Abstract
If water saving methods of rice management are to be adopted, the interaction between rice plants and arbuscular mycorrhizal (AM) fungi will grow in agronomic significance. As yet there are very few studies on the interaction between rice and AM fungi and none on host genetics. A subset 334 cultivars from the Rice Diversity Panel 1 were grown in 250 L boxes filled with phosphorus (P) deficient aerobic soil without addition, with added rock phosphate and with rock phosphate and the AM fungus Rhizophagus irregularis. Statistical analysis of position of plants revealed a positive effect of their neighbors on their dry weight which was stronger in the presence of rock phosphate and even stronger with rock phosphate and AM fungi. A weak but significant difference in the response of cultivars to AM fungus treatment in terms of shoot dry weight (SDW) was revealed. Neighbor hyphal colonization was positively related to a plant’s hyphal colonization, providing insights into the way a network of AM fungi interact with multiple hosts. Hyphal colonization ranged from 21 to 89%, and 42% of the variation was explained by rice genotype. Colonization was slightly lower in aus cultivars than other rice subgroups and high in cultivars from the Philippines. Genome wide association (GWA) mapping for hyphal colonization revealed 23 putative quantitative trait loci (QTLs) indicating there is an opportunity to investigate the impact of allelic variation in rice on AM fungal colonization. Using published transcriptomics data for AM response in rice, some promising candidate genes are revealed under these QTLs being a calcium/calmodulin serine/threonine protein kinase at 4.9 Mbp on chromosome 1, two ammonium transporters genes at 24.6 Mbp on chromosome 2 and a cluster of subtilisin genes at 1.2 Mbp on chromosome 4. Future studies should concentrate on the biological significance of genetic variation in rice for AM colonization.
Highlights
The symbiotic interaction between land plants and mycorrhizal fungi is ancient and is thought to be driven by the provision of nutrients ( P and N) to the plant in exchange for carbon (Smith and Read, 2008) in the form of sugar and lipids (Keymer and Gutjahr, 2018)
For example, been shown that in flooded conditions arbuscular mycorrhizal (AM) fungi are very scarce on rice (Ilag et al, 1987) while it has been demonstrated that flooding of aerobically-grown rice roots decreases AM fungal colonization within 7 days- it does not eliminate AM fungi completely (Vallino et al, 2014)
It has recently been shown that AM fungi colonization and AM fungal species richness were substantially higher under system of rice intensification (SRI) than conventional flooding (Watanarojanaporn et al, 2013)
Summary
The symbiotic interaction between land plants and mycorrhizal fungi is ancient and is thought to be driven by the provision of nutrients ( P and N) to the plant in exchange for carbon (Smith and Read, 2008) in the form of sugar and lipids (Keymer and Gutjahr, 2018). Most grasses, including major crop plants, form symbioses with arbuscular mycorrhizal (AM) fungi that can affect agricultural plant productivity (Van Der Heijden et al, 2015), but research on the interaction between the grass crop rice and AM fungi has been very limited. This is probably because in flooded soil, in which most rice is grown, this association is traditionally considered unimportant. It is timely to investigate the interaction more closely in order to consider the possibility that future rice breeding might need to incorporate the knowledge gained
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