You are working alongside Dr Abdul Razack Mohammed on your investigations. What skills and experiences do you each impart? My experience lies in metabolic plant physiology. This involves understanding the control of the partitioning of photosynthate and other compounds among plant parts, and how they are allocated among different chemical forms within tissues. I am interested in determining how these events affect the yield and quality of the crop product and plant development. Dr Mohammed brings experience in environmental plant physiology and an understanding of the response of whole- plant activities. This includes photosynthesis, respiration, morphology (plant growth form), and cell membrane damage in particular environments and in response to variation in specific environmental factors. What environmental stresses are you focusing on specifically? We are interested in the effects of high night temperature, which can occur under conditions of high humidity and low wind speed. We also study the effects of elevated ultraviolet-B (UVB) radiation levels, which have been increasing in recent years in some parts of the world. To a lesser extent, we study the effects of low water (drought) stress and cold soil temperatures. Recently, we have been examining root pruning shock, which is a frequent occurrence during machine transplanting of rice. Could you explain your studies on high night temperature stress and how these temperatures affect crops? High night temperature stresses are commonly considered to affect crop plants by increasing their respiration (the breakdown of stored carbohydrates for use as energy), which decreases the supply of photosynthate available to fill the grains, and possibly by interfering with normal reproduction events. We have also provided evidence suggesting that the action of the plant ‘stress’ hormone, ethylene, under high night temperatures can lead to increased oxidative stress (the formation of oxygen free radicals). This disrupts cell membrane integrity in leaves and elsewhere – and it can lower the efficiency of various physiological processes, such as the transport of photosynthate. It therefore indirectly affects key events, such as pollen development or seed set. What information have you garnered from the evidence collected directly from farmers? Our studies on high night temperature effects partially arose as a result of reports of yield losses by farmers who felt these losses were related to heat stress. We also received reports Dr Lee Tarpley and Dr Abdul Razack Mohammed are investigating environmental stresses on crop productivity. International Innovation spoke to the former about the findings and applications of his current research and how he sees his collaborative projects progressing in the future Harvesting the future INTERNATIONAL INNOVATION PLANT BIOLOGY 1
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You are working alongside Dr Abdul Razack Mohammed on your investigations. What skills and experiences do you each impart?
My experience lies in metabolic plant physiology. This involves understanding the control of the partitioning of photosynthate and other compounds among plant parts, and how they are allocated among different chemical forms within tissues. I am interested in determining how these events affect the yield and quality of the crop product and plant development.
Dr Mohammed brings experience in environmental plant physiology and an understanding of the response of whole-plant activities. This includes photosynthesis, respiration, morphology (plant growth form), and cell membrane damage in particular environments and in response to variation in specifi c environmental factors.
What environmental stresses are you focusing on specifi cally?
We are interested in the effects of high night temperature, which can occur under conditions of high humidity and low wind speed. We also study the effects of elevated ultraviolet-B (UVB) radiation levels, which have been increasing in recent years in some parts of the world. To a lesser extent, we study the effects of low water (drought) stress and cold soil temperatures. Recently, we have been examining root pruning shock, which is a frequent occurrence during machine transplanting of rice.
Could you explain your studies on high night temperature stress and how these temperatures affect crops?
High night temperature stresses are commonly considered to affect crop plants by increasing their respiration (the breakdown of stored
carbohydrates for use as energy), which decreases the supply of photosynthate available to fi ll the grains, and possibly by interfering with normal reproduction events. We have also provided evidence suggesting that the action of the plant ‘stress’ hormone, ethylene, under high night temperatures can lead to increased oxidative stress (the formation of oxygen free radicals). This disrupts cell membrane integrity in leaves and elsewhere – and it can lower the effi ciency of various physiological processes, such as the transport of photosynthate. It therefore indirectly affects key events, such as pollen development or seed set.
What information have you garnered from the evidence collected directly from farmers?
