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Agrociencia
versión On-line ISSN 2521-9766versión impresa ISSN 1405-3195
Agrociencia vol.50 no.1 Texcoco ene./feb. 2016
Crop science
Detasseling in parental single crosses of maize (Zea Mays L.) hybrids for high valleys of Mexico
1Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias-Campo Experimental Valle de México, Km. 13.5 Carretera Los Reyes-Texcoco, 56250. Coatlinchán, Texcoco, Estado de México. México.
2Instituto Politécnico Nacional, Sección de Posgrado e Investigación, Escuela Superior de Ingeniería Mecánica y Eléctrica Zacatenco. Unidad Profesional ‘Adolfo López Mateos’. 07738. Colonia Lindavista, México, D.F. México. (rzb0509@ hotmail.com).
3Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias-Campo Experimental Bajío, Km. 6.5 Carretera Celaya-San Miguel de Allende, 38110 Celaya, Guanajuato, México.
4Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias-Sitio Experimental Tlaxcala, Km. 2.5 Carretera Tlaxcala-Santa Ana, 90800. Tlaxcala, México.
Good quality seed is a crucial input for the increase of maize productivity (Zea mays L.), and must be produced using strict procedures and controls. Technology for the production of hybrid seed is limited and, therefore, the effect of removing the tassel of the female parent (detasseling) was evaluated on seed productivity and quality and the interaction with the environment of simple cross females in hybrids for the High Valleys OF Mexico. Between 2006 and 2008 in Texcoco, Estado de México (2250 masl), 15 treatments were evaluated: five simple crosses (CML-239xCML-242, M-43xM-44, M-47xM-46, CML-241xCML-243, and M-55xM-54) and three levels of detasseling (removing tassel, tassel and flag leaf and tassel not removed) in a randomized complete block design with three repetitions. Differences (p≤0.01) were found between simple crosses and years, yield and physical quality of seed; there were no significant differences for detasseling. The interaction was significant for the beginning of male flowering and yield. Crosses averaged 70 to 72 d for the start of male and female flowering, with floral synchrony, and two days to begin detasseling and avoid self-pollination; yields were 4.79 to 9.43 t ha-1, 32 to 78 % for large seeds, and 62 to 68 kg hL-1 test weight. Removing the tassel increased yield by 6.31 % and reduced the amount of small seed by 10.5 % in comparison to the control. In 2006 there was a difference of 4 d for the start of female flowering and 2 din 2008 in comparison with 2007; in 2008 yield was 9.4 t ha-1, and in 2006 it was 44.68 % lower. In 2008, M-43xM-44 yielded 11.24 t ha-1, and in 2006 and 2007, yields were 42.32 and 14.11 % lower. To determine where, when, and how to produce hybrid seeds, one must know the parents, place of production, and interaction.
Key words: Zea mays L.; seed; detasseling; Genotype x Environment Interaction; parents
La semilla de calidad buena es insumo básico para aumentar productividad en maíz (Zea mays L.), debe producirse con procedimientos y controles estrictos. La tecnología para producir semilla híbrida es limitada; por ello, se evaluó el efecto de eliminar la espiga del progenitor hembra (desespigamiento) sobre la productividad y la calidad de semilla y la interacción con el ambiente de cruzas simples progenitoras de híbridos para Valles Altos de México. Entre 2006 y 2008, en Texcoco, Estado de México (2250 msnm) se evaluaron 15 tratamientos: cinco cruzas simples (CML-239xCML-242, M43xM-44, M-47xM-46, CML-241xCML-243 y M-55xM-54) y tres niveles de desespigamiento (eliminación de la espiga, la espiga más la hoja bandera y sin eliminación de la espiga) en un diseño de bloques completos al azar con tres repeticiones. Diferencias (p≤0.01) se encontraron entre cruzas simples, años, rendimiento y calidad física de semilla; no existió diferencia significativa para desespigamiento: y la interacción entre inicio de floración masculina y femenina sí fue significativa. Las cruzas promediaron entre 70 y 72 d para el inicio de la floración masculina y femenina, con sincronía floral y dos días para iniciar el desespigue y evitar autofecundaciones; rindieron entre 4.79 y 9.43 t ha-1, semilla grande entre 32 y 78 % y peso hectolítrico entre 62 y 68 kg hL-1. Al eliminar la espiga aumentó 6.31 % el rendimiento y disminuyó la semilla chica (10.5 %) en comparación con el testigo. En 2006 hubo 4 d de diferencia para el inicio de la floración femenina y 2 d en 2008 en comparación con 2007; en 2008 el rendimiento fue 9.4 t ha-1 y en 2006 fue 44.68 % menor. En 2008, M43xM-44 rindió 11.24 t ha-1 y en 2006 y 2007 los rendimientos fueron 42.32 y 14.11 % menores. Para determinar dónde, cuándo y cómo producir semilla híbrida se debe conocer los progenitores, sitio de producción e interacción.
