Decline of seedling phosphorus use efficiency in the heterotic pool of flint maize breeding lines since the onset of hybrid breeding

Abstract

Improved management and breeding increased maize (Zea mays L.) yields over the last century, but nutritional efficiency was usually not the focus. This study investigates whether old and recently released flint and dent maize seedlings vary in the phosphorus (P) acquisition and utilization. P use efficiency (PUE) and related traits were measured and compared at two P levels in a calcareous soil. PUE and P acquisition efficiency (PAE) from founder flints to elite flints declined over the last decades. This was associated with smaller root systems, reduced ability to exploit external P, decreased rhizosphere pH and shorter root hairs in low P. Comparing flints with doubled haploid landraces (DH_LR), old and elite dents and hybrids revealed that dents started to acquire exogenous P earlier and had improved PUE. Most DH_LRs had similar PUE as elite flints. When evaluating root traits associated with P efficiency, seed P was also critical, and it is important to stack different root traits to optimize PUE, P utilization efficiency (PUtE) and PAE in breeding programmes. The root hair length, the ability to acidify the rhizosphere and the root diameter in flint and dent pools may be utilized to improve P use in maize germplasm.

Genetic analyses of root traits: Implications for environmental adaptation and new variety development: A review

“…However, the effects of N deficiency on the root system vary widely across different studies. The acute angles are formed as the roots attempt to develop vertically but N deficiency interferes with essential processes such as the synthesis of protein, nucleic acid and enzymes required for proper root development (Li, Mang, et al, 2021). Phosphorous availability in the soil affects root traits, including root diameter, length, surface area and lateral root development (Wang et al, 2021).…”

Nitrogen Fertilizer Type and Genotype as Drivers of P Acquisition and Rhizosphere Microbiota Assembly in Juvenile Maize Plants

“…Interestingly, these adaptations to P deficiency are strongly dependent on the maize genotype. For example, under low-P conditions, several recently released maize elite flint lines developed a smaller root system with shorter root hairs compared to older founder flint lines at juvenile stages [ 16 ]. In addition, maize inbred lines differed greatly in their responsiveness to arbuscular mycorrhizal fungi under low-phosphorus conditions [ 17 , 18 ].…”

“…Furthermore, the availability of different nitrogen forms may affect the presence or activity of beneficial soil microbes in the context of P i acquisition. Such mechanisms may, however, only become relevant at later growth stages, as young developing maize plants initially exclusively rely on nutrient remobilization from the seeds, especially under low P i availability [ 16 ], as maize initially has generally a rather small root for supplying the large shoot.…”

Can we abandon phosphorus starter fertilizer in maize? Results from a diverse panel of elite and doubled haploid landrace lines of maize (Zea mays L.)

“…Genotypes being PUE would provide the same yield even under reduced P soil concentration and PUE is, therefore, a desired goal in breeding. Performance comparisons between doubled haploid landrace lines and modern elite lines revealed a similar or even a reduced PUE in modern lines (Li et al, 2021). A prevailing hypothesis for this putative trend is that landraces have an enriched gene pool with beneficial alleles, which may have been lost during the breeding process of modern varieties under optimal fertilized conditions (Bellon, 2009;Wissuwa et al, 2009).…”

“…We approached this question with a diverse panel of maize genotypes, including both Flint and Dent elite lines that represent the heterotic pattern prevalent in Central Europe and at the same time two populations that have been separated for centuries. In addition, doubled haploid lines from six European Flint landraces were also investigated in this study to test the hypothesis that selection of elite material mainly under optimal agricultural conditions eroded the need for specialized adaptions, such as traits for efficient phosphorus acquisition (Li et al, 2021). The doubled haploid lines from the landraces allow the preservation of the genetic variation in only one step from a heterogenous population and facilitate replicated trials (Strigens et al, 2013) to examine the potential of doubled haploid lines under varying P levels in this study.…”