Effect of Ug99 Race of Stem Rust (Puccinia Graminis F.Sp. Tritici) on Growth and Yield of Barley (Hordeum Vulgare L.) in Kenya

Barley stem rust caused by Puccinia graminis f.sp. tritici Eriks. & E. Henn, was previously contained through the use of genetic resistance resulting from genes such as rpg1 but, in 1999 and 2001 a new race Ug99 or TTKSK with virulence to stem rust resistant cultivars carrying resistance gene rpg1, was detected in Uganda and Kenya, respectively. The new variants of Ug99 like PTKST, TTKSF, TTKST and TTTSK with virulence to genes Sr21, Sr24, and Sr36 of wheat have been detected implying that the race Ug99 is evolving. The experiment was carried out at the Kenya Agricultural Research Institute (KARI) Njoro for two seasons (2008 and 2009) to find out the effect of the new race of Ug99 on the growth and yield of barley. The genotypes included three Kenyan commercial cultivars (Nguzo, Sabini and Karne), two (1512-5 and 1385-13) new introductions from the Kenya malting company and 15 introductions from ICARDA selection. The genotypes were screened for their level of resistance to stem rust disease in the field where each cultivar was sown in plots of 3m length at spacing of 20 cm, at seed rate of 125 kg ha-1 . The same set was sown as control under fungicides application of tebuconazole (folicur) at 0.75 L ha-1 , 3 times in the season starting at stem elongation stage (Zadoks et al., 1974) at an interval of 21 days. The experimental design was randomized complete block design (RCBD) in split plot arrangement with the main plots as the 20 barley cultivars, while the subplots consisted of fungicide (protected and unprotected), replicated three times. Susceptible wheat cultivars, Chozi was planted perpendicular to test plots in the middle of the 1-m pathways on both sides of experimental plots to serve as spreader. Genotype 1512-5 showed the highest severity of (93%) in season 1, while Sabini had the highest severity of 30% in the second season. Nguzo had the lowest disease severity of 16% and 5% in season 1 and 2, respectively. The highest dry matter loss of 41.1 and 43.1% was observed in ICARDA-07 and ICARDA-09 in season 1 and 2, respectively. The highest and lowest loss of 67.3% and 17.8% in leaf area was recorded on Sabini and 1385-13 in season 1 respectively. Irrespective of season, higher chlorophyll index was noted in treated plots than in untreated ones. Genotypes ICARDA-14 and ICARDA-13 had the highest (45.8%) and lowest (8.7%) reduction in number of effective tillers in season 1. The new race Ug99 (TTKS) of stem rust caused severe loss on the susceptible genotypes. The highest yield loss of 53.8% was observed in ICARDA-08 while the lowest loss of 6.9% was obtained in ICARDA-12 in season 1. In season 2 the highest loss of 32.1% was obtained in 1385-13 a Kenyan line. In the present study stem rust Ug99 has a great impact on growth and development of barley. The growth and development factors have an impact on the final yield of the crop and if they are disturbed in the initial stages then they can negatively affect the yield of the crop at the end.