Threshing Damage to Radicle Apex Affects Geotropic Response of Winterfat

Abstract

The acute end of a winterfat [Eurotia lanata (Pursh) Moq.; Ceratoides 1. (Pursh) J.T. Howell] seed is formed by the apex of the radicle and of the cotyledons. It is postulated that this shape makes the embryo root cap especially susceptible to damage during threshing and that such damage is the cause of a high percentage of threshed germinated seed (germinant) lacking positive geotropism. This study consisted of examining germination behavior and post germination anatomy of the root apex of germinants with and without positive geotropism. The radicle apex was found to be damaged in 25% of the threshed seed. Eighty-five percent of the germinants from undamaged seed had positive geotropism as compared to 53% from the damaged seed. The latter had a range of anatomical aberrations in which the root cap was missing or seriously abnormal. It is concluded that the standard method of hammer mill threshing of winterfat fruits results in 25% of the seed sustaining damage to the radicle apex. This damage causes a loss of root cap functions, particularly the sensing of gravity. It is recommended that plantings be made by broadcasting whole fruits, rather than by drilling threshed seed.