Inheritance in lettuce.

Abstract

^HE INVESTIGATIONS described in this publication were conducted for the purpose of determining some of the facts of inheritance in lettuce (Lactuca scariola L.), a plant for which no extensive genetic investigations have been reported, so far as the author is aware.The experiments were conducted at the Illinois Ag- ricultural Experiment Station at Urbana, Illinois.They were started in 1913 and were continued for five years.Crosses were made between typical varieties of the important cultivated types of lettuce, and between these and the wild forms of L. scariola found in the vicinity of Urbana.The parental varieties and hybrids grown in this investigation were studied with reference to anthocyanin pigment, seed color, leaf form, prickliness, leaf length, leaf width, width index (leaf width divided by leaf length), leaf area, time required to reach the flowering period, height of plants at date of first bloom, and habit of growth in the rosette stage.The relations of these characters to one another have also been studied.Finally, some general conclusions have been drawn as a result of the study as a whole. MATERIALS AND METHODS Varieties Used in the InvestigationFor the purposes of this investigation, typical forms of each of the important types of both wild and cultivated lettuce were selected.Wild Forms.For some of the early crosses the pinnatifid, or lobed form, of L. scariola was used.Later the unlobed form was used also.Typical specimens of each form were chosen after rather extended observation of the types prevalent in the vicinity of Urbana.Each specimen was taken from a location in which uniformity existed with reference to the type in general and to leaf form in particular.Photo- graphs of each form in the rosette stage are shown in Fig. 1.Cultivated Types.Representative varieties of each of the important cultivated types of lettuce were selected for hybridization.For the heading type Big Boston and May King were used; for the leaf type, Grand Rapids; and for the Cos type, Paris White Cos.'The results presented in this bulletin form part of a thesis