Palabras clave: Zea mays L.; semilla; desespigamiento; interacción genotipo x ambiente; progenitores
Introduction
In 2014, Mexico produced 23.27 x 106 Mg of maize (Zea mays L.), covering a surface of 7.06 x 106 ha, with an average yield of 3.3 t ha-1. In the central High Valleys of Mexico, at over 2200 masl, in the states of Tlaxcala, Puebla, Hidalgo, Querétaro, Michoacán, Morelos, Distrito Federal, and Estado de México, 2 million ha of maize grain were harvested with a yield of 2.82 Mg ha-1, 83.21 % of which was rainfed, representing 28.46 % of the surface harvested in the country with maize (SIAP, 2014). Productivity is low and needs increasing. An alternative for this is the use of improved variety maize seeds, with outstanding agronomic and productivity characteristics for rainfed and irrigation adapted to this region.
High-quality seeds are the basic input for the increase of crop productivity (Copeland and McDonald, 2001; Barrón, 2010). In Mexico, 9403 ha of certified category maize were harvested in 2014, with an average seed yield of 5.7 Mg ha-1 and a production of 53 580 Mg. This amount is required to plant around 2 679 008 hectares (considering 20 kg of certified category seed per hectare), or 36.07 % of the surface planted with this crop (SIAP, 2014). In the High Valleys of Mexico, certified seeds are only used in 6 % of the surface planted with maize (González et al., 2008) and in the area of de Amecameca, Estado de México, in only 4 % (Jolalpa et al., 2014).
In this regard, the Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (INIFAP) generates improved varieties and produces maize seed adapted to the different regions of Mexico. Between 2005 and 2014, the Campo Experimental Valle de México (CEVAMEX) produced and sold registered category seed of hybrids H-40, H-48, H-50, H-52, H-66, H-70, and H-161, and of varieties VS- 22, V-54A, and V-55A to 31 small seed companies and generated seed production technology (Virgen et al., 2010; Larqué et al., 2013; Virgen-Vargas et al., 2014). The production of certified seed carried out by small companies is an alternative for the adoption of technology and the production of grain in the High Valleys; Vallejo et al. (2008), Barrón et al. (2010), and Barillas et al. (2010) pointed out that in Michoacán, Guerrero, and Tlaxcala there are organized groups of seed producers that supply the certified seeds with INIFAP varieties, which means saving at least 50 % in the cost of seeds for producers, in comparison with foreign companies. Domínguez and Donnet (2014) reported that 75 % of the maize hybrids and varieties generated for the High Valleys and sold by seed companies come from INIFAP and account for 9.35 % of the potential surface for maize plantation in this region (700 000 ha in irrigation and good rainfall), and 6.55 % of the potential seed market quantified by Donnet et al. (2012).
The study of the factors that determine the productivity and quality of seed of maize hybrid parents, lines and simple crosses, in the production environments is crucial in the production of certified category hybrid seed. In hybrids, the potential yield and seed quality of the parents were evaluated (lines and simple crosses), and production sites were identified (Ávila et al., 2009; Virgen et al., 2010), along with population densities (Rojas et al., 2009; Espinosa-Calderón et al., 2010a; Tadeo et al., 2013; Virgen-Vargas et al., 2014), planting dates (Virgen et al., 2013), use of androsterility in the production of hybrid seeds (Martínez-Lázaro et al., 2005; Tadeo et al., 2007; Espinosa et al., 2012), crop nutrition (Zepeda et al., 2002; Cervantes-Ortiz et al., 2013), and their Genotype x Environment interaction (Tadeo et al., 2013; Virgen et al., 2013; Virgen-Vargas et al., 2014).
