Integration of Viral Sequences:

• Statement (I) is CORRECT: Retroviruses, pararetroviruses (such as Badnaviruses like Banana streak virus - BSV, and Caulimoviruses), and certain DNA viruses routinely integrate reverse-transcribed viral DNA sequences into the nuclear genome of their host plants (termed Endogenous Viral Elements / EVEs).
• Statement (II) is INCORRECT: In nature, the vast majority of integrated endogenous viral sequences undergo epigenetic transcriptional silencing (via DNA methylation and RNA-directed histone modification). They remain dormant and silenced without inducing major visible phenotypic alterations in the healthy host under standard conditions (they only express under specific stress or tissue culture shock triggering episomal release).

Azospirillum Physiology and Nitrogenase Oxygen Sensitivity:

• Assertion (A) is TRUE: When Azospirillum lipoferum or A. brasilense is inoculated into nitrogen-free malate medium and subjected to vigorous rotary shaking, it completely fails to grow.
• Reason (R) is TRUE and correctly explains (A): In nitrogen-free medium, Azospirillum depends entirely on the activity of its nitrogenase enzyme to fix atmospheric $\text{N}_2$ for cellular growth. Nitrogenase is extremely oxygen-sensitive and irreversibly inactivated by oxygen. Because Azospirillum lacks specialized protective structures (such as heterocysts in cyanobacteria or high respiratory protection in Azotobacter), it is an obligate microaerophile for diazotrophic growth. Shaking saturates the medium with dissolved $\text{O}_2$, which destroys nitrogenase activity and completely halts growth.

Structure and Genome of Tobacco Mosaic Virus (TMV):

• Statement (I) is CORRECT: TMV is a rigid, cylindrical rod-shaped virion measuring $300\text{ nm} \times 18\text{ nm}$ with helical symmetry, comprising 2,130 identical coat protein subunits and RNA as its genetic material.
• Statement (II) is INCORRECT: The genome of TMV is a single-stranded positive-sense RNA (ssRNA) molecule of 6,395 nucleotides, NOT double-stranded.

Bacterial conjugation is a unidirectional horizontal gene transfer process discovered by Lederberg and Tatum (1946).
The donor strain ($F^+$ or $Hfr$) must possess the Fertility factor (F-plasmid). The F-plasmid carries the $tra$ (transfer) operon genes that encode the sex pilus (F-pilus) required to establish physical contact and form a mating bridge with the recipient ($F^-$) cell, as well as the relaxosome enzymes that initiate rolling circle replication and strand transfer.