early stage. Complementary research should focus on work to maximise recovery of applied N, to examine more precisely the relationship between N requirement and yield, to define how N can be used to modify the canopy for maximum crop growth, to develop the potential of foliar applied nitrogen (Section 4.4.3, page 126), and to deduce the optimum pattern of N application to conform with the needs of the malting and baking industries.

Both the recognition and restriction of lodging risk (Section 3.7, page 73) need close analysis (Section 4.4.5, page 133), particularly with winter barley, because so often lodging is what governs the benefit for both yield and quality from decisions on nitrogen, as well as early sowing, seed rate change, and crop protection measures.

The grower is constantly exhorted to produce high quality grain (Section 3.8, page 80), and yet so often quality defies control. We assert (Section 4.4.6, page 135) that there is much existing physiological knowledge which could be used by the grower during those few crucial weeks, providing up-to-the- minute intelligence on which to monitor (and maybe mediate) the success of grain-filling as it unfolds, and focus his expectations. Quick and reliable tests must be developed for use, not only at the point of trade, but on the farm, to determine levels of germination, protein concentration, alpha- amylase and grain size characteristics.

It is woeful and perplexing that the industry can reach the penultimate stage in the long production process with little advance knowledge of its success. Intelligence for merchants, traders, processors and end users, let alone growers, of both the volume and the quality of grain that they are to handle is surprisingly weak until harvest is under way. It is high time that cereal physiologists addressed this conundrum (Section 4.4.7, page 138), not with tl1e promise of perfect foresight, but to state the narrowing probabilities as growth proceeds.

Underlying all assertions in our Report rests a recurring reference to 'the model'. It is both undesirable and unfortunate that 'modelling' has been allowed to assume a mystique which alienates the layman (Section 4.2, page 114). Without doubt we are all modellers in our different ways; our thoughts on crops are models and modelling is at the root of communication in crop science. We therefore make no apology for homing in on models as the cornerstone of crop improvement programmes. We do not claim that they offer quick solutions, or a direct route to the laws of nature, but we do assert that, for what has been allowed to remain a most inexact science, recorded models can confer a common and beneficial discipline and provide that all-important access to physiological know-how.

With the many opportunities for physiological research identi fied in th s summary and those others given in the full report (there is a list on page 116) we recognise the need to devise a strategy which will most effectively exploit resources limited in terms of finances and skilled staff. There are some projects which are not appropriate for extensive collaborative teams, for instance the study of the origins of high amylase grain or of predicting dormancy. There are others for which a multidisciplinary approach seems essential, both for economy and synergy. An example is that in devising a technology for uptake of nitrogen through leaves, parts should obviously be played by the spray engineers, plant biochemists, formulation chemists and soil scientists, as well as by physiologists who can determine the N needed for growth.

However, in developing solutions to its fundamental problems, there is another synergism to be found, through harnessing more disparate interests in the industry. It becomes clear that it would be of benefit if the industry were to become involved in the execution of research projects. We therefore advocate that concerted programmes are constructed which allow cross communication through the grower-adviser-supplier-journalist-scientist chain of intelligence by forging specific partnerships which hold a focus on the problems in practice. We have looked at research needs, identifying areas where a 'vertical' collaborative stratagem could be used to good effect.

For instance:
a) Anticipation of crop performance during growth depends on the interest of growers and traders, and rapid communication through journalists, as well as the work of physiologists.
b) When analysing elements of the risk of lodging, observations must be garnered not only from agronomic experiments, but from specialists in structures, growers and advisers.
c) The integration of concepts of how leaf diseases affect yield needs epidemiologists, physiologists and meteorologists and holds a close interest for fungicide manufacturers.
20. If the admirable integration that the Authority has established on a . horizontal plane between researchers were complemented by such a vertical integration linking science through physiology to practice, benefits would accrue to the industry on a scale far exceeding those which come from piecemeal funding of isolated projects.

This review was completed in January 1990 and consists of 156 pages.

HGCA Project Number: 0072/1/87
Price: £15.00

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