In a hybrid maize seed production lot it is essential to remove the tassel of the female parent (detasseling) to maintain genetic quality and avoid contamination by self-pollination. The activity requires, on average, 24 to 50 worker days ha-1, depending on the uniformity of the soil and the female parent, the presence of offspring and the easy removal of the tassel (Martínez-Lázaro et al., 2005). According to Espinosa-Calderón et al. (2010a), removing the tassel in the hybrid H-49 affected yield positively, while removing the tassel and three leaves affected it negatively. After detasseling in INIFAP and CIMMYT lines, Espinosa et al. (1999) observed an average increase of 30.3 % in yields and, in three lines, a decrease of 4.1, 14.7, and 32.9 %. In the parental single crosses of the hybrid H-47, androsterile and fertile, there was a reduction of 26 % in seed yield when detasseling (Espinosa-Calderón et al., 2010b). In hybrids H-47 and H-49, the elimination of one or two leaves did not affect yield (Tadeo et al., 2013).
There is specific information on the technology of seed production and quality, certified category, of simple crosses and parent hybrid lines in particular locations. Thus the aim of this investigation was to determine the effect of levels of removal of tassels in the female parent (detasseling) on the yield and physical seed quality of parental single crosses of maize hybrids in the High Valleys of Mexico and its interaction with the environment. Our hypotheses were: 1) The female parental single crosses have different desirable genetic attributes for seed production, and 2) removing the tassel plus one leaf does not affect the seed’s yield and quality.
Materials and Methods
The investigation was part of the activities of the project “Generación de tecnología para la producción de semilla de maíz para Valles Altos y Zona de Transición” (Generating technology for maize seed production in the High Valleys and Transition Zone), carried out in the Programa de Tecnología de Semillas of the Campo Experimental Valle de México (CEVAMEX), Coatlinchán, Texcoco, Estado de México (19° 17’ N, 98° 53’ W and 2250 m above sea level). The weather is temperate sub-humid with rainfall in the summer, an average annual temperature between 12 and 18 °C, average annual rainfalls of 645 mm (INIFAP, 2012). Average monthly temperature and rainfall data for the years 2006, 2007, and 2008 were retrieved and processed in the agro-weather station of the Colegio de Postgraduados (km 36.5 carretera federal Los Reyes-Texcoco, Montecillo, Texcoco, Estado de México, 5 km away from the experiment).
During the spring-summer agricultural cycles of 2006, 2007, and 2008, fifteen treatments, product of the 5x3 factorial combination, were evaluated: Five simple crosses (CML-239xCML-242, M-43xM-44, M-47xM-46, CML- 241xCML-243, and M-55xM-54), and three levels of detasseling (removal of tassel, removal of tassel and flag leaf, and no removal of neither tassel nor flag leaf ) in a randomized complete block design with three repetitions. The evaluation did not include the male parent. The experimental unit consisted of four rows, each 5 m long and separated by 0.80 m; the two central rows were used as the effective plot size. The CML crosses, generated by the Centro Internacional de Mejoramiento de Maíz y Trigo (CIMMYT), are homogenous and uniform, since they are formed with lines that have an average of six to eight self-pollinations in comparison to the M crosses, generated by INIFAP, with a higher variability and three to five self-pollinations (Espinosa et al., 2003; Ávila et al., 2009; Arellano et al., 2011). The simple crosses are parents of the maize hybrids adapted to the Mexican High Valleys: H-44, H-52, H-66, H-68E, H-70, and H-153E, generated by INIFAP.
Agronomic management was performed according to the recommendations for planting maize in the CEVAMEX. The land was prepared with a fallow, dredge, and furrow with machinery. Seeds were sown by hand on dry soil on May 16, 11, and 21, in 2006, 2007, and 2008, respectively, at a population density of 62,500 ha-1, with a distance between plant and plant of 20 cm. To fertilize, we used the formula 150-70-30 (NPK), half of N and all the P and K was added using machinery while planting, and the rest of the N in the second hoeing, and 326 kg ha-1 of urea, 152 kg ha-1 of triple calcium superphosphate and 50 kg ha-1 of potassium chloride were used as sources of N, P, and K. Weeds were controlled by applying a preemergence 1.5 L ha-1 dose of Primagran gold® (i.a. Atrazina + S-metolaclor), and in postemergence, when the weeds were 5 cm in height, 2.0 L ha-1 of Marvel® (i. a. Dicamba + Atrazina). An average of eight irrigations were performed during sowing and in stages V3, V6, V10, V13, VT, R1, and R3 (Ritchie et al., 1993); gravity irrigation was performed using a 12 cm irrigation depth, considering the efficiency of conduction and application, which was estimated in 65 % and evapotranspiration of the plant (Rendón and Fuentes, 1997) in the absence of rainfall for a period of 8 d.
