Heterosis

Heterosis, often referred to as "hybrid vigor", manifests in the superiority of first-generation hybrids over parental forms in key biological and economic traits. The effect is most noticeable in quantitative traits with low heritability, such as growth energy, fertility, adaptability, and total yield. A characteristic feature is its maximum expression exclusively in the first generation, with a gradual attenuation in subsequent ones, which precludes the use of hybrid seeds for further sowing.

The evaluation of heterosis is carried out quantitatively through the percentage excess of the hybrid's indicators relative to parents or standards. A distinction is made between true heterosis, comparing the hybrid with the best parent; hypothetical heterosis, based on the average value of both parents; and competitive heterosis, where the best variety currently on the market is taken as a baseline. The stability of this effect depends on the combining ability of the parental lines and specific agro-climatic growing conditions.

Within the framework of variety testing, the success of a hybrid is determined by a complex of economically valuable traits and an analysis of its performance in field conditions. The lack of superiority or indicators lower than parental forms are qualified as the absence of heterosis or depression. The relative values of the effect vary depending on the crop, with high indicators reaching tens of percent confirming the efficiency of the chosen combination of parental forms.