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Pesquisa Agropecuária Brasileira

Print version ISSN 0100-204X

Pesq. agropec. bras. vol.49 no.5 Brasília May 2014 


Field performance of new cowpea cultivars inoculated with efficient nitrogen-fixing rhizobial strains in the Brazilian Semiarid

Desempenho em campo de novas cultivares de feijão-caupi inoculadas com estirpes de rizóbio eficientes na fixação de nitrogênio no Semiárido brasileiro

Rita de Cássia Nunes Marinho1 

Rafaela Simão Abrahão Nóbrega2 

Jerri Édson Zilli3 

Gustavo Ribeiro Xavier3 

Carlos Antônio Fernandes Santos4 

Saulo de Tarso Aidar4 

Lindete Míria Vieira Martins5 

Paulo Ivan Fernandes Júnior4 

1Universidade Federal do Piauí, Campus Professora Cinobelina Elvas, Rodovia BR-135, Km 03, Planalto Horizonte, CEP 64900-000 Bom Jesus, PI, Brazil. E-mail:

2Universidade Federal do Recôncavo da Bahia, Centro de Ciências Agrárias, Ambientais e Biológicas, Rua Rui Barbosa, nº 710, Centro, CEP 44380-000 Cruz das Almas, BA, Brazil. E-mail:

3Embrapa Agrobiologia, BR 465, Km 7, CEP 23890-000 Seropédica, RJ, Brazil. E-mail:,

4Embrapa Semiárido, BR 428, Km 152, Caixa Postal 23, CEP 56302-970 Petrolina, PE, Brazil. E-mail:,,

5Universidade do Estado da Bahia, Departamento de Tecnologia e Ciência Sociais, Avenida Edgard Chastinet Guimarães, s/nº , São Geraldo, CEP 41150-000 Juazeiro, BA, Brazil. E-mail:


The objective of this work was to evaluate the contribution of efficient nitrogen-fixing rhizobial strains to grain yield of new cowpea cultivars, indicated for cultivation in the Brazilian Semiarid region, in the sub-medium of the São Francisco River Valley. Two experiments were set up at the irrigated perimeters of Mandacaru (Juazeiro, state of Bahia) and Bebedouro (Petrolina, state of Pernambuco). The treatments consisted of single inoculation of five rhizobial strains - BR 3267, BR 3262, INPA 03-11B, UFLA 03-84 (Bradyrhizobium sp.), and BR 3299T(Microvirga vignae) -, besides a treatment with nitrogen and a control without inoculation or N application. The following cowpea cultivars were evaluated: BRS Pujante, BRS Tapaihum, BRS Carijó, and BRS Acauã. A randomized complete block design, with four replicates, was used. Inoculated plants showed similar grain yield to the one observed with plants fertilized with 80 kg ha-1 N. The cultivars BRS Tapaihum and BRS Pujante stood out in grain yield and protein contents when inoculated, showing their potential for cultivation in the sub-medium of the São Francisco River Valley.

Key words: Bradyrhizobium; Microvirga vignae; Vigna unguiculata; biological nitrogenfixation; inoculant


O objetivo deste trabalho foi avaliar a contribuição de estirpes de rizóbio, eficientes na fixação de nitrogênio, sobre a produção de grãos de novas cultivares de feijão-caupi, indicadas para cultivo no Semiárido brasileiro, no Submédio do Vale do Rio São Francisco. Dois experimentos foram implantados nos perímetros irrigados de Mandacaru (Juazeiro, BA) e Bebedouro (Petrolina, PE). Os tratamentos consistiram da inoculação isolada de cinco estirpes de rizóbio - BR 3267, BR 3262, INPA 03-11B, UFLA 03-84 (Bradyrhizobium sp.) e BR 3299T (Microvirga vignae) -, além de um tratamento com nitrogênio e de um controle sem inoculação ou aplicação de N. As seguintes cultivares de feijão-caupi foram avaliadas: BRS Pujante, BRS Tapaihum, BRS Carijó e BRS Acauã. Utilizou-se o delineamento experimental de blocos ao acaso, com quatro repetições. As plantas inoculadas apresentaram produtividade de grãos similar à observada em plantas adubadas com 80 kg ha-1 de N. As cultivares BRS Tapaihum e BRS Pujante destacaram-se quanto à produtividade e ao teor de proteínas nos grãos, quando inoculadas, o que mostra seu potencial para cultivo na região do Submédio do Vale do São Francisco.

