Heterotic grouping facilitates continuous heterosis exploitation for efficient hybrid breeding in maize

Abstract

The terms “heterotic groups” and “heterotic patterns” are often used interchangeably, leading to confusion regarding the concept of heterotic grouping. This concept, developed centuries ago, has been refined and extensively utilized for identifying and developing superior corn hybrids, particularly in the USA. Heterotic groups are identified based on the genetic diversity between parental lines or populations. By increasing this genetic distance through inter-population mating, distinct and diverse genetic expressions emerge over time, forming heterotic patterns. These patterns are crucial for developing hybrids with heterosis. It is often questioned whether heterotic groupings can be established at any time. The answer is yes; however, developing heterotic patterns requires multiple generations of intermating. Inbred lines derived from populations based on heterotic patterns will exhibit consistent reactions across different hybrids, climatic conditions, and stress environments, showing no variation in their expression over seasons or years. Misunderstandings arise when heterotic grouping is perceived as a static concept, leading to questions about the varying heterotic reactions of different lines under different climatic conditions. The explanation lies in the genetic diversity that produces heterosis and the interaction between hybrids and their environment, which influences yield performance and trait expression, independent of heterotic grouping. To initiate a breeding program without pre-established heterotic patterns, one should start by grouping materials into different heterotic groups and then establish heterotic patterns within the program. This approach simplifies the development of heterotic hybrids, allowing for continuous enhancement of genetic diversity between groups. Consequently, this enables the development of heterotic hybrids suited for various environments, maturities, climates, and geographies. In this research review article, I will use the information generated by several researchers and try to put it in simpler form for better use with four clear objectives 1) Combining ability and heterotic grouping. 2) Evaluate the pros and cons of heterotic groups and patterns. 3) Historical understanding of heterotic patterns across regions. 4) A strategy for Heterotic Grouping for Heterotic Patterns.