Field Trials Reveal Ecotype-Specific Responses to Mycorrhizal Inoculation in Rice.

Abdala Gamby Diedhiou,Daouda Mbodj,Laurent Laplaze,Mathieu Ndigue Faye,Aboubacry Kane,Souleymane Gaye,Sarah Pignoly,Baboucarr Manneh,Antony Champion,Fatou Kine Mbaye,Ibrahima Ndoye,Koffi Djaman

doi:10.1371/journal.pone.0167014

Abstract

The overuse of agricultural chemicals such as fertilizer and pesticides aimed at increasing crop yield results in environmental damage, particularly in the Sahelian zone where soils are fragile. Crop inoculation with beneficial soil microbes appears as a good alternative for reducing agricultural chemical needs, especially for small farmers. This, however, requires selecting optimal combinations of crop varieties and beneficial microbes tested in field conditions. In this study, we investigated the response of rice plants to inoculation with arbuscular mycorrhizal fungi (AMF) and plant growth promoting bacteria (PGPB) under screenhouse and field conditions in two consecutive seasons in Senegal. Evaluation of single and mixed inoculations with AMF and PGPB was conducted on rice (Oryza sativa) variety Sahel 202, on sterile soil under screenhouse conditions. We observed that inoculated plants, especially plants treated with AMF, grew taller, matured earlier and had higher grain yield than the non-inoculated plants. Mixed inoculation trials with two AMF strains were then conducted under irrigated field conditions with four O. sativa varieties, two O. glaberrima varieties and two interspecific NERICA varieties, belonging to 3 ecotypes (upland, irrigated, and rainfed lowland). We observed that the upland varieties had the best responses to inoculation, especially with regards to grain yield, harvest index and spikelet fertility. These results show the potential of using AMF to improve rice production with less chemical fertilizers and present new opportunities for the genetic improvement in rice to transfer the ability of forming beneficial rice-microbe associations into high yielding varieties in order to increase further rice yield potentials.

Highlights

Rice (Oryza saliva L.) is one of the oldest staple crops in the world [1], and the main source of calories for more than half of humanity [2]
No arbuscular mycorrhizal fungi (AMF) colonization was observed in the roots of non-inoculated plants, whereas typical arbuscular mycorrhizal (AM) structures such as arbuscules, hyphae and vesicles were observed within the roots of plants inoculated with one or the two AMF strains (G. aggregatum and R. irregularis) alone or in combination with PGPR strains
We analyzed the impact of inoculation with beneficial soil microorganisms on rice growth and yield in controlled and field conditions over two years

Summary

Introduction

Rice (Oryza saliva L.) is one of the oldest staple crops in the world [1], and the main source of calories for more than half of humanity [2]. Incentive policies were set up to increase local rice production with three objectives: creation and dissemination of high-yielding varieties, development of irrigation facilities and availability of inorganic fertilizers. In countries such as Senegal, this has led to increased crop yields and quality [5,6]. The yields are still low [7] and the prohibitive cost and environmental problems caused by chemical inputs [8,9,10] support the search for new sustainable strategies to promote soil fertility and improve rice production. These approaches include the application of organic fertilizers, the use of nitrogen-fixing green manure (Azolla sp., fallow legumes) and of beneficial rhizospheric microorganisms such as arbuscular mycorrhizal fungi (AMF) and plant growth promoting bacteria (PGPB) and the selection of root systems for improved water and nutrient acquisition [4]

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Conclusion