Palavras-Chave: Bradyrhizobium; Microvirga vignae; Vigna unguiculata; fixação biológica de nitrogênio; inoculante


Cowpea [Vigna unguiculata (L.) Walp] has great importance in the Brazilian Semiarid region, especially for small farmers. This crop is mainly cultivated for the production of dry and green beans for human consumption, and it is considered an essential source of proteins, carbohydrates, fibers, vitamins, and minerals for the populations in the Semiarid region of northeastern Brazil (Santos et al., 2008). According to Freire Filho (2011), the area cultivated with cowpea in the Northeast region achieved almost 1.3 million hectares and produced more than 382 thousand tons, with productivity around 330 kg ha-1 in 2009.

Water and thermal stresses in the Semiarid region, as well as the few technological resources available for use in cowpea cropping systems, are the main responsible for the low productivity in the region (Fernandes Júnior & Reis, 2008; Fernandes Júnior et al., 2012). Some low-cost technologies can contribute to increase cowpea production in the Brazilian Northeast. Among these, the use of inoculants containing selected efficient rhizobia strains can be highlighted. The use of rhizobial inoculants has beneficial economic and environmental impacts for leguminous crops (Moreira & Siqueira, 2006; Araújo et al., 2012). Currently, four Bradyrhizobium strains (BR 3267, BR 3262, INPA 03-11B, and UFLA 03-84) are authorized for use in the commercial production of cowpea inoculants in Brazil (Martins et al., 2003; Lacerda et al., 2004; Zilli et al., 2009). However, the rather insignificant productive response of cowpea genotypes to inoculation resulted in low diffusion of the technology among farmers in the Semiarid region. Nevertheless, over the past few years, researches have shown that some rhizobial strains, with high agronomic efficiency, can increase the productivity of cowpea in the region (Almeida et al., 2010; Costa et al., 2011; Fernandes Júnior et al., 2012; Freitas et al., 2012; Ferreira et al., 2013; Alcantara et al., 2014).

Despite these studies, there is still a lack of knowledge on the efficiency of these strains at the sub-medium of the São Francisco River Valley. Martins et al. (2003) studied the agronomic efficiency and the competitive ability of the strain BR 3267 and those results supported its inclusion in the list of bacteria used as cowpea inoculants. Up to now, field evaluations of the other three strains available for cowpea inoculation were not carried out in the region. Additionally, the field performance of the promising new strain BR 3299T, isolated from cowpea grown in the state of Sergipe and recently described as the new specie Microvirga vignae (Radl et al., 2014), in the São Francisco River Valley, still needs to be assessed.

Moreover, the interaction between macro- and microsymbionts is an important factor that affects productive response to inoculation (Alcantara et al., 2014). The evaluation of this interaction might make it possible to more properly indicate specific inoculants, enhancing the technical recommendations for cowpea genotypes.

The inoculation response of new cowpea genotypes developed for the Brazilian Semiarid region has not yet been assessed. Among the newly developed cultivars, only the "Mulato" type, BRS Pujante, had its responses to inoculation studied and has been proven to be highly responsive to the practice (Chagas Junior et al., 2010). The "Canapu" type, 'BRS Acauã'; the "Fradinho" type, 'BRS Carijó'; and the black-coated 'BRS Tapaihum' have short cycle and high levels of minerals and micronutrients in grains (Santos et al., 2008; Santos, 2011); but, in spite of their favorable technological features, the efficiency of their association with rhizobia is still unknown.

The objective of this work was to evaluate the contribution of efficient nitrogen-fixing rhizobial strains to the development and grain yield of new cowpea cultivars, indicated for cultivation in the Brazilian Semiarid region, in the sub-medium of the São Francisco River Valley.

Materials and Methods

Two experiments were carried out under field conditions. In both assays, the inoculation treatments consisted of four strains of Bradyrhizobium sp.: BR 3267 (SEMIA 6462), BR 3262 (SEMIA 6464), INPA 03-11B (SEMIA 6463), and UFLA 03-84 (SEMIA 6461). These strains are officially indicated for cowpea inoculant production in Brazil (Brasil, 2011). Besides them, the strain BR 3299T was also evaluated. Besides the inoculation treatments, a treatment with N fertilization and a control without inoculation and without N were assessed. The N fertilization treatment was equivalent to 80 kg ha-1 N, applied as urea, split in two times. The cowpea cultivars BRS Pujante, BRS Tapaihum, BRS Acauã, and BRS Carijó were evaluated. The rhizobial strains were supplied by the Johanna Döbereiner Culture Collection of Diazotrophic Bacteria, from Embrapa Agrobiologia, Seropédica, state of Rio de Janeiro. The cowpea seeds were acquired in Petrolina, state of Pernambuco, from Embrapa Produtos e Mercados.

