| Wheat breeding in Kenya G. E. DIXON Plant Breeding Station, Njoro, Kenya The breeding efforts of the past, and progress and plans for the future, are set against the story of continuing changes of rust races. Black stem rust, brown leaf rust, and yellow rust all afflict Kenya wheat, but stem rust is the most important, with yellow rust a serious factor only at the higher altitudes. Stem rust resistance is therefore the main topic of this paper. Breeding began in 1910, following the failure of the first imported varieties to stand up to stem rust and yellow rust. The early work was based on the Italian variety Rieti, an Egyptian wheat and a series of Australian wheats. This was interupted by the first world war and staff difficulties and progress was only sporadic. Nevertheless the foundation for Kenya wheats was laid at that time. Real progress dated from the starting of a special station in 1928, but even then the emphasis was on the exploitation of the range of material already available from earlier years. As new physiologic races of stem rust arose, so new parents were brought into the programme to combat them on the basis of additive resistances. The range of additional parents was small and again the strong Australian component is stressed. From this breeding a very successful range of Kenya wheats was built up during the 1930-1950 period, wheats which are in fact now known internationally. Unfortunately the release of a large number of these varieties just after the second world war was marked by their very rapid eclipse by a new series of stem rust races. Clearly the wheats, though the best yet achieved from the agronomic viewpoint, were too closely related and therein lay their weakness. Bad rust attacks have occurred over the last decade aud during this time much loss of confidence has resulted; the range of varieties available has been much reduced and general suitability has fallen. In particular the varieties in current use are causing marked concern to the millers. However certain foreign varieties have been helpful, most notably the quick variety H462 from Wisconsin. Current lines of wheat work of the recently expanded Plant Breeding Service are discussed under three headings. However the accent is on maximum diversity rather than quantity, though with the great expansion both of staff and facilities during the last three years, the quantity and intensity of the work on hand has very greatly increased. Work on the International and F.A.O. Nurseries dates from 1953 and 1954, and this now forms a very important function in the provision of new material. The range covered since 1953 has been very large, and during this time many varieties have been extracted both for direct multiplication and for breeding. The names of ten varieties are quoted which are under multiplication for direct release at the 50 ton stage. These came into the Nurseries from the U.S.A., Brazil, Portugal, South Africa and particularly Mexico. They show useful ranges of seedling resistance to stem rust, five being fully resistant to all 9 stock races, and they should be very useful as a group of stop-gap varieties. The derivation of two of them from inter-generic hybridisation is specially noted. In 1955 a number of chosen varieties from the Nurseries was used to give new breadth to the crossing work; 11 such parents are listed. However in 1957 special new collections were formed, based on both local data and international results, containing the widest possible range of varieties for resistance to stem rust and yellow rust. These, numbering 188 and 153 respectively, are too big to quote, but the breadth of genetic base is the important point involved. Crossing the stem rust resistant collection to five locally valued varieties has yielded 940 crosses which are now being rapidly taken through back-crosses. There will thus be a wealth of material in which to select, and the accent will be on maximum genetic diversity so that the narrowness of earlier years is never repeated. Selection for breadth of resistance is the aim, rather than the discarding of individual susceptibilities. |
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