History & Principles of Plant Pathology

• Edible vs. Poisonous Mushrooms: Edible oyster mushrooms belong to the genus Pleurotus (e.g., Pleurotus ostreatus - pearl oyster, Pleurotus citrinopileatus - golden oyster, Pleurotus salmoneostramineus/salmoneus - pink oyster).
• Pleurotus olearius (Jack-o'-Lantern Mushroom): Pleurotus olearius (now classified as Omphalotus olearius) is an orange-yellow bioluminescent wood-decay mushroom that strongly resembles chanterelles and oyster mushrooms. It is highly poisonous and non-edible, containing illudin sesquiterpene toxins that cause severe gastrointestinal cramps, vomiting, and diarrhea.
• Conclusion: Pleurotus olearius is the non-edible/toxic species (Option 4).

Correct option: (4) Pleurotus olearius

• Model Organism Neurospora crassa: The red bread mold, Neurospora crassa (Ascomycota), is a celebrated eukaryotic genetic model organism.
• Significance in Classical Genetics: In 1941, George Beadle and Edward Tatum used X-ray-induced nutritional auxotrophic mutants of Neurospora crassa to prove that metabolic pathways are governed by specific enzymes produced by individual genes, formulating the foundational 'One gene-one enzyme' hypothesis (Nobel Prize in 1958).
• Other Features: Its haploid life cycle and ordered linear octad of ascospores inside asci made it ideal for tetrad analysis and genetic mapping of crossing-over.
• Conclusion: Neurospora is the key fungus in genetic studies (Option 4).

Correct option: (4) Neurospora

• Mode of Action of Phaseolotoxin: Phaseolotoxin is a non-host-specific chlorosis-inducing phytotoxin produced by Pseudomonas syringae pv. phaseolicola (halo blight of bean):
• Inhibition of OCTase: Inside plant tissues, phaseolotoxin is cleaved into octicidin (phosphosulfamylornithine), which irreversibly inhibits the urea cycle enzyme ornithine carbamoyltransferase (OCTase).
• Accumulation of Ornithine: Blocking OCTase prevents the conversion of ornithine and carbamoyl phosphate into citrulline, resulting in a dramatic buildup of the amino acid ornithine and an arginine deficiency (Statement II is true).
• Disruption of Apical Dominance: The systemic physiological shock and hormonal imbalance cause chlorotic halos, stunted bushy growth, and loss of apical dominance in affected bean shoots (Statement I is true).
• Conclusion: Both Statement (I) and Statement (II) are true (Option 1).

Correct option: (1) Both Statement (I) and Statement (II) are true.