Diversity and Biological function of Indigenous Arbuscular Mycorrhizal Fungi in Rice

Abstract

Rice forms a symbiotic interaction with arbuscular mycorrhizal fungi (AMF). AMF provides rice with the improvement of nutrient acquisition through the AMF uptake pathway. Moreover, AMF enhances phosphorus availability by the release of acid phosphatase. In lowland rice paddies, AMF symbiosis deteriorated by flooding. However, some AMF genera were preferentially detected in rice roots under flooded conditions. To examine the influence of flooding on AMF diversity in lowland rice paddies, Sangyod Muang Phatthalung (SMP) rice seedlings were cultivated in organic rice paddy soil under non-flooded and flooded conditions. Based on the SSU-ITS-LSU ribosomal DNA sequences, there were 21 AMF operation taxonomic units (OTU) in the rice roots. Acaulospora was the dominant AMF genus in the flooded roots. Later, Acaulospora spores were isolated and propagated by trap culture. Based on their SSU-ITS-LSU sequenes, the cultured Acaulospora spores were Acaulospora morrowiae. To characterize the symbiotic function of the dominant Acaulospora morrowiae in rice, a lowland indica SMP rice, an upland indica Rai Dawk Kha Phangna (DK), and a lowland japonica Nipponbare rice were grown in 0.8-L pots containing sterile sand and compost, recolonized with a native microbial filtrate in the greenhouse for 6 weeks. The result showed that 60-70 % of the rice roots were colonized by A. morrowiae. The inoculation of A. morrowiae suppressed rice growth but did not change the efficiency of photosynthesis. In soil, A. morrowiae increased P availability via the higher activity of acid phosphatase. We anticipated that the growth suppression due to the A. morrowiae might be mitigated by the limitation of AMF colonization during rice cultivation due to flooding. However, the Acaulospora fungi might form a symbiosis with weedy plants in dry seasons, indirectly improving soil P for rice growth in the next cultivation seasons