Histology of Arrested Development in Embryo Sacs and Embryos of Two Uncultivated Peanut Species Arachis Spp.

Abstract

Some disease resistant wild species of Arachis (peanuts) have a low seed yield although they flower and produce fertile pollen. Probable causes of the reduced seed-yield may include inadequate selfpollination, pollen-stigma incompatibility, egg sterility, syngamy failure, or embryo abortion. These phenomena were investigated in a study which is part of a peanut breeding program designed to incorporate disease resistance from wild species of Arachis into cultivated types of peanuts. Plants investigated were pollinated by hand, flowers collected 1-7 days after pollination, and the styles and ovaries dissected from the flowers. Styles were observed for pollen tube growth using fluorescent microscopy, and sectioned ovaries of killed and fixed material were studied to determine if embryos were present. It was found that the two rhizomatous species studied had low seed yield which may be caused by two different types of incompatibility. Arachis hagebeckii Harms (PI 276233) appeared to have postfertilization embryo abortion and either sterile egg cells or failure in fertilization. Arachis sp. (PI 262286) appeared to have incomplete pollen tube growth with only a few pollen tubes reaching the ovule, and then only triple fusion of the polar nuclei took place. However, these observations are inconclusive because of the relative small amount of materials examined.