New cassava cultivars for starch and flour production in the Cerrado of Central Brazil

The cassava cultivars BRS 417, BRS 418 and BRS 419 are the first specifically developed for flour and starch production in the Cerrado biome of Central Brazil. They are promising for higher yields, lower production costs (mechanical planting) and the increase of genetic variability in cassava crops.


INTRODUCTION
Cassava root in Brazil is mainly grown for industrial purposes such as flour and starch production. Cassava flour is mostly produced by small industrial family units across the Brazilian territory, although there are some larger companies in the business, mainly in the states of Paraná, Santa Catarina and Mato Grosso do Sul (Valle and Lorenzi 2014). Starch, on the other hand, is usually produced at larger scales, although there are small units spread throughout Brazil, concentrated in the states of Paraná, Mato Grosso do Sul, São Paulo and Santa Catarina.
In the states where large cassava processing industries predominate, cassava cultivation has come under increasing competitive pressure for cultivation areas with other crops such as soybean, maize and sugarcane (Vilpoux 2008). This indicates the need for a diversification of the cassava cultivation areas for industrial use (flour or starch production) in Brazil.
The ecoregion of the Cerrado, which covers about 23% of the Brazilian territory (Klink and Machado 2005), is regarded as one of the world's last agricultural frontiers (Sano et al. 2019). The climate and soil in this region are favorable for cassava cultivation, i.e., the Cerrado is an alternative cultivation area for the diversification of cassava production areas in Brazil.
In spite of the production potential of the Brazilian Cerrado region for cassava, currently only 13.4% of the crop area and 11.8% of the national cassava output are located in the region, where a mean yield of only 13.02 t ha -1 is produced on an area of 210,826 ha (IBGE 2016). Two factors are the major causes for this low cassava production in the region: insufficient application of modern agricultural technologies by producers (lack of knowledge and/or financial difficulties); and lack of cultivars developed and selected specifically for flour and starch production in this biome.

EA Vieira et al.
To solve the above problems, the cassava breeding program of Embrapa Cerrado addressed the development of specific cultivars for flour and/or starch production in the Cerrado region of Central Brazil. Ideal cultivars should produce high starch yields, have white pulp, be resistant to pests and diseases and have a favorable architecture for crop management and mechanical planting (adaptation to large-scale cultivation) (Carvalho et al. 2011, Vieira et al. 2018, 2019.
To meet the demand for cassava flour and starch production, specific cultivars for the cultivation conditions of the Cerrado of Central Brazil are being released by Embrapa Cerrados, namely the cultivars BRS 417, BRS 418 and BRS 419.

BREEDING METHOD
The cassava cultivars BRS 417, BRS 418 and BRS 419 for flour and/or starch production were selected from segregating populations, derived from crosses among varieties deposited in the Banco Regional de Germoplasma do Cerrado (BGMC), namely: BGMC 1304 (clone 9661/06) x BGMC 788 (IAC 14), BGMC 1304 (clone 9661/06) x BGMC 56 (Branca de Santa Catarina) and BGMC 982 (IAPAR 19) x BGMC 436 (IAC 12-829), respectively. The crosses were made in the 2007/2008 growing season. The resulting seeds were taken to the laboratory and soaked in water to test their viability; floating seeds were immediately discarded and the submerged ones dried at room temperature. The seeds were left to germinate in a greenhouse and the seedlings transferred to the field 45 days after emergence.
In all breeding stages, the crops were planted in November of the respective year and the recommendations for cassava cultivation in the Brazilian Cerrado were implemented in all treatments . In two selection cycles (2008/2009 and 2009/2010), evaluations were carried out 12 months after planting, while in the other selection cycles, the agronomic evaluations were performed 18 months after planting.
As the cassava plants grown from seeds have a pivotal root system, the main selection criteria applied in the first selection cycle (growing season 2008/2009) were: i) white tuberous root pulp; ii) architecture (high plant height and high height of the first branch); and iii) bacterial resistance. The selected seedlings were cloned and planted in the field from stem cuttings, in rows of five plants, at a spacing of 0.60 between plants and 1.00 between rows, prior to the second selection cycle.
In the second selection cycle (2009/2010), when cassava plants began to be propagated vegetatively by stem cuttings, and when they had developed a tuberous root system typical of commercial plantations, the following selection criteria were addressed: i ) architecture (high plant height and high first branch height); ii) bacterial resistance; iii) root yield; and iv) starch content in tuberous roots. The clones selected in this selection cycle were planted in blocks of five rows spaced 1.00 m with five plants spaced 0.60 apart, followed by the third selection cycle.
The third selection cycle (2010/2012) was also carried out at Embrapa Cerrados. The same criteria as during the second cycle were used for selection. The clones selected in the third selection cycle were subjected to the distinguishability, homogeneity and stability tests of cassava (Manihot esculenta Crantz) cultivars of the Ministry of Agriculture, Livestock and Food Supply (MAPA), in the 2011/2013 and 2012/2014 growing seasons. At this stage, in addition to the parameters evaluated in the previous two selection cycles, the root hydrocyanic acid content (HCN -in mg kg -1 ) of five randomly selected storage roots per plot was also estimated, based on the qualitative method described by Willams and Edwards (1980).