The experiments used a factorial arrangement of five inoculation plus control treatments per four cultivars (7x4), in a total of 28 treatments. A randomized complete block design was used, with four replicates. The experimental plots measured 12 m2 and consisted of eight 3-m lines. A 0.50x0.25-m spacing between plants was adopted, in accordance to the agronomical recommendations for the crop.

The first experiment was carried out from June to August 2012, in the irrigated perimeter of Mandacaru, at the Mandacaru Experimental Field (MEF) (09º24'S, 40º26'W) of Embrapa Semiárido, in Juazeiro, state of Bahia. The soil of the area is classified as Vertissolo Háplico (Vertisol) (Santos et al., 2013), with a clayey texture. The second experiment was carried out from December 2012 to February 2013, at the Bebedouro Experimental Field (BEF) (09º09'S, 40º22'W), located at the Bebedouro irrigated perimeter of Embrapa Semiárido, in Petrolina, state of Pernambuco. The soil is classified as Argissolo Amarelo distrófico (Ultisol), with a sandy loam texture. The soils from both experimental areas were prepared with a plowing and a harrowing.

The soil at the MEF showed the following chemical attributes (Claessen, 1997): pH, 6.8; P, 44.62 mg dm-3; K, 0.36 mg dm-3; Ca2+, 20.4 cmolc dm-3; Mg2+, 5.6 cmolcdm-3; Al3+, 0.05 cmolc dm-3; H+Al3+, 4.62 cmolc dm-3; S, 26.45 cmolc dm-3; CTC, 31.07 cmolc dm-3; V, 85%; and organic matter, 7.2 g kg-1. The soil at the BEF had the following chemical characteristics: pH, 6.3; P, 11.92 mg dm-3; K, 0.33 mg dm-3; Ca2+, 2.0 cmolc dm-3; Mg2+, 0.4 cmolc dm-3; Al3+, 0.05 cmolc dm-3; H+Al3+, 0.66 cmolcdm-3; S, 2.78 cmolc dm-3; CTC, 3.44 cmolc dm-3; V, 81%; and organic matter, 6.3 g kg-1. Basal fertilizations were carried out with 20 kg ha-1 P 2 O5, using simple superphosphate, and with 20 kg ha-1 K2O, with potassium chloride. The experiment carried out at the BEF was further fertilized with 20 kg ha-1 MgO, using magnesium sulfate.

Soil samples were collected during planting in order to determine rhizobial populations. This analysis was carried out with the most probable number (MPN) method, using infected cowpea plants ('BRS Pujante'), as described in Hungria & Araújo (1994).

To prepare the inoculant, the bacteria were cultivated in YM liquid medium (Vincent, 1970), under constant stirring, for five days. Then, 10 mL of the culture broth of each bacteria were inoculated individually in plastic bags containing 30 g of sterilized peat, in order to reach the cell concentration of 109 viable cells per gram of inoculant. The inoculation was performed with 40 g of inoculant per 1 kg of seeds, in plastic bags containing the seeds, the inoculant, and a sugar solution (sucrose 10% w/v), and then hand mixed. The inoculated seeds were shade-dried, and sowing was performed manually soon after inoculation.

Weed control was done manually, according to necessity. The control of plagues and diseases was done with products recommended for the crop in the region. For the experiment implemented at the MEF, a furrow irrigation system was used, applying a daily irrigation depth of approximately 5.5 mm. For the experiment implemented at the BEF, a dripper irrigation system was used, with drippers spaced at 0.5 m and with a 1.6 L h-1 water flow. During the execution of the experiments, average monthly precipitation was between 1.4 and 27.6 mm at the MEF and BEF, respectively, with a daily average temperature of 24 to 28°C.

