Crop Breeding and Applied Biotechnology - 20(3): e323420318, 2020 Amazonian Robustas - new Coffea canephora coffee cultivars for the Western Brazilian Amazon

: Amazonian Robustas are ten new clones of high yield potential with characteristics typical of the botanical varieties conilon and robusta. With in dividual registration, the new cultivars were developed to be grown together with other clones, with flexibility of composition of the crops according to the preference of the producer.


INTRODUCTION
Coffee production in the state of Rondônia (RO) developed from the cultivation of C. canephora plants with characteristics of the botanical varieties conilon and robusta. The conilon botanical variety is distinguished by its small size, greater tolerance to water stress, and less resistance to coffee leaf rust (Hemileia vastatrix). In turn, the robusta botanical variety has greater resistance to rust and to root-knot nematode (Meloidogyne spp.), fruit with greater potential for preparing specialty coffee beverages, and taller plants that are less tolerant to water stress (Charrier and Eskes 2004). From the natural or directed breeding of plants of these two botanical varieties, hybrid plants appear, which can combine the best characteristics of the two varieties (Rocha et al. 2015, Oliveira et al. 2018.
In order to offer new options for growers and increase the genetic variability of coffee in the Western Amazon, Embrapa Rondônia has developed ten new cultivars with high yield potential and agronomic characteristics typical of the conilon and robusta botanical varieties.
The development of these cultivars is the result of 16 years of research, initiated in 2003 with controlled hybridization between parent plants of the conilon and robusta varieties from the Embrapa Active Germplasm Bank (Souza et al. 2013). The most notable advances obtained from development of these cultivars include the following: the individual clone record, the hybrid nature of the cultivars, and the wealth of information on each cultivar.
With individual registration, the new cultivars were developed for growing together with other clones and flexibility of crop composition based on growers' AL Teixeira et al.
preferences. To that end, evaluations of yield potential, resistance to pests and diseases, beverage quality, plant spacing, management practices, and compatibility between clones were considered.
As a result of their hybrid nature, the best characteristics of the conilon and robusta botanical varieties are expressed, associated with the greater vigor of the hybrid plants. The intermediate size, resistance to rust (H. vastatrix) and nematodes (Meloidogyne incognita -EI2), and the potential for higher beverage quality are some of the characteristics observed in the cultivars.
The information obtained on the new cultivars is the result of experiments carried out in different environments, in the field, greenhouse, and laboratory, considering specific crop traits, such as yield, compatibility, response to biotic stresses, and beverage quality.

METHODS
The name of each cultivar consists of the acronym BRS, which begins the name of cultivars released by Embrapa, and four numerical digits that express the compatibility group, the maturation cycle, and the cultivar identification number ( Table 1). The first digit identifies the compatibility group to which the clone belongs, which can be one (1), two (2), or three (3). The second digit refers to the maturation cycle, differentiating early, intermediate, and late, identified respectively by the numbers one (1), two (2), and three (3). The last two digits are the cultivar identification number (Table 1). Thus, clone 1216 (read twelve, sixteen) is part of compatibility group 1, has an intermediate maturation cycle, and its identification number is 16 (sixteen).

Yield
Yield is affected both by plant yield potential and by environmental conditions, such as climate, soil, and management techniques (Fonseca et al. 2004, Partelli et al. 2019, Moraes et al. 2020. Although all cultivars have a yield potential greater than 100 bags per hectare, there is genetic variability among the selected plants, which supports their classification in three distinct categories. The cultivars BRS 1216, BRS 2336, BRS 3210, and BRS 3213 have the greatest yield potential, an average of 80.75 bags ha -1 over three years, evaluated in four environments in the states of Rondônia and Acre (Table 3). The cultivars BRS 2299, BRS 3137, and BRS 3220 have potential yield of more than 110 bags of processed coffee, with an average of 66.00 bags ha -1 over three years, evaluated in four environments in the states of Rondônia and Acre (Table 3). The cultivars BRS 2314, BRS 2357, and BRS 3193 have potential yield of more than 100 bags of processed coffee, with an average of 61 bags ha -1 over three years (Table 3).

