Inoculação com rizobactéria promotora do crescimento de plantas em Myracrodruon urundeuva (Allemão) confere maior tolerância ao estresse hídrico

Abstract

Nowadays there is a great concern about the recovery of degraded areas, mainly due to the threat of extinction of native plant species, such as the aroeira do sertão (Myracroduon urundeuva) native of the Caatinga biome. In line with this, inoculation of plant growth promoting rhizobacteria (PGPR) has been an alternative to minimize the adverse effects caused by drought stress in cultivated plants. However, little is known about the effects of RPCPs in native plant species of Caatinga. Therefore, it’s believed that the inoculation of a PGPR, Azospirillum lipoferum, in M. urundeuva plants might confer greater tolerance to drought stress. In this context, the present study evaluated the influence of A. lipoferum on the growth of M. urundeuva under drought stress. The experiment was conducted in a completely randomized design (DIC). In factorial 2 x 4 (with and without inoculum x four irrigation levels), ANOVA performed in software R and the means of treatments were compared by the LSD test (P < 0.05). Firstly, seeds of M. urundeuva were sanitized, and then part was inoculated with A. lipoferum, and another was not inoculated (control). Ten days after germination, the seedlings were submitted to four irrigation levels: 180 mm (control), 135 and 90 mm (moderate stress), and 45 mm (severe stress). The plants grew under photoperiod conditions of 12 hours at 28 ° C and 12 hours in the dark at 26 ° C, with relative humidity of 50% and light intensity of μmol of photons m-2 s-1. After 81 days biometric measures of the shoot and roots of the plants, and in the leaflet was quantified the leaf water potential (ΨWL), electrolyte leakage, chlorophyll content, soluble protein content, proline content, superoxide dismutase (SOD) activity and general appearance of the plants, as well as the percentage of fallen leaflets were evaluated. The inoculation was confirmed by the change of the colour of the semi-solid nitrogen-free bromothymol blue (NFB) culture medium from yellowish green to blue. In the inoculated plants, the adverse effects of moderate drought stress were minimized, while there was less leaflet drop and greater green tint, this was confirmed by the maintenance of the highest levels of chlorophyll a, b and total. The association of PGPR with the roots of the plants provided increases of 30% root length, 50% root dry weight, 34% root shoot dry weight and 10% soluble protein content. The inoculated plants still maintained 5% higher leaf water potential than those not inoculated, as well as presented lower membrane damage in moderate drought stress. On the other hand, SOD activity was significantly lower in the inoculated plants, possibly due to the induction of a non-enzymatic protective feature. In addition, the inoculated plants shown better morphological and physiological characteristics than those not inoculated. In this way, the inoculation of PGPR in M. urundeuva can be an alternative for the production of plants that are more tolerant to drought stress. In addition, this technique has a strong potential for use in reforestation and recovery plans of degraded areas in tropical dry forests (TDF). Nevertheless, further studies on the biochemical and physiological mechanisms that confer these tolerances are needed, as well as studies about these same mechanisms in other native plants.