Fungal disease control — Which polyoxin variant is reported as most effective against the rice sheath blight pathogen Pellicularia sasakii (Rhizoctonia solani)?

Introduction / Context:
Polyoxins are nucleoside-peptide antibiotics produced by Streptomyces species that inhibit chitin synthase, thereby suppressing fungal growth. Rice sheath blight, caused by Pellicularia sasakii (syn. Rhizoctonia solani), is a major disease where specific polyoxin variants show differing efficacy.

Given Data / Assumptions:

• Polyoxin variants (B, C, D, L) differ in structure and potency.
• Target pathogen is a basidiomycete forming sclerotia and infecting sheaths.
• Mode of action is inhibition of chitin biosynthesis in fungal cell walls.

Concept / Approach:
Among the polyoxins, Polyoxin D has been cited as particularly effective against R. solani. Efficacy relates to uptake, stability, and binding to the chitin synthase target complex, leading to impaired cell wall synthesis and pathogen suppression.

Step-by-Step Solution:

Verification / Alternative check:
Plant pathology references and historical trials document Polyoxin D’s superior activity on Rhizoctonia spp. compared to several other variants.

Why Other Options Are Wrong:

• B, C, L: active but generally less effective against this target organism.
• Kasugamycin is an aminoglycoside primarily used against blast; it is not a polyoxin and has a different target (protein synthesis).

Common Pitfalls:
Conflating rice blast (kasugamycin-responsive) with sheath blight (polyoxin-responsive); they involve different pathogens and antibiotic classes.

Final Answer:
Polyoxin D