What is true for Clavibacter xyli subsp. xyli? (A). Raton... | Agrigyan

• Insect Vectors and Plant Virus Transmission:
• Pair-by-Pair Matching:
• Aphids $\rightarrow$ (III) Potyvirus: Aphids (e.g., Myzus persicae, Aphis gossypii) are the primary non-persistent stylet-borne vectors of the vast Potyviridae family (e.g., Potato virus Y, Papaya ringspot virus).
• Thrips $\rightarrow$ (I) Tospovirus: Thrips (e.g., Frankliniella occidentalis, Thrips palmi) transmit tospoviruses (e.g., Tomato spotted wilt virus, Groundnut bud necrosis virus) in a circulative propagative manner.
• Mealybugs $\rightarrow$ (IV) Badnavirus: Mealybugs (Pseudococcidae) transmit badnaviruses such as Sugarcane bacilliform virus and Cacao swollen shoot virus in a semi-persistent manner.
• Whiteflies $\rightarrow$ (II) Begomovirus: Whitefly (Bemisia tabaci) is the obligate circulative-persistent vector of geminiviruses (genus Begomovirus, e.g., Tomato leaf curl virus, Cotton leaf curl virus).
• Correct Choice: Option 2 represents (A)-(III), (B)-(I), (C)-(IV), (D)-(II).

Correct option: (2) (A)- (IID, (B) - (0), (C) - (IV), (B) - (I)

• Biochemical Stabilization During Plant Virus Isolation:
• Statement (I) is false: Divalent cations like $ ext{Mg}^{2+}$ can induce aggregation of virions or activate endogenous plant nucleases during tissue extraction; therefore, chelating agents like EDTA (which sequester divalent cations) are routinely included in isolation buffers to prevent virion degradation.
• Statement (II) is true: Homogenizing plant tissues releases vacuolar polyphenols and polyphenol oxidases (PPO). The oxidation of polyphenols into toxic quinones inactivates virions; hence, antioxidants and reducing agents such as ascorbic acid, sodium sulfite, or $eta$-mercaptoethanol are essential to prevent oxidation and preserve virus infectivity.
• Conclusion: Statement (I) is false but Statement (II) is true (Option 4).

Correct option: (4) Statement (I) is false but Statement ({I) is true.

• Infection Process of Foliar Fungal Pathogens:

• Germ tube (C): Conidium germinates on the host leaf cuticle in the presence of free water to produce a vegetative germ tube.
• Appressorium (D): The germ tube tip swells and forms a melanized, dome-shaped infection structure called an appressorium, generating extreme turgor pressure.
• Penetration peg (A): A slender penetration hypha emerges from the appressorium base, piercing the host cuticle and epidermal cell wall via mechanical force and cell-wall degrading enzymes (cutinases, cellulases).
• Haustorium (B): Within the host mesophyll cell, the invading hypha invaginates the plant plasma membrane to differentiate a specialized nutrient-absorbing haustorium.
  • Sequential Order: (C) $\rightarrow$ (D) $\rightarrow$ (A) $\rightarrow$ (B) (Option 2).