The role of root size versus root efficiency in phosphorus acquisition in rice

Abstract

In rice, genotypic differences in phosphorus (P) uptake from P-deficient soils are generally proportional to differences in root biomass or surface area (RSA). It is not known to what extent genotypic variation for root efficiency (RE) exists or contributes to P uptake. We evaluated 196 rice accessions under P deficiency and detected wide variation for root biomass which was significantly associated with plant performance. However, at a given root size, up to 3-fold variation in total biomass existed, indicating that genotypes differed in how efficiently their root system acquired P to support overall plant growth. This was subsequently confirmed, identifying a traditional genotype, DJ123, with 2.5-fold higher RE (32.5 µg P cm(-2) RSA) compared with the popular modern cultivar IR64. A P depletion experiment indicated that RE could not be explained by P uptake kinetics since even IR64 depleted P to <20nM. A genome-wide association study identified loci associated with RE, and in most cases the more common marker type improved RE. This may indicate that modern rice cultivars lost the ability for efficient P uptake, possibly because they were selected under highly fertile conditions. One association detected on chromosome 11 that was present in a small group of seven accessions (including DJ123) improved RE above the level already present in many traditional rice accessions. This subspecies is known to harbor genes enhancing stress tolerance, and DJ123 may thus serve as a donor of RE traits and genes that modern cultivars seem to have lost.

Superior Root Hair Formation Confers Root Efficiency in Some, But Not All, Rice Genotypes upon P Deficiency

“…To investigate natural variation of rice root hair formation 10 genotypes varying in their RE under P deficiency (Mori et al, 2016) were grown in an easy to handle and reproducible nutrient solution setting. Average root hair length and density at low (1 μM) or high (100 μM) P supply are shown in Figure 1 for main roots and in Supplementary Figure S1 for L-type LRs, S-type LRs, and second order LRs.…”

“…The same genotypes used for the Rhizobox experiment were grown in the upland field, with the only exception being Sadri Tor Misri, which was not available at the time of planting, and replaced by Mudgo, another lowland-adapted genotype with a similar root system and similar RE performance. Four rows of each genotype were sown in three randomized replicate blocks at each P treatment simultaneously with the 2014 field experiment published in Mori et al (2016). For all measurements and both harvests (at 50 and 100 DAS) the middle two rows were utilized providing two border rows per genotype.…”

“…Building on this idea, a recent study investigated root traits in a broad rice association panel under P deficient field conditions. Generally, performance under P deficiency was positively associated with root size, however, a small subset of accessions was identified as having high root efficiency (RE), meaning above-average P uptake with a rather small root system (Mori et al, 2016). The traditional variety DJ123 consistently ranked as having high RE, taking up 2.5-fold more P per cm 2 of RSA compared to the modern variety IR64.…”

Genotypic Differences in Phosphorus Efficiency and the Performance of Physiological Characteristics in Response to Low Phosphorus Stress of Soybean in Southwest of China

“…These results corresponded well with previous studies which showed that the P-efficient plant genotypes demonstrated greater biomass compared to the P-inefficient when grown in low P condition. Some scholars had reported that P-efficient plants of soybean (Zhao et al, 2004), rice ( Oryza sativa L.) (Wissuwa and Ae, 2001; Mori et al, 2016), maize ( Zea mays L.) (Zhang, 2012), and Brassica napus (Zhang et al, 2009) showed significantly biomass ascendancy compared with P-inefficient plants in P shortage conditions.…”

“…In this study, P accumulation of E141 and E311 was higher than the other genotypes in low P solution (Figure 4C). Some scholars reported that P-efficient soybean genotypes are able to obtain sufficient P from acid red soil and alkaline soil under P lack conditions (Zhao et al, 2004; Pan et al, 2008), and other P-efficient plant species also showed positively P accumulation grown in P lack conditions, like maize (Liu et al, 2004), wheat ( Triticum aestivum L.) (Fageria and Baligar, 1999) and rice (Mori et al, 2016). It indicated that the P-efficient soybean genotypes (especially E141 and E311) demonstrate great capability on P absorption and accumulation potentials.…”