Plus-hybrid system in maize (Zea mays L.) production: A new approach combining the effect of cytoplasmic male sterility and xenia for grain yield increase and nutritional improvement
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Cytoplasmic male sterility (cms) in maize is used to increase the quality of hybrid seed production and reduce its costs. Sterile hybrids often outyield their fertile counterparts, especially if pollinated by a genetically unrelated pollinator. This fact can be used in modern production to increase grain yield of maize hybrids, and to improve agronomic traits. The combined effect of cytoplasmic male sterility and xenia (the influence of pollinators in the year of pollination) is called the Plus-hybrid effect. Accordingly, Plus-hybrid system refers to commercial production of two hybrids in the mixture, one of which is male sterile and high yielding, and other is unrelated fertile hybrid pollinator. Potential Plus-hybrid mixture consists of 75-80% of sterile hybrid and 20-25% of fertile hybrid. In modern agriculture continuously is searched for increased both grain yield and quality of cultivated hybrids. Plus-hybrid system represents one of these attempts. Investigations on Plus-hybrid... effect in the world began in the late 20th century through a series of micro-trials and larger strip-trials in several locations and countries. The best Plus-hybrid combinations had significantly higher grain yield, without compromising quality, than the individual hybrids. The greater the genetic distance between the hybrids combined in the mixture, the expected Plus-hybrid effect is higher (due to the increased effect of xenia). Research conducted in Serbia was done at one location in three years and included two sterile hybrids as mothers and five fertile hybrids as fathers. It turned out that the Plus-hybrid effect had different influence on the investigated traits of the two hybrids, and this effect highly depends on the genotype of the mother. The increase in yield was accompanied with the increase in oil content in one of the sterile hybrids. In addition, health condition of the grain was not affected. It turned out that characteristics of fathers may influence the characteristics of pollinated mothers due to the xenia effects, so the choice of superior fathers increases the profits of the Plus-hybrid effect, also it seems that xenia effects with the same pollinator differ in sterile and fertile version of the same hybrid, and this phenomenon should be further investigated (it could be a kind of interaction between the sterile cytoplasm and xenia, that is different from the Plus-hybrid effect). What is significant is that the Plus-hybrid system can be successfully used to prevent pollination of genetically modified plants (GMO), growing the genetically modified cms maize hybrids mixed with unmodified fertile pollinators. The objective of this study was to determinate both, individual and combined (Plus-hybrid) effects, of cms and xenia on grain yield, chemical composition and grain health condition of examined hybrids. Although studies related to the Plus-hybrid system are very new, we believe that this unconventional approach of maize growing could enter the commercial use, which could be the most important significance of this research. The seed production of Plus-hybrid mixture is not more expensive than production of conventional hybrids, and this fact should increase its commercial use. Therefore, we would like to present results achieved so far and introduce a Plus-hybrid system of maize production.