The process of detasseling (removal of the tassel from the female parent) was performed manually. It began 3 to 5 d after the apprearance of the first tassel (male flower), since there was no pollen release in the effective plot size and continued during 10 to 15 d every third day, until all tassels were removed. The harvest was carried out by hand when the formation of a black layer was observed, which indicated physiological maturity; the grains of the middle section of five ears were sampled in each experimental unit. Samples were taken twice: First, when the plant looked dry, with a humidity of 24 % in the grain, and another one 15 d later. The drying process was natural and the cleaning of the seed was done manual.
The variables measured were: 1) beginning of male and female flowering, where the days were counted from the first irrigation to the appearance of the first tassel and first silking, measured in lateral rows of the experimental unit; 2) yield, Mg ha-1 at 14 % humidity, calculated using the formula: REN=[(PC x MS % x G x FC %) /8600]/1000, where PC = ear field weight, in kg per effective plot size; MS %= percentage of dry matter, by means of the difference of 100 minus the percentage of humidity in the grain, obtained using the equipment Stenlite®; G % = percentage of grain, relation between the weight of grain and the weight of the ear without bracts, average of five ears, multiplied by 100; FC = correction factor, obtained by dividing 10000 m2 (1 ha) by the effective plot area (8 m2); 8600 = factor to adjust the yield to 14 % humidity per hectare, parameter used in Mexico; and 3) physical quality of the seed by means of size and weight. Seed sizes were classified as: large (SG), médium (SM), and small (SC), with round drilling jigger sized 8, 7, and 6 mm, and the values were reported as percentages. For the weight of 200 seeds (P200S), five groups or repetitions of 200 seeds were weighed using an analytic scale (Ohaus), ad the average was calculated; the test weight (PH) was taken using an OHAUS® scale and expressed in kg hL-1.
Data was used to perform ANOVA using GLM procedure (SAS, 1989) for the main factors and interactions. Treatments means were compared using Tukey (p≤0.05). The data expressed as percentages were previously transformed into arcsine values.
Results and Discussion
Parental single crosses of maize hybrids
Between parental single crosses of the hybrids H-44, H-52, H-66, H-68E, H-70, and H-153E there were significant differences (p≤0.01) for the beginning of male flowering, yield, and seed quality (Table 1). This was due to the genetic characteristics of each one of the lines that form the simple cross (Virgen-Vargas et al., 2014) and to the response of the plant to the damage caused by the removal of the tassel (Espinosa-Calderón et al., 2010a and b); mainly the difference in the number of self-pollinations between them (Espinosa et al., 2003; Ávila et al., 2009; Arellano et al., 2011). These results are similar to those obtained by Virgen et al. (2010) and Virgen et al. (2013) when evaluating parental single crosses of the maize hybrids H-50, H-52, H-64, H-66, H-68, and H-70 in Estado de México and Tlaxcala.
Table 1 Flowering and yield, average size and weight of seeds of parental single crosses of maize hybrids. Texcoco, Estado de México (2006-2008).
Años | IFM (días) | IFF (días) | REN (Mg ha-1) | Tamaño de semilla (%) | PH (kg hL-1) | P200S (g) | ||
---|---|---|---|---|---|---|---|---|
SG | SM | SC | ||||||
CML-239xCML-242 | 70.1b | 73.0a | 7.3b | 71.4b | 19.4cd | 8.9b | 65.6b | 67.7b |
M-43xM-44 | 71.1b | 75.0a | 9.1a | 70.4b | 21.7c | 7.9b | 62.6c | 85.5a |
M-47xM-46 | 68.6c | 71.3a | 8.1b | 49.8c | 30.2b | 19.9a | 64.8b | 71.2b |
CML-241xCML-243 | 72.8a | 72.7a | 4.7c | 32.4d | 46.1a | 21.5a | 68.3a | 48.3c |
M-55xM-54 | 68.1c | 70.5a | 9.4a | 78.3a | 16.1d | 5.6b | 62.8c | 88.7a |
P > F | <0.01 | 0.08 | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 |
DSH (0.05) | 1.06 | 4.63 | 0.86 | 6.44 | 5.46 | 4.14 | 1.17 | 5.64 |
Media | 70.19 | 72.53 | 7.79 | 60.51 | 26.74 | 12.78 | 64.87 | 72.33 |
CV (%) | 2.00 | 8.46 | 14.73 | 11.68 | 17.97 | 26.29 | 2.38 | 10.31 |
R2 | 0.74 | 0.29 | 0.87 | 0.94 | 0.88 | 0.94 | 0.92 | 0.92 |
p>F: Probability; Means with different letter in a column are statistically different (Tukey, p≤0.05); DSH: honest significant difference; CV: coefficient of variation; REN: seed yield; IFM: male flowering begins; IFF: female flowering begins; SG: percentage of large seeds; SM: percentage of medium seeds; SC: percentage of small seeds; PH: test weight, in kg hL-1; P200S: weight of 200 seeds, in g.
