M. V. RAO
Division of Botany, Indian Agricultural Research Institute, New Delhi, India
In the major wheat growing regions of north India all the three rusts namely black or stem rust (Puccinia graminis tritici (Pers.) Erikss. & Henn.), brown or leaf rust (P. recondita Rob. Ex-Desm.) (P. triticina Erikss.) and yellow or stripe rust (P. glumarum (Schmidt) Erikss. & Henn.) attack the crop leading to considerable losses in yield. The data available till today indicate that there are 13 races and 5 biotypes in the stem rust (14, 15, 17, 21, 24, 34, 40, 42, 72, 75, 117, 122, 194; 15-C, 21-A, 21-A-1, 34-A and 42-B), 13 races in leaf rust (10, 11, 17, 20, 26, 63, 70, 77, 106, 107, 108, 131 and 162) and 10 races in stripe rust (13, 19, 20, 31, A, D. E, F, G, and H ). In addition some colour mutants in 15C and 192 of stem rust have also been isolated.
All the indigenous wheats, with the exception of Khapli emmer which also shows only partial resistance to stem rust, are susceptible to one or the other of the three rusts. Among the wheats obtained from outside the country Thatcher, Hope, Kenya C 10854, Yalta, Ridley, Charter, (Gabo x Dundee) and Kenya 58-F (L. 1) were at one time resistant to stem rust but these have become susceptible to the races subsequently isolated. Same was the fate with the leaf rust resistant wheats Mediterranean and Democrat. Spalding's Prolific and Carsten's V have however, maintained their resistance to stripe rust all these years in the field. It is interesting that Thatcher in spite of its susceptibility to some of the stem rust races of India gave highly resistant segregates like N. P. 789 and N. P. 790 in cross with another susceptible wheat N. P. 165 (N. P. or Pusa 4 x Australian Federation).
Efforts are being made to build up an extensive collection of Indian and foreign wheats at the Division of Botany of the Indian Agricultural Research Institute, New Delhi and this number already stands at 8000 at present. Out of this collection, the most promising at present from the view point of resistance to one or the other of the three rusts are :
A number of dicoccums received recently from Ethiopia showed resistance to all the existing Indian races of leaf and stripe rusts. So also one monococcum received from Japan, showed resistance to all the Indian races of stem rust and leaf rust. More sources of resistance to the Indian races of the rusts are expected to be available from the International Rust Nurseries material which is now under critical study here. Crosses between some of the susceptible wheats of T. aestivum, T. durum and T. dicoccum have recently yielded strains which are resistant to all the existing Indian races of stem and leaf rusts.
Studies were undertaken to find out the mode of inheritance of field and seedling resistance of some of these rust resistant wheats to the Indian races of the three rusts. The following is the summary of results so far obtained with regard to field resistance (data on seedling resistance would be published later) to a mixture of races of the rusts prevalent in India.