A first evaluation of plant nodulation was performed during flowering (45 days after the emergence of the plants). Ten plants were collected in 1.0 m of the second row of each plot. These plants were cut at soil level, and the radicular system was separated and packed in plastic bags (Fernandes Júnior et al., 2012). The roots were washed, and the nodules were separated from the radicular system and counted. The aerial part and the nodules were packed in paper bags, dried at 65°C in a forced air chamber until constant weight, and then weighed. The following characteristics were determined: number of nodules (NN), shoot dry matter mass (DMS), nodule dry matter mass (DMN), and nitrogen accumulated in the shoots (NAS) using the semimicro Kjeldahl method (Liao, 1981).

A second evaluation was done during harvest. Beans were gathered from the useful plot (4 m2, central to each plot). The grains were threshed for weighing, and grain yield (GY) was calculated. Grain protein content (GPC) was determined according to Williams (1984).

Data were subjected to analysis of variance, using the Sisvar 4.2 statistical analysis system (Ufla, Lavras, MG, Brazil). Means were compared by Student's test, at 10% probability. Previously to the analysis, data were transformed by (x+1.0)0.5.

Results and Discussion

Rhizobial populations of the experimental areas were estimated at 2.8x103and 4.3x103 cells per gram of soil, for the MEF and BEF, respectively. These populations can be considered high. In soils with established native rhizobia populations, the efficiency of the inoculation may be compromised because the introduced rhizobial strains need to compete with the indigenous isolates for nodulation sites (Zilli et al., 2013).

At the MEF, the NN in the cultivar BRS Pujante was influenced by the inoculated strain (Table 1). Inoculation treatments had higher NN than the fertilization treatment with 80 kg ha-1 N. BR 3262, BR 3299T, INPA 03-11B, and UFLA 03-84 provided greater NN than the control treatment (without inoculation and N fertilization). Nodule formation inhibited by N fertilization was also observed by Silva et al. (2012), when evaluating rhizobia inoculation in the cultivar BRS Pujante.

Table 1 Response of cowpea (Vigna unguiculta) cultivars to the inoculation of rhizobial strains, at the experimental field of Mandacaru, Juazeiro, state of Bahia, Brazil(1)

Inoculation treatment Number of nodules Nodule dry matter N accumulation in shoots Dry matter of shoots
  ------------------(mg per plant)------------------ (g per plant)
BRS Pujante
BR 3267 21bc 49.5bc 920a 23.0a
BR 3262 42a 148.6a 650bc 18.9a
BR 3299T 36a 101.2ab 690abc 18.8a
INPA 03-11B 28ab 98.8abc 590bc 19.1a
UFLA 03-84 33ab 97.2abc 850ab 21.6a
80 kg ha-1 N 11d 86.5bc 500c 18.2a
Control 15cd 49.8c 680abc 19.6a
BRS Tapaihum
BR 3267 20a 102.0a 700ab 18.9a
BR 3262 19a 95.2a 640ab 17.0a
BR 3299T 17a 61.7a 770a 20.6a
INPA 03-11B 13a 49.8a 510b 20.0a
UFLA 03-84 16a 68.0a 750ab 21.9a
80 kg ha-1 N 17a 78.5a 650ab 18.6a
Control 12a 53.7a 570ab 17.7a
BRS Carijó
BR 3267 12a 55.2a 810ab 24.0a
BR 3262 13a 68.3a 890a 26.1a
BR 3299T 10a 45.5a 730ab 23.8a
INPA 03-11B 17a 84.1a 730ab 23.8a
UFLA 03-84 19a 64.6a 760ab 25.7a
80 kg ha-1 N 13a 64.7a 780ab 22.7a
Control 12a 58.0a 630b 17.9a
BRS Acauã
BR 3267 11a 56.5a 430a 16.6a
BR 3262 12a 63.9a 460a 15.3a
BR 3299T 9a 29.2a 550a 15.5a
INPA 03-11B 10a 43.5a 630a 17.2a
UFLA 03-84 9a 26.0a 530a 15.6a
80 kg ha-1 N 12a 53.3a 670a 19.6a
Control 12a 50.1a 530a 15.91a
CV (%) 27.2 32.2 6.5 24.5

(1)Means followed by equal letters, for a same cultivar, do not differ by Student's test, at 10% probability.

Cultivars BRS Tapaihum, BRS Carijó, and BRS Acauã did not respond to the inoculation treatments, regarding NN. Chagas Junior et al. (2010) found that the cultivar BRS Pujante nodulated abundantly with all evaluated strains, with lower nodulation rates observed in the nitrogen fertilization and in the absolute control treatments.