The number of days until male and female flowering were, on average, 70 and 72 (Table 1). This indicates that the simple crosses showed floral synchrony, which is why the female parent must be detasseled within no more than two days to avoid self-pollination and maintain the genetic quality of the certified category seed (Vallejo et al., 2008). In the simple cross CML-241 x CML-243, the number of days until the beginning of male and female flowering was equal, therefore the exact moment in which to remove the tassel must be defined carefully. In M-43 x M-44 the difference between the beginning of flowering was 4 d, indicating more time to begin detasseling. Another factor to consider is the uniformity of the flowering of the female parent (Martínez-Lázaro et al., 2005); the more uniformity there is, the lower the number of detasseling steps and the lower the cost of this activity in comparison to other parent variables, the male flowering period of which is broad (10 to 20 d). Crosses CML-239 x CML-242 and CML-241 x CML-243 have a greater uniformity, since they are formed with lines of six to eight self-pollinations, in comparison to crosses M-43 x M-44, M-47 x M-46, and M-55 x M-54, which have more variability (Espinosa et al., 2003; Avila et al., 2009; Arellano et al., 2011).
Average seed yield was 7.79 Mg ha-1 and 80 % of the parental single crosses of hybrids yielded between 7 and 9 Mg ha-1 (Table 1). Crosses M-43 x M-44 and M-55 x M-54, parents of hybrids H-52, H-66, and H-70, had the highest yields, with 9.1 and 9.4 Mg ha-1, and the lowest yield was in CML-241 x CML- 243, parent of the H-68E, with 4.79 Mg ha-1. These results are similar to those reported by Avila et al. (2009) and Espinosa et al. (2012). The results were obtained in experimental lots, as opposed to a hybrid seed detasseling lot, where yield is lower due to factors such as asynchrony in male and female flowering between parents, scarce control of weeds, pests, and diseases, and genetic quality, as well as losses during the cleaning of the seed. In this regard, Barrón (2010) pointed out that in the production of certified seeds of hybrids H-515 and H-516 they obtained 3 Mg ha-1 of marketable seeds, and for the hybrid H-318 between 4 and 7 Mg ha-1 were obtained (Vallejo et al., 2008). The yields of seeds from female simple crosses of hybrids H-44, H-52, H-66, H-68E, H-70, and H-153E make seed production profitable for domestic businesses, since the cost-benefit is >1; it is 1.9 to produce a trilinear hybrid, indicating that for each peso invested, one can recover this plus another 1.9 pesos (Vallejo et al., 2008; Virgen et al., 2013).
Simple crosses had, on average, 60, 27, and 13 % large, medium, and small seeds, respectively (Table 1). CML-239 x CML-242, M-43 x M-44, and M-55 x M-54 displayed percentages of large seeds (8 mm) of over 70 % and of small seeds (6 mm) of 5 to 8 %, since they have conical ears (Avila et al., 2009; Arellano et al., 2011), whereas M-47 x M-46 and CML-241 x CML-243 had between 49 and 39 % large seeds, 30 to 46 % of small seeds (7 mm), and 19 to 21 % small seeds, indicating a conical-cylindrical ear. Seed size is an important characteristic for the sale and profitability for seed companies, since producers prefer large and medium seeds, although small seeds have good physiological quality. Laynez-Garsaball et al. (2007) and Tadeo-Robledo et al. (2010) did not find significant differences in the vigor of plantlets between sizes of maize seed varieties. However, at the beginning of growth of the small seeds there was a lower accumulation of dry matter than in large seeds (López-Santillán et al., 2004).
