Seleção de rizóbios nativos para guandu, caupi e feijão-de-porco nos tabuleiros costeiros de Sergipe

Abstract

Resumo -A inoculação de estirpes de rizóbios em sementes de feijão-de-porco (Canavalia ensiformis), caupi (Vigna unguiculata) e guandu (Cajanus cajan), recomendadas para outras regiões do País, não tem resultado em incrementos nas taxas de fixação biológica de N 2 nem no crescimento dessas leguminosas em solos dos tabuleiros costeiros de Sergipe. Os objetivos deste trabalho foram avaliar a eficiência simbiótica de rizóbios nativos dos tabuleiros costeiros associados a essas leguminosas e a tolerância deles a estresses. Das 17 estirpes de rizóbios isoladas e analisadas em casa de vegetação, quatro foram selecionadas para o guandu, sete para o caupi e três para o feijão-de-porco. O número e a massa de nódulos secos por planta correlacionaram-se com a massa da parte aérea seca, a área foliar e o N total acumulado nas folhas das três leguminosas. Os mesmos rizóbios foram eficientes para o caupi e para o guandu. Três estirpes do guandu (R35, R43 e R45) e duas do caupi (R10 e R17) foram caracterizadas in vitro e todas apresentaram tolerância às concentrações elevadas de ácido nalidíxico, cloranfenicol e tetraciclina, porém, foram sensíveis à estreptomicina e à kanamicina. Todas as estirpes cresceram a 35ºC e, exceto a R17, toleraram o alumínio (10 mg L -1 ).Termos para indexação: Cajanus cajan, Canavalia ensiformis, Vigna unguiculata, biologia molecular, fixação de nitrogênio. Selection of indigenous rhizobia to the cowpea, pigeonpea and jackbean crops in the coastal tableland of Sergipe, BrazilAbstract -The inoculation of rhizobial strains in jackbean (Canavalia ensiformis), cowpea (Vigna unguiculata) and pigeonpea (Cajanus cajan), recommended for other regions of Brazil, has not resulted in increases of biological nitrogen fixation rates and plant growth in soils of the coastal tableland of Sergipe (Brazilian Northeast). The objectives of this work were to evaluate the symbiotic effectiveness of indigenous rhizobia from that coastal tableland associated to these three legumes and their tolerance to stresses. Seventeen rhizobia strains were isolated and evaluated in a greenhouse. Four strains were selected for pigeonpea; seven for cowpea and three for jackbean. Nodules number and dry weight were related to shoot dry weight, leaf area and leaf N content, in all three legumes. The same strains were efficient for both cowpea and pigeonpea. Three pigeonpea (R35, R43 and R45) and two cowpea (R10 and R17) rhizobia were characterized in vitro and all showed tolerance to high levels of nalidix acid, chloramphenicol and tetracycline; however, they were sensitive to streptomycin and kanamycin. All strains were able to grow at 35ºC and, except for R17, were tolerant to aluminium (10 mg L -1 ).

Phenotypic diversity and amylolytic activity of fast growing rhizobia from pigeonpea [Cajanus cajan (L.) Millsp.]

“…The sub-cluster B1 has three isolates that did not change the pH of YMA culture medium while the subcluster B2 harbored isolates that acidify the medium. Although some studies have shown that fast growing strains are not resistant to streptomycin (10), the IAR results found in the present study, corroborate to some recent results which pigeonpea rhizobial IAR also presented high resistance to streptomycin and low kanamycin resistance (6). It is very common to find fast growing rhizobial isolates that exhibiting high tolerance to streptomycin (6,28).…”

“…The dishes were incubated at 28°C until the proper growth time of each isolate. It was attributed score 1 to isolates which were able to grow only at the first section (low resistance); 2 to the isolates which were able to grow in first and second sections of the dish, but were not at the third section (intermediate resistance); 3 to the isolates that presented positive growth through every three zones (high resistance) (10,28).…”

Phenotypic and molecular fingerprinting of fast growing rhizobia of field-grown pigeonpea from the eastern edge of the Brazilian Pantanal

“…The isolates also showed a generally low IAR for kanamycin, which is a very common characteristic for tropical rhizobia. Previous studies evaluating bacterial isolates of pigeonpea reported a generally low or intermediate resistance to chloramphenicol and a high susceptibility to kanamycin (Anand and Dogra, 1991;Fernandes et al, 2003;Fernandes Jr. et al, 2012). Other studies also showed that cowpea and common bean rhizobia also presented intermediate to low resistance to kanamycin, as was observed in the present study; however, these isolates presented a low resistance to chloramphenicol (Xavier et al, 1998;Souza et al, 2003;Zilli et al, 2004;Florentino et al, 2010).…”

“…In spite of the great number of isolates that presented high or intermediate resistance to chloramphenicol (17 isolates in all), this is a very uncommon characteristic for pigeonpea nodulating rhizobia (Anand and Dogra, 1991;Fernandes et al, 2003;Fernandes Jr. et al, 2012). The isolates also showed a generally low IAR for kanamycin, which is a very common characteristic for tropical rhizobia.…”

“…The dishes were incubated at 28°C for 3 days. A score of 0 was attributed to isolates that did not present any growth (no resistance), 1 to isolates that were able to grow only on the 1st section (low resistance), 2 to isolates that were able to grow on the 1st and 2nd sections of the dish, but were not able to grow on the 3rd section (intermediate resistance), and 3 to isolates that presented positive growth through all three zones (high resistance) (Xavier et al, 1998, Fernandes et al, 2003.…”