Protecting crop species from biotic and abiotic constraints in the era of Global Change: are we ready for this challenge?
Marco Landi and Giovanni Benelli
DOI : 10.3844/ajabssp.2016.51.53
American Journal of Agricultural and Biological Sciences
Volume 11, Issue 2
Reliable andaffordable supply of food is of crucial importance to the progress andstability of human societies. During the last century, we have assisted to anextraordinary increase of crop yields, especially for the most widespread andconsumed crop species, such as rice, wheat, corn and soybean. The Broadbalkexperiment, one of the oldest continuous agronomic experiments in the world,have showed how half of the increase of crop productivity is mainly due to the improvementsintroduced through plant breeding and half through to agronomical practices,although both are dependent on each other (Rasmussen et al., 1998). The development of a huge numbers of scientificplant breeding programs has been of vital relevance in improving crop varietiesand productivity. In addition, collection and spread of improved germplasmaround the world have ensured that all breeders could quickly benefit from theadvances obtained by others. On the other side, based on Lawes and Gilbert'swork in the previous century, the main advances in agronomy consisted on thecontinued use of fertilizers, the true value of which could only be realized inthe presence of suitable varieties and in the absence (or under controlledpressure) of competition from weeds, pest and diseases. Therefore, cropprotection became crucial and it was achieved by the improvements of theagrochemical industry, which has developed sophisticated, high-targeting andmore efficient agrochemicals. Taken together, the use of new high-yieldvarieties in association with chemical fertilizers and agrochemicals,controlled water-supply (irrigation), and new methods of cultivation, includingmechanization, are commonly identified under the term “Green Revolution” which wasconied between ’30 and ’60 and was responsible in some cases for doubling (oreven triplicating) the agricultural production for many crops species, inparticular cereals.
The incremented crop productivity hasbrought many social gains, such as reducing the malnutrition, lowering foodprice, increasing food security. Moreover, since the economic sustainability isthe most important factor for the adoption of a crop for farmers (Sgroi et al., 2014; Testa et al., 2015), the increased crop productivity occurred in the lastdecades, has determined a positive impact on the development of several ruralareas.
The increase of cropyield, has caused, on the other side, large changes in rural societies due tothe migration of population from the countryside (caused by the decrease ofmanpower needs) to towns and cities where the industrialization offered moreopportunities. The better living conditions lead to the highest increment ofword population that has ever been documented: from 2.5 b people to 5.2 b in 40years (1950-1990; UNR, 2004). Nowadays, word population is predicted toincrease from 7.4 b people (May, 2016), to 8.4 b in 2030 and 9.5 b in 2050 (U.SCensus Bureau). In addition, people rise out of poverty, higher livingstandards, such as greater meat consumption, and personal mobility will increaseeven more the demand on food production (and quality), animal feed, fiber, andfuels. Thus feeding, clothing and fueling a more densely populated planet isprobably the key challenge of our century.
Industrializationand anthropic activities have also imposed profound alterations to theenvironment and, decade after decade, have contributed to alter dramaticallythe life conditions on Earth leading to the so called “Global Change” (alsoreferred as “Global Warming” or “Climate Change”), phenomenon from which we areactually trying to run for cover. Based on several reports produced by theIntergovernmental Panel on Climate Change, it emerges as the most hazardouseffects of Global Change, such as rising temperatures and heat waves, prolongedperiods of drought, and incremented levels of pollutants in all the compartmentsof biosphere can cause more frequent and severe fluctuations in cropproductivity, but also can seriously threaten the availability of arable land;for example increasing the amplitude of soil/water salinization or soilerosion. The total surface of arable soil is also undermined by the constantrequirement of lands for human activities that, beyond the direct effect ofoverbuilding, in many cases also increase the pollution of surrounding areas, forexample through the release of heavy metals, hydrocarbons, xenobiotics or otherpollutants in soil, water, and/or in the atmosphere. Global Change alsoinfluences the ecology of weeds, pests and disease, with possible implicationsfor crop protection and pesticide use.
The ability of science to makepredictions on the impact of Global Change on ecosystem interactions is limitedbecause models that include multiple interactive effects of Global Change arestill relatively rare and the comprehension of results obtained from modelsystems results quite complicated. For this reason, despite the scientificcommunity concords on the dramatic impact of Global Change on cropproductivity, predictions may have sometimes-different facets depending on theinformation source. Some researchers reported however that in the time span1981-2001, changes in precipitation and increased temperatures have already inducedannual losses of wheat, maize and barley production of about 40 million tons peryear (Lobell and Field, 2007). Thus, beyond future prediction(s) of GlobalChange effect, humanity is still experiencing the effects this phenomenon forat least three decades.
