Effects of Ionizing Radiations on Germination of Seed and Morphology of Seedlings of Puerto Rican Coffee, Coffea arabica L.

Abstract

Seed lots from five individual tree selections of Puerto Rican coffee, Coffea arabica L., were irradiated with gamma-ray doses of 1,000 to 50,000 r, and neutron doses of 1 to 5 hours. Gamma-ray doses of 1,000 to 7,000 r raised the germination percentages of many of the seed lots and reduced those of others. Gamma-ray doses of 8,000 to 20,000 r reduced the germination percentages of all the seed lots approximately in direct proportion to the strength of the dose. Gamma-ray doses higher than 20,000 r completely inhibited the seed germination of all the seed lots. One of the seed lots had a 3-percent germination when treated with a neutron dose of 1 hour. All the other seed lots treated with neutrons failed to germinate. Gamma-ray doses of 1,000 to 5,000 r raised, and the higher doses lowered the average heights of the seedlings from the seed lots of Puerto Rican coffee selection 268. However, the radiations reduced the average heights of the seedlings from the seed lots of all other coffee selections in approximately direct proportion to the strength of the dose. Many seedlings from irradiated seed had abnormal leaves, branches, internodes, and so on. The frequency of abnormal plants and the degree of abnormality generally increased as the strength of the radiation dose increased.