CG PICAÇO : a new cultivar of sudangrass with high forage performance and seed yield

A new cultivar of sudangrass [Sorghum sudanense (Piper) Stapf.] was developed by the method of selection of individual plants with progeny testing. The most important traits are high forage performance, good leaf:stalk ratio, and high seed yield.


INTRODUCTION
Numerous studies have been carried out to select and genetically improve forage crops, always seeking to associate high yields of dry matter with bromatological quality (Neumann et al. 2011).Therefore, the pressure of natural or artificial selection in species facing animal production aim at obtaining genotypes with emphasis on forage traits, mainly on green and total dry matter and leaf dry matter (Assis et al. 2008).Thus, studies hardly ever aim at a combined selection regarding genetic gain in seed yield (Lopes and Franke 2011).
In Brazil, few forage cultivars are currently commercially available, most derived from apomictic reproduction.Therefore, they are genetically homogeneous and do not generate new variation.This is a threat to national security due to the possible emergence of new pests and most serious diseases (Jank et al. 2011).On the other hand, most tropical forages of agronomic interest have large genetic variability, which can be exploited in the selection of new cultivars with desirable traits (Araújo et al. 2008).Sudangrass [Sorghum sudanense (Piper) Stapf.] is a forage species which has been increasingly used in southern Brazil.It presents annual cycle, and grows in tropical and temperate climates, being tolerant to acidity and low fertility soils, with high biomass yield and optimal recovery after cutting and grazing (Bibi et al. 2010).
The advancement of sudangrass in areas previously occupied by other annual species is a consequence of the high resistance of the species to water deficits, which notoriously occurs during the summer (Pacheco et al. 2013).This culture is widely used for ground cover due to its large biomass, and therefore, it leaves great amount of sudangrass trash on soil.Moreover, its use as forage is relatively new; thus, there are few cultivars registered (MAPA 2014).Its great potential for biomass yield, its tolerance to drought, heat, acid and low fertility soils, its disease resistance, and its ability to compete with weeds (Silva et al. 2014) have been notorious to the production of interspecific hybrids (Sorghum bicolor x Sorghum sudanense), combining the benefits of both species.Zamfir et al. (2001) reinforce that the biomass yield of sudangrass is superior to that of pearl millet and maize, and so is the ability on roots and shoots growth.In addition, Tomich et al. (2004) did not find differences between the forage potential of sorghum hybrids compared with sudangrass; therefore, they present forage yield similar to a hybrid and with a significantly reduced cost for obtaining seeds.

PEDIGREE AND BREEDING METHODS
The cultivar CG PICAÇO was obtained by the method of selection of individual plants within the "common" original population with subsequent progeny test (VCU tests).In the year 2009, three populations of "common" sudangrass, originated from different edaphoclimatic regions, were sown in the field evidencing great genetic variability within and between populations.Two populations were collected in the fields of Cegil Agro Seeds Company, in São Borja-RS and in Campos de Júlio-MT, and another one was collected by farmers in the municipality of Melo (province of Cerro Largo, Uruguay).The seeds of each population were sown 0.45 m between plants and between lines, on a density of three to four seeds per pit-hole.The established order sought to force competition between plants in the pit-hole, and the one which expressed greater competitive ability in the vegetative stage would remain.There was selection pressure of approximately 3% in 1272 of plants obtained from three populations, based on forage traits and seed yield.In the field, the main trait of analysis was tillering, and it was selected plants which had at least 10 fertile tillers (viable panicles).These plants were cut close to the soil surface at the physiological maturity of seeds, separating the panicles for kiln drying (40 o C) until seed moisture reached close to 13%.The rest of the genotype of each plant was weighed in order to assume the potential for biomass yield.Before the cutting, the main panicle of each plant was identified, harvested and packed in paper bags for drying and taken to the laboratory for analysis of traits related to inflorescence components, such as panicle length, panicle mass, number of grains per panicle, mass of grains per panicle, fertility and panicle harvest index.Thus, after analysis of selected genotypes, plants with higher performance for the simultaneous production of forage and seeds were sown in the field, in 2010, in individual plots.In that year, selection occurred between plots, and the selected ones needed to present great uniformity and superior performance.The selected plots were submitted to value of cultivation and use (VCU) test in the following years.The cultivar was called CG 236AR09 in field.
For analysis of seed yield, another experiment was carried out in order to obtain greater reliability of selection applied on components of seed yield of the cultivars.Thus, the experiment was carried out in randomized block design with three replications.Each experimental unit, which included a genotype to be tested, consisted of 5 rows of 5 m length, spaced 0.20 m apart to compose a plot of 5 m².The seeding rate was 25 kg seed ha -1 for cultivars of sudangrass and pearl millet, and 12 kg seed ha -1 for sorghum cultivars.To estimate the yield of seeds, it was carried out harvesting of the three central rows of each plot, comprising an area of 3 m 2 , as soon as seeds reached the stage of physiological maturity.Panicles were weighed and threshed with estimated values in kg ha -1 .For not having available seeds of this cultivar (IPA Sudan 4202) registered at MAPA when the study was carried out, it was used as control, in both experiments, one pearl millet cultivar (ADR 500 -"SuperMassa"), two forage sorghum hybrid cultivars (AG2501C and JUMBO) and the sudangrass "common" population.In these same year in Augusto Pestana, the experiment was carried out with the purpose of doing the DHS tests (Differentiation, Homogeneity and Stability), comparing with the same cultivars control.
In the second year of evaluation of VCU test (2012), due to the favorable year of production, all genotypes had higher performance than the previous year.This fact did not change the behavior of genotypes since the cultivar CG PICAÇO had forage performance superior to the other controls at all locations evaluated, and hybrids of sorghum obtained higher seed yield mean (Table 2).

SEED MAINTENANCE AND DISTRIBUTION
CG PICAÇO is registered in the Ministry of Agriculture, Livestock and Food Supply, number 32394 (MAPA 2014).Cegil Agro Seeds (Celso L. Arenhardt & Cia Ltda.) is responsible for maintaining the cultivar genetics and basic seeds.Seeds are sold to producers accredited by the company.

Table 1 .
Performance of forage cultivars value for cultivation and use assay, carried out in 2011, in three different soil and climatic regions

Table 2 .
Performance of forage cultivars value for cultivation and use assay, carried out in 2012 in three different soil and climatic regions

Table 3 .
Mean performance of cultivars of forage value for cultivation and use assay, carried out in the years of 2011 and 2012, in three different soil and climatic regions