The test weight and weight of 200 seeds were, on average, 64 kg hL-1, and 72.33 g, the cross CML- 241 x CML-243 had the highest test weight (68.33 kg hL-1) and the lowest weight for 200 seeds with 48.33 g, whereas crosses M-55 x M-54 and M-43 x M-44 had the lowest weight of 200 seeds with 88.64 and 85.59 g and the lowest test weight (62.88 and 62.66 kg hL-1) (Table 1). These figures are similar to those obtained by Zepeda et al. (2002) with simple crosses H-14 and H-214. The seeds with the highest weight have the least number of seeds, and vice-versa. The number of seeds per kilogram is important when establishing a detasseling lot to determine the population density of both parents, and for the sowing ratio of male and female rows, as well as the greater amount of seeds of the male parent that can be used in case planting more rows is required to obtain more pollen or as border for isolation, in compliance with seed certification regulations (SAG, 1975).
Effect of removing the tassel in the female parent (detasseling)
There were no significant differences (p>0.05) in yield and physical seed quality between levels of detasseling (Table 2), due probably to the fact that the tassel demands nutrients, and removing it did not alter the physiology of the plant, but rather contributed to photosynthates being directed at filling the seeds (Martínez et al., 2005). There was no significant reduction (p>0.05) in yield when removing the tassel and flag leaf because the photosynthetic capacity of the plant was not affected, since the area of the flag leaf removed was less than in comparison to other leaves, which were enough to carry out photosynthesis. De Brito (2011) pointed out that reductions of over 41.01 % of the foliar area in maize plants jeopardize their productivity. Similar results were observed by Espinosa-Calderón et al. (2010b) when removing the tassel with or without a different number of leaves in maize hybrid H-49; and in hybrid H-47 was reduced seed yield of 26 % with the removal of the tassel (Espinosa-Calderón et al., 2010a). But removing one or two leaves in both hybrids did not affect yield (Tadeo et al., 2013).
Table 2 Flowering and yield, effect on size and yield of seed from eliminating the spike in parental single crosses of maize hy brids. Texcoco, Estado de México (2006-2008).
Años | IFM (días) | IFF (días) | REN (Mg ha-1) | Tamaño de semilla (%) | PH (kg hL-1) | P200S (g) | ||
---|---|---|---|---|---|---|---|---|
SG | SM | SC | ||||||
Sin eliminar | 70.42 | 73.04 | 7.61 | 59.91 | 26.20 | 14.00 | 65.00 | 72.02 |
Espiga | 69.93 | 71.44 | 8.09 | 60.71 | 26.64 | 12.53 | 64.73 | 71.42 |
Espiga + hoja bandera | 70.20 | 73.09 | 7.66 | 60.93 | 27.38 | 11.82 | 64.89 | 73.56 |
P > F | 0.26 | 0.35 | 0.09 | 0.73 | 0.64 | 0.31 | 0.71 | 0.37 |
DSH (0.05) | 0.71 | 3.08 | 0.57 | 4.27 | 3.62 | 2.74 | 0.77 | 3.74 |
p>F: Probability; Means with different letter in a column are different (Tukey, p≤0.05); DSH: honest significant difference; REN: seed yield; IFM: male flowering begins; IFF: female flowering begins; SG: percentage of large seeds; SM: percentage of medium seeds; SC: percentage of small seeds; PH: test weight, in kg hL-1; P200S: weight of 200 seeds, in g.
In a hybrid maize seed production lot, it is crucial to remove the tassel of the female parent (Martínez-Lázaro et al., 2005), which is why it is important to count the days until the beginning and male and female mean flowering in both parents. Simple crosses had an average of 70 d to begin male flowering, and 72 d for female flowering (Table 2). There is a period of two days to remove the tassel from the female parent, so as to maintain genetic quality and avoid self-pollination. It is recommendable to begin 2 to 4 d after the appearance of the first tassel (male flowe) and continue for 10 and 20 d every third day until all tassels have been removed, depending on the genetic characteristics of both parents, the effect of the environment and their interaction in a detasseling lot (Virgen et al., 2013; Virgen-Vargas et al., 2014).
