Evaluation of Agronomic Traits and Severity of Foliar Disease of Three Commercial Hybrids and Five Advanced Triple Hybrids of Hard Yellow Maize

: Field experiments were conducted to evaluate ag-ronomic traits and response to foliar fungal diseases of five advanced triple hybrids of hard yellow maize ( Zea mays L.) and three commercial hybrids. An A × B factorial experiment with eight treatments, four repetitions and the Tukey test was used to compare means of the treatments ( P >0.05). The most limiting disease is rust. The agronomic characteristics of breeding lines: h1, h2, h3, h4 and h5 (triple hybrids) were evaluated and compared with h6, h7, and h8 (commercial hybrids). Field trials were conducted in two locations of Central Coast of Ecuador (Quevedo & Balzar). Both locations showed significant differences for agronomic traits; Balzar presented lower yield (6,205.46 kg ha -1 ) and greater severity of curvularia leaf spot (3.34 CIMMYT scale) compared to Quevedo (7,368.21 kg ha -1 and 2.47 CIMMYT scale). For hybrids, h6 had significantly lower yield (5,306.83 kg ha -1 ), compared to h5 (6,914.09 kg ha -1 ), h1 (7,211.80 kg ha -1 ), h3 (7,266.83 kg ha -1 ), and h8 (8,036.85 kg ha -1 ). Significant differences were also detected for the orthogonal comparison (INIAP


INTRODUCTION
Maize is one of the world' s most important cereal crops, currently grown on every continent except Antarctica, and is most productive where rainfall or irrigation is adequate.The origin of maize has long been debated.The most widely accepted theory today is a combination of the work of George Beadle and Deborah Pearsall.Beadle proposed that modern maize originated from a mutation of a wild grass, teosintle, in southern Mexico about 9,000 years ago (Matsuoka et al., 2002).
Many different maize products can be obtained.Approximately 24% of the crops produced in the United States are transformed for food, alcohol, and industrial uses.The US produces approximately 40% of the world's maize.Other important producers are China, Brazil, Europe, Mexico, Argentina, India, and South Africa (OECD/FAO, 2020).
Maize breeding and production programs in each country are based on knowledge of the environments in which they are targeted.The success of maize for food and livestock feed is due in large part to its hybrids.Farmers embraced these hybrids because of their superior yields and more vigorous growth.Varietal hybridization through controlled pollination or open pollination has been the origin of the development of many corn varieties; even today, new varieties are created in farmers' fields through open-pollinated crosses (Troyer, 1996) and adaptation to increased planting density (Wang et al., 2020).
In Ecuador, maize is a crop of greater importance at the national level for its production and consumption.More than 291,867 ha of maize are planted for 2022 and the main destination is the formulation of food balanced to generate protein type meat, chicken and pork (Ibarra-Velásquez et al., 2023).
Maize is attacked by a large number of insects and affected by several pathogens causing significant economic damage; therefore, evaluations of genotype × environment are necessary to identify the type of hybrid more suitable and productive for different zones exacerbated by climate change (OECD/ FAO, 2020).Some additional features that influence the adaptation and acceptance of maize genotypes in a specific environment are: a) the type of maturity; b) the type of grain; and c) color of the grain, which shows the area sown in the most important environments of the coastal zone of Ecuador, adding flowering time, days to anthesis and the relative height of the ear from genome-wide changes that occurred during maize domestication (Wang et al., 2020).
Farmers use local varieties or their own varieties or seed from open-pollinated varieties and various types of hybrids.As a general rule, farmers on marginal land or in environments unfavorable to their cultivation use seeds of their own varieties, thus lowering the cost of this input.On the other hand, farmers in safe rainfall areas or in irrigated crops more quickly adopt the use of hybrids and use higher levels of inputs.Understanding the socio-economic aspects of maize environments is essential for proper planning and for carrying out breeding and production programs (Beck & Vasal, 1993), known in Ecuador as recycled seed (Ibarra-Velásquez et al., 2023).
The introduction of new corn hybrids will provide information that will help maintain high production capacity in the area and good grain quality and agronomic parameters that are important to farmers (Ibarra-Velásquez et al., 2023).Therefore, the objectives of this study were to evaluate the agronomic behavior and foliar disease severity of five promising triple hybrids of hard yellow maize and compare them with three commercial hybrids in the rainy season, also to determine the best location for adaptation and cost-benefit analysis of these hybrids.

