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

Abstract

Root hairs are a low-cost way to extend root surface area (RSA), water and nutrient acquisition. This study investigated to what extend variation exists for root hair formation in rice in dependence of genotype, phosphorus (P) supply, growth medium, and root type. In general, genotypic variation was found for three root hair properties: root hair length, density, and longevity. In low P nutrient solution more than twofold genotypic difference was detected for root hair length while only onefold variation was found in low P soil. These differences were mostly due to the ability of some genotypes to increase root hair length in response to P deficiency. In addition, we were able to show that a higher proportion of root hairs remain viable even in mature, field-grown plants under low P conditions. All investigated root hair parameters exhibited high correlations across root types which were always higher in the low P conditions compared to the high P controls. Therefore we hypothesize that a low P response leads to a systemic signal in the entire root system. The genotype DJ123 consistently had the longest root hairs under low P conditions and we estimated that, across the field-grown root system, root hairs increased the total RSA by 31% in this genotype. This would explain why DJ123 is considered to be very root efficient in P uptake and suggests that DJ123 should be utilized as a donor in breeding for enhanced P uptake. Surprisingly, another root and P efficient genotype seemed not to rely on root hair growth upon P deficiency and therefore must contain different methods of low P adaptation. Genotypic ranking of root hair properties did change substantially with growth condition highlighting the need to phenotype plants in soil-based conditions or at least to validate results obtained in solution-based growth conditions.

Phosphorus Efficient Phenotype of Rice

“…Lateral roots were recently proposed to have different, specialized functions depending on their developmental type [74]. Supporting this proposal, we showed that the thinner lateral roots of rice produced shorter and fewer root hairs [75], and found a positive linear relationship between lateral root diameter and root hair length [56]. These results were reproduced in different growth conditions, with main roots (seminal and crown axile roots) consistently producing the longest and most root hairs, followed by L-type and S-type lateral roots (Figure 2) (see Section 4 for experimental details).…”

“…Earlier studies in one set of near-isogenic rice lines differing in root size and P uptake showed these differences remained unchanged in sterilized soil [55]. Based on the limited evidence available to date, one may tentatively conclude that the AM symbiosis contributes less to rice genotypic differences in P uptake compared to root attributes such as size, fineness or root hair length and density [56].…”

Farm yard manure enhances phosphate fertilizer use efficiency in different upland rice genotypes through mitigating aluminium toxicity

“…FOFIFA 172 is more responsive (less performant under low P input) than Chomrong Dhan. The generally P-efficient genotype DJ123, known for its good performance on low P soils (Mori et al, 2016; Nestler & Wissuwa, 2016; Vandamme, Wissuwa, et al, 2016), was not high yielding in the low P environment of this study and it even showed comparable or lower yields than the generally P-inefficient rice genotype, NERICA 4. Hence, this indicates that this P-efficient genotype (DJ123) is likely not adapted to the cold highlands of Madagascar while NERICA 4 seems somehow more robust in such environment.…”

“…The main significant effects of genotypes (Table 4) are more affected by their growth potential, i.e. under TSP+FYM application, rather than by their inherent differences in in PAE and PUE that exist among rice genotypes (De Bauw et al, 2019; Nestler and Wissuwa, 2016; Vandamme et al, 2016a). This indicates that genotype selection likely becomes inferior to management options when soil limitations are very severe.…”

“…Genotypic variation exists in both PUE and PAE (Vandamme, Rose, et al, 2016; Vandamme, Wissuwa, et al, 2016; Wissuwa & Ae, 2001). Genotypic variation in PAE is related to a combination of differences in effective root surface area (Nestler & Wissuwa, 2016) per plant or in P acquisition strategies (Clark, 1983). For example, it is well established that plants can mobilize soil-adsorbed P by secreting root exudates, with different underlying P-solubilisation strategies from the inorganic P pool, or that plants can access organic P forms by the excretion of phosphatases (Richardson et al, 2011; Rose et al, 2013).…”