A major indicator of an improvement programmes efficiency comprises the cultivars released for commercial planting. Thus, one can infer that the Brazilian programme for improving populations through recurrent selection is efficient. In only 12 years of existence, it has succeeded in releasing SCSBRS 113-TioTaka for cultivation in the State of Santa Catarina. This irrigated rice cultivar is the first to be released for commercial planting in Brazil from a line derived from a population being improved through recurrent selection. Indeed, it is the first such cultivar to be released, not only in Brazil, but also in the world.
Santa Catarina is the third largest rice-producing state and second for irrigated rice in Brazil. It has an area of 130,000 hectares planted to rice and produced about 934,000 tons in the 2001/02 cropping season (CONAB, 2002). In this state, small farmers predominate, cultivating, on average, 6 ha with an average yield of 6.5 t ha-1, but with yields as high as 13 t ha-1 being frequent.
Origin of cultivar SCSBRS 113- TioTaka
Cultivar SCSBRS 113-TioTaka originates from the recurrent selection population CNA-IRAT 4, which was synthesized from the crosses of 10 varieties or lines of the indica group. Nine varieties were used as male parents in crosses with IR36 (msms), which was the source of genetic male sterility. F1 individuals were crossed as male parents with the varieties, to have the 9 cytoplasms represented in the population. F2 seeds of heterozygous plants were mixed, forming population CNA-IRAT 4/0/0. This population underwent three recombination cycles to give rise to population CNA-IRAT 4/0/3 (Rangel and Neves, 1997).
The procedure for population improvement began with the visual selection and development of 100 S0:1 families, of which 15 were harvested and 10 plants per family selected. The selected plants were crossed, giving rise to population CNA-IRAT 4/1/1, of which 164 early maturing and 164 intermediately maturing S0:1 plants were selected to progress to S0:2.
In the 1992/93 cropping season, these families were evaluated in the states of Goiás, Tocantins, Paraná, Rio Grande do Sul (two sites) and Santa Catarina.
Considering the data on means, mainly of yield, the 50 best early and intermediately maturing families were selected in trials carried out in the states of Rio Grande do Sul and Santa Catarina.
These families were recombined between harvests in the Experimental Field of Formoso do Araguaia, constituting, respectively, populations CNA-IRAT 4P/2/1 (short cycle) and CNA-IRAT 4M/2/1 (intermediate cycle).
The selected families were also incorporated into Embrapa Arroz e Feijãos programme for extracting lines. Of these, family no. 75 was submitted to two new cycles of plant selection, and several lines were obtained. Of these lines, after evaluation for various agronomic traits, CNA-8644 stood out sufficiently to become part of the National Network for Evaluating Irrigated Rice (RENAI, its Portuguese acronym).
Obtaining cultivar SCSBRS 113-TioTaka
Figure 1 shows the procedure for obtaining SCSBRS 113-TioTaka. The stages followed were:
Fertile plants selected from population CNA-IRAT 4M/2/1 at the Experimental Field of Fazenda Palmital, Goiás, in the 1991/92 cropping season.
S0:1 families advanced to S0:2 at the Experimental Field of Formoso do Araguaia, Tocantins, between harvests, 1992.
In the 1992/93 cropping season, 164 S0:2 families that were early or intermediately maturing were evaluated in trials set up with a triple-lattice (10 × 10 and 8 × 8) experimental design at two sites in the State of Rio Grande do Sul and one site in the State of Santa Catarina. Considering mainly the mean yield across the three sites, family no. 75, presenting an intermediate cycle, was selected.
In the 1993/94 cropping season, using the genealogical method, individual plants within family no. 75 were selected at the Experimental Field of Palmital Farm.
A new selection of individual plants and elimination of the male-sterility gene were carried out at the Experimental Field of Palmital Farm, in the 1994/95 cropping season.
Line CNA-IRAT 4M/2/1-75-B-B-2-2 in the S4:5 generation was advanced to the S4:6 generation: (CNA-IRAT 4M/2/1-75-B-B-2-2-B) between harvests, 1995, at the Experimental Field of Formoso do Araguaia to accelerate homozygosis and increase seed quantity for the first phenotypic evaluations.
In the 1995/96 cropping season, line CNA-IRAT 4M/2/1-75-B-B-2-2-B was named CNA-8644. It was evaluated on a preliminary basis on experimental plots at the Palmital Farm for yield, resistance to diseases, and grain quality for industrial and culinary purposes.
Line CNA-8644 was made available to other Brazilian research institutions for evaluation through the network of Observation Trials for Irrigated Rice (EOB-I, its Portuguese acronym), in the 1996/97 cropping season. It performed best in the State of Santa Catarina, and was selected to continue in more advanced trials.
Figure 1. Procedure used to obtain the irrigated rice cultivar SCSBRS 113-TioTaka from a line originating from population CNA-IRAT 4, which was improved through recurrent selection.
Evaluation in the State of Santa Catarina
In the 1997/98 cropping season, CNA-8644, known as SC 169 in the State of Santa Catarina, was first evaluated with 43 other lines. It stood out for its high yield, resistance to blast and tolerance of iron toxicity, and was promoted to advanced trials.
In 1998/99, it was evaluated in the advanced yield trial, together with 15 other genotypes. This experiment aimed to evaluate all agronomic traits of economic interest and, especially, resistance to lodging, the principal trait a variety should have to be adopted into the pre-germination cropping system that predominates in the State of Santa Catarina. Pre-germinated seeds of lines were planted into a layer of water, 15 to 20 cm deep. The irrigation conditions were held until maturity to increase selection pressure for resistance to lodging. This experiment was carried out at three sites in the state. Again, CNA-8644 was selected for its superior performance.
From 1999/00 to 2001/02, CNA-8644 was evaluated in regional yield trials in Santa Catarina that aimed principally to define the lines that would be released as new irrigated rice cultivars for the state. The trial comprised nine genotypes: eight lines (SC 162, SC 13, SC 164, SC 165, SC 167, SC 168, SC 169 and SC 170) and a check (Epagri 108). It was conducted under the pre-germination cropping system at six sites (Itajaí, Joinville, Massaranduba, Pouso Redondo, Tubarão and Turvo) for three cropping seasons.
The experimental design used was random complete blocks with three replications representing the years of evaluation. The plot had a total area of 60 m2. Data were collected on grain yield in kg ha-1 (GY), lodging (LOD), plant height (PH), planting to harvest cycle, whole- (WGY) and broken-grain yield (BRG), amylose content (AC), gelatinization temperature (GELT), tolerance of iron toxicity (FeTox) and resistance to leaf blast.
Table 17 shows the data collected from the trials. Cultivar SCSBRS 113-TioTaka was the most productive with a mean of 8561 kg ha-1 across 18 treatments. It was also resistant to lodging, had a plant height of about 100 cm and a cropping cycle from emergence to harvest of 141 days, which is considered long. In the evaluations for grain industrial traits, SCSBRS 113-TioTaka showed a 63% wholegrain yield, which is considered very good and suitable for parboiling. Its grain appeared vitreous when polished and parboiled. In cooking trials, the grains were loose and firm, with a normal aroma.