Abstract
BackgroundArbuscular mycorrhizal (AM) fungi form symbiotic associations with roots in most land plants. AM symbiosis provides benefits to host plants by improving nutrition and fitness. AM symbiosis has also been associated with increased resistance to pathogen infection in several plant species. In rice, the effects of AM symbiosis is less studied, probably because rice is mostly cultivated in wetland areas, and plants in such ecosystems have traditionally been considered as non-mycorrhizal. In this study, we investigated the effect of AM inoculation on performance of elite rice cultivars (Oryza sativa, japonica subspecies) under greenhouse and field conditions, focusing on growth, resistance to the rice blast fungus Magnaporthe oryzae and productivity.ResultsThe response to inoculation with either Funneliformis mosseae or Rhizophagus irregularis was evaluated in a panel of 12 rice cultivars. Root colonization was confirmed in all rice varieties. Under controlled greenhouse conditions, R. irregularis showed higher levels of root colonization than F. mosseae. Compared to non-inoculated plants, the AM-inoculated plants had higher Pi content in leaves. Varietal differences were observed in the growth response of rice cultivars to inoculation with an AM fungus, which were also dependent on the identity of the fungus. Thus, positive, negligible, and negative responses to AM inoculation were observed among rice varieties. Inoculation with F. mosseae or R. irregularis also conferred protection to the rice blast fungus, but the level of mycorrhiza-induced blast resistance varied among host genotypes. Rice seedlings (Loto and Gines varieties) were pre-inoculated with R. irregularis, transplanted into flooded fields, and grown until maturity. A significant increase in grain yield was observed in mycorrhizal plants compared with non-mycorrhizal plants, which was related to an increase in the number of panicles.ConclusionResults here presented support that rice plants benefit from the AM symbiosis while illustrating the potential of using AM fungi to improve productivity and blast resistance in cultivated rice. Differences observed in the mycorrhizal responsiveness among the different rice cultivars in terms of growth promotion and blast resistance indicate that evaluation of benefits received by the AM symbiosis needs to be carefully evaluated on a case-by-case basis for efficient exploitation of AM fungi in rice cultivation.
Highlights
Arbuscular mycorrhizal (AM) fungi form symbiotic associations with roots in most land plants
Effect of Arbuscular mycorrhizal fungi (AMF) Inoculation on Growth of Rice Plants We conducted experiments to assess the phenotypic response to inoculation by an AM fungus, Funneliformis mosseae and Rhizophagus irregularis, in a panel of temperate japonica rice cultivars
Rice seedlings that had been inoculated with either F. mosseae or R. irregularis grew better compared to noninoculated seedlings in most rice cultivars, a phenomenon generally known as positive Mycorrhizal Growth response (MGR) (Johnson and Graham 2013)
Summary
Arbuscular mycorrhizal (AM) fungi form symbiotic associations with roots in most land plants. Root colonization by AM fungi has been shown to improve nutrition, helping in plant growth and development Another benefit conferred by the AM symbiosis in several plant species is improved resistance to biotic and abiotic stress (Fritz et al 2006; Pozo and Azcón-Aguilar 2007; CamposSoriano et al 2012; Nair et al 2015; Cornejo et al 2017; Wang et al 2018; Rivero et al 2018). AM symbiosis is not always advantageous, as the effects can be positive, negative, or neutral to the host plant (Tawaraya 2003; Grace et al 2009; Sawers et al 2017; Watts-Williams et al 2019) Environmental factors, such as soil properties, nutrient availability, or agricultural management practices, can affect the association of crop plants with AM fungi. AM fungi have been proposed as an alternative production practice to promote yield in crops, root colonization by AM fungi might not always be favorable for the host plant
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