BRSMG Rubelita: irrigated rice cultivar for low- lands in the state of Minas Gerais

The lowland rice breeding program, developed in the state of Minas Gerais, has as basic objective to release new commercial cultivars. In this way, this program is making available a new cultivar named BRSMG Rubelita, which has as main characteristics: medium cycle, high tillering, lodging tolerance, diseases tolerance, high grain quality, and high grain yield.


INTRODUCTION
Minas Gerais is among the major rice consumer states in the country.Upland and lowland rice crops account for about 80% of rice production in this state, equally distributed to each ecosystem.The remainder (20%) is produced in lowland under irrigation conditions.
During the agricultural years of 2000-2010, there was a decrease in the planted area and in the amount of rice produced by the state of Minas Gerais.The planted area and yield obtained in 2000 were about 135,000 ha and 263,000 t; and the records of 2010 were lower, 53,000 ha of planted area, and 115,000 tons of rough rice.In 2013, the records for planted area and yield decreased even more when compared with 2010, i.e., 23,000 hectares of planted area, and 43,000 tons of rough rice (CONAB 2015).
One of the main factors that contribute to rice production is the use of improved cultivars adapted to each type of crop.This is because the technology generated (new cultivars) is of low cost and easy adoption by farmers, providing significant gains in crop yields.Rice cultivars recommendation for commercial cropping is continuous and dynamic, i.e, from time to time new cultivars are recommended in replacement to the less yielding cultivar and/or with less commercial acceptance.Thus, the research partnership between EPAMIG and Embrapa Rice and Beans, by means of the lowland rice breeding program, tests every year several lines and cultivars, in different locations of Minas Gerais, aiming at offering the best options to rice farmers, regarding the most appropriate cultivars to their lowland crops.
Both for upland rice and for lowland rice, the role of research, especially breeding, with the obtainment of improved cultivars, is essential to increase rice production and yield in Minas Gerais, and thus contributes to increase the income of rice farmers and the State Value-added Tax on Goods and Services (ICMS -Imposto sobre Circulação de Mercadorias e Serviços), in addition to making the state and the country less dependent on imports to meet the increasing domestic demand.
As a recent contribution of these integrated researches, a new lowland rice cultivar was made available to farmers of the state of Minas Gerais: BRSMG Rubelita.This is the 17 th lowland cultivar released by this research program.

PEDIGREE AND BREEDING METHOD
In the lowland ricebreeding program carried out in Minas Gerais, the Trials of Value of Cultivation and Use (VCU's) are designed to evaluate, with replications of years and local, cultivars and lines that stood out in the Preliminary Comparative Trials, aimed at the recommendation of new cultivars.
BRSMG Rubelita originated from the simple cross involving the lines CNA 4990 and CNA 7882, which aimed at gathering greater resistance to blast, hardiness, yield potential and grain quality.The cross was carried out by Embrapa Rice and Beans, in 1996.After the multiplication of F 1 seeds, the F 2 generation was sown in the first semester of 1997, in Goianira-GO.After mass selection of plants with good phenotypic acceptance, the F 3 generation was sown during the 1997/98 agricultural year, also in Goianira, when the population was harvested in bulk.The F 4 generation was subjected to selection of individual plants in 1998/99, and in the following year, a new selection of plants within the best F 4:5 progenies was carried out.F 6 lines were incorporated into the observation trial of lowland rice families in 2001/02, Goianira-GO.In 2002/03, the F4-2-6-B line, identified as BRA 02697, participated in the yield preliminary trial of lowland rice (PT), sown in Goianira-GO, Formoso do Araguaia-TO, Boa Vista-RR, and Leopoldina-MG.With the analysis of the PTs, the line BRA 02697 was selected to proceed the evaluation in Minas Gerais, under the Minas Gerais Agreement.In the 2004/05 agricultural year, BRA 02697 was included in the value of cultivation and use (VCU's) of Minas Gerais, and remained in this trial category for five years (2004/05 to 2009/10).Furthermore, the cultivar was evaluated in DUS trials (Distinctness, Uniformity and Stability Trial) in Goianira-GO, in the 2012/13 agricultural year.The cultivar was also evaluated regarding grain cooking quality by Embrapa Rice and Beans, with gelatinization temperature and apparent amylose content classified as intermediate.

PERFORMANCE
VCU experiments have been carried out with 25 genotypes, including five controls.The experiments were carried out under continuous flood irrigation in lowlands in the Experimental Farm of EPAMIG, in the municipalities of Janaúba, Lambari, Leopoldina, and Prudente de Morais.Table 1 shows the geographical coordinates of these municipalities.
The experimental design was a randomized block with four replications.Plots consisted of five 5 m long rows, spaced 0.3 m apart.The central 4m of the 3 internal rows were considered the useful plot.Sowing density was 300 seeds m -2 .In each agricultural year, lines with inferior performance were replaced by supposedly better lines; however, the five control cultivars remained throughout the evaluation period, except for Jequitibá, which did not participate in the VCU trials in 2009/10.Planting fertilization consisted of 500 kg ha -1 of the 08-28-16 + Zn formula.In topdressing, it was applied 200 kg ha -1 of the 20-05-20 fertilizer, in two plots, being the first at 30 days, and the second at 60 days after sowing, respectively.Weeds were controlled by hoeing and by the application of herbicides.Disease control was not carried out in order to enable the plant's emergence and discarding of susceptible lines.The implementation of field trials occurred from the first ten days of October until the second ten days of December of each year, depending on local weather conditions.

