Plant–fungus symbiosis for better phosphorus uptake: Which fungus, when infecting crop roots, most effectively improves absorption of phosphorus and other mineral nutrients?

Introduction / Context:
Mycorrhizal symbioses are among the most important biofertilizer strategies in sustainable agriculture. Vesicular–arbuscular (now termed arbuscular) mycorrhizae colonize roots and extend hyphal networks into soil, greatly improving plant access to phosphorus (P) and micronutrients. This question tests recognition of the correct symbiotic fungal group used to enhance nutrient uptake.

Given Data / Assumptions:

• P is often poorly mobile; hyphal networks increase the effective absorptive surface.
• VA mycorrhizae enter root cortex cells forming arbuscules/vesicles.
• Common bakery or opportunistic yeasts are not root symbionts improving P uptake.

Concept / Approach:
Identify fungi with established mutualistic root colonization and proven agronomic benefit. Arbuscular mycorrhizal fungi (Glomeromycota) transfer P and water to the plant in exchange for photosynthate, improving growth especially in low-P soils. Saprophytes or yeasts listed in distractors lack this root symbiosis and field-proven P-delivery mechanism.

Step-by-Step Solution:
Recognize “VA mycorrhiza” as the classical term for arbuscular mycorrhiza.Recall their structures (arbuscules/vesicles) and extraradical hyphae that explore soil micro-pores.Understand the functional outcome: increased P, Zn, Cu uptake and drought tolerance.Select VA mycorrhiza as the correct choice.

Verification / Alternative check:
Field trials show enhanced P-use efficiency and reduced fertilizer needs when crops are inoculated with arbuscular mycorrhizal fungi (e.g., Rhizophagus irregularis) under P-limited conditions.

Why Other Options Are Wrong:

• Saccharomyces/Candida: yeasts without root-symbiotic nutrient transfer roles.
• Aspergillus niger: industrial enzyme producer; not a root symbiotic P-mobilizer via arbuscules.
• Rhizopus: common mold lacking arbuscular root symbiosis.

Common Pitfalls:
Assuming any soil fungus improves P uptake; confusing phosphate-solubilizing microbes in rhizosphere with intimate mycorrhizal symbiosis.

Final Answer:
VA (vesicular–arbuscular) mycorrhiza.