Inoculação de Herbaspirillum seropedicae em duas variedades de arroz irrigado: qualidade do inoculante e necessidade da reinoculação

Abstract

The demand for the use of diazotrophic bacteria as biofertilizant in differents non leguminous crops grew a lot in the last years mainly due to the fact that there is no commercial inoculant available in Brazil. The aim of this work was to evaluate some aspects that can influence the quality of the inoculant and the contribution of the inoculation and reinoculation of the Herbaspirillum seropedicae strain ZAE 94 (BR 11417), applied as peat inoculant in two varieties of lowland rice: IR 42 and IAC 4440. The quality of the inoculant was evaluated following the survival of the strain used in the inoculant prepared with different moisture levels, pH and type of package bags storage in refrigerator during the period of 180 days and your contribuition was evaluated using the parameters yield, N-total and total of proteins accumulated in the grains. The effect of inoculation and reinoculation, on the community of the bacteria present in the stem of the rice plants was evaluated using the technique of DGGE. The strain ZAE 94 was grown in culture medium at 30° C and 100 rpm for 24 h and the obtained cell suspension was used in the different experiments. The inoculant was prepared using grounded dry peat, pH adjusted to 7.0 and with 43% of moisture. The produced inoculant was applied on the seeds of the rice varieties just before planting. One experiment was carried out in pots and two consecutive experiments in the field, the soil in the area classified as Udult, in a randomized block design. The data obtained showed that the moisture and package type were the aspects that had more influence on the survival strain. The results of the inoculation and reinoculation experiments showed that the inoculated ZAE 94 strain was statistically similar to the treatment of 20 kg. ha-1 of ammonium sulfate applied as the nitrogen source in the variety IR42 and equivalent to 50 kg. ha-1 in the variety IAC4440 for the parameters yield, N-total and proteins of grains. The reinoculation experiments showed the necessity to reinoculate the strain ZAE 94 in the following planting years, since that the inoculated and reinoculated treatments were statically similar but significantly superior to the non inoculated treatment and the treatment was inoculated only in the previous year for both parameters and rice varieties used. The DGGE technique applied to analyze the bacterial community present in the rice plants of both experiments showed wide occurrence of bands in the same height of the Herbaspirillum seropedicae species, even for the treatments that was not inoculated, suggesting that this bacterium has great capacity of dispersion and colonize the host plant. This study also showed occurrence of bands of different sizes from the control patterns, suggesting that rice plant varieties are colonized by different bacterial species.