Stages of Fungal Pathogenesis and Direct Penetration:
Spore: The fungal disseminative unit lands on the host plant surface (phylloplane).
Germ tube: In the presence of free moisture, the spore germinates to produce an elongated germ tube.
Appressorium: The tip of the germ tube swells and adheres tightly to the host cuticle, forming a specialized, melanized infection structure called the appressorium.
Infection Hypha (Penetration peg): Huge turgor pressure generated within the appressorium pushes an extremely fine penetration peg / infection hypha through the cuticle and epidermal cell wall into host tissue.
Correct developmental sequence: (A) $\rightarrow$ (D) $\rightarrow$ (B) $\rightarrow$ (C). Correct Answer: Option 2 ((A), (D), (B), (C)).
विस्तृत व्याख्या:
Stages of Fungal Pathogenesis and Direct Penetration (कवक संक्रमण एवं प्रवेश के चरण):
Spore: The fungal disseminative unit lands on the host plant surface (phylloplane).
Germ tube: In the presence of free moisture, the spore germinates to produce an elongated germ tube.
Appressorium: The tip of the germ tube swells and adheres tightly to the host cuticle, forming a specialized, melanized infection structure called the appressorium.
Infection Hypha (Penetration peg): Huge turgor pressure generated within the appressorium pushes an extremely fine penetration peg / infection hypha through the cuticle and epidermal cell wall into host tissue.
Correct developmental sequence: (A) $\rightarrow$ (D) $\rightarrow$ (B) $\rightarrow$ (C). Correct Answer: Option 2 ((A), (D), (B), (C)).
Explanation not matching this question?क्या व्याख्या इस प्रश्न से मेल नहीं खा रही?Report
Saprotrophs: Feed entirely on non-living dead organic matter; cannot infect living tissue.
Necrotrophs: Actively kill living plant host cells by secreting toxins and cell wall degrading enzymes, and subsequently colonize and feed on the dead plant tissue (e.g., Sclerotinia, Botrytis).
Hemibiotrophs: Initially establish an asymptomatic biotrophic relationship with living host cells, but later switch to a destructive necrotrophic phase killing the host tissues (e.g., Colletotrichum, Magnaporthe).
Biotrophs: Obligately require living host cells throughout their life cycle, deriving nutrition via haustoria without immediately killing host cells (e.g., rusts, powdery mildews).
Transitioning from dead to strictly living host requirements gives the sequence: (A) $\rightarrow$ (D) $\rightarrow$ (C) $\rightarrow$ (B). Correct Answer: Option 2.
विस्तृत व्याख्या:
Trophic continuum from Dead to Living (पोषण विधियों का सातत्य - मृत से जीवित):
Saprotrophs (मृतोपजीवी): Feed entirely on non-living dead organic matter; cannot infect living tissue.
Necrotrophs (ऊतकक्षयी परजीवी): Actively kill living plant host cells by secreting toxins and cell wall degrading enzymes, and subsequently colonize and feed on the dead plant tissue (e.g., Sclerotinia, Botrytis).
Hemibiotrophs (अर्ध-बायोट्रोफ): Initially establish an asymptomatic biotrophic relationship with living host cells, but later switch to a destructive necrotrophic phase killing the host tissues (e.g., Colletotrichum, Magnaporthe).
Biotrophs (अविकल्पी परजीवी): Obligately require living host cells throughout their life cycle, deriving nutrition via haustoria without immediately killing host cells (e.g., rusts, powdery mildews).
Transitioning from dead to strictly living host requirements gives the sequence: (A) $\rightarrow$ (D) $\rightarrow$ (C) $\rightarrow$ (B). Correct Answer: Option 2.
Explanation not matching this question?क्या व्याख्या इस प्रश्न से मेल नहीं खा रही?Report
Phase 2 (B) - Effector-Triggered Susceptibility (ETS): Successful pathogens inject specialized virulence effectors into host cells to suppress PTI, resulting in disease (ETS).
Phase 3 (C) - Effector-Triggered Immunity (ETI): Plants evolve nucleotide-binding leucine-rich repeat (NBS-LRR) resistance proteins ($R$ genes) that directly or indirectly recognize specific pathogen effectors (now called avirulence / Avr factors), triggering an accelerated, robust hypersensitive defense response (ETI).
Phase 4 (A) - Restoration of ETS: Natural selection drives the pathogen to shed or alter recognized effectors or acquire novel effectors that suppress ETI, restoring effector-triggered susceptibility.