For DMN, BRS Pujante stood out, whereas the other cultivars showed equal means. Inoculation of the strain BR 3262 increased DMN of the cultivar BRS Pujante, when compared to the control treatment, but it did not differ from inoculation with the strains BR 3299T, UFLA 03-84, and INPA 03-11B.

Regarding DMS, inoculated treatments did not differ from the control treatment. However, a significant increase in NAS was observed for the cultivar BRS Pujante inoculated with BR 3267, and for BRS Carijó, inoculated with BR 3262, when compared to the N fertilization and to the control treatment, respectively. Apart from nodulation, nodule efficiency may be influenced by plant genotype and by the efficiency of the strain in the nodules, which also depends on the macrosymbiont genotype (Alcantara et al., 2014). Therefore, the difference in nitrogen accumulation in shoots indicates that the genotypes BRS Carijó and BRS Pujante can benefit from inoculation.

At the BEF, NN differed according to the treatments (Table 2). Cultivar BRS Pujante, inoculated with BR 3267 and BR 3262, showed higher NN. Once again, N fertilization inhibited the formation of nodules, and the strains BR 3267 and BR 3262 provided an increase in nodule mass compared to the other treatments.

Table 2 Response of cowpea (Vigna unguiculta) cultivars to the inoculation of rhizobial strains, at the experimental field of Bebedouro, Petrolina, state of Pernambuco, Brazil(1)

Inoculation treatment Number of nodules Nodule dry matter N accumulation in shoots Dry matter of shoots
  ------------------(mg per plant)------------------ (g per plant)
  BRS Pujante
BR 3267 53a 170.4a 17.9c 660c
BR 3262 25b 135.5a 25.8abc 900abc
BR 3299T 12c 55.6b 30.9a 1,220a
INPA 03-11B 14bc 51.5b 20.7bc 780bc
UFLA 03-84 13c 60.0b 28.0ab 1,120ab
80 kg ha-1 N 4d 13.3c 24.6abc 830abc
Control 16bc 87.6ab 22.2abc 880abc
  BRS Tapaihum
BR 3267 5a 19.1a 27.4abc 1,070abc
BR 3262 7a 43.3a 39.9a 1,430a
BR 3299T 5a 44.0a 31.4ab 1,140ab
INPA 03-11B 6a 42.6a 15.8c 580c
UFLA 03-84 7a 42.2a 18.6bc 780bc
80 kg ha-1 N 4a 13.6a 29.2ab 1,090abc
Control 6a 21.2a 24.2bc 850bc
  BRS Carijó
BR 3267 10a 63.8ab 23.6ab 1,030a
BR 3262 8ab 70.7a 22.3ab 950a
BR 3299T 4ab 41.8abc 32.1a 900a
INPA 03-11B 6ab 46.2abc 18.0b 720a
UFLA 03-84 4ab 27.5abc 29.4ab 1,120a
80 kg ha-1 N 2ab 11.7c 25.8ab 910a
Control 2.b 24.5bc 19.7ab 850a
  BRS Acauã
BR 3267 6ab 29.3ab 21.1bc 810bc
BR 3262 7a 53.3a 37.2a 1,420a
BR 3299T 3ab 16.9ab 35.3a 1,260ab
INPA 03-11B 3ab 14.6ab 25.4ab 1,000ab
UFLA 03-84 3ab 21.5ab 14.2c 480c
80 kg ha-1 N 1b 17.2b 28.2ab 850bc
Control 3ab 20.5ab 26.1abc 930abc
CV (%) 35.2 37.0 19.5 9.7

(1)Means followed by equal letters, for a same cultivar, do not differ by Student's test, at 10% probability.

For the cultivar BRS Carijó, the strains BR 3267 and BR 3262 stood out regarding NN and DMN, respectively. For 'BRS Acauã', however, only the strain BR 3262 differed from the treatment with nitrogen fertilization, but it did not differ from the other treatments. 'BRS Tapaihum' was not significantly affected by the treatments, regarding NN and DMN. The inoculation with the strain BR 3299T increased DMS of the four studied cultivars.

Regarding NAS, cultivar BRS Pujante performed better when inoculated with the strain BR 3299T, but did not differ from the N fertilization and the control treatments. For 'BRS Tapaihum', the strain BR 3262 provided the highest NAS. For 'BRS Carijó', inoculation treatments did not differ from the control. For 'BRS Acauã', BR 3262 provided higher NAS than the nitrogen fertilization and the other inoculated treatments.

