Biochemical analyses of inbreds and their heterotic hybrids in maize

Since Shull's original description of heterosis, breeders have made wide use of this phenomenon. However while breeders and agronomists have been utilizing heterosis as a means of improving crop productivity, the biological basis of heterosis remains unknown. It is generally believed that our understanding of heterosis will greatly enhance our ability to form new genotypes either to be used directly as F1 hybrids or to form the basis for the selection programs to follow. Efforts have been made to understand the phenomenon. They have been directly related to our capabilities for genetic analyses through the years. So, while the original data came out of studies at the phenotypic morphological level they were followed by physiological and later by biochemical data. With the advent of electrophoresis and the consequent ease of accumulation of data related to isozyme variability, a number of attempts have been made to relate genetic relatedness of inbreds with the performance of their F1 hybrid. An inherent difficulty of this approach arises because of the pedigree diversities among the parental lines. To overcome this problem the same approach is followed in lines of similar pedigree, e.g., coming out of the same original population (F2 of a single F1 hybrid) after selection. The data indicate a significant positive correlation between heterozygosity of parental inbreds and heterosis of their respective F1 hybrid estimated as deviation from the mid-parental value. Some recent data from studies at the total protein level will also be discussed.