PROMISING INDUCED MUTATIONS IN SOYBEAN VARIETIES RESISTANT TO
LEAF SPOT FUNGI.
Irradiated seeds 2O krad of gamma rays) of three soybean varieties. Calland, Williams
and Columbus. were sown (Mi) on the farm of the Faculty of Agriculture. Shebin El-Kom,
Egypt. The M plants were kept free from disease and insect infection. Different morpho
logical mutations were recorded visually and the seeds of the phenotypicaily normal plants of
each variety were harvested and sown in bulk populations for the M, generation. The plants
were subjected to heavy artificial epiphytosis with two physiological isolates of Alternana
aùernara and Drechslera australeinsis in two separate fields. The seeds of the M, and M4
selection progenies were sown in two separate disease nurseries as line to row. Susceptible
and abnormal plants were removed. Single plant yield components were determined for the
selected mutants. The number of resistant mutants of the cultivars Calland. Williams and
Columbus was 16, 21 and 18 (M3), which were screened to 12, 12 and li mutants (M4),
respectively. Further screening was carried out and the data revealed that six, six and five
mutants. respectively, showed resistance in the M, generatIo. The mutants of M6 and M,
were grown in a randomized block design-surrounded by the susceptible parents as a border.
This border was inoculated with the two fungal isolates to serve as disease spreaders. The
results obtained in M, revealed that one and four mutants proved their supenor yield and
disease resistance over the parent cultivars Williams and Columbus, respectively.