Plant Material
Original crosses to develop maize triple hybrids were conducted in 2003 by the Unidad de Investigación Científica y Tecnológica (UICYT) of Universidad Técnica Estatal de Quevedo (State Technical University of Quevedo).Two selection cycles per year were conducted and are summarized in Table 1 and Figure 1.
Commercial hybrids evaluated in this study were: INIAP H-553, simple hybrid, that has as parents two inbred lines (S4 L49 Pichilingue 7928 × L237 Population A1); INIAP H-551, a triple hybrid that has as parents three inbred lines (S4B-523 × S4B-521) × S4B-520.These lines were obtained by successive free cross pollination and come from different basic maize with a broad genetic base and good yield potential.The third hybrid evaluated was AGROCERES AG-003, a semi-early triple hybrid of the latest generation, with semi-erect leaves with excellent performance, with good tolerance to insect pests and diseases.

Location and description of the experimental site
Field trials were carried out in the localities, location 1 (Quevedo) in the experimental farm "La María" of the State Technical University of Quevedo (UTEQ) located at km 7 of the Quevedo-El Empalme road, whose geographical coordinates are: 79°47" W and 01°32" S, at 76 meters above the sea level (m a.s.l.).
Location 2 (Balzar) corresponded to the experimental farm of the Agrarian University of Guayaquil located at km 37 of the Guayaquil Road, whose geographical coordinates are: 79°46" W and 1°09" S, at 60 m a.s.l.The research was carried out in 2011.

Planting and management of the crop
Experimental plots were 5.00×3.60m with a net plot size of 5.00×1.80m, 9.00 m 2 with 4 rows.Row distance was 0.90 m, and distance between plants was 0.20 m.For calculations the total population was 55.500 plants/ha .
Plots were arranged in a randomized complete blocks design (RCBD), with a factorial experiment (A×B) where A is localities (two) and B is hybrids (eight) in four repetitions.To evaluate the hybrids, standard agricultural practices were conducted.Soil preparation consisted of manual cleaning of the experimental area, sowing was done manually using an "espeque"1 , holes were made at a depth of 4 to 5 cm, in which two seeds were deposited per site.
After 12 days (d) the most vigorous plant per site was selected, and manual removal of the second plant was done.Weed control was performed using a pre-emergent Paraquat in doses of 1.5 L ha -1 and after 50 d weeds were removed manually.
Fertilization was done applying 138 kg ha -1 of N, 46 kg ha -1 of P 2 O 5 and 60 kg ha -1 of K 2 O. Nitrogen application was carried out at 8, 15, and 35 days after planting (dap).
Insect control was done with Syngenta® Karate insecticide cihalotrina-lambda, in doses of 40 mL in 20 L of water, and also chlorpyrifos was applied mixing with sand (bait) in doses of 100 mL in a liter of water in 100 pounds of sand directly to the bud of the plant.Harvesting was done manually at 120 dap.

Agronomic traits and foliar disease severity
Days to flowering was determined by the number of days elapsed from planting to 51 % of the plants in each plot that were presented of 2-3 cm of their visible pistils or male panicles.Plant height was measured from the ground to the base of the male flower.The sample was 10 plants randomly taken from each net plot.Height of insertion of the cob was determined by the distance between the ground level and the main cob.Acame (stem lodging) was evaluated at 95 dap by counting the number of plants inclined to the ground, and root lodging by counting all plants broken from the insertion of the cob to the ground level.
Rates  1985) and rated on 1 to 5, where 1 indicates no diseases and 5 very heavy infection.The field guide for identification of corn diseases was used to differentiate symptoms (CIMMYT, 2004).Although other studies have used more accurate phytopathometry, quantifying the number of lesions by cm 2 (Garcés et al., 2011), we used a simpler scale due to time constrictions.
Length of the cob was done in ten cobs randomly taken and then individually measured their length in centimeters from the base to the apex.Diameter of the cob was done using a calibrator, the diameter was measured in the third of each cob and its unit expressed in centimeters.Number of rows per cob was counted.Cob uniformity was evaluated following the CIMMYT 1-5 scale where 5 is large and 1 is small.Yield per hectare was done using the weight of the grains obtained in each net plot and adjusting to moisture content at 13%.The methodology of the economic analysis determination: yield, benefit (1 kg of corn = USD 0.34), fixed cost, variable cost, total cost, benefit, benefit/cost ratio, cost-benefit and is detailed in Table 9.