It is evident that in a near future akey challenge for humanity is to increase the productivity of crop specieswhile decreasing water supply, the use of fossil fuels, chemical fertilizer,pesticides (and more in general agrochemicals), and other negativeenvironmental inputs. On the other side, less clear is how agriculture’s outputcan increase so substantially without significantly increasing itsenvironmental footprint.
Plant physiologyand biochemistry have developed as powerful disciplines during the 20thcentury, but only in a few cases they have led to relevant crop improvement,and in any case, nothing as compared to the amazing gains on crop productivityobtained through the classical genetic breeding from 1930 to 1960. This islikely because the links between the biochemistry and genetics of the processesdescribed were not established, but rather high-yield genotypes were selectedonly for this desired feature lacking to explore the reason on the bases ofthis gain. The situation has changed after the discovery of the DNA structureby Watson and Crick (1953) and even more after ’70, when the first positiveresults with transgenic plants were obtained. From that time onward, theability to control one or few genes has also deepened the knowledge on the biochemicalmechanisms underlying the genetic process that has been modified. This newapproach, associated with the rapid development of “omic” sciences, has thepotentiality to lead to significant advances either in crop yield, quality,and/or plant protection in a near future.
The future need for higher cropproductivity must parallel with a reduction of agronomical inputs as in thepast high-yield genotypes have been selected for their performances with highinputs, especially fertilizers and pesticides. Agricultural emissions from cropand livestock production grew from 4.7 billion tons of carbon dioxideequivalents (CO2 eq) in 2001 to over 5.3 billion tons in 2011. Inthe same period, annual emissions from fertilizers increased by 37% and in 2011the world total annual emissions fromsynthetic fertilizers averaged 725 Mt CO2 eq, about 14% of total emissionsfrom agriculture in the same year (Tubiello etal., 2014). Advances in the basic knowledge of plant genetic, physiologyand biochemistry should thereby be address to increase the efficiency of inpututilization by plants in order to reduce the input level. Technologicaladvances on instrumentations, such as precision farming tools (such as GPStracking devices designed for farming), as well as agronomical practices (i.e.advanced organic farming, eco-friendly soil amendments) can also significant contributeto achieve this goal.
The extensiveemploy of synthetic pesticides against pests of agricultural and veterinaryimportance, especially in developing countries, lead to important concerns forhuman health and the environment (Desneux etal., 2007; Hemingway and Ranson, 2000; Naqqash et al., 2016). In this scenario, the need for effective and eco-friendlycontrol tools has gained increasing attention in latest years (Benelli, 2015;2016). Besides this, a further challenge for crop and livestock protectionnowadays, is the improvement of the success of biological control programs,developing effective quarantine procedures and proper evaluation of thenon-target effects of biocontrol agents (Hajek et al., 2016).
Furthermore, chemoecological knowledgeabout pests and biocontrol agents may represent a valid help to improve integratedpest management strategies. Indeed, foraging kairomones exploited bycarnivorous arthropods have been successfully tested as field lures to attractcarnivores in damaged agricultural habitats. However, practical applications offoraging kairomones seem to be restricted by major concerns including carnivorousarthropod habituation, carnivorous arthropod time-wasting on victim-free crops,exploitation of host-borne cues by hyperparasitoids and lack of foraging kairomones specificity due totri-trophic interactions sharing a given habitat that use identical chemicalsignals, thus confounding species-specific biological control agents (Kaplan,2012). Further research on new applications of physical and chemical signalsexploited by carnivorous arthropods is urgently required. Physical andolfactory cues can be used to experience mass-reared predators and parasitoids,via sensitization or associative learning practices (Giunti et al., 2016). This could help toovercome critical steps in mass rearing of biocontrol organisms and improvebeneficial performances of carnivorous arthropods in the field.
In view of the growing scientificinterest on the effects of Global Changes factors on the relationship betweenplant-pest-environment, in this issue a collection of papers focused on thistopic are presented. Beyond awareness of the deleterious impact of GlobalChange, factor which should lead humanity to a wiser use Earth’s resources, we believethat only the in-depth comprehension of mechanisms adopted by crop species toendurance under stress (Landi et al.,2012; 2013; 2014; 2015; Pardossi et al.,2015; Penella et al., 2016; Tattini et al.,2014) associated with new eco-friendly methods to control crop pests anddiseases may represent a way to contrast the effect of Global Change meanwhilewe are attempting to increase crop productivity for supporting the needs of anincreasingly crowded planet.
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© 2016 Marco Landi and Giovanni Benelli. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.