Better trials...from the Scrapyard

by Mike Robbins

It started with Hassan Ouabbou of France's Institut de la Recherche Agronomique (INRA). Some time ago he travelled around Morocco with cereals plant physiologist John Peacock of ICARDA. The two men talked long and hard about the problems of breeding wheat for heat stress. Hassan Ouabbou was at that time working on his PhD thesis at Kansas State University in the United States. It was titled Physiological aspects of recovery and evaluation of wheat during high temperature stress, an appropriate field for a scientist in a country where drought and heat can be devastating.

Ouabbou, who is in the Agronomy Department at INRA's regional center at Settat, described how, in certain conditions, growth in cereals completely stopped at the grain-filling stage. It was not clear why. What was needed was a way of simulating heat stress so that the problem could be studied and sources of resistance found.

The challenge had a familiar ring to it. John Peacock had been working on the simulation of heat stress and its effects on seedling development. In some conditions, seedling development simply stopped, and Peacock wondered what was really happening. He had got together with ICARDA engineer Peter Eichhorn and Mahalakshmi, a visiting scientist from ICRISAT in India, and together they modified a system which Peacock had developed earlier at the University of Arizona for subjecting seedlings to this type of stress.

These experiments, and earlier ones in Arizona and India, proved successful. "What we found was that heat shock prevented the products of photosynthesis from reaching the root system," he explains. "Put simply, a plant has two basic parts to it. One is the source and the other is the sink. The source develops energy; the sink uses it. In extreme heat, the products- carbohydrates- find their journey between source and sink blocked, possibly by proteins which coagulate in the phloem as a result of the high temperatures and block the sieve plates.

"The circumstances under which this coagulation occurs is genetically governed. This means that we can look for sources of resistance; that is, either a higher coagulation temperature or something that stops blockage."

While doing this research, Peacock found that the principle of growth stopping because of a blockage between source and sink had a long time ago been described by others. "Cut a ring of bark off a tree and it will die, but not at once. That's because the bark provides a route between source and sink. When it is removed and the route is blocked, the tree roots starve and eventually die. Before that happens, a bulge will develop at the edge of the cut bark. That's the products of photosynthesis trying to get through.

"This phenomenon was, in fact, observed by Marcello Malphighi in 1675 and by the father of modern plant physiology, Stephen Hales, in 1727. Perhaps we should use the indigenous knowledge of the scientific community..."

The stimulus for the next move came from Ouabbou. If it had been possible to simulate heat-stress in seedlings, and find out why their growth was stopping, could not the same be done for the grain-filling stage? The problem was that Morocco, and the other North African countries, had a special constraint, the sirocco.

"We're not just talking about heat here," says Peacock. "Hassan and I wondered if the aridity of this wind was a factor. It's important to find out, because there are at least two stresses that could be stopping the growth at that stage. We need to know what it is, so that eventually we will be able to map genes for thermotolerance."

The first possible cause would be overheating of the leaves and their photosynthetic apparatus. "What happens is that a combination of heat and aridity could disrupt the plant's cooling system. The plant then stops producing energy or photosynthates.

"But what about, again, a blockage between source and sink?"

When the plant reaches the grain-filling stage, explains Peacock, the head which is producing seeds is now the sink and there is a heavy demand for the 'fuel supply'. It is possible, he says, that once again the proteins are coagulating because of sheer heat stress, accentuated by the failure of the plant's air-conditioning system.. "If this is the case, the aridity of the sirocco is not a factor. The only way to find out is to perform trials in the field which test for performance under heat and wind and aridity." Hence the need for a machine which could simulate heat, wind speed and relative humidity. In the field!

The problem was put to Peter Eichhorn, who built a prototype. Hassan Ouabbou came from Morocco to assist with its development. They were joined by Mohamed Iskandar from Egypt; an agronomist, who carries out research for the Egyptian national program in the Northern Sinai. Egypt also faces fierce onshore winds between Marsa Matrouh and El Arish. His visit was arranged by ICARDA's Nile Valley and Red Sea Regional Project (NVRSRP).

The four-man team made some modifications to the original machine. Hassan Ouabbou wanted a machine that would function in the field. The design that emerged burns diesel-oil to heat water, which is then circulated through a truck radiator. A truck fan driven by an electric motor blows through this and sends a pretty good sirocco down through a plastic tunnel, in which a sprinkler system is calibrated to simulate different levels of relative humidity. Electricity is needed to run the electric motors for the fan and circulation pump, but the power consumption is low, so that a small generator can be used to run one or more machines in the field.

"It's a line-source system," says John Peacock. "This is familiar to anyone who's ever seen water-use efficiency trials. Basically, you have the pipe that is the water source running at a right angle to your plots so that you create a gradient of water away from the source. The sirocco simulator will do the same with air." The machine is being calibrated with the help of data on wind speed and relative humidity for Morocco supplied by Hassan Ouabbou. The temperature data was collected by ICARDA agroclimatologist Wolfgang Goebel. The data being used stretches back over thirty years. The next step will be for John Peacock and Peter Eichhorn to thoroughly field-test the machine before the Mk II version is developed in North Africa.

The simulator should not only answer Peacock's questions about the actual physiological process of heat-stress at grain-filling. It should also speed up breeding trials. Droughts in the Maghreb are all too frequent, but they do not happen every year and it follows that testing for drought-resistance has hitherto been a longish process.

The simulator is also a piece of appropriate technology which national programs will be able to build for themselves. The second prototype had a notional cost of around 2,500 US-Dollars, but this was because an expensive type of boiler was used; it just happened to be available. A more normal heat source would be an ordinary domestic diesel-burning water-heater, of a type which is in common use all over the Maghreb and Mashreq regions. The motor for the fan came from an old high-pressure pump, the fan and radiator from a scrapped generator. As for the fuel, diesel is sometimes subsidized in the region; in Syria, for example, it is markedly cheaper than ordinary petroleum.

As head of ICARDA's workshop, Peter Eichhorn is well used to being asked for this sort of solution. He and his staff have helped develop appropriate technology for (for example) seed sweepers and pod-threshers, designed for use directly by farmers; some of this machinery has been put into production by an engineering company in Aleppo. "National programs are often short of funds," he says, "and this can be a constraint to research work. Machines like the simulator can greatly reduce this constraint. It's not a miracle solution; certain standards have to be observed, for example accuracy of temperature and consistency of wind-speed, and there will always be one or two components that can't come from the scrapyard. Even so, this is something national programs can put together for themselves.

International Center for Agricultural Research in the Dry Areas (ICARDA)