Data analysis
Statistical analysis consisted in ANOVA.To measure the differences between the means of the treatments, the Tukey test (P>0.05)was used in INFOSTAT (Universidad de Córdoba, Argentina).

Agronomic parameters
For days to male flowering and female flowering, significant statistical differences were observed for localities (Quevedo & Balzar) and for hybrids, and without differences between the interaction localities × hybrids.The overall average for days to male flowering was 52.29 d and for female flowering was 55.89 d.Mean squares of the ANOVA for male flowering and female flowering, in the evaluation of the agronomic behavior of five advanced triple hybrids of hard yellow corn (Zea mays L.) and three commercial hybrids in the rainy season are presented in Table 3.Additionally, the hybrids presented significant differences for days to male flowering (h6 51.5 d and h8 55.75 d).
Significant differences were found for days for flowering between locations, Quevedo showed 50.94 d for male flowering and Balzar 54.84 d.The days to flowering in Quevedo were shorter because it had higher relative humidity (83.5%) compared to Balzar (72.9%) (Table 5).The average plant height was 2.11 m, and the cob insertion height was 0.95 m (Table 3).Significant differences were found for the localities, Balzar with 1.89 m and Quevedo 2.34 m in plant height.In the same way, significant differences were found in the height of the insertion of the ear with 1.03 m in Quevedo and 0.8 m in Balzar (Table 6).This indicates that the locality of Balzar under conditions of greater heliophany (Table 5) has a lower plant height.H8 with 2.29 m of height of the plant was significantly taller than the other hybrids (Table 4).Acame (stem lodging) and root lodging showed percentages above 50% in all hybrids (data not shown).There were significant differences between hybrids and for the orthogonal comparison h6 and h7 (INIAP hybrids) vs. h1, h2, h3, h4 and h5 (promissory hybrids) in root lodging, showing higher resistance to lodging in the promissory lines (Table 3).Performance depends on when lodging occurs and whether the cobs remain in contact with the ground.Poor lodging is the result of two sub processes stem bending and root pulling out (Wang et al., 2022).In the case of the hybrids, although a significant effect was detected, lodging occurred late in the growing season so hybrids were not susceptible to yield loss due to root lodging.
The analysis of variance showed significant differences between locations for ear length, but not for ear diameter.Likewise, the hybrids presented differences for both variables (Table 3).The overall mean for cob diameter was 4.68 cm and for cob length was 15.99 cm.
The differences between hybrids were significant, placing the hybrid h6 with 4.51 cm the small diameter of the cob and the best h1 hybrid with 4.77 cm.For length of the cob, the shortest hybrid was h7 with an average length of 14.78 cm and the largest cob h8 with 17.53 cm (Table 4).The agroclimatic conditions of the Central Coastal of Ecuador are good for the development of the cob for h1 being the hybrid with the largest diameter of the cob and the hybrid h8 is the one with the longest length of the cob.
Analysis of variance for the number of rows per cob, showed significant statistical differences for localities and no significant differences for cob uniformity (Table 3).Given the statistical significance for the hybrids, the total average rows per cob was 13.26 rows/cob and for cob uniformity was 2.50.
According to the CIMMYT scale, moderately large cobs were detected in this study (CIMMYT, 1985).Hybrid h6 had significantly lower threads per cob (12.85 threads/cob) compared to h8 with 13.70 threads/cob.According to the CIMMYT scale, cob uniformity was significantly higher in h6 (large cobs) compared to h8 (medium-large cobs).The agronomic advantage it has is on grain yield and production.
Number of cobs, and weight were variables related to yield.When performing the analysis of variance for yield, statistical significance was detected for localities and hybrids.No statistical significance for the interaction between localities × hybrids (Table 3).The overall mean of the yield was 6786.83 kg ha -1 and the coefficient of variation for the experiment was 10.68 %.The yield small was Balzar with 6205.46 kg ha -1 , and best for Quevedo with 7368.21 kg ha -1 , due to increased water supply (Table 2 and 5).
The yield showed significant differences between hybrids in four groups, the first of h6 and h7 with 5306.83 and 5962.06 kg ha -1 , respectively; the second h3, h4 and h5 with 6881.97,6714.25 and 6914.09kg ha -1 , respectively; the third by h1 and h2 with 7211.80 and 7266.83kg ha -1 ; and the fourth for h8 with 8036.85 kg ha -1 , the fourth rank for hybrids (Table 4).Significant differences were detected for the orthogonal comparison h6-h7 (INIAP hybrids) with 5634.44 kg ha -1 and h1, h2, h3, h4 and h5 (promising lines) with 6997.68 kg ha -1 (Table 3).Yields in maize cultivation are very essential for successful agriculture, they have increased over time thanks to more resistant maize hybrids and agronomic improvement.

