Developing heterotic groups for hybrid breeding in crop plants with emphasizing on forage crops

Exploitation of heterosis in hybrid breeding and development of synthetic cultivars is an essential procedure in plant breeding programs. The main goal of hybrid breeding programs is to select desirable parental genotypes to maximize the expression of heterosis. However, since development of high yielding hybrids and synthetic cultivars are costly and time-consuming, the accurate prediction of heterotic groups of parental inbred lines for obtaining superior hybrid cultivars is of high priority. Generally, parental genetic distance is the most critical factor in determining the heterosis, from which one may expect to maximize its value. It is, hence, an efficient method which enhances conventional methods for categorizing a large number of inbred lines originated from diverse germplasm sources into heterotic groups. In addition to the parental genetic distance the relative rate heterosis also depends on environmental factors. Environmental stresses may variably influence the performance of parental lines and hybrids, and the relationship between parental distance and heterosis, thereby the rate of heterosis can either increase or decrease depending on traits and genetic materials. Under conditions of climate change, water is likely to become more limited in many areas of Iran agricultural lands. Considering that forage crops show high genetic diversity in their populations, which makes them adaptable to a wide range of environmental conditions, breeding these crops and developing drought-tolerant cultivars with high yield potential is an effective approach towards the development and rehabilitation of part of the country's degraded rangelands. In this way, one of the most important strategies is to use diverse genetic resources to select parents and take advantage of their differentiated diversity toward exploitation of heterosis for development of desirable hybrids and synthetic cultivars. The efficiency of molecular markers in parental selection and the effect of parental genetic distance on progeny performance in forage crops suggest the existence of heterotic effects in hybrids and synthetic cultivars and emphasizes the benefit of marker-assisted breeding for selecting polycross parents to achive maximum yield and improve drought tolerance in successive generations.