Our studies on high night temperature effects partially arose as a result of reports of yield losses by farmers who felt these losses were related to heat stress. We also received reports
Dr Lee Tarpley and Dr Abdul Razack Mohammed are investigating environmental stresses on crop productivity. International Innovation spoke to the former about the fi ndings and applications of his current research and how he sees his collaborative projects progressing in the future
Harvesting the future
INTERNATIONAL INNOVATION
PLANT BIOLOGY
1
Plant physiologists at Texas A&M AgriLife Research are investigating methods for preventing a range of negative environmental impacts on crops. Their ongoing research signifi cantly and positively impacts upon the sustainability of crop production, both locally and globally
Food for thought
A recent population forecast from the UN estimates that the number of people on Earth will increase to 9.7 billion by 2050. Not only ar e more babies being born, but average life expectancy is also increasing. The burden this will place on the planet’s resources in the future is signifi cant; as well as hampering the ability of governments to meet the healthcare and energy needs of citizens, the burgeoning population necessitates improved crop yields to ensure there is enough food to sustain lives.
In 2007, the Intergovernmental Panel on Climate Change (IPCC) – assuming the continuation of post-war trends – predicted there would be a global crop yield increase of 80 per cent by 2050. However, since then, yields of some crops have ceased to improve at the anticipated rate. Indeed, according to the Food and Agricultural Organization (FAO) of the UN, while rice production in China increased by 17 per cent from 1987 to 1997, in the following decade it only increased by 2 per cent.
Throughout the world, the slowing rate of improvement in crop productivity has been further exacerbated by global warming and other climate change factors. Thus there is a pressing need to understand how crop plant populations function and interact with the environment. Only then will this enable the agronomic and genetic improvement of crop production.
MERCURY RICEINGDr Lee Tarpley is a plant physiologist at Texas A&M AgriLife Research who has been working with crops to address these issues and to aid the improvement of specifi c production systems. Rice is the major crop where Tarpley conducts his studies and, along with his collaborator Dr Abdul Razack Mohammed, he has been investigating how rice responds physiologically to warm nights. It has been shown that high night temperatures can have a negative infl uence on both crop yield and quality, so the team has been trying to understand possible methods of mitigating these effects.
High night temperatures occur naturally as the seasons change, but global warming has increased their intensity and frequency. As levels of mercury rise, so too do the levels of ethylene (a naturally occurring plant hormone), which can cause degradation of leaf chlorophyll, membrane damage, disruption of normal physiological processes and, ultimately, yield loss. Tarpley, Mohammed and their interdisciplinary team therefore investigated the use of 1-Methylcyclopropene – a synthetic plant growth regulator capable of inhibiting the effects of ethylene.
In one study, the team found it was possible to negate the effects of high night temperatures in rice plants through the application of
of unexpected crop sensitivity to herbicides in some circumstances. About 15 years ago, a major local concern was the inconsistent stand of the rice ratoon crop – the regrowth or second crop, growing from the stubble after the harvesting of the main crop. The inconsistency was largely addressed by a team of researchers and farmers, indicating a need for more intensive management of the ratoon crop. The concerns voiced by the farmers also led to a novel plant growth regulator application, which we developed to increase ratoon crop yield by enhancing the rate of early growth of the ratoon tillers (branches emerging from near the base of the plant). All of these concerns can potentially be addressed using a plant physiology approach.
You have recently been exploring the prevention of root pruning shock in rice. Could you tell us more about the discoveries you have made here?
Root pruning decreased the number of tillers, which could eventually decrease yield because each tiller can form a head of grain. Photosynthesis, leaf chlorophyll concentration and shoot dry weight were also reduced with root pruning. Application of an ethylene activity inhibitor called 1-Methylcyclopropene before transplanting prevented this damage – and it also led to greater root dry weight compared to the untreated control when measured a month after transplanting the rice. These results suggest that certain plant growth regulators could be used to prevent root pruning effects.
Finally, where will you next be focusing your research efforts?
The understanding that we have gained can also be applied to the development of tools for screening large numbers of crop plant lines for tolerance and sensitivity to particular environmental stresses. This requires developing a parsimonious set of rapid screening tools based on our physiological fi ndings, but also sometimes requires the development of novel instrumentation for appropriately, yet economically, applying the controlled stress to large numbers of diverse lines under fi eld conditions.
We have also been developing novel remote-sensing methods that are sensitive and specifi c enough to detect crop nutritional and water statuses, and that can be used for prescribing precision crop management measures, thereby preventing economic losses.