The similarity of nodulation parameters and vegetative development between some inoculated and non-inoculated treatments indicates that the native rhizobial population was efficient to establish symbiosis with cowpea, which is able to nodulate with a wide range of tropical soil rhizobia (Leite et al., 2009; Jaramillo et al., 2013). The capacity of the native rhizobial population to establish an efficient symbiosis with cowpea has already been observed in the Brazilian Semiarid (Martins et al., 2003; Freitas et al., 2012; Alcantara et al., 2014).

Grain yield results suffered the interaction between inoculation treatments and cowpea genotypes, in both experiments. Grain yield ranged from 1,091 to 1,629 kg ha-1 in the MEF, and from 817 to 1,824 kg ha-1 in the BEF (Table 3). Grain yield levels were considerably higher than 330 kg ha-1, which is the average for the northeastern region, but within the expected levels for inoculation experiments under irrigated conditions in the Brazilian Semiarid (Santos et al., 2008; Santos, 2011).

Table 3 Grain yield and grain protein content of the evaluated cowpea (Vigna unguiculta) cultivars, according to the inoculation treatments in the experimental fields of Mandacaru (MEF) and Bebedouro (BEF)(1)

Inoculation treatment MEF   BEF
Grain yield (kg ha-1) Protein (%)   Grain yield (kg ha-1) Protein (%)
  BRS Punjante
BR 3267 1,495a 24.4a   1,157b 24.0ab
BR 3262 1,219bc 24.8a   1,435ab 24.9a
BR 3299T 1,475ab 25.4a   1,353ab 26.6a
INPA 03-11B 1,091c 21.9a   1,323ab 25.6a
UFLA 03-84 1,629a 25.9a   1,423ab 24.3a
80 kg ha-1 N 1,375ab 26.5a   1,824a 24.7a
Control 1,477ab 16.0b   1,088b 19.4b
  BRS Tapaihum
BR 3267 1,340ab 21.4ab   1,346ab 23.6ab
BR 3262 1,322ab 21.8ab   1,551a 26.3a
BR 3299T 1,198ab 24.9a   1,291ab 22.9ab
INPA 03-11B 1,087b 26.7a   1,769a 24.8a
UFLA 03-84 1,337ab 24.8a   1,589a 26.7a
80 kg ha-1 N 1,145ab 25.3a   1,320ab 26.1a
Control 1,379a 19.3b   934b 19.1b
  BRS Carijó
BR 3267 1,048b 23.2ab   1,373a 23.7a
BR 3262 1,467a 21.2ab   1,570a 24.8a
BR 3299T 1,436a 26.4a   1,370a 24.6a
INPA 03-11B 1,261ab 26.1a   1,222a 17.1b
UFLA 03-84 1,505a 25.0ab   1,197a 23.9a
80 kg ha-1 N 1,277ab 20.8b   1,526a 21.8a
Control 1,387a 21.4ab   1,048a 23.7a
  BRS Acauã
BR 3267 1,210a 24.2a   1,535a 24.1a
BR 3262 1,198a 25.5a   951bc 23.2a
BR 3299T 1,305a 24.9a   1,494a 24.3a
INPA 03-11B 1,151a 25.6a   1,494a 25.2a
UFLA 03-84 1,186a 25.0a   1,001bc 24.5a
80 kg ha-1 N 1,413a 24.9a   1,406ab 24.4a
Control 1,319a 20.3a   816c 26.3a
CV (%) 9.07 12.62   14.01 8.70

(1)Means followed by equal letters, for a same cultivar, do not differ by Student's test, at 10% probability.

In the MEF experiment, when cultivar BRS Pujante was inoculated with the strains BR 3267 and UFLA 03-84, productivity ranged from 1,496 to 1,629 kg ha-1, higher than the ones observed with the strains BR 3262 and INPA 03-11B.

In the BEF, grain yield of non-inoculated treatments did not differ from the ones obtained with the strains BR 3267, BR 3299T, and UFLA 03-84. Inoculation treatments had a similar yield to the one of the control and the N fertilization treatments. However, the strains UFLA 03-84 and BR 3262 had an increase of 30 and 31% in grain yield, respectively, compared to the control treatment. Ferreira et al. (2013) reported that the cultivar BR 17 Gurguéia, inoculated with the strain BR 3262, had a significant increase in grain yield, of 50.17%, in comparison to the untreated mineral N treatment without inoculation.