Foliar disease severity
There was low corn stunt spiroplasma (S. kunkelii) incidence and severity in the experimental plots (Table 7).The overall mean of stunt spiroplama was 1.65 -CIMMYT scale.Environmental conditions (rainy and hot) were not favorable for the development of the vector (Empoasca sp.) (Donoso, 2008).Hybrid resistance to corn stunt spiroplasma have shown that antibiosis could be related to the resistance as decreased nymph survival and adult longevity has found on X1297J (Carpane, 2007).Ciencia y Agricultura, e-ISSN: 2539-0899 • Enero-mayo de 2023 • Vol.20(1): 15544 Curvularia leaf spot (C.lunata) had the highest level of damage of all the diseases evaluated.Statistical significance was determined for localities and hybrids, and the Tukey test at 5% AG-003 (h8) vs. INIAP promissory hybrids (h1-h5) (Table 7).The overall mean of the variable was 2.90 according to the CIMMYT scale, which affected the presence of the disease almost half of the plant.When performing the 5% Tukey Test for localities it was determined that location1 (Quevedo) had significantly lower curvularia leaf spot incidence (2.47) than location 2 (Balzar) with (3.34), according to the CIMMYT scale, (Table 8), which is equivalent to the established presence of the disease in more than half of the plant.In a different study, in location 1 (Quevedo) curvularia leaf spot severity was evaluated on promissory auto pollinated S4 lines and found values as higher as 8 lesions by cm 2 which can have a significant effect on yield due to plant stage and the part of the plant affected (lower leaves) (Garcés et al., 2011).The significant differences between the hybrids (Table 9) it was determined that the hybrid h2 with 2.00 had a lower severity of curvularia leaf sopt than h8 with 3.5, according to the scale of CIMMYT.It is important to note that the curvularia species are saprophytic or phytopathogenic and are mainly found in tropical and subtropical areas, and can be isolated from the soil, air, organic matter, plants, animals, including humans.As with other foliar pathogenic fungi, this fungus is transmitted by seed, affecting yield by infecting the ear and causing rotting of the grain.
Physoderma brown spot is caused by the Chytridiomycete fungus, P. maydis (Wise et al., 2018).Physoderma brown spot severity was significantly different in Quevedo (2.00 according to the CIMMYT scale) compared to Balzar (2.13).Physoderma was distinguishable from curvularia due to brown-purple spots appearing or near the midribs (Wise et al., 2019) (data not shown).
For helminthosporium leaf blight, analysis of variance showed statistical significance for hybrids.The hybrids h6 and h4 had significantly lower helminthosporium leaf blight severity than hybrid h8 (Table 9).
Rust had the lowest disease severity under the field conditions of locations (Quevedo & Balzar).A significant effect of location was detected, with Balzar showing significantly higher foliar disease severity (1.28 scale-CIMMYT) compared to Quevedo (1.00).

