[1]Amhara Agricultural Research Institute, P. O. Box 527, Bahir Dar, Ethiopia.;
[2]Department of Crop Science and Production, Botswana University of Agriculture and Natural Resources, Private Bag 0027, Gaborone, Botswana.;
[3]Institute of Forest Ecology, University of Natural Resources and Life Sciences, Peter Jordan Strage 82 A-1190, Vienna, Austria.;