In self-pollinated cereal crops (such as wheat, rice, barley), the Ear-to-Row (or Head-to-Row / Panicle-to-Row) method is the standard protocol for maintenance of nucleus and breeder seed:

• Several hundred typical, disease-free individual ears/panicles are selected from a pure crop stand.
• The seeds from each ear are threshed individually and grown in single individual rows ('ear-to-row').
• Throughout the season, each row is rigorously inspected for diagnostic varietal morphological traits. Any progeny row showing off-types, segregation, or disease susceptibility is completely rogued out and discarded.
• The uniform, true-to-type rows are bulked to constitute the nucleus seed.

Seed Replacement Rate (SRR) indicates the percentage of cropped area sown with certified/quality seeds relative to farm-saved seeds.
In the case of $F_1$ hybrids (e.g., in maize, pearl millet, sorghum, cotton, rice):
Farmers cannot save and reuse $F_2$ grain as seed because segregation and recombination in the $F_2$ generation causes heterosis breakdown, high morphological variability, and a drastic yield depression of 20-35%.

Maize (Zea mays) is a monoecious crop with unisexual flowers separated on the same plant: the terminal staminate inflorescence is the tassel, while the lateral pistillate inflorescence is the ear/cob.
In commercial hybrid maize seed production plots:
Male (pollen parent) and female (seed parent) inbred lines are planted in alternating row ratios (e.g., 2 male : 4 female or 2 male : 6 female).
Before anthers begin shedding pollen, the tassels of all plants in the female rows are manually removed (detasseling) or genetically sterilized (CMS).
This ensures that female plants receive pollen exclusively from the adjacent male rows.