Endophytic bacteria associated with sugarcane stem and their contribution to the crops nitrogen uptake
2004
Asis, C.A., Jr,National Agricultural Research Center for Kyushu, Okinawa Region, Miyakonojo, Miyazaki 885-0091 (Japan). Dept. of Upland Farming | Akao, S.
Many reports have shown the potential role of endophytic bacteria in sustainable agricultural production. In this study, the authors surveyed the number of endophytic bacteria in the stem of sugarcane cultivars and isolated the diazotrophic strains. They also estimated the contribution of biological nitrogen fixation to the total nitrogen uptake (percent Ndfa) of sugarcane and determined the effect of sugar and organic contents in sugarcane stem on the growth of diazotrophic isolates. The number of endophytic diazotrophs which ranged from 10 E4 to 10 E9 cells mL juice, was correlated with sugar content (percent Brix)of the juice, and varied between cultivars and sampling sites. Of the 49 isolates, 28 were putative strains of Gluconacetobacter diazotrophicus, 9 isolates showed similar characteristics to Herbaspirillum seropedicae, and 12 isolates consisted of H. rubrisubalbicans-like strains. Using the l5 N dilution technique, the estimated percent Ndfa ranged from 24.9 to 27.4 percent in the roots, 13.6 to 14.6 percent in the stem, and 15.7 to 20.54 percent in the leaves. Using the 15N abundance method, percent Ndfa ranged from 26.15 to 37.5 percent. The organic acid contents of the apoplast solution of sugarcane stem were aconitate, malate, and citrate while the sugar components were sucrose, glucose, and fructose. The contents of all the compounds varied with the cultivars, growth stages, and internode portions. Aconitate showed the highest content among organic acids and sucrose was the predominant sugar compound. Moreover, G. diazotrophicus ATTCC 49037 strain preferred sucrose to aconitate while H. rubrisulbalbicans PA18 preferred aconitate to sucrose as carbon source. This study confirmed the existence of endophytic bacteria in the stem of sugarcane cultivars and their significant contribution on the nitrogen uptake of the crop.
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