SCREENING FOR STEM RUST RESISTANCE IN MUTANT BARLEY (Hordeum vulgare L.) LINES
Stem rust is a devastating disease in barley that is caused by a fungi (Puccinia graminis f.sp tritici, Eriks. and E. Henn).The disease has been controlled for quite some time due to the presence of cultivars carrying the resistant gene Rpg1 .This was so until the emergence of the race Ug99 from Uganda in the year 1998. This race did break all the resistant genes that were there hence the need to get new sources of resistance. In the current study mutation breeding was used to create variation for stem rust resistance (Ug99) and screen the barley lines for resistance. Seeds of barley (Nguzo variety- MO) were sent to Vienna in Austria for irradiation at the International Atomic Energy Agency at a dosage of 250 gray. The M1 seeds were multiplied at the University of Eldoret farm. A thousand plants were selected from the M1 population and two ears harvested and divided into two corresponding groups. The seeds from these ears were designated as M2. One group was planted at University of Eldoret experimental field while the corresponding groups of a thousand ears were planted at KARI Njoro. Each ear formed a line. A susceptible line of wheat was planted as a spreader and inoculated with stem rust Ug99 in both sites. After the disease pressure was high selection was done basing on severity and infection type. A total of 183 lines were selected from the two sites which showed acceptable level of resistance. These lines were again replanted in University of Eldoret as M3 in a RCBD design with three replicates to determine the effect of mutation on agronomic traits, and the parent as a control. it was found that mutation had a significant effect on a number of tillers, height, weight of 1,000 seeds, spike length and days to 50% heading (p<0.001).The following mutant lines showed superiority in terms of the agronomic traits studied. Molecular screening of the lines was done using SSR markers and 12 mutant barley lines were found to be probably carrying the resistant genes for Ug99 race of stem rust. In terms of correlation, the number of tillers of the mutant barley lines had a positive correlation with spike length at P<0.05,Spike length had a positive correlation with weight of 1000 grains of the mutant barley lines at P<0.001.The height of the mutant barley lines correlated positively with the number of tillers at P<0.01 and with days to 50% heading. These lines could be positively selected for further stabilizing and evaluation of other agronomic traits.
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