Seed yield increased 6.31 % (480 kg ha-1) with the removal of the plant’s tassel in comparison to the control (tassel not removed). This could be due to the fact that by removing the source of demand, nutrients were translocated to the cobs and used for plant growth, and reduced the percentage of small seeds (10.5 %). Removing the tassel, and the tassel and flag leaf had no significant negative effects on the yield and quality of the seed. Espinosa-Calderón et al. (2010b) also observed a positive effect on yield when removing the tassel from the female parent. This indicates the possibility of reducing at least one step towards detasseling seed production lots or the posibility of callibrating machinery to make the cut in the point of insertion of the flag leaf. However, in each female parent it is important to know the effect of eliminating the tassel along with one, two, or three leaves, because in some parents, seed yield is affected (Espinosa-Calderón et al., 2010a).
Effect of the environment (years of production)
Significant differences (p≤0.01) were observed between the spring-summer planting cycles of the years 2006, 2007, and 2008 for the beginning of male and female flowering, yield, and physical quality in seeds (Table 3). This indicated that at least one characteristic was different from one year to the next, perhaps due to the difference in temperature (average of 16 °C in each year) and amount and distribution of rainfall; the rainy season covered between June and September, and rainfall was 722.7 mm in 2007, and 20 and 32 % higher than in 2006 (583 mm) and 2008 (495.2 mm) (Figure 1, Agro-Weather Station of the Colegio de Postgraduados, 2013). These differences probably contributed to the differences in both days for the beginning of flowering, yield, and the physical quality in seeds for
Table 3 Effect of the environment on flowering and yield, size and weight of seeds in parental single crosses of maize hybrids. Texcoco, Estado de México (2006-2008).
Años | IFM (días) | IFF (días) | REN (Mg ha-1) | Tamaño de semilla (%) | PH (kg hL-1) | P200S (g) | ||
---|---|---|---|---|---|---|---|---|
SG | SM | SC | ||||||
2006 | 71.4a | 74.6a | 5.2c | 26.5b | 41.7a | 31.5a | 64.1b | 49.2b |
2007 | 69.6b | 70.1b | 8.5b | 79.3a | 20.0b | 0.6c | 60.5c | 82.3a |
2008 | 69.4b | 72.9ab | 9.4a | 75.6a | 18.4b | 6.1b | 70.0a | 85.3a |
P > F | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 | <0.01 |
DSH (0.05) | 0.71 | 3.08 | 0.57 | 4.27 | 3.62 | 2.74 | 0.77 | 3.74 |
p>F:= Probability; Means with different letter in a column are statistically different (Tukey, p≤0.05); DSH: honest significant difference; REN: seed yield; IFM: male flowering begins; IFF: female flowering begins; SG: percentage of large seeds; SM: percentage of medium seeds; SC: percentage of small seeds; PH: test weight in kg hL-1; P200S: weight of 200 seeds, in g.
![](/img/revistas/agro/v50n1//1405-3195-agro-50-01-43-gf4.gif)
Figure 1 Average monthly temperature and rainfall for 2006 and 2008 (Agro- Weather Station of the Colegio de Post graduados, 2013).
Between years there was a difference of 4 d for the beginning of female flowering; 2006 displayed the most days, and 2007, the least (Table 3). This may be due to the fact that during the stages of germination, vegetative stage, and floral differentiation of the maize plant, temperatures fell between 2.4 and 0.5 °C, causing lower growth and development of the plant. Similar results were observed by Zepeda-Bautista et al. (2009) and Virgen et al. (2013) in parental single crosses of maize hybrids for the High Valleys of Mexico.
Average seed yield was 7.79 t ha-1; in 2008 it was 17.12 % higher, and in 2006, 33.24 % lower (Table 3). This may be due to the greater avaiability of water in the stages of flowering and grain filling, due to rainfall; in 2008, rainfall was highest in September (week 40, 53.50 mm) in comparison to 2006 (week 40, 12.40 mm) (Figure 1). This confirms the effect of the environment on the productivity of female parental single crosses in maize hybrids (Virgen et al., 2010; Virgen et al., 2013), which is useful to determine the location, date, and how to establish a seed production lot. Avila et al. (2009) observed a similar environmental effect when increasing the female simple cross of the hybrid H-52 in the Texcoco Valley; production was between 9 and 10 Mg ha-1 with 70 % of large seed, and in Tlaxcala, 6.5 Mg ha-1 in yield for registered seed. In 2008 a greater seed size was observed than in 2006 (Table 3), in which large seeds along with the el test weight and the weight of 200 seeds were 64.94, 8.42, and 42.32 % smaller.
