P-efficient Varieties Research Articles

Root Architectural Adaptations to Phosphorus Deficiency: Unraveling Genotypic Variability in Wheat Seedlings

Understanding the changes in the root system architecture of bread wheat under phosphorus (P)-limited conditions is critical for identifying specific traits contributing to improved P uptake. Phenotypic variability in root, biomass, and P index-related traits among 204 diverse wheat genotypes at the seedling stage was examined under low and optimum P treatments. Strong genotypic and phenotypic associations between P utilization efficiency (PUtE) and total root volume, dry weight of root and shoot, total P uptake, and total plant biomass were observed under optimum P. Under low P, strong positive correlations between PUtE and total root length, total root volume, total surface area, and total biomass were observed, while it was negatively correlated with average diameter. These traits exhibited medium to high heritability. Under low P, average root diameter, primary root length, root mass ratio, total root tips, and surface area showed high Shannon–Weaver diversity index (H’) values (>0.79). The agglomerative hierarchical clustering analysis grouped the genotypes into four distinct clusters. The best performing genotypes in Clusters I and II indicated their strong relationship with P use efficiency due to higher percent increases in total root length, total surface area, total root volume, total root tips, total biomass, P efficiency ratio, specific root length, and PUtE under low P as compared to optimum P conditions. The present study identified specific root system architectural traits and P use-efficient genotypes (SHANGHAI, Pavon F76, BWL 5233, SONALIKA, KHARCHIA LOCAL, WH 102, BWL 4425, HD 2888.2, CBW 12, MN75136/PGO, KRL 19, and WH 1022) associated with efficient P uptake and utilization. These identified genotypes and traits may be useful in wheat breeding programs to develop P-efficient varieties with better adaptations for sustainable agriculture.

Genetic variation associated with the shoot biomass of upland cotton seedlings under contrasting phosphate supplies

As over-fertilization leads to environmental concerns, selecting cultivars that can produce high yields on phosphorus (P)-deficient soils and understanding the genetic basis underlying P-starved tolerance have become crucially important. In this study, we evaluated the variation of ten P deficiency-related traits at the seedling stage of 419 core accessions in two different environments. The results showed that the shoot dry weight (SDW) could be considered an indicator for screening P-tolerant germplasm resources. A genome-wide association study (GWAS) was performed for two SDW-related traits using 3.66 million high-quality single-nucleotide polymorphisms (SNPs). A total of 102 significantly associated SNPs were located within or near 137 genes, of which, 27 of the SNPs were consistently detected for multiple traits or multiple environments. We further identified and validated a novel candidate gene, Gh_D11G2219, by qRT-PCR analysis and virus-induced gene silencing (VIGS), and the results suggested that Gh_D11G2219 plays a role in the positive regulation of tolerance to P deficiency stress in cotton. In addition, the elite SNPs linked to tolerance to P-starved stress have undergone negative selection pressure during the cotton breeding process. This is the first GWAS of P deficiency tolerance, and the identified SNPs and candidate genes provide valuable information for breeding highly P-efficient varieties.

Rapid identification of phosphorus-efficient genotypes from commercially grown tomato (Solanum lycopersicum L.) varieties in a simulated soil solution

ABSTRACTThis study aimed at developing a successful scheme to identify P-efficient varieties. A simulated soil solution (SSS), comprised of Hoagland solution slightly modified with tri-calcium phosphate (TCP) as the sole P source, was evaluated. The identified SSS was then used to screen P-efficient tomato varieties based on their relative shoot dry biomass in a low P SSS condition (LP). The identified varieties were characterised for their P efficient traits including root characteristics and low-P stress factor (PSF). The nutrient solution with TCP and 15 mM extra CaCl2 was the best SSS for identifying P-efficient varieties. Among the tested varieties, ‘Japanese Black Trifele Og’ (JBT) and ‘Great White Og’ (GW) were the most P-efficient; ‘Green Tiger’ (GT) and ‘Chefs Choice Orange F1ʹ (CCO) were the least P-efficient varieties. JBT had the greatest relative root morphological traits (root dry mass, length, volume, and fork number) and the lowest PSF (30%). On the contrary, CCO had the greatest PSF (80%) indicating poor performance in LP condition. The selected P-efficient tomato varieties can also be used to identify the P efficiency regulating genes. In the future, improved tomato varieties can be developed through biotechnology and breeding programmes using the identified P-efficient genotypes.