Inoculation treatments with the cultivar BRS Tapaihum had similar grain yield to that of the control treatment. At the BEF, however, the association of this cultivar with the strains BR 3262, UFLA 03-84, and INPA 03-11-B resulted in grain yield equal to the one obtained with the N-supplied control, but greater than the one of the absolute control. Inoculation with the strain INPA 03-11B stood out, increasing yield in 89%, when compared to the absolute control.

For 'BRS Carijó', the inoculation of the strains BR 3262, BR 3299T, and UFLA 03-84 provided higher means at the MEF than the strains BR 3267 and INPA 03-11B, but similar yield to that of the absolute control. At the BEF, cultivars did not differ also. For 'BRS Acauã', grain yield at the MEF did not differ. However, at the BEF, the association with the strains BR 3267, BR 3299T, and INPA 03-11B increased productivity in 88, 83, and 83%, respectively, achieving higher yields than the one of the control treatment, but similar ones to that of the N fertilization treatment.

The obtained results are similar to the ones observed in regions of the Brazilian Semiarid. Costa et al. (2011) found that inoculation with INPA 03-11B promoted similar yields to that of N fertilization, in Bom Jesus, state of Piauí, with productivity of up to 1,604 kg ha-1. Almeida et al. (2010) in an experiment carried out at Teresina, state of Piaui, reported a grain yield of 1,637 kg ha-1 for the cultivar BR 17 Gurguéia inoculated with the strain BR 3267, and of 1,823 kg ha-1 when inoculated with the strain BR 3262, a 24.6 and 38.9% increase, respectively, compared to that of the control treatment.

Grain protein contents in 'BRS Pujante' were influenced by the inoculation treatments and by N fertilization (Table 3). In both trials, these treatments showed higher GPC than those observed in the absolute control, especially with the strain BR 3299T, which increased GPC in 58.8 and 37.1%, at the MEF and BEF, respectively. For 'BRS Tapaihum', higher GPC at the MEF was obtained with the strains INPA 03-11B, BR 3299T, and UFLA 03-84, with 26.7, 24.9, and 24.8%, respectively. These GPC values represented a respective increase of 38.3, 29, and 28.5% in comparison to the control treatment, which showed GPC of 19.3%. At the BEF, this genotype performed better with the strains UFLA 03-84, BR 3262, and INPA 03-11B, which increased GPC in 39.8, 37.7, and 29.8%, respectively, compared to the control. Therefore, 'BRS Tapaihum', which has a peculiar black-coated seed, despite not responding to inoculation regarding grain yield, had more nutritious grains with these treatments. For genotypes BRS Carijó end BRS Acauã, inoculation treatments had no effect on GPC, except when BRS Carijó was inoculated with INPA 03-11B, which provided lower values. In the Semiarid region, GPC is an important trait, since the production is mostly destined for human consumption and cowpea is considered one of the main protein sources for rural populations (Santos et al., 2008; Freire Filho, 2011).

The observed dependence of the inoculation treatments on genotypes, rhizobia strain, and environment is corroborated by other studies (Melo & Zilli, 2009; Alcantara et al., 2014). Therefore, plant breeding may have an important role in improving N supply for cowpea by biological fixation (Xavier et al., 2006; Araújo et al., 2012). The present study also emphasizes the importance of testing the response to inoculation of different varieties, under distinct edaphoclimatic conditions.

For cowpea, a lot of attention has been given to the selection of the microsymbionts, since the selection of the strain is the main resource for optimization of biological nitrogen fixation (BNF) (Fernandes Júnior al., 2012). However, an adequate interaction between symbiotic partners is essential to BNF efficiency and, for this reason, it should be prioritized in breeding programs for this species, taking the well-succeeded example of soybean (Glycine max L.) in Brazil.


1. Cowpea cultivars respond differently to the inoculation of rhizobial strains, in the Brazilian Semiarid.

2. The inoculation of rhizobial strains can be beneficial to grain yield and protein contents in cowpea, mainly for the cultivars BRS Pujante and BRS Tapaihum, in the sub-medium of the São Francisco River Valley.


To Embrapa, for financial support; and to Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Capes) and to Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), for the fellowships granted.


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Received: February 03, 2014; Accepted: April 30, 2014

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