Characterization of rhizobacteria isolated from wild plants of Physalis sp. and study of its biofertilizing effect in vitro, and in seedlings and fruits of tomatillo (Physalis ixocarpa Brot.)

Abstract

The use of plant growth promoting rhizobacteria (PGPR) is a sustainable way in agriculture to reduce the use of chemical fertilizers which have caused a deterioration in the composition and structure of the soil and as well as contamination of water reservoirs. Rhizobacteria have shown a set of characteristics that they use for their survival, but that directly and indirectly help improve some agronomic parameters in crops. The most reported mechanisms include: nitrogen fixation, phosphorus (P) and potassium (K) solubilization, ammonia and indole acetic acid (IAA) synthesis, siderophore and 1aminocyclopropane-1-carboxylate (ACC) deaminase enzyme production, biocontrol of pathogens in the soil, and the induction of resistance and/or tolerance to biotic and abiotic stress. On the other hand, the production of the tomatillo crop in Mexico has shown an increase in recent years due to the fact that it is part of the consumption of the Mexican diet, mainly as a base for the preparation of sauces and typical dishes. This research work consisted of 2 stages: 1) Isolation of 30 bacteria from the rhizosphere soil of wild tomatillo plants, which were characterized cellular and morphologically and by 4 growth promotion mechanisms (P and K solubilization, and ammonia production and IAA). Based on their results, 6 bacteria were chosen for identification and of these, 4 were evaluated on the growth of tomatillo seedlings; 2) The biofertilizing effects of 1 bacterium (Acinetobacter calcoaceticus) in combination with different doses of K, were evaluated in plants and tomatillo fruit quality and mineral content. The results in 1) showed that the bacterium identified as Atlantibacter sp. showed activity in all biofertilization mechanisms evaluated, with the best results in phosphorus solubilization and indole acetic acid synthesis. In the seedlings experiment, the seedlings with bacterial treatments presented higher leaf weight (>349%) and root length (>11%) than the control. Seedlings treated with Priestia megaterium resulted in the highest height of seedlings, 140% compared to the control. In addition, P. megaterium and Acinetobacter calcoaceticus were significantly higher in the concentration of three minerals: K (54 and 37%), Ca (88 and 80%), and Mg (89 and 81%). The results in 2) indicated that the inoculant increased the chlorophyll content, dry weight and height at low K fertilizer doses (0 and 50%) compared to the non-inoculated treatments. The application of the inoculant increased the yield of fruits (g plant-1) and number of fruits per plant in the treatment with no K fertilization, which was similar to the treatments with high K doses without inoculation (75 and 100%). The protein content was higher in K fertilizer 100% doses combined with the inoculant in comparison to K fertilizer 100% doses treatment non-inoculated. The content of K, P, Ca, Mg, and Mn in the inoculated tomatillo plants combined with low K fertilizer doses (0 and 50%) was higher in comparison with the non-inoculated. Tested strains: Priestia megaterium, Acinetobacter calcoaceticus and Atlantibacter sp. demonstrated outstanding biochemical and agronomical characteristics in vitro and in vivo, making them excellent biofertilizers candidates for tomatillo crop production. A. calcoaceticus also showed benefic traits in the physiological and agronomic parameters, and in the mineral content in plant and fruit when was combined at low K fertilization doses. This rhizobacteria can be used to decrease the application of the K fertilizer in tomatillo crop.