Mapping and cloning of quantitative trait loci for phosphorus efficiency in crops: opportunities and challenges

Phosphorus (P) is an essential mineral element required in large quantities by plants. Globally, the availability of P in many soils is poor. Breeding crops that can acquire and utilise this limited resource with high efficiency is an important goal for agricultural sustainability in the future. The mapping and cloning of quantitative trait loci (QTLs) provides an effective tool in analyzing the genetic mechanisms underlying P efficiency and breeding P-efficient varieties. This paper describes the QTL mapping of traits related to P efficiency which impact on shoot biomass or yield of crops in the past 20 years. It summarises the progress of studies on crop P-efficiency related QTLs and discusses the challenges for the cloning of QTLs. It proposes a scheme to develop crop genotypes with improved P efficiency. It also describes emerging methods, such as QTL-seq, genome-wide association analysis, and RNA-seq, that aid the rapid identification of P-efficiency related genes in crops. Traits conferring P efficiency are heritable. Thus, it is feasible to incorporate phenotyping and selection for P efficiency in crop breeding programs. Identification of QTLs for target traits is a key step to enhancing the P efficiency of crops. Numerous QTLs have been identified that affect P efficiency in key crops, but few causal genes have been identified and breeding P-efficient crop varieties using marker-assisted selection (MAS) has not progressed far. The challenge now is to identify the specific genes controlling P-efficiency related traits. The availability of complete genome sequences for more crops, and the combination of conventional linkage mapping, association mapping, QTL-seq, transcriptomics and gene editing technologies can accelerate the cloning and confirmation of genes underlying QTL affecting P-efficiency related traits. Knowledge of these genes will be helpful in revealing the molecular mechanisms underlying P efficiency in crops, as well as providing the opportunity to improve crop P efficiency through MAS or gene manipulation.

Overcoming Phosphorus Deficiency in West African Pearl Millet and Sorghum Production Systems: Promising Options for Crop Improvement.

West Africa (WA) is among the most food insecure regions. Rapid human population growth and stagnating crop yields greatly contribute to this fact. Poor soil fertility, especially low plant available phosphorus (P) is constraining food production in the region. P-fertilizer use in WA is among the lowest in the world due to inaccessibility and high prices, often unaffordable to resource-poor subsistence farmers. This article provides an overview of soil P-deficiency in WA and opportunities to overcome it by exploiting sorghum and pearl millet genetic diversity. The topic is examined from the perspectives of plant breeding, soil science, plant physiology, plant nutrition, and agronomy, thereby referring to recent results obtained in a joint interdisciplinary research project, and reported literature. Specific objectives are to summarize: (1) The global problem of P scarcity and how it will affect WA farmers; (2) Soil P dynamics in WA soils; (3) Plant responses to P deficiency; (4) Opportunities to breed for improved crop adaptation to P-limited conditions; (5) Challenges and trade-offs for improving sorghum and pearl millet adaptation to low-P conditions in WA; and (6) Systems approaches to address soil P-deficiency in WA. Sorghum and pearl millet in WA exhibit highly significant genetic variation for P-uptake efficiency, P-utilization efficiency, and grain yield under P-limited conditions indicating the possibility of breeding P-efficient varieties. Direct selection under P-limited conditions was more efficient than indirect selection under high-P conditions. Combining P-uptake and P-utilization efficiency is recommendable for WA to avoid further soil mining. Genomic regions responsible for P-uptake, P-utilization efficiency, and grain yield under low-P have been identified in WA sorghum and pearl millet, and marker-assisted selection could be possible once these genomic regions are validated. Developing P-efficient genotypes may not, however, be a sustainable solution in itself in the long-term without replenishing the P removed from the system in harvested produce. We therefore propose the use of integrated soil fertility management and systems-oriented management such as enhanced crop-tree-livestock integration in combination with P-use-efficiency-improved varieties. Recycling P from animal bones, human excreta and urine are also possible approaches toward a partially closed and efficient P cycle in WA.

PHOSPHORUS DEFICIENCY IMPAIRS SHOOT REGROWTH OF SUGARCANE VARIETIES

SUMMARYThe shoot regrowth vigour of sugarcane varieties having contrasting phosphorus (P) efficiency was evaluated under varying soil P availability. The P-inefficient (IAC91–1099 and IACSP94–2101) and -efficient (IACSP94–2094 and IACSP95–5000) sugarcane varieties were grown under low (25 mg P kg−1 soil) or high (400 mg P kg−1 soil) P supply at planting. After 90 days (first cycle of growth), the shoots were harvested and regrowth was studied 70–75 days later by evaluating photosynthesis, leaf area formation, biomass production and P uptake. The shoot dry matter (DM) of sugarcane regrowth subjected to a low P supply was genotype-dependent, with the P-efficient varieties exhibiting greater values than the inefficient ones. This result was explained by the greater efficiency of IACSP94–2094 and IACSP95–5000 in acquiring P rather than P utilization efficiency for shoot biomass production. The root P stored during the first cycle of growth would represent only a minor fraction (< 20%) of the total P content in the shoots at the end of the regrowth period. Thus, we argue that the improved shoot P uptake of the P-efficient varieties was related to their ability to sustain P acquisition after harvesting rather than to the remobilization of root P reserves. Moreover, our data revealed that net CO2 assimilation per leaf area was not associated with differential performance among varieties under P deficiency, suggesting a more critical role of total leaf area in photosynthate supply for sugarcane regrowth. In conclusion, sugarcane regrowth is improved in P-efficient varieties under P deficiency conditions, a finding of practical relevance as such ability might benefit the productivity and the longevity of sugarcane ratoons in low P tropical soils.