Genotype x environment interaction
The interactions parental single crosses x years of evaluation were significant (p≤0.01) for the beginning of male flowering and seed yield, as well as the percentage of large, medium, and small seeds, test weight and the weight of 200 seeds (data not shown), since at least one simple cross had a different behavior in each agricultural year. This was due to their genetic characteristics and agroclimatic conditions that determine the production and quality of the hybrid seed (Virgen et al., 2013; Virgen-Vargas et al., 2014).
Days until the beginning of male flowering
Between years, a change in the number of days until the beginning of male flowering was observed in 100 % of the simple crosses (Figure 2). This parameter is important to define the moment in which to remove the tassel of the female parent and the synchrony of male and female flowering, for pollination and formation of the seed. Similar results were observed by Virgen et al. (2010) after evaluating parental single crosses of hybrids in locations in Tlaxcala. The simple cross M-55 x M-54, female parent of the hybrid H-70, displayed a difference of 2 d until the beginning of male flowering (67 to 69 d). CML- 239 x CML-242 displayed a higher variation in days until the beginning of male flowering. In 2007 it flowered at 68 d and 5 d later in 2006. This difference causes problems when establishing a detasseling lot, since it may cause synchronicity problems, and in consequence, a lack of seed formation, the loss of genetic quality due to pollution of foreign pollen, and self ’pollination of the female due to badly-timed pollination.
Seed yield
In all the parental single crosses between years, different seed yields were obtained, since it is a trait determined by many genes and influenced by the environment (Poehlman, 1979; Márquez, 1988). The simple cross CML-241 x CML-243 had the lowest variation in seed yield: in 2007 and 2008, it produced an average of 5.16 Mg ha-1, which could be due to the higher rainfalls during flowering and grain filling (Figura 1); in 2006 yield was 21.45 % lower (1.11 Mg ha-1). The cross CML-239 x CML- 242 had its highest yield (10.28 Mg ha-1) in 2008, and its lowest, 14.19 and 70.55%, in 2007 and 2006 (Figure 3).
The simple cross M-43 x M-44, female parent of hybrids H-52 and H-66 (Avila et al., 2009; Arellano et al., 2010), displayed its highest yield (11. 24 Mg ha-1) in 2008. In 2007 and 2006, they were lower by 14.11 and 42.32 % (Figure 3). Avila et al. (2009) observed seed yield of 9 to 10 Mg ha-1 for the cross M-43 x M-44 in a detasseling lot located in the Texcoco Valley, at altitudes of 2300 masl; and the Valle de Mexico Experimental Field, at 2250 masl. During the spring-summer 2011 cycle 3.79 and 3.52 Mg ha-1 were obtained of the direct (M-43 x M-44) and reciprocal crosses (Virgen et al., 2013). Simple cross M-55 x M-54 displayed a lower variation in seed yield, in 2007 and 2008, it yielded an average of 10.75 Mg ha-1, and in 2006, yield was 36.77 % lower (3.95 Mg ha-1). Virgen et al. (2013) produced, in the Valle de Mexico Experimental Field, in the spring-summer 2011 cycle, 1.55 and 3.19 Mg ha-1 of the direct (M-54 x M-55) and reciprocal (M-55 x M-54) crosses. This shows the unstable behavior of the female parents, which as a direct effect on yield and seed quality, crucial for success in production, economic and technical profitability in domestic businesses (Vallejo et al., 2008; Virgen-Vargas et al., 2014).
Conclusions
In the production of hybrid seeds, the removal of tassels in female parental single crosses of maize hybrids for the Mexican High Valleys increases seed yield and reduces the percentage of small seeds. Removing the tassel or the tassel and the flag leaf does not have a negative effect on yield or seed weight or size.
The female parental single crosses of maize hybrids have an unstable behavior regarding yield and physical seed quality, and the beginning of male flowering in the female to begin detasseling (removal of the tassel in the female parent) between production years.
The female parental single crosses of maize hybrids H-44, H-52, H-66, H-68E, H-70, and H-153E, generated by INIFAP for the High Valleys of Mexico have desirable productivity, size and test weight characteristics for the production of hybrid seed.
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Received: April 01, 2015; Accepted: November 01, 2015