Effects of phosphorus availabilities on growth and yield of foxtail millet: insights from high-throughput phenotyping platforms.

Main conclusion: Foxtail millet performance under low phosphorus (P) is determined by growth potential, with tiller number as a key indicator. Yield is influenced by P dilution rather than total P concentration. Foxtail millet, renowned for its high nutrient content and drought resilience, faces limited breeding investment despite being cultivated in vulnerable agri-systems. Low phosphorus (P) levels affect approximately 50% of global agricultural soils, and particularly impact regions like Sub-Saharan Africa and Southeast Asia, the latter where foxtail millet is extensively grown. This study explores the effects of low P (< 5 ppm; Hedley Fractionation Method; Cross and Schlesinger 1995) on foxtail millet plant growth and yield-related traits, utilizing high-throughput platforms (HTP) with a selected subset of genotypes (n = 10) from the core collection of ICRISAT Genebank. Results uncover substantial variation in plant growth and agronomical traits at both treatment and genotype levels. Under low-P conditions, genotypic variation is noted, with a sixfold difference in tiller count, 2.4-fold in grain yield, 2.7-fold in 3D-leaf area, and 2.3-fold in root surface area. A significant relationship was found between grain yield under low-P and high-P conditions (R² = 0.65; P < 0.01). This suggests that genetic yield potential (vigor) under high-P conditions strongly influences grain yield and tiller numbers under low-P conditions. Residual grain yield under low-P conditions, not explained by high-P conditions, had a strong positive association with tiller numbers (R² = 0.70; P < 0.01) and showed a significant negative association with total P concentration (R² = 0.54; P < 0.05). Conversely, under high-P conditions, grain yield (GY_LF) from Lysi-Field exhibited significant positive correlations with P use efficiency (PUE) (r = 0.94; P < 0.001) and total biomass (r = 0.84; P < 0.01). These findings underscore the critical role of P availability in influencing grain yield and related traits. Under low-P conditions, performance is primarily driven by growth potential, with tiller number serving as a reliable marker of this potential. The significant genotypic variation observed highlights the importance of selecting for growth-related traits in P-limited environments. In addition, P dilution, rather than total P concentration, appears to play a key role in determining yield under low P. Optimizing P management strategies and breeding for improved growth potential may significantly enhance crop performance in regions facing P limitation.