Towards understanding the traits contributing to performance of pearl millet open-pollinated varieties in phosphorus-limited environments of West Africa

Pearl millet [Pennisetum glaucum (L.) R. Br.] open-pollinated varieties, which are the predominant cultivars, have never been systematically evaluated for adaptation to low-soil phosphorus (P), a major constraint on pearl millet production in West Africa (WA). We evaluated grain yield (GY), flowering time (FLO), harvest index (HI), and residual grain yields (RGY) of 102 open-pollinated varieties from WA under low-P (−P) and high-P (+P) field conditions in six environments of WA. In addition, PE-related traits of the varieties were evaluated at early growth stage in a pot experiment. Significant genetic variation was observed for GY, FLO, HI and PE-related traits. P-efficient varieties had higher yield under −P conditions. Varietal performance under −P varied across environments depending on FLO, relative flowering delay under −P (FD) and RGY measured in the field. Low-P-susceptible varieties had higher FLO, lower HI than low-P-tolerant varieties. Response to direct selection under −P field conditions was 20.1 g m−2, whereas indirect selection response under +P was 16.3 g m−2. Selection under −P field conditions while taking into account seasonal variations for FLO, FD and PE is expected to be important for improving GY specifically targeting −P environments in WA.

Unmasking Novel Loci for Internal Phosphorus Utilization Efficiency in Rice Germplasm through Genome-Wide Association Analysis

Depletion of non-renewable rock phosphate reserves and phosphorus (P) fertilizer price increases has renewed interest in breeding P-efficient varieties. Internal P utilization efficiency (PUE) is of prime interest because there has been no progress to date in breeding for high PUE. We characterized the genotypic variation for PUE present within the rice gene pool by using a hydroponic system that assured equal plant P uptake, followed by mapping of loci controlling PUE via Genome-Wide Association Studies (GWAS). Loci associated with PUE were mapped on chromosomes 1, 4, 11 and 12. The highest PUE was associated with a minor indica-specific haplotype on chromosome 1 and a rare aus-specific haplotype on chromosome 11. Comparative variant and expression analysis for genes contained within the chromosome 1 haplotype identified high priority candidate genes. Differences in coding regions and expression patterns between genotypes of contrasting haplotypes, suggested functional alterations for two predicted nucleic acid-interacting proteins that are likely causative for the observed differences in PUE. The loci reported here are the first identified for PUE in any crop that is not confounded by differential P uptake among genotypes. Importantly, modern rice varieties lacked haplotypes associated with superior PUE, and would thus benefit from targeted introgressions of these loci from traditional donors to improve plant growth in phosphorus-limited cropping systems.

Sugarcane performance under phosphorus deficiency: physiological responses and genotypic variation

Developing genotypes with enhanced performance under phosphorus (P) deficiency can be described as an approach to improving production sustainability. This study investigated the physiological responses of sugarcane varieties to varying P availability and the plant traits contributing to P efficiency (shoot dry matter production under low P availability). Sugarcane varieties IACSP94-2101, IACSP95-5000, RB86-7515, IAC91-1099, IACSP94-2094 and IAC87-3396 were grown under low (25 mg P kg−1 soil) and high (400 mg P kg−1 soil) P supply, and the leaf gas exchange, photochemical activity, plant growth and P uptake were evaluated. The sugarcane varieties responded distinctly to a low P supply, as indicated by differences in root and shoot growth, leaf area, net CO2 assimilation, photosynthetic P utilization efficiency, leaf P concentration and P uptake. The following ranking was obtained for P efficiency: IACSP94-2094 = IACSP95-5000 > IAC87-3396 = RB86-7515 = IACSP94-2101 = IAC91-1099. Greater leaf area, net CO2 assimilation and P acquisition efficiency were combined in the more P-efficient varieties but not in the less efficient ones. Although it was not possible to separate cause and effect, such finding might be explained by the positive effect of improved leaf P concentration on leaf area and net CO2 assimilation, which in turn contributed to sustaining improved plant performance under a low P supply.