Researchers study the regions of the genome and the mechanisms that are activated against pathogens or heat shock.
Originally from Central America and domesticated by man for the last 10,000 years, corn (Zea mays) is one of the three most cultivated cereals in the world that, thanks to its ability to adapt, managed to consolidate in production systems.
Used for both human, animal and biofuel production, among many other industrial uses, the global expansion of this crop is linked to the genetic improvement and development of varieties adapted to the needs of each place: today the cereal can be found from the warmest latitudes to the most temperate and from sea level to over 3,500 meters.
Sequenced in 2009 by an international team of scientists, it is now known that corn DNA is made up of 32,000 genes inserted into 10 chromosomes.
This finding confirmed the complexity of the cereal genome because 85% of its genomic sequences are repeated multiple times.
In other words, transposons - a genetic element that can move to different parts of the genome - jump around carrying part of the DNA that surrounds them, which generates mutations, increases genetic variability and makes DNA sequencing more difficult.
Because of this, his study was a great challenge.
Gerardo Cervigni is an expert in Genomics and works at the Conicet Center for Photosynthetic and Biochemical Studies, located in Rosario-Santa Fe.
There, he studies the structure, function and evolution of the genes that make up the DNA of corn. With the genome deciphered, Cervigni can map the genes, know how they work and predict the interactions that prevail.
"The exact location of the genes is essential to know their function," Cervigni said and said:
"With the map of corn, complete and orderly, and through the use of molecular markers, we can identify and associate the genes of resistance of a disease , plague or some characteristic of interest ".
Knowing exactly where the genes are will make it easier for plant breeders to create varieties that produce more grains, larger ones, or that are more tolerant of extreme heat or drought.
Corn DNA: study how to design multi-resistant seeds
The assisted improvement by molecular markers works directly with the DNA information.
This means that the researcher identifies which genes will provide the desired characteristics.
"This selection can be applied in the seedling stage, so the time to obtain better genotypes is reduced and the times and costs of the research are reduced considerably," Cervigni said.
Selecting the best characteristics and minimizing the likelihood that crops will be harmed by external factors are basically the objectives of classical genetics applied to vegetables.
"Knowing where are the genes that contain the characteristics of agricultural interest and how they work is very important for the future development of varieties," said Marcelo Ferrer, specialist in Genetic Resources of INTA.
According to Ferrer, the corn grown today is the result of a process of domestication, carried out by indigenous peoples of America, which consisted in selecting the best seeds and discarding the rest.
"In Argentina, there are more than 40 types of different varieties or local races of corn that are cultivated by farmers since ancestral times and that continue today in some regions of the north of the country, as in the Quebrada de Humahuaca," said Ferrer. He added:
"Adaptation to these climatic conditions was possible due to the great genetic richness of crops such as corn, potatoes and beans."
With the advance of technology and the incorporation of techniques for plant breeding it was possible to obtain crops adapted to the climate and soil conditions of a place.
However, to enrich the knowledge and possible agricultural improvements that can be incorporated, Ferrer stressed the importance of working with local materials as basic germplasm inputs both for breeding and for various basic genetic research for cultivation.
"Argentine materials grown more than 50 years ago, contained great genetic variability," Ferrer said, adding:
"At present, the most common - both in the core zone and in the rest of the country where large-scale maize is produced - is to find lots planted only with 'commercial hybrids' that are very productive, but they are very uniform and, in general, they are vulnerable since they resist or tolerate the attack of some plague or disease.
This is because they lost the variability that characterized their genome. "
Since 1950, the Germplasm Bank of INTA Pergamino has preserved seeds of more than 2,500 corn entries from all over the country.
"In addition to conserving the genetic resources of a country, the germplasm bank, through the characterization and evaluation works, allows us to identify materials that resist biotic and abiotic factors, which adapt to saline soils, at higher temperatures or in the absence of water ", exemplified Ferrer.
Ferrer: "The Argentine materials cultivated more than 50 years ago, contained a great genetic variability".
Super resistant corn
With a population that continues to increase, the need for increasingly efficient, yielding, stable and resistant to pests, diseases, as well as water stress -by excess or deficit- and thermal effects becomes imperative.
According to data from the United States Department of Agriculture (USDA), in 2017, world corn production reached 1031.86 million tons.
However, year after year, these values are modified by various diseases that affect their productivity and the quality of the grains.
In this sense, a team of researchers from INTA Pergamino -Buenos Aires- seeks to identify in the maize genome which mechanisms are put in place against the attack of various pathogens.
Juliana Iglesias, a specialist in plant genetics at INTA and responsible for the study, uses genomic association tools to find gene regions of corn that are activated and allow the plant to resist multiple diseases.
Churches along with María Belén Kistner -bearer INTA-Conicet- aim to detect plants that possess the greatest genetic attributes to resist the most common diseases of economic interest.
"We focus on the search and identification of individuals that have genetic resistance to various diseases, in the future, to develop varieties that have better behavior to the attack of multiple pathogens,"
Iglesias said, adding: "We bet that it is a tool to reduce the use of phytosanitary products and contribute to their sustainable management ".
Iglesias: "We focus on the search for individuals that have genetic resistance to various diseases to develop varieties with better behavior against multiple pathogens."
According to Iglesias, the search for resistance to multiple diseases (MDR) is based on being able to find resistance hotspots (according to the academic term).
"Known as the genomic regions where genes accumulate for resistance to various diseases, the finding of hotspots, in addition to enabling the location of the gene or group of genes that are lit to resist diseases, will help us in the study of the mechanisms that are launched against the attack of various pathogens, "he explained.
"The groups of genes speak to us of patterns, of a relation between the pathogenic habits and the response of defense or susceptibility that the plant can give", analyzed Iglesias, who did a PhD in Cellular and Molecular Biology, at the University of Strasbourg, France.
Studies carried out in Pergamino -Buenos Aires- and in Leales -Tucumán- allowed us to identify which genotypes have the best behavior to pathogens and diseases.
Preliminary results showed that it is possible to group them according to their behavior against pathogens that have the same attack mode.
The pathogens can be biotrophs, hemiótrofos and necrotrophs, each one has different mechanisms to nourish, infect and produce symptoms.
In turn, the plants have different defense strategies that are put into operation according to the type of attack they receive.
"Diseases such as rusts, spike rot and blights generate certain defense responses that are due to the recognition of the pathogen that causes the attack," said the INTA biologist, adding:
"With these results, we can combine those genes, which are activated against similar mechanisms of attack and replicate its structure to obtain varieties with improved characters ".
"We studied the health response of approximately 100 inbred lines, which are part of the INTA Maize Improvement Program," Iglesias said.
The evaluation of foliar diseases in Parchment (rust, blight, bacteriosis, charcoal or charcoal of the spike) and in Loales (gray spot and blight), plus the information obtained on spike and grain rot (Fusarium and Aspergillus), allowed the team of researchers identify genotypes with resistance to more than one disease.
For Cervigni, this is an important finding in the general knowledge of the crop.
"We can establish an efficient protocol for phenotypic characterization and rapid selection of genotypes, whose genomes combine the desirable genes needed to obtain better results in the production of corn," he said.
Read the full story in spanish on the RIA Magazine site
INTA
