Entomopathogenic fungi-based mechanisms for improved Fe nutrition in sorghum plants grown on calcareous substrates

Abstract

Although entomopathogenic fungi (EPF) are best known for their ability to protect crops against insect pests, they may have other beneficial effects on their host plants. These effects, which include promoting plant growth and conferring resistance against abiotic stresses, have been examined in recent years to acquire a better understanding of them. The primary purposes of the present study were (i) to ascertain in vitro whether three different strains of EPF (viz., Metarhizium, Beauveria and Isaria) would increase the Fe bioavailability in calcareous or non-calcareous media containing various Fe sources (ferrihydrite, hematite and goethite) and (ii) to assess the influence of the EPF inoculation method (seed dressing, soil treatment or leaf spraying) on the extent of the endophytic colonization of sorghum and the improvement in the Fe nutrition of pot-grown sorghum plants on an artificial calcareous substrate. All the EPFs studied were found to increase the Fe availability during the in vitro assay. The most efficient EPF was M. brunneum EAMa 01/58–Su, which lowered the pH of the calcareous medium, suggesting that it used a different strategy (organic acid release) than the other two fungi that raised the pH of the non-calcareous medium. The three methods used to inoculate sorghum plants with B. bassiana and M. brunneum in the pot experiment led to differences in re-isolation from plant tissues and in the plant height. These three inoculation methods increased the leaf chlorophyll content of young leaves when the Fe deficiency symptoms were most apparent in the control plants (without fungal inoculation) as well as the Fe content of the above-ground biomass in the plants at the end of the experiment. The total root lengths and fine roots were also increased in response to fungal applications with the three inoculation methods. However, the soil treatment was the most efficient method; thus, its effect on the leaf chlorophyll content was the most persistent, and the effects on the total root length and fine roots were the most apparent. In conclusion, EPF improved the Fe nutrition of the sorghum plants, but their effects depended on the inoculation method.

Bottom-up effects of endophytic Beauveria bassiana on multitrophic interactions between the cotton aphid, Aphis gossypii, and its natural enemies in melon

“…The recent discovery that entomopathogenic fungi can be endophytic with a new systemic biological control role raises concerns about previously unconsidered interactions with beneficial and non-target organisms, including other biological control agents (Jaber and Ownley 2018; Vega 2018). Endophytic plant colonization by entomopathogenic fungi induces a wide range of changes in the composition and quantity of plant nutrients and/or defensive compounds within the plant; this has implications for the quality of the plant as a food source for herbivores (Gualandi et al 2014;Shrivastava et al 2015;Sánchez-Rodríguez et al 2015;Liao et al 2017;Raya-Díaz et al 2017;Krell et al 2018). These changes may lead to a cascade of positive or negative changes in the life history characteristics and behaviour of herbivores and their interactions with natural enemies.…”

Soil Nutrients Effects on the Performance of Durum Wheat Inoculated with Entomopathogenic Fungi

“…Secondly, the role of M. brunneum as a growth promoter seems to be related to the content of poorly crystalline Fe oxides in the soil ( Figure 4B). This may be a result of M. brunneum increasing soil Fe availability [14,16] via the mean increase in Fe DTPA found in the group of 12 soils (0.23 mg kg −1 ), especially for the GSGYI > 15 (0.68 mg kg −1 ) after harvest ( Figure S4). Moreover, the positive and significant correlation found between the relative increase of Fe available between M. brunneum and the Control at harvest with the relative increase in ADM (R = 0.585, p = 0.045) supports this hypothesis, as the fungus was able to directly mobilize more Fe in the soil or stimulates the plant to do so, thereby triggering a growth promotion effect.…”

“…Success in the mutualistic relationship between EF and wheat plants depends on the fungal strain and soil properties. been investigated as plant growth promoters [10-12] and nutritional enhancers [10,[13][14][15][16]. Although B. bassiana, M. brunneum or both fulfill the expectations of most studies, these studies were largely conducted under conditions far from typical field settings.…”

“…Zinc deficiency is, therefore, especially important in countries with diets based on cereals grown in soils with low soil Zn availability [22] but also in countries such as Spain, where farmers seek to improve wheat quality. Although previous studies have shown Beauveria bassiana and Metarhizium brunneum to increase the bioavailability of micronutrients such as Fe [14,16], the effects of EF on biomass in the plants they colonize, P and Zn plant uptake and grain quality remain largely unexplored. Further, there is a well-known negative interaction between P and Zn in soil [23], and a lack of information about how EFs may affect such interactions in soils with limited bioavailability of these nutrients.The main objective of this study was to elucidate the effects of soil properties on the relationship between EFs (B. bassiana and M. brunneum) and durum wheat plants, with an emphasis on plant growth and the uptake of nutrients (primarily P and Zn).…”

Evaluation of commercial products based on Isaria fumosorosea and Verticillium lecanii fungi as an alternative in the biocontrol of Phenacoccus solenopsis Tinsley (Hemiptera: Pseudococcidae)

“…Although the mechanism of reduction of the pest is not known yet, some studies suggest that the insects could cause a significant loss of plant nutrients through their feeding damage. In addition, the plants seem to have a mechanism to recover those nutrients, through the entomopathogenic fungi (Raya-Díaz et al, 2017).…”