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PHYSIOLOGICAL PRINCIPLES OF US SUB-TROPICAL CROP PRODUCTION
OBJECTIVESTo develop methods that prevent the negative effects of environmental stresses on crop productivity.
KEY COLLABORATORSDr Eslam Elfadly, University of Alexandria, Egypt •Dr Ganghua Li, Nanjing Agricultural University, China • Dr Shannon Pinson, USDA Agricultural Research Service, USA
PARTNERSNational Institute for Agro-Environmental Sciences, Japan • Arcadia Biosciences, Inc., USA • AgroFresh, USA
LEE TARPLEY is a plant physiologist whose research primarily focuses on crop plants. In his work, he investigates ways of minimising adverse environmental effects
on crop production and attempts to develop new interventions through crop management or breeding. He is passionate about teaching students to understand how physiological, ecological and genetic factors can be manipulated when improving crop plants and about reaching end users with fi ndings from his innovative research.
1-Methylcyclopropene. Indeed, the results showed increased rice yield, photosynthetic rate, pollen germination and fertility, as well as reduced respiration and injury to the membrane.
UNLOCKING SUNBLOCKSunlight is made up of three ultraviolet (UV) radiation bands: UVA, UVB and UVC. Of these, only UVA and UVB reach us, as UVC is absorbed by the ozone layer. It is known that changes in levels of UV radiation can majorly impact food production and, as climate change also includes depletion in stratospheric ozone around the world, levels of UVB radiation are increasing. Studies have shown that enhanced UVB radiation can seriously harm rice yields, so Tarpley and his team have explored methods that aim to reverse the deleterious effects to boost food production.
Moreover, while many studies have investigated the impact of plant growth regulators (PGRs) on higher plants, there has been virtually no research into their effects on rice in the context of changing climates. The team therefore attempted to fi ll this knowledge gap by analysing various PGRs in relation to rice yields – and they discovered that α-tocopherol, glycine betaine and salicylic acid increased yield by 23 per cent, 18 per cent and 29 per cent respectively under elevated UVB. Additionally, they found that applying PGRs protected rice crops from increased UVB radiation, providing potential solutions for future increases in UVB levels.
ROOTING OUT THE PROBLEMRice farming in Asian countries typically begins by cultivating plants in a nursery before replanting (transplanting) them to a fi eld. This replanting often results in a condition known as ‘transplanting shock’, which can negatively affect growth and development, thereby decreasing crop yield. Tarpley and Mohammed studied the condition to determine whether there was a means of preventing this from happening.
The researchers found that root pruning often happened during the transplantation process, reducing the photosynthetic rate of the plant and directly inhibiting its growth. The team therefore decided to apply 1-Methylcyclopropene to see what effect this would have on the rice. Interestingly, they
found that it prevented transplanting shock by making the rice plants unaware that their roots had been pruned. Their future research in this area will focus on the application of 1-Methylcyclopropene in the US. Although rice farmers in the States tend to direct seed the crops, root pruning still occurs as a result of rice water weevil larvae feeding on the roots, resulting in damage that represents a major cause of reduced yields.
The fi eld of plant physiology is essential for increasing understanding of how plants function in relation to the environment. In their work, Tarpley and Mohammed have clearly demonstrated that a greater understanding of crop productivity problems can lead to the development of viable solutions. The hope is that their fi ndings will be used globally to alleviate the challenges posed by a burgeoning population, global warming and other climate change factors.
METHODS MAPPED OUT
Tarpley and Mohammed’s approach to developing methodologies to address crop yield reductions can be exemplifi ed through three bases:
1. Be as comprehensive as possible when measuring the crop response. In a typical study, the two researchers measure plant photosynthesis, respiration, photochemistry, leaf membrane stability, pollen viability, seed set and fi lling, grain yield and quality, and morphological and phenological characters.
2. Always include a potential modifi er of the plant stress response as a factor in the study. These are typically plant growth regulators – compounds that act like plant hormones or affect plant hormonal action. This helps the team identify the particular plant stress responses involved, enabling them to identify potential crop management tools for minimising the environmental effects on crop yield and quality.
3. Try to avoid artefacts when delivering the stress agents to the plants. Both active and passive delivery systems are prone to a loss of control and/or alteration of other environmental factors.
