Pests on the move

Abstract

There is a wide range of pests and pathogens that may endanger food security by moving, spreading, or evolving new variants. Commercially important crops for producers in the developing world, such as coffee and citrus fruit, are sensitive to such attacks, as a survey of the alerts issued by the disease database ProMED shows (http://www.promedmail.org/).The greatest danger to human lives, however, comes from those pests that threaten the world’s leading staple crops, including rice, wheat and potato. Among those threats, unfortunately, the species that caused the Irish Famine raises its ugly head again. Although chemicals and resistant variants are available to keep it in check, late blight still causes harvest losses that could feed upwards of 80 million people.The groups of David Cooke from the James Hutton Institute in Dundee and Sophien Kamoun at the Sainsbury Laboratory at Norwich, UK, have recently analysed the genetic diversity of the European population of the late blight pathogen Phytophthora infestans (PLoS Pathogens (2012) 8, e1002940). They found that a new lineage, called multilocus genotype (MLG) 13_A2 has rapidly spread across Great Britain, displacing other variants and reaching a 75% share of the pathogen population in only three years.Cooke and colleagues show that the new strain is highly aggressive in terms of the severity of disease it inflicts on susceptible hosts, that it outcompetes other aggressive strains, and that it can overcome the resistance of some widely used potato cultivars. The authors also reported the full genome sequence of this strain in comparison to an earlier reference genome. They found frequent copy number variations and clues to the genetic foundations of the aggressiveness of the pathogen.The researchers also discovered novel RXLR effector genes, which are the targets of the R proteins conferring resistance to the host plant. Thus, knowledge of the genome will facilitate breeding of new potato lineages resistant to this particularly dangerous pathogen strain.Kamoun’s group also collaborated with Hernan Burbano and others at the Max Planck Institute for Developmental Biology at Tubingen, Germany, to clarify the genetic identity of the historic late blight pathogen that caused the Irish Famine (eLife (2013) 2, e00731). Comparing genomes of 11 historic strains from herbaria and of 15 modern ones, the authors conclude that the Irish Famine pathogen was a genetically distinct clonal lineage with no direct relation to those found in Europe today. It persisted for around five decades in the 19th century and was then displaced.The breeding ground and diversity hotspot for the pathogens is located in Mexico, but the authors conclude from their analyses that the deadly strain originated in a secondary population before conquering Europe.Examples of changing and emerging pests threatening global staple crops, like wheat and potato, show that there are real dangers to global food security, and that these may be heightened by human activities. Improved monitoring, especially in the developing world, and research commitment from the richer countries will be necessary, if the world is to stay ahead of these fast-moving threats.