Plant Pathology- ICAR JRF/SRF 2024

• Parasitic Weed Striga (Witchweed):
• Host Range and Parasitism: Striga (family Orobanchaceae) is an obligate root hemiparasite that infects tropical cereal crops in semi-arid regions.
• Target Crops: Major Striga species (Striga hermonthica, Striga asiatica) infect C4 graminaceous cereals including sorghum, maize, sugarcane, and pearl millet (Pennisetum glaucum), causing severe chlorosis, stunting, and drought-like symptoms by siphoning water, nutrients, and photosynthates.
• Cowpea Parasite: Striga gesnerioides attacks cowpea, but among the cereal options listed, pearl millet is the classic host.
• Conclusion: Striga parasitizes pearl millet (Option 3).

Correct option: (3) Pearimillet

• Physiological Disorder 'Exanthema':
• Exanthema / Dieback: A serious physiological disorder of pear, citrus, and other fruit trees characterized by gum pocket formation on bark, bark eruption (exanthema), deep bark cracking with reddish-brown exudations, and severe dieback of terminal shoots.
• Causal Micronutrient Deficiency: Exanthema is caused specifically by the deficiency of Copper (Cu). Copper is an essential cofactor for polyphenol oxidase and plastocyanin; its deficiency disrupts lignification and xylem development, leading to vessel necrosis and dieback.
• Conclusion: Exanthema is caused by Copper (Cu) deficiency (Option 2).

Correct option: (2) Cu

• Phosphorus Deficiency Symptoms in Plants:
• Physiological Symptoms: Phosphorus is mobile within plants and central to energy transfer (ATP, ADP), nucleic acids, and phospholipids.
• Visual Diagnostics: Phosphorus-deficient plants exhibit severe stunting (dwarfing) with abnormally dark green or blue-green foliage. Under severe deficiency, carbohydrate transport is restricted, triggering excessive synthesis and accumulation of anthocyanin pigments that impart a distinct purple or reddish discoloration to older leaves, stems, and petiole veins.
• Conclusion: Plants become dwarfed and foliage becomes dark green (Option 1).

Correct option: (1) Dwarfed and foliage become dark green