Compatibility between cultivars
Fruit production of C. canephora coffee depends on pollination between compatible plants. The impossibility of pollination between incompatible clones is a trait of this species of great importance for clonal cultivation (Rocha et al. 2013, Ferrão et al. 2017. Two plants are considered compatible when they are clustered in different compatibility groups. Although in the African continent, the center of origin of this species, six distinct compatibility groups have been reported, in Brazilian coffee plantations only three compatibility groups have been observed (Moraes et al. 2018). Based on targeted pollinations and fluorescence microscopy, the clones under evaluation were clustered into three different compatibility groups (Table 1).
To increase pollination efficiency, the use of pollinator lines or the cultivation of a minimum number of clones is considered. Technically, the cultivation of six clones, two from each compatibility group, in equal proportions, provides good pollination efficiency. However, when clone compatibility is not known, cultivating around nine clones is recommended to achieve high pollination efficiency.

Responses to biotic stresses
Each cultivar has its own characteristics, reflected in different responses of resistance to the main coffee diseases. When choosing the best genotypes to form a coffee plantation, it is important to consider that there is no perfect cultivar that brings together all the desired characteristics and has a superior response in all environments. Thus, the selection of cultivars must take into account the intended management conditions. Currently, the diseases that most damage coffee crops in Brazil are coffee leaf rust, caused by Hemileia vastatrix, and root-knot nematode, caused by species of the genus Meloidogyne. Less aggressive and of difficult diagnosis, Meloidogyne exigua is the most widespread species that causes damage to Coffea arabica plants. The species Meloidogyne incognita -EI2 has occurred most in C. canephora cultivation in the state of Rondônia (Santos et al. 2018).  AL Teixeira et al.
Assessments carried out over a three-year period, in the field and greenhouse, were interpreted to determine manifestation of rust resistance. Less than 1% diseased plants in a population characterize resistant clones, whereas higher percentages characterize susceptible clones (Table 4).
The resistance response to nematodes was evaluated based on tests conducted in a greenhouse in Porto Velho and Ji-Paraná, RO. Clones considered susceptible through observation showed root knots, eggs, and juveniles of the nematode in the roots exceeding the established standards (Santos et al. 2018). When choosing clones for planting, care should be taken when using clones considered to be very susceptible in areas whose history indicates high nematode infestation (Table 4).

Beverage quality
For a long time, C. canephora beans were used only for blends with arabica coffee beans. However, more recently, the beverage quality of the beans from this coffee tree has been appreciated for aroma and flavor traits: less sweetness, less acidity, and greater bitterness (Souza et al. 2018). According to the Fine Robusta protocol, the main organoleptic attributes for evaluation of the Canephora species are aroma, flavor, aftertaste, salt/acidity ratio, bitterness/sweetness ratio, mouth-feel, cup balance, uniformity, cleanness, and overall aspects. The average score for each attribute is used to obtain a final score, which ranges from 0 to 100, and classifies the beverage according to its quality.
Among the ten new hybrid cultivars recommended for cultivation in the Amazon region, the BRS 2314 cultivar is noteworthy. According to the Fine Robusta cupping protocol, it had an average score of 83.8, ranging from 80 to 87.2 points in different environments of the states of Rondônia and Acre. The main characteristics of its beverage are sweetness and a chocolate flavor. It also has nuances of citrus fruits and almonds, creating a balanced mixture with pleasant acidity.
The BRS 1216 and BRS 3220 cultivars are noteworthy for their potential to produce coffee beans with specialty coffee quality. The BRS 1216 cultivar achieved an average score of 79.6 points, ranging from 78.3 to 80 points; it has medium sweetness, with chocolate flavor and aroma. The BRS 3220 cultivar, in turn, created a beverage with a combination of almond and pepper flavors and brief aftertaste. It obtained an average score of 79.1, ranging from 76 to 82 points.
The other cultivars have beverage quality considered good, without prominent beverage attributes (Table 5). In general, they have neutral beverages, low sweetness, and discreet aroma, attributes that are valued by the soluble coffee industry and for composition of blends with arabica.

Foundation seed production
A Basic Plant Field is maintained by Embrapa at its Experimental Station in Ouro Preto do Oeste (lat 10º 43' 55'' S, long 62º 15' 19'' W, alt 237 m asl), RO, which serves as a repository for the cultivars. Cuttings (vegetative propagules) from the basic plant field were made available to private nurseries, associations, and public institutions through a partnership contract established between the interested party and Embrapa. Currently, 11 nurseries have authorization for commercial production, ten in the state of Rondônia and one in the state of Amazonas, and 30 observation units have been established in ten other states of Brazil, including all its regions.