Criteria for the Selection of Vegetable Growth-Promoting Bacteria to be applied on Roselle Crop (Hibiscus Sabdariffa L.) and Bioremediation

The study of microorganisms that promote plant growth has gained importance worldwide because of the multiple advantages they represent (Ortiz-Texon et al., 2016). Currently, research is focused on the evaluation of various rhizosphere microorganisms, selecting those most efficient in inoculation experiments under controlled environmental conditions in the laboratory, greenhouse and in the field. This seeks to increase yield and reduce the amount of agrochemicals used (PazosRojas et al., 2016).

Plant Growth-Promoting Rhizobacteria (PGPR) are bacteria influenced by exudates from plant roots that can improve plant growth in the short term (Molina-Romero et al., 2017), through the production of plant Growth-Promoting substances, which are synthesized indifferent structures of the plant. These molecules exhibit effects on plant physiology, such as increasing root volume and root respiration rate, resulting in the absorption of soluble mineral elements (Molina-Romero et al., 2015). The beneficial bacteria applied to agricultural crops allow the phytostimulation and bioremediation of toxic compounds associated with plants; having a positive impact on human health and the environment (Sing and Trivedi, 2016; Pazos-Rojas et al., 2016). These can interact effectively with plants in contaminated agricultural soils, carrying out the degradation of pollutants and increasing the yield of crops (Báez-Rogelio et al., 2016). Among the satisfactory results for the control of phytopathogenic microorganisms is the genus Pseudomonas spp. (Anguloa, et al., 2014). They are a group of bacteria that can exert a direct beneficial effect, through the synthesis of phytohormones and vitamins, stimulation of seed germination and emergence of seedlings, inhibition of ethylene synthesis, solubilization of inorganic phosphorus (P). Indirectly, they exercise the function of controlling pathogenic microorganisms through the synthesis of antibiotics and fungicides, competition for nutrients, production of siderophore or by inducing systemic resistance to pathogens (Alcarraz-Curi et al., 2019). For example, in P. fluorescens G20-18 the ability to efficiently control infection by P. syringae has been identified, which allows the maintenance of tissue integrity, reflecting on the biomass yield (Großkinsky et al., 2011). Some criteria commonly used to testa crop are: Total germination: it is the maximum germination percentage got under previously defined conditions (Durán and PérezGarcía, 1984).

Germination speed: Maguire (1962) defines it as the ratio of the number of germinated seeds to the germination time. 𝑛 𝑖 𝑀 = 𝑡 where M = germination speed, n = number of seeds germinated on day i, t = germination time from sowing to germination of the last seed. 1.1 Accumulation and distribution of dry matter The accumulation of dry matter is commonly used as a parameter to characterize growth, because it usually has great economic significance (Ñústez et al., 2009). The distribution of dry matter plays an important role in the final yield of a crop, since it is given by the ability to accumulate biomass in the organs that are destined for harvest (Barrientos-Llanos et al., 2015). 1.2 Chlorophyll content Allows us to relate it to the nutritional level of the plants, it also has a close relationship with the photosynthesis index and these two factors, considerably influence the performance of a plant, both in its development and in the final yield of harvest (López-Tolentino et al., 2016).

Roselle (Hibiscus sabdariffa L.),is a species belonging to the Malvaceae family (Ríos et al., 2013). It is native to India and Malaysia. It has been widely distributed in the tropics and subtropics of both hemispheres, in addition, it has become naturalized in many areas of the Antilles and Central America (Morton, 1987). During the colonial era, the Spanish were the ones who introduced Roselle to Mexico (Romano-Cadena et al., 2017). It is a crop that is currently gaining more importance in Mexico and is part of the sector of spices and medicinal plants (Sánchez-Prado et al., 2019). In recent years it has had a potential use for lowering cholesterol and hypertension, in addition, it is attributed diuretic and antipyretic properties (Caamal et al., 2020). These benefits are supported by various scientific investigations that relate them to compounds such as vitamins E and C, polyphenolic acids and antioxidants such as flavonoids and anthocyanins (Cid and Guerrero, 2012). However, the information devoted to the study of Plant Growth-Promoting Bacteria in this crop is almost nil. Considering the above, the present work was developed, with the aim of defining which are the most important criteria for the selection of bacterial strains that promote plant growth in seedlings of two varieties of Roselle.