Plant Bacteriology

• Blackleg and Bacterial Soft Rot of Potato:
• Statement (I) is true: Blackleg of potato (characterized by inky-black stem necrosis arising from the decaying seed tuber) in temperate regions is caused specifically by the enterobacterium Pectobacterium atrosepticum (formerly Erwinia carotovora subsp. atroseptica).
• Statement (II) is true: The pathogen overwinters and survives latently in the vascular rings and lenticels of infected seed tubers, transmitting the disease when infected seed pieces are planted in cold, wet soils.
• Conclusion: Both Statement (I) and Statement (II) are true (Option 1).

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

• Yellow Vein Mosaic Virus (YVMV) of Okra (Abelmoschus esculentus):
• is true: Transmitted in nature in a persistent, circulative manner by the whitefly (Bemisia tabaci).
• is true: The characteristic diagnostic initial symptom is intense vein clearing followed by brilliant yellow network of veins contrasting with green interveinal areas.
• is false: YVMV is a bipartite or monopartite begomovirus with satellite DNA that is not mechanically (sap) transmissible under normal field conditions.
• is false: While late-infected plants produce small yellowish fruits, infected plants are not necessarily 'severely stunted' unless infected at the earliest seedling stage.
• Conclusion: Statements (A) and (B) only are true (Option 3).

Correct option: (3) (A) and (B)

• Biology of Potato Virus Y (PVY):
• Statement (I) is true: Potato Virus Y (the type member of the genus Potyvirus) is transmitted naturally by over 50 aphid species (predominantly the green peach aphid, Myzus persicae) in a classic non-persistent, stylet-borne manner, where aphids acquire virions within seconds of probe feeding.
• Statement (II) is false: PVY virions are flexuous, filamentous particles ($730-740\text{ nm} \times 11\text{ nm}$) containing a positive-sense single-stranded RNA (+ssRNA) genome ($\sim 9.7\text{ kb}$), NOT double-stranded RNA (dsRNA).
• Conclusion: Statement (I) is true but Statement (II) is false (Option 3).

Correct option: (3) Statement (I) is true but Statement (II) is false.