Therefore, the correct chronological sequence is (D) $\rightarrow$ (B) $\rightarrow$ (C) $\rightarrow$ (A).
Correct Answer: Option 1.
विस्तृत व्याख्या:
Zig-Zag Model of Plant Immune System (पादप प्रतिरक्षा प्रणाली का जिग-जैग मॉडल - Jones & Dangl, 2006):
The co-evolutionary arms race between plants and pathogens is described in four evolutionary phases:
Phase 2 (B) - Effector-Triggered Susceptibility (ETS): Successful pathogens inject specialized virulence effectors into host cells to suppress PTI, resulting in disease (ETS).
Phase 3 (C) - Effector-Triggered Immunity (ETI): Plants evolve nucleotide-binding leucine-rich repeat (NBS-LRR) resistance proteins ($R$ genes) that directly or indirectly recognize specific pathogen effectors (now called avirulence / Avr factors), triggering an accelerated, robust hypersensitive defense response (ETI).
Phase 4 (A) - Restoration of ETS: Natural selection drives the pathogen to shed or alter recognized effectors or acquire novel effectors that suppress ETI, restoring effector-triggered susceptibility.
Therefore, the correct chronological sequence is (D) $\rightarrow$ (B) $\rightarrow$ (C) $\rightarrow$ (A).
Correct Answer: Option 1.
Explanation not matching this question?क्या व्याख्या इस प्रश्न से मेल नहीं खा रही?Report
Assertion (A) is INCORRECT (False): Obligate biotrophic pathogens (such as rust fungi Puccinia, powdery mildews Erysiphe, downy mildews Peronospora, and viruses) cannot be cultured on standard synthetic nutrient agar media because they strictly depend on metabolic signals and living host plant cytoplasm to survive and reproduce.
Reason (R) is CORRECT (True): Over millions of years of co-evolution and genome reduction with their plant hosts, biotrophic organisms have lost critical metabolic biosynthetic genes (such as nitrate and sulfate assimilation pathways and inorganic nitrogen reduction), rendering them entirely reliant on living host cellular metabolism for their nutrition.
Therefore, (A) is not correct but (R) is correct.
Correct Answer: Option 4.
विस्तृत व्याख्या:
Nature of Obligate Biotrophs (अविकल्पी परजीवी / बायोट्रोफ्स की प्रकृति):
Assertion (A) is INCORRECT (False): Obligate biotrophic pathogens (such as rust fungi Puccinia, powdery mildews Erysiphe, downy mildews Peronospora, and viruses) cannot be cultured on standard synthetic nutrient agar media because they strictly depend on metabolic signals and living host plant cytoplasm to survive and reproduce.
Reason (R) is CORRECT (True): Over millions of years of co-evolution and genome reduction with their plant hosts, biotrophic organisms have lost critical metabolic biosynthetic genes (such as nitrate and sulfate assimilation pathways and inorganic nitrogen reduction), rendering them entirely reliant on living host cellular metabolism for their nutrition.
Therefore, (A) is not correct but (R) is correct.
Correct Answer: Option 4.
Explanation not matching this question?क्या व्याख्या इस प्रश्न से मेल नहीं खा रही?Report
Q.5
ICAR AIEEA PG Plant Sciences 09 July 2023 (Shift 1) Paper (Q.68)
Transfer RNA (tRNA), originally termed the 'soluble RNA' or 'adaptor molecule' by Francis Crick, performs two essential roles in translation:
Its $3'$-CCA terminus covalently binds a specific activated amino acid catalyzed by aminoacyl-tRNA synthetase.
Its anticodon loop reads the triplet mRNA codon at the ribosomal A-site, thereby shuttling individual amino acids from the cytoplasmic pool to the elongating polypeptide chain on the ribosome.
Hence, tRNA is the molecule involved.
स्थानांतरण आरएनए (tRNA), जिसे फ्रांसिस क्रिक ने 'अनुकूलक अणु' (Adaptor molecule) कहा था, प्रोटीन संश्लेषण (अनुवाद/Translation) के दौरान साइटोप्लाज्म से सक्रिय अमीनो एसिड को अपने $3'$ सिरे पर ग्रहण करता है और राइबोसोम पर mRNA के कोडॉन के अनुसार उन्हें पॉलीपेप्टाइड श्रृंखला में जोड़ने हेतु स्थानांतरित करता है।
mRNA आनुवंशिक संदेश वहन करता है।
rRNA राइबोसोम का संरचनात्मक और उत्प्रेरक (पेप्टिडिल ट्रांसफेरेज) घटक है।
अतः सही उत्तर tRNA है।
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