Evaluation of field inoculation of Kocuria rhizophila and Streptomyces violaceoruber as biostimulants under water availability conditions in grapevines

Abstract

Agricultural productivity must promote management systems that incorporate sustainability principles, and viticulture is no exception. In this regard, several studies have shown that certain symbiotic microorganisms can enhance plant development and growth. Growth-promoting rhizobacteria (PGPR) are soil bacteria that stimulate vegetative growth and improve stress resistance. The aim of this experiment was to assess the effects of the growth-promoting rhizobacteria Kocuria rhizophila and Streptomyces violaceoruber under irrigation and drought conditions on Merlot grapevine development, physiology, physicochemical properties and enzymatic activity (urease, phosphatase, and β-glucosidase) of the rhizospheric soil. The planting was designed in blocks with a total of 30 plants per treatment (Control, Kocuria, and Streptomyces) grafted onto R110 and SO4 rootstocks. The drought treatment was based on the application of 40% of the water requirements applied in a single irrigation dose per week. For inoculation, the roots were immersed in bacterial suspensions (1×107 CFU/ml for Kocuria and 1×106 CFU/ml for Streptomyces) for 60 minutes. The control plants were treated with plain water. At the time of planting, the inoculation was reinforced by watering each plant with 500 ml of bacterial suspensions at same concentration. At different sampling times (flowering, ripening, and harvest), growth measurements (maximum height) and gas exchange parameters were taken using a portable gas exchange system. The analysis of the physicochemical parameters of the soil were analyzed by the Eurofins Agro-Environmental Laboratory. To study the enzymatic activity, the methodology described in ISO 20130:2020 was used, based on the measurement of colorimetric substrates in micro-well plates. During flowering, the bacterial treatment showed a slight increase in photosynthesis in drought-stressed plants compared to the control, while under irrigation conditions, there were significant differences between Kocuria and Streptomyces. In the subsequent sampling times, it is the irrigation treatment that shows significant differences. During the harvest period, maximum height growth showed significant differences in the irrigation treatment, with irrigated plants exhibiting greater height. In contrast, during the ripening phase, significant interactions were found between irrigation and R110 rootstock. The principal component analysis of the physicochemical properties didn’t show significant differences between treatments. In enzymatic activity, urease was higher under drought conditions during flowering. At harvest, significance was observed in the bacterial treatment, with Kocuria exhibiting higher activity than Streptomyces. These results suggest that Kocuria performs better than Streptomyces as a biofertilizer in vineyards and highlight the importance of considering factors in the field such as root colonization and competition with other microorganisms.

Acknowledgments

This experiment was carried out within the framework of the project PID2021-125575OR-C22, funded by MCIN/AEI/10.13039/501100011033/ and FEDER, A way of making Europe. AM – Predoctoral fellowship FPI/089/2022, Govern de les Illes Balears.