Plant Pathology- ICAR JRF/SRF 2024

• Cell Wall Composition of Oomycota: Oomycetes (such as Phytophthora, Pythium, and downy mildews) belong to the kingdom Stramenopila (Chromista) rather than true fungi (Eumycota). Their cell wall is predominantly composed of cellulose ($eta$-1,4-glucan) and $eta$-1,3- and $eta$-1,6-glucans, with hydroxyproline-rich glycoproteins.
• Distinction from True Fungi: True fungi (Ascomycota, Basidiomycota, Zygomycota) possess cell walls containing chitin ($eta$-1,4-linked $N$-acetylglucosamine polymer). Oomycetes completely lack chitin or contain only minute trace amounts.
• Conclusion: The cell wall of oomycetes is rich in cellulose (Option 2).

Correct option: (2) Cellulose

• 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

• Fungal Spore Types and Fructifications:
• Pycnidiospores: Asexual conidia formed within a flask-shaped, ostiolate fruiting body known as a pycnidium (characteristic of coelomycetous fungi).
• Pathogen Identification: Ascochyta pisi (causal agent of Ascochyta blight / leaf and pod spot of pea) produces immersed pycnidia bearing two-celled hyaline pycnidiospores.
• Other Pathogens Listed:
• Pyrenophora avenae: Ascomycete producing pseudothecia with ascospores (asexual: Drechslera conidia).
• Cercospora apii: Produces long, filiform conidia on free conidiophores.
• Drechslera maydis (Bipolaris maydis): Produces dark, distoseptate conidia on free conidiophores.
• Conclusion: Ascochyta pisi produces pycnidiospores (Option 4).

Correct option: (4) Ascochyta pisi

• 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

• Dolipore Septum Architecture: The dolipore septum is a specialized, barrel-shaped cross-wall structure characteristic of the subphylum Agaricomycotina of the Basidiomycetes.
• Structural Features: The central septal pore swells into a prominent doughnut- or barrel-like ring surrounded on both sides by curved, dome-shaped endoplasmic reticulum membranes known as parenthesomes (septal pore caps), regulating the passage of cytoplasm and nuclei between adjacent hyphal compartments.
• Ascomycetes Comparison: Ascomycetes possess simple septal pores associated with spherical Woronin bodies.
• Conclusion: Dolipore septum is found in Basidiomycetes (Option 3).

Correct option: (3) Basidiomycetes