Abstract
The effect of soil type on establishment of arbuscular mycorrhizal (AM) fungi, and their effects on plant growth and resistance to rice pests are poorly understood. We investigated the effects of inoculation with AM fungi on rice plants in two different unsterilized field soils under greenhouse and field conditions in two consecutive years in Louisiana, United States. We tested whether inoculation with AM fungi in the two soils changed plant biomass, nutrient concentration, resistance to pests, and yields. Inoculation with a commercial formulation of AM fungi increased root colonization by fungi in all soils, regardless of soil P availability; it also increased densities of root-feeding rice water weevil larvae and growth of leaf-feeding fall armyworm larvae, but these effects were soil-dependent. Inoculation with AM fungi had no effect on N and P concentrations or rice yields. The effect on plant biomass was also soil-dependent. Our study provides evidence for the first time that inoculation with AM fungi can increase colonization of roots of rice plants, but the effects of colonization on resistance to pests and plant biomass appear to be soil dependent. Moreover, the increased susceptibility to pests of rice colonized by AM fungi does not appear to be related to nutrient concentrations.
Highlights
Arbuscular mycorrhizal fungi (AM fungi) belong to the phylum Glomeromycota and are obligate symbionts that form mostly mutualistic associations with the roots of ca. 90% of terrestrial plants[1]
The effect of inoculation with arbuscular mycorrhizal (AM) fungi was significant in rice water weevil (RWW)-M1 (29 dai, F1,8 = 23.04, P = 0.001), Rice Water Weevil Mamou 2 (RWW-M2) (40 dai, F1,8 = 140.31, P < 0.0001), and Rice Water Weevil Crowley 1 (RWW-C1) (44 dai, F1,8 = 25.57, P = 0.001) (Table 1)
For Rice Water Weevil Mamou 1 (RWW-M1), in which colonization was assessed both before and after flooding, 29-day-old rice plants inoculated with AM fungi exhibited a colonization rate of 13% before flooding
Summary
Arbuscular mycorrhizal fungi (AM fungi) belong to the phylum Glomeromycota and are obligate symbionts that form mostly mutualistic associations with the roots of ca. 90% of terrestrial plants[1]. The disadvantages of soil inoculation with commercial formulations of AM fungi in agricultural fields include high application costs, the lack of positive effects of AM fungi under conditions of high nutrient (especially P) availability, and lack of effect on plant growth in some plants in some environments[24]. Bernaola et al.[12] demonstrated that AM fungi inoculation increases local and systemic susceptibility of rice plants to different pest organisms, including RWW and FAW, under field and greenhouse conditions It is still not clear how soil characteristics influence colonization by AM fungi or the effects of colonization by AM fungi on the interactions between rice and its insect herbivores. A commercial formulation of AM fungi containing six species of Glomus was used, and effects of inoculation with AM fungi on performance of two insects were assessed
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