CYTOGENETICS OF SOLID STEM IN COMMON WHEAT. V. LINES OF S-615 WITH WHOLE CHROMOSOME SUBSTITUTIONS FROM APEX

Abstract

Introduction S-615, a solid-stemmed variety of common wheat, T r i t i c z ~ m n e s t i z p z m z L. emend Thell., was the source of solid stem and sawfly resistance in the conlmercial varieties Rescue, Chinool:, and Cypress. Rescue originated from a hybrid of S-615 and the hollow-stemmed variety Apex. It is more rcsistant than S-615 to the whcat stem sawfly, and it has a different distribution of pith. being less solid than S-615 in the lower part of the top culnl internode, but more solid near the top of each internode (Larson and MacDonald, 1959a). These differences nlust have been derived from Apex. Aneuploid analyscs have been used to determine the effects of each cl~ron~osonic n common wheat on solid stem, and to resolve the interaction of c l~ron~oson~es from solidand hollow-stemmed varieties. T h e F, analysis of Chinese Spring monosomics X S-6 15 idcntified the chroniosomes in Chincsc Spring and in S-615 that tend to malte the culm hollow (Larson, 1959). It did not distinguish the chromosomes by which S-615 and Chinese Spring differ from thosc cl~romoson~es for which they are alilte. The tests of S-615 monosomics identified the chromosomes that carry genes for both solidness and hollowness that are not effective in a single dose (Larson and MacDonald. 1959a). They did not identify critical chromosomes carrying genes fullv effectivc in single dose. Further, any plant with a chromosomal deficience. especially whcn a pair of chroniosomes is missing, may be altered sufficientl?by decreascd size or vigor to influence the character being tested (Larson and A lacDonald, 1959b). Thc method of whole chromosomc substitutions was advocated by Sears (1944 and 1953) for the study of characters for which individual plants could not be reliably classified, and for analysis of inheritancc where interacting gencs or modifying gcnes wesc responsible. Substitution lines have been uscd succcssfullp to analyze the inheritance of disease resistance (Sears et dl . , 1957 and 1960 and Unrau et dl., 1958), and the inheritance of quantitative characters (Kuspira and Unrau, 1957 and 1958). T o further analyze the inheritance of solid stem, whole cl~ron~osomcs of Apex wcre substituted for thcir l~oniologues in S-615. Both monosomic and normal lincs of these substitutions were testcd for solid stem, and compared with S-615, Apex, and Rescue. This paper gives the results of the tests with 16 lines.