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Modification of morphological traits of common beans through gamma-ray irradiation: analysis of three consecutive generations

Gismar S. Vieira; Luiz R. Goulart; Julio C. Viglioni Penna; Jonas J. Fernandes

Departamento de Agronomia, Centro de Ciências Biomédias, Universidade Federal de Uberlândia, Caixa Postal 593, 38400-902 Uberlândia, MG, Brasil. Send correspondence to L.R.G.

ABSTRACT

The objectives of this investigation were to study the effects of different levels of gamma-rays on some morphological characteristics of a nearly-white seed coat color bean (Phaseolus vulgaris L.) cultivar, and to determine the radiation level which would generate the greatest genetic variability. Breeder seeds of EMGOPA 201 - "Ouro" cv, a beige seed coat color cultivar, were submitted to gamma-ray irradiation (⁶⁰Co). Treatments consisted of eight levels of radiation: 0, 10, 15, 20, 25, 30, 35 and 40 Krad. The experimental design was a randomized complete block with four replications. In the field, plots consisted of 100 seeds. The following data were collected: percent germination, plant height, final stand, plant yield and yield components, number of chlorotic and albino mutants, leaf mutants, growth habit alterations, earliness, seed coat color, seed coat brightness, halo color, seed size and format. Among traits greatest variations were observed for seed morphology. Seed coat color varied from completely white to a dark-brownish color. Halo color was also modified from yellow (normal) to pink. Brightness of seeds varied from opaque to bright. Seed varied from squared to rounded, and from very small to large. Treatments with 20 and 25 Krad generated the greatest variability for several morphological traits from the M₁ to M₃ generations, a dosage equivalent to the LD₅₀ observed in the M₁ generation. Traits such as percent germination, plant height and some yield components were highly and negatively affected by increasing levels of radiation. Modification of yield components as well as many unusual characteristics with late onset were observed in advanced generations, suggesting that late selection would also be useful.

Keywords: morphological traits; beans; gamma-ray.

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