Economic analysis
The economic analysis (Table 10), it is observed that the highest gross income USD 2732.53 was obtained with the hybrid h8, on the two localities, followed by the hybrid h2, with USD 2470,73.The total costs were higher for the AG-003 hybrids with the highest yield; with USD 1485,07.The item with Ciencia y Agricultura, e-ISSN: 2539-0899 • Enero-mayo de 2023 • Vol.20(1): 15544 highest production cost is fertilization, while for the rest of hybrids the total costs were similar.The highest net profit was achieved with the h2 hybrid with USD 1405.76 followed by the h1 hybrid with USD 1385.92,obtaining a Benefit-Cost ratio of 2.32 and 2.30 respectively, which indicates that for each monetary unit invested USD 1.56 and 1.54 additional or profit was obtained for the two hybrids.Results found are due to genetic factors specific to each of these materials since maize is a plant endowed with a wide response to the environmental conditions, quality being exploited by man to obtain varieties and hybrids adapted to scattered conditions (Matsuoka et al., 2002;Wang et al., 2020).
In the tropics, corn grows from sea level to altitudes close to 4,000 m.The best yields are obtained in the range of 0 to 900 MASL and a size of 2 to 2.65 m.Corn is a plant endowed with a wide responsiveness to the opportunities (IICA, 2019).
Maize plants are factories that produce energy.To obtain high yields, it is sought to increase the quantity and weight of each grain (Yara Ecuador, 2023).
This study found that in location Quevedo, an average of 50.94 and 54.84 d were obtained for male and female flowering respectively in contrast to the 53.66 and 56.94 d for male and female flowering respectively in the location 2 (Balzar).This is because in location 1 (Quevedo) agro-climatic conditions favor the development of maize crop.
Foliar disease severity: corn stunt spiroplasma (S. kunkelii), curvularia leaf spot (C.lunata), helminthosporium leaf blight (E.turcicum), physoderma brown spot (P.maydis), and rust (Puccinia spp.) was low.However, disease severity was consistently higher in location 2 (Balzar), compared to location 1 (Quevedo); therefore, adaptability of hybrids was due to higher tolerance as well as agronomic traits.The hybrid SM45-1XSV35-1 × SV39-1 had better tolerance than the commercial hybrid AG-003.In the area of Quevedo the highest yield was obtained with an average of 7368.21 kg ha.Finding that hybrids had greater adaptability to location 1 (Quevedo).Maize hybrid (AG-003) was the hybrid that presented the highest yield and better yield (8036.85 kg ha -1 ), followed by the promising hybrid SM45-1XSV35-1 × SV39-1 (7266.83kg ha -1 ) which also had better tolerance to curvularia leaf spot.The economic analysis presented the highest gross income USD 2732.53 with the hybrid AG-003 followed by the hybrid M45-1XSV35-1 × SV39-1 with USD 2470.73.

TABLE 1 .FIGURE 1 .
FIGURE 1.The promising triple hybrid lines used in this study were developed by Unidad de Investigación Científica y Tecnológica (UICYT) of Universidad Técnica Estatal de Quevedo.

TABLE 3 .
Mean squares of the analysis of variance for days to male and female flowering, agronomic traits: plant height, cob insertion height, acame (stem lodging), lodging (root), cob diameter and length, number of rows, and cob uniformity and yield of five promissory triple hybrids of hard yellow corn (Zea mays L.) and three commercial hybrids in the rainy season in Central Coast of Ecuador.

Df Days to male flowering Days to female flowering Plant height Cob insertion Acame (stem lodging) Root lodging Cob diameter Cob length Number of rows Cob uniformity Yield Total 63
* = significant at level 0.05.ns = not significant.h1

TABLE 4 .
Days to male and female flowering, plant height, cob diameter, cob length, number of rows, cob uniformity (CIMMYT scale) and yield of five advanced triple hybrids of hard yellow corn (Zea mays L.) and three commercial hybrids in the rainy season in Central Coast, Ecuador.
*Numbers followed by the same letter in a column are not significantly different (Tukey, P<0.05)

TABLE 5 .
Agroecological and meteorological characteristics of the experimental site.

TABLE 6 .
Plant height and cob insertion height of five advanced triple hybrids of hard yellow corn (Zea mays L.) and three commercial hybrids in the rainy season in Central Coast -Ecuador.
* Numbers followed by the same letter in a column are not significantly different (Tukey, P<0.05).

TABLE 8 .
Curvularia leaf spot incidence in five promising triple hybrids of hard yellow corn (Zea mays L.) and three commercial hybrids during the rainy season in the Central Coast Ecuador.
*Numbers followed by the same letter in a column are not significantly different (Tukey, P<0.05).

TABLE 7 .
Mean squares of the analysis of variance for corn stunt spiroplasma, curvularia leaf spot, helminthosporium leaf blight, phishoderma brown spot, and rust, in the evaluation of the agronomic traits and foliar disease severity of five promissory triple hybrids of hard yellow corn (Zea mays.L.) and three commercial hybrids during the rainy season in the Central Coast Ecuador.

TABLE 9 .
Foliar disease severity (scale 1-5 CIMMYT) of curvularia leaf spot and helminthosporium leaf blight of five promissory hybrids of hard yellow maize (Zea mays L.) and three commercial hybrids during the rainy season in the Central Coast of Ecuador.Numbers followed by the same letter in a column are not significantly different (Tukey α = 0.05) *

TABLE 10 .
Economic analysis of five promising hard yellow corn hybrids (Zea mays L.) and three commercial hybrids during the rainy season, in the Central Coast of Ecuador.