Due to the high costs of certified maize hybrids seeds, in many agricultural regions of the country growers prefer to grow free-pollinated varieties, which may be of different vegetative cycle, according to their preferences, grain requirements, or their environmental and production conditions; some of them argue that they cultivate varieties of free pollination because the seed is less expensive than that of the hybrids and can continue to sow for several years without their production diminishing as much as that of the hybrids. In 1990, the Central Experimental Field of Chiapas of the National Institute of Forestry, Agriculture and Livestock Research (INIFAP) released a variety of maize, called V-534, for cultivation in the tropical area of Chiapas, mainly in warm regions with up to 1 000 m, (^{Ramirez et al., 1990}). After its release and during the first two years, the V-534 was highly appreciated by the producers, since it was grown to certified seed in more than 50 000 ha, but then declined because of lack of seed.

Taking into account the good acceptance that V-534 still has among corn producers, as well as its age, the Maize Genetic Improvement Program of the Experimental Center of Chiapas Center of INIFAP carried out a process of genetic improvement for its renewal, which started in 2001. It started with a group of 155 pairs of plants, which were crossed to form families of complete siblings and were selected for their plant phenotype, flowering period, type of ear, health and weight of grain, among other characteristics. These selected plants were genetically improved during four years by the method of combined selection of families of complete siblings (^{Marquez, 1985}). Pairs of plants that coincided in their flowering and in their plant phenotype were crossed, to have a better parental control in the selection of the best families of the whole group evaluated (^{Hallauer and Miranda, 1981}).

The 155 families of complete siblings, plus the original population (V-534) were evaluated in the agricultural cycle of temporal and genetic recombination’s of the upper families were made in the agricultural cycle of irrigation, during the years 2003 to 2005. The experiments were established in cooperative producers’ plots in the municipalities of Ocozocoautla, Villaflores, Venustiano Carranza and Jiquipilas, in the central region of the State and in localities of the municipalities of Frontera Hidalgo and Tuxtla Chico in Soconusco, Chiapas.

With the data obtained from the agronomic evaluation, the best 10 families from each locality and the entire region of each year were genetically recombined by manual pollinations to form new varieties. At the end of the whole selection process, the 14 experimental varieties formed in the three combined selection cycles, plus the original variety V-534, were evaluated in four locations during 2006.

Among the varieties, differences in grain yield were significant (p< 0.04), standing out 11 of the 15 evaluated; the best of them was “V-534 Coita C3” with an average yield of 6 t ha^-1 and 0.841 t ha^-1 more grain than the C0 (^{Coutiño et al., 2008}), so in January 2015 was registered in the National Plant Variety Catalog of the National Seed Inspection and Certification Service (SNICS) of SAGARPA, under the name of V-561, with provisional registration number 3104-MAZ-070415/C.

The plants of V-561 are very similar to those of V-534, from 1.61 to 2 m of plant height (Figure 1) and the cob is inserted at a height of 0.6 to 1 m, the average flowering is 56 days in temporal and between 65 to 70 days in irrigation sowings; they reach the stage of corncob at 86 days and these are very sweet (15.15 ° Brix). For each ton of stubble and cob, 423 kg of grain are produced. The ears are cylindrical in shape, 17 to 20 cm long and 4.1 to 5 cm in diameter, they have 14 to 16 rows of grain and each row can have 42 to 50 grains of creamy white endosperm (Figure 1) and medium-textured, with a content of 11.6% protein, which make it more nutritious than other varieties; its hectoliter weight is of 77.7 kg hL^-1, reason why the grains are of first quality for the preparation of tortillas with a very pleasant taste for the consumer; for each kilogram of nixtamalized grain is obtained 1.85 kg of mass and 1.52 kg of tortilla, which are of nice white color and good quality.

Figure 1 Plant and ear of the variety V-561. 

This variety can be cultivated in the Tuxtla Gutierrez, Villaflores, Comitan (warm part) and Tapachula mainly, and in those tropical areas, similar to subhumid warm climates, with rainfall greater than 600 mm annually, as in Nayarit. In good season crops, the V-561 variety can produce 7.71 t ha^-1 and exceeds 1.4 t ha^-1 at V-534 and at 1.2 t ha^-1 at V-526. In irrigation plantings can produce 10 to 16% more.

Currently, the Experimental Field Center of Chiapas has registered seed available for seed companies that are interested in the production and commercialization of certified seed of V-561.