Abstract
A vast number of plant pathogens from viroids of a few hundred nucleotides to higher plants cause diseases in our crops. Their effects range from mild symptoms to catastrophes in which large areas planted to food crops are destroyed. Catastrophic plant disease exacerbates the current deficit of food supply in which at least 800 million people are inadequately fed. Plant pathogens are difficult to control because their populations are variable in time, space, and genotype. Most insidiously, they evolve, often overcoming the resistance that may have been the hard-won achievement of the plant breeder. In order to combat the losses they cause, it is necessary to define the problem and seek remedies. At the biological level, the requirements are for the speedy and accurate identification of the causal organism, accurate estimates of the severity of disease and its effect on yield, and identification of its virulence mechanisms. Disease may then be minimized by the reduction of the pathogen’s inoculum, inhibition of its virulence mechanisms, and promotion of genetic diversity in the crop. Conventional plant breeding for resistance has an important role to play that can now be facilitated by marker-assisted selection. There is also a role for transgenic modification with genes that confer resistance. At the political level, there is a need to acknowledge that plant diseases threaten our food supplies and to devote adequate resources to their control.
Generated Summary
This review article explores the significant threat that plant diseases pose to global food security. It provides an overview of various plant pathogens, their mechanisms of causing disease, and the challenges they present to food production. The study emphasizes the importance of understanding pathogen identification, disease severity, and the evolution of virulence in order to develop effective control strategies. The article also discusses the role of conventional plant breeding, marker-assisted selection, and genetic modification in mitigating the impact of plant diseases. The overarching aim is to highlight the need for increased resources and political attention to address the global issue of plant disease and its impact on food security, especially in developing countries.
Key Findings & Statistics
- More than 800 million people do not have adequate food.
- 1.3 billion people live on less than $1 a day.
- At least 10% of global food production is lost to plant disease.
- In Ireland, about a million people died of starvation in the 1840s due to potato blight.
- An estimated 2 million people died in the Great Bengal Famine of 1943.
- In the USA, the corn (maize) crop was completely destroyed in some areas due to a fungal disease.
- World production of cassava from 2000 to 2003 averaged 185 million tons/year, with over 100 million tons harvested in Sub-Saharan Africa.
- In 1990, losses in the southeastern United States from nematodes were estimated at $88.4 million.
- Striga species infect more than two-thirds of the 73 million ha of cereals and legumes grown on the African continent.
- More than 100 million people in 25 countries are affected by Striga.
- The rice blast disease (caused by Pyricularia oryzae) results in losses of 10%-30% of the rice crop every year.
- More than 700 ha of rice of diverse genotypes with varying levels of resistance in Bhutan were affected in 1995, resulting in losses of 1090 tonnes.
- Rice is second only to maize in global production.
- The cost of losses and control measures for potato crop due to P. infestans is over $5 billion annually.
- The area of transgenic crops increased 40-fold from 1.7 to 67.7 million ha between 1996 and 2003.
- 30% of the area of transgenic crops is grown in developing countries.
Other Important Findings
- Plant pathogens range from viroids to higher plants.
- Pathogens are difficult to control due to their variability.
- Plant breeding for resistance plays a crucial role.
- Transgenic modification with resistance genes is also important.
- More than 700 plant viruses cause devastating diseases.
- The globalization of agriculture has led to the spread of pathogens.
- Exclusion through quarantine is the first line of defense.
- Plant pathology is underfunded in relation to its importance.
- Identification of pathogens is fundamental to control.
- Virulence characteristics include production of degradative enzymes, toxins, and effector molecules.
- Horizontal gene transfer can disseminate pathogenicity genes.
- Genetic resistance is a low-cost and durable method of control.
- Marker-assisted selection (MAS) can help breeders.
- Genetic uniformity can lead to genetic vulnerability.
- Exploiting knowledge of biochemistry and molecular biology can increase resistance.
- The GM option holds promise for disease resistance.
Limitations Noted in the Document
- The measurement of disease severity is often subjective.
- The relationship between symptoms and yield loss is not always clear.
- Data on disease outbreaks and their impact in developing countries are often lacking.
- The study does not provide a comprehensive analysis of all plant diseases.
- The review is limited in its discussion of post-harvest losses.
- The reliance on traditional morphological analysis in pathogen identification can be inaccurate.
- The acceptance of transgenic traits in plant improvement may be slow in some cultures.
- The review acknowledges that the use of GM technology is limited by public opinion.
Conclusion
The review underscores the critical need to address plant diseases as a major threat to global food security. The article emphasizes that more than 800 million people worldwide are undernourished and that significant proportions of global food production are lost each year to plant diseases. The study calls for a multi-faceted approach to combatting these threats, including enhanced pathogen identification, improved disease measurement techniques, and a focus on virulence characteristics. It highlights the importance of conventional breeding, marker-assisted selection, and transgenic modifications. The conclusion stresses that the genetic vulnerability of crops, coupled with the ease with which pathogens can spread and evolve, poses a continuous and growing threat to the world’s food supply. The review concludes that the international community, including governments and funding agencies, must increase resources and attention to plant pathology to support food security, particularly in developing countries. The adoption of innovative technologies, like genetic modification, is presented as a potentially crucial step. The review emphasizes that the current state of the world demands immediate and sustained action to mitigate the impact of plant diseases, safeguarding the future of global food supplies.