Sugarcane red-rot resistance: Which phytoalexin compound has been reported as a key 3-deoxyanthocyanidin accumulating in resistant sugarcane tissues?

Introduction / Context:
Phytoalexins are antimicrobial compounds synthesized de novo by plants in response to pathogen attack. In sugarcane challenged by red-rot pathogens, a distinctive group of 3-deoxyanthocyanidins accumulates, playing a role in resistance. Identifying the principal compound illustrates how specific metabolites correlate with disease outcomes.

Given Data / Assumptions:

• Focus is sugarcane phytoalexins under red-rot stress.
• Candidate molecules belong to the 3-deoxyanthocyanidin family.
• Several specific congeners (luteolinidin, apigeninidin) may be present.

Concept / Approach:
Among 3-deoxyanthocyanidins, luteolinidin is frequently reported as a predominant phytoalexin in resistant sugarcane cultivars, with apigeninidin also detected. These pigments contribute to the characteristic reddish coloration and possess antifungal properties, limiting pathogen spread in host tissues.

Step-by-Step Solution:

Verification / Alternative check:
Biochemical profiling and pathogen-challenge studies show increased luteolinidin accumulation correlating with enhanced resistance; antifungal assays support its defensive role.

Why Other Options Are Wrong:

• Class name alone is nonspecific; the question asks for a compound.
• Apigeninidin also occurs but is not as consistently cited as the principal compound across studies.
• 5-O-apigeninidin is a derivative with narrower reporting.
• Chalcone synthase is an enzyme, not the phytoalexin end product.

Common Pitfalls:
Conflating class names with specific molecules; when asked for a compound, choose a named metabolite rather than the family name.

Final Answer:
Luteolinidin