Um enrolamento das fôlhas do fumo de causa genética

A type of leaf-roll has been noticed for many years in commercial tobacco plantings in the State of S. Paulo. Leaf-roll plants were supposed to be affected by a virus disease, but repeated attempts to transmit it by grafting, juice inoculation and by insect vectors failed consistently. Later studies showed that the leaf-roll condition is due to genetic factors and that probably more than a pair of recessive genes are involved in its transmission. Even after the genetic nature of the leaf-roll condition was definitely established, attempts were made to induce the leaf-roll condition in plants genetically normal by several methods : 1. Spraying their leaves with the juice from leaf-roll plants ; 2. Approach-grafting a leaf-roll scion onto a normal plant and vice-versa, following with defoliation, cutting back or shading of the normal graft component. This was done to stimulate translocation of the phloem contents from the leaf-roll scion or stock into the normal stock or scion respectively. It was thought that if leaf-roll were due to the genetically controlled production of a hormone-like substance, these treatments might induce the leaf-roll condition in plants genetically normal. The results, however, have been negative.