The impact of plant pathogens on food security

26th January 2017

Biological factors such as pathogens, animal pests and weeds represent a significant threat to our food system, impacting on crop growth and quality. Understanding these threats and how we can reduce their impact will be key to ensure a robust and secure food supply.

Plant pathogens

Pathogens are estimated to cause around 12.5% of global crop losses[1], threatening many commercially and socially valuable crops, such as coffee, cassava, oranges, olives, wheat and rice. Bacteria, viruses, and fungi can reduce crop yields, impact on crop quality and in some cases kill their hosts.

As part of global efforts to better understand and mitigate crop disease risk, 3Keel have partnered with Exeter University, looking at a new strain of the Panama disease. This disease has caused devastating losses of the Cavendish banana cultivar in Asia and Australasia, and threatens production in South America. This has the potential to have far-reaching consequences for both producers and consumers.

Plant pathogens are likely to be of increasing interest to food and agricultural businesses due to their dependence on pesticides and fungicides to control disease, many of which face increasingly stringent regulations. Global movements of people and goods also increases the risk of diseases spreading to new regions. The uncertain impact that climate change will have on pathogen ranges and host susceptibility adds an additional layer of risk to global crop production.

Existing crop protection strategies

Crop protection strategies aim to limit the impact of pathogens through a number of approaches[2]:

  • Removal of infected plants and sterilisation prevents the spread of pathogens.
  • Chemical treatments of crops with fungicides and antibacterial compounds pathogens have been important in controlling pathogens for over 4,000 years, but have faced increasing opposition in the last few decades due to their negative impact on the environment.
  • Selective breeding of cultivars over thousands of years has created landraces with resistance to the biotic and abiotic stresses they face locally.
  • Genetic engineering has allowed the expression of resistance proteins in crops over the last 20 years.

The papaya ringspot virus almost wiped out papaya production in Hawaii in the 1990s, but the introduction of two transgenic varieties has largely controlled the virus, recovering production on the islands[3]. However, there is widespread opposition to GMOs, and reports of pathogens evolving resistance to these varieties have questioned their effectiveness.

Crop protection mechanisms make individual crops more resistant to the threat of disease, animal and plant pests. However, the system as a whole remains vulnerable to these threats.

In an all too familiar situation, the Gros Michel banana cultivar was effectively wiped out by a strain of the Panama disease in the 1950s[4]. The majority of commercial bananas were clones, meaning that when the fungus reached Central and South America, entire plantations were decimated, as every banana was susceptible to the fungus. 60 years later, the Gros Michel’s successor, the Cavendish banana, is threatened by a new strain of the same disease.

Increasing system resilience

In the case of bananas, implementing a crop protection strategy (breeding a new resistant banana cultivar) only delayed the devastating impact of the pathogen. This is because nothing was done to address the inherent vulnerability of the system – its genetic uniformity. Genetically homogenous systems of this kind are extremely susceptible to pathogens because a virulent strain can transmit easily through the whole crop without facing any resistant individuals.

The issue of genetic uniformity is not limited to banana systems. 75% of plant genetic diversity has been lost since the 1900s as farmers favour a few improved commercial varieties over local landraces[5] and specialise in fewer crops in order to remain profitable. These improved crop varieties have resulted in an increase in yield since their introduction, but can increase crop vulnerability to disease when used grown in monocultures, as evidenced by the southern corn leaf blight epidemic of 1970, which caused huge losses of the genetically uniform US maize crop[6].

If we are to limit the impact of pathogens, especially with the uncertainty of climate change, we need to look towards making our farming systems more resilient.

One way in which we may be able to achieve this is through diversification of our agricultural systems[7]. Introducing a greater diversity of crops and crop varieties is likely to disrupt the transmission of pathogens between hosts[8]. Crop rotations may interrupt disease cycles by removing potential hosts and other factors such as differences in the crop microclimate could also be important. Disease suppression using diversification has been trialled successfully in China, resulting in the discontinuation of fungicides in the experimental area[9]. The study found that rice blast was less severe in crops grown in mixtures than those grown in monocultures for both susceptible and non-susceptible varieties. However, more studies are needed to fully understand the impact of diversification on plant pathogens and system resilience.

The benefits of a diverse system are not limited to pathogen suppression, but are likely to make agriculture more robust to other biotic and abiotic threats to production. Increasing the resilience of our agricultural systems will have far-reaching benefits and may be a necessary next step if we are to ensure global food security.

[1] Oerke, E. C. (2006). Crop losses to pests. The Journal of Agricultural Science, 144(01), 31-43.

[2] Oerke, E. C., & Dehne, H. W. (2004). Safeguarding production—losses in major crops and the role of crop protection. Crop protection, 23(4), 275-285

[3] (Accessed 2:00, 08/11/16)

[4] (Accessed 2:00, 08/11/16)

[5] FAO 1999b; Women-users, preservers and managers of agrao-biodiversity

[6] Heal, G., Walker, B., Levin, S., Arrow, K., Dasgupta, P., Daily, G., … & Schneider, S. (2004). Genetic diversity and interdependent crop choices in agriculture. Resource and Energy Economics, 26(2), 175-184.

[7] IPES-Food. 2016. From uniformity to diversity: a paradigm shift from industrial agriculture to diversified agroecological systems. International Panel of Experts on Sustainable Food systems.

[8] Lin, B. B. (2011). Resilience in agriculture through crop diversification: adaptive management for environmental change. BioScience, 61(3), 183-193.

[9] Zhu, Y., Chen, H., Fan, J., Wang, Y., Li, Y., Chen, J., … & Mew, T. W. (2000). Genetic diversity and disease control in rice. Nature, 406(6797), 718-722.

If we are to limit the impact of pathogens, especially with the uncertainty of climate change, we need to look towards making our farming systems more resilient.