PC Soares et al.
The main agronomic characteristics evaluated were: leaf color, pubescence, angle of flag leaf, tillering, mean flowering, full maturation cycle, plant height, lodging, resistance to diseases, glumes color, apiculus color at maturity, presence of awns, shaterring, mean length of panicles, grain yield, dehulled grain size, weight of 100 grains, grain class, whole grain yield and broken grain yield, gelatinization temperature, and amylose content.These evaluations were carried out according to Embrapa (1977).Statistical analysis was carried out for grain yield every agricultural year, and combined analysis was performed with six genotypes common to the five agricultural years (2004/05 to 2009/10), using the GENES software (Cruz 2006).Table 2 shows the means of grain yield obtained in 10 VCU trials carried out in Minas Gerais during five agricultural years (2004/05 to 2009/10) for BRSMG Rubelita and control cultivars (Jequitibá, Rio Grande, Ourominas, Seleta and Predileta).It was observed that the new cultivar BRSMG Rubelita, with overall mean of 6178 kg ha -1 (Table 2), did not significantly differ (p>0.05) from the control cultivars Seleta, Rio Grande, Ourominas and Predileta; however, it had higher (5.31%) grain yield than Jequitibá.
Nevertheless, the new cultivar presented grain yield inferior to that of cultivar Seleta.It should be noted that Seleta presents excellent growth performance in commercial fields, with great grain quality and resistance to major diseases that attack rice crops.Seleta has been recently released for the state of Minas Gerais (Soares et al. 2005).Predileta is the other irrigated rice cultivar for lowlands in the state of Minas Gerais with excellent performance in commercial fields (Soares et al. 2008).
Table 3 shows the main botanical, morphological and phenological characteristics evaluated for cultivar BRSMG Rubelita.The cultivar fits the plant modern group; it is a medium-sized plant (95-100 cm plant height), with upright, light-green colored leaves, high tillering, and resistance to lodging.It is moderately resistant to major diseases that attack rice (leaf and panicle blast, brown spot, grain spot, and leaf scald).At maturity, the glumes are straw-colored, the apiculus are yellow with the presence of awns of varying size.The maturation cycle is of about 135 days.Table 4 shows the result of the analysis of some grain characteristics of BRSMG Rubelita.The grains are long and thin, translucent, loose and soft after cooking, due to the amylose content and to the intermediate gelatinization temperature, which meets the market requirements.This cultivar has excellent performance in relation to whole grains yield in the processing (over 55%), according to Vieira and Rabelo (2006).
Cultivar BRSMG Rubelita apresents long and thin grains ("agulhinha"), which are the most valued in the Brazilian market.For the grains to be classified as long and thin, they must present at least 80% of whole grains measuring 6.00 mm or more in length, 1.90 mm in width, and the length/ width ratio must exceed2.75 after polishing (Vieira and Rabelo 2006).Table 4 shows the dimensions of the grains of the new cultivar (long and thin).
In summary, BRSMG Rubelita associates very interesting characteristics, which are valued by rice farmers, such as: yield potential, medium cycle, lodging resistance, tolerance/resistance to major diseases, long and thin grains, high whole grains yield in the processing, and good cooking quality.Thus, this new cultivar can greatly contribute with rice crops of the state of Minas Gerais.
Cultivar BRSMG Rubelita, for its high genetic potential for grain yield, and for presenting other relevant characteristics, was released for lowland cropping under continuous flood irrigation, throughout the state of Minas Gerais.

SEED AND PRODUCTION DITRIBUITION
BRSMG Rubelita is registered in the Ministry of Agriculture under the number 33218.The Company of Agricultural Reaseach of Minas Gerais -EPAMIG is responsible for the production of genetic seeds, while the basic seed production is in charge of EPAMIG and EMBRAPA.Production stages of certified or inspected seeds are outsourced through agreements with seed producers.

Table 1 .
Geographical data of the location where VCU trials of the lowland rice breeding program of the state of Minas Gerais, Brazil, were carried out Source: United States Department of State Geographer (2013).Software Google Earth.

Table 3 .
Plant characteristics of the cultivar BRSMG Rubelita

Table 2 .
Mean grain yield (kg ha -1 ) of BRSMG Rubelita and of the control cultivars in VCU trials carried out in Minas Gerais, in the period from 2004/05 to 2009/10