Adaptation to Environmental Stresses in Corn
Corn is perhaps nature’s greatest gift to mankind. Its growth has been phenomenal, making it the world’s leading crop. Its contribution to the global food basket is significant. I consider it a crop of extraordinary features, with options and opportunities to make improvements, tackle problems and generate a spectrum of germplasm products.
Corn has a distinct reproductive system which permits exploiting its potential strength and weakness in various breeding operations and seed production practices. Its weakness can be exploited as a secondary trait in stress-related activities. Worldwide germplasm wealth is rich and voluminous thus facilitating a big way to solve problems. The importance of abiotic stresses and their ever-increasing global awareness and concerns can’t be underestimated. Losses occurring every year are massive, resulting in fluctuating production and market price. The environmental stresses are many, and it is important to breed for drought, Low Nitrogen, Water logging and acid soil tolerance.
These traits are certainly difficult and complex to breed for, requiring good field conditions and the ability to manage different water regimes and soil nutrient depletion. The choice of germplasm is critical. It should have excellent agronomic performance and be hybrid-oriented. The identification of secondary traits can be observed visually and show changing behavior under normal, medium, and severe stress levels. In corn, anthesis-silking interval (ASI) has been used with good success. Selection strategies may be direct or indirect. The direct strategies involve cyclic recurrent selection for the trait in question. The performance data on grain yield, ASI, and Ear aspect from different stress levels will be used to select superior progenies followed by recombination to complete a cycle of selection. The selected breeding procedure may involve a type of progeny that will increase heritability of the trait.
The research activities on different stresses mentioned earlier have been going on for more than two decades at the International Maize and Wheat Improvement Center (CIMMYT), the International Institute of Tropical Agriculture (IITA) and in some stronger national agricultural research programs. Several drought-tolerant populations and lines are available worldwide. Two populations, namely across 8328 BN and Pool18 BN, have been improved for Nitrogen Use Efficiency (NUE). It seems that drought-tolerant populations are also good for NUE. For water logging, several lines and hybrids have been identified in materials which had no previous history of selection for this trait. For acid tolerance, four populations, 14 yellow lines and two white lines have been developed in CIMMYT’s regional program in South America.
The indirect strategy is based on Line and hybrid evaluation trials on materials which have no previous history of selection for the traits. The results have been quite encouraging. Several lines and hybrids were detected for individual as well as for multiple traits. Thus it makes a strong case for inbred-hybrid technology for identifying superior genotypes for stress traits, biotic as well as abiotic. Caution, however, should be taken to evaluate only superior genotypes. Since resources are limited, this strategy will prove its worth but will require building a strong, diverse, inbred base germplasm for different traits. Recycling of superior inbreds for each trait should be emphasized and new sources of trait specific germplasm be developed as part of inbred-hybrid technology.
By harnessing these traits in breeding processes, we can ensure that corn remains in supply to feed the world, just as Dr. Norman Borlaug did when he bred high-yielding wheat and saved billions of lives. Through our research, we can continue to honor his legacy and preserve his vision for a world without hunger.