MODIFICATION OF MORPHOLOGICAL TRAITS OF COMMON BEANS THROUGH GAMMA-RAY IRRADIATION - ANALYSIS OF 3 CONSECUTIVE GENERATIONS

The objectives of this investigation were to study the effects of diff erent levels of gamma-rays on some morphological characteristics of a nearly-white seed coat color bean (Phaseolus vulgaris L.) cultivar, an d to determine the radiation level which would generate the greatest g enetic variability. Breeder seeds of EMGOPA 201 - ''Ouro'' cv, a beige seed coat color cultivar, were submitted to gamma-ray irradiation (Co -60). Treatments consisted of eight levels of radiation: 0, 10, 15, 20 , 25, 30, 35 and 40 Krad. The experimental design was a randomized com plete block with four replications. In the field, plots consisted of 1 00 seeds. The following data were collected: percent germination, plan t height, final stand, plant yield and yield components, number of chl orotic and albino mutants, leaf mutants, growth habit alterations, ear liness, seed coat color, seed coat brightness, halo color, seed size a nd format. Among traits greatest variations were observed for seed mor phology. Seed coat color varied from completely white to a dark-browni sh color. Halo color was also modified from yellow (normal) to pink. B rightness of seeds varied from opaque to bright. Seed varied from squa red to rounded, and from very small to large. Treatments with 20 and 2 5 Krad generated the greatest variability for several morphological tr aits from the M(1) to M(3) generations, a dosage equivalent to the LD( 50) observed in the M(1) generation. Traits such as percent germinatio n, plant height and some yield components were highly and negatively a ffected by increasing levels of radiation. Modification of yield compo nents as well as many unusual characteristics with late onset were obs erved in advanced generations, suggesting that late selection would al so be useful.