Learn about the comparison between the three rusts of wheat.
Comparison # Black Rust (P. Graminis):
i. Stems are most seriously attacked, followed by leaf sheaths, leaves and ‘ears’, in decreasing order. First noticed in plains in March-April.
ii. Uredosori rust-red, large and elongated which coalesce to form continuous pustules. The overlying epidermis breaks irregularly.
iii. Uredospores oval with four equatorial germ pores.
iv. Teliosori resembles the uredosori except the black colour. Found on all parts, but mostly on stems and least on leaf blade. No paraphyses. Teliospores spindle- shaped (apex pointed).
v. Pycnia and aecia formed on Berberis and Mahonia.
vi. 240 races of the pathogen are known; 14 are reported from India.
vii. The annual recurrence of the disease on the plains is through uredospores blown down from hills late in the wheat season.
Comparison # Orange or Brown Rust (P. Recondita (=P. Triticina)):
i. Attacks leave almost exclusively, very rarely leaf sheaths or stem. First noticed in January; can cause more damage than black rust.
ii. Uredosori orange, which later turn brown, smaller, oval or round, not coalescing; epidermis breaks to form a circular fringe around the sorus.
iii. Uredospores round and have 7-10 scattered germ pores.
iv. Teliosori rare; when present formed on the lower surface of leaves; epidermis never bursts. Paraphyses divide the sorus into compartments. Teliospores round at the apex.
v. Formed on Thallictrum and Isopyron but not observed in India
vi. 100 races are known but only 14 are reported from India
vii. Same as of black rust.
Comparison # Yellow Rust (P. Striiformis (P. Glumarum)):
i. Leaves are most severely attacked followed by leaf sheaths, stems and ears. Occurs early, from January and causes more damage than black rust.
ii. Uredosori lemon- yellow, small of pin head size, never coalesce, arranged in rows which appear as yellow stripes of discrete pustules.
iii. Round with 6-10 scattered germ pores.
iv. Teliosori is frequently formed; dull black, sori appear on the lower surface of leaves. Paraphyses surround the sori. Epidermis does not burst. Teliospores much flatted at the apex.
v. These stages are not reported for yellow rust.
vi. Out of the 14 races, 10 are reported from India.
vii. In addition to uredospores from hills, the inoculum initiating primary infection is provided by some locally growing “collateral hosts”.