PERFORMANCE CHARACTERISTICS
The The crops were planted in November and harvested 18 months later. The agricultural practices were applied according to the recommendations for cassava cultivation in the Brazilian Cerrado . The experiment was arranged in a randomized complete block design with three replications. Each plot consisted of four 10-plant rows, spaced at 0.60 m between plants and 1.00 m between rows, and 16 plants per plot were evaluated.
Cultivar IAC 12-829 was used as control, identified as 'BGMC 436' in the Cerrado Cassava Germplasm Bank (BGMC), which is the most widely planted cultivar in the Cerrado region of Central Brazil.
The following traits were assessed in the harvested cassava plants: i) height of the first branch (FBH -in m); ii) plant height (PH -in m); iii) root weight (RW -in kg ha -1 ); iv) starch percentage in roots (RSt) by the hydrostatic balance method; and v) starch yield (StY -in kg ha -1 ).
The new cassava cultivars BRS 417, BRS 418 and BRS 419 for flour and/or starch production and the control have a high starch yield per hectare and moderate bacterial resistance and an advantageously high first branch height (FBH) and high plant height (PH) (Tables 1 and 2). Both FBH and PH are important traits, for being correlated with ease of cultivation, availability of stem cuttings and suitability for mechanical planting; genotypes with a higher FBH and total PH are therefore preferred (Vieira et al. 2018).
Suitability for mechanical planting is essential for cassava cultivation in the Cerrado region of Central Brazil, where predominantly medium and large crops are grown. This is an issue, since the currently recommended cultivar, the most planted in the region (cv. IAC 12-829), is unfit for mechanical planting (Vieira et al. 2015).
Cultivar BRS 417, with a mean root yield of 38.005 kg ha -1 , root starch percentage of 31.53%, starch yield of 11,984 kg ha -1 and favorable architecture for mechanical planting, has the advantage of medium-length roots (which greatly facilitates mechanical harvesting). On the other hand, cv. BRS 418 has a mean root yield of 38,940 kg ha -1 , a root starch percentage of 32.35%, starch yield of 12,651 kg ha -1 , a favorable architecture for mechanical planting, and a light brown external root color (which facilitates peeling in the processing industry). Lastly, cv BRS 419 has a mean root yield of 42,010 kg ha -1 , root starch percentage of 30.29%, starch yield of 12,870 kg ha -1 , a favorable architecture for mechanical planting and produces the highest absolute mean starch yield.
In summary, the cultivars BRS 417, BRS 418 and BRS 419 are promising new options of cultivation for cassava producers in the Cerrado region, with a view to increasing yields and reducing production costs (mechanical planting), aside from increasing the genetic diversity of crops.

REGISTRATION, PROTECTION, BASIC PLANT STOCK AND LICENSED SEED MANUFACTURERS
The cultivars BRS 417, BRS 418 and BRS 419 for starch and flour production were registered by the National Cultivar Registry (RNC) and the National Plant Variety Protection Service (SNPC) of the Ministry of Agriculture, Livestock and