English 103of Mancheter

Breeding to improve stem strength is a major objective of researchers of sunflower (Helianthus annuus L.). This study was undertaken to investigate genetic factors controlling reduced plant height and increased stem diameter in three sources of sunflower, DDR, Donsky, and Donskoi 47, crossed with a conventional height line, HA 89. As these two characters may lead to improved standability, knowledge of their inheritance will assist researchers in utilizing proper breeding methods. Estimates of additive, dominance, and epistatic genetic effects controlling reduced height indicated that the additive component was most important in two of the three crosses with the additive and epistatic component nearly equal in the third cross. Breeding efforts to reduce height of sunflower hybrids utilizing these lines in crosses could be effective due to the magnitude of additive effects. The dominance component of genetic effects controlling stem diameter was the most important for two crosses, with both dominance and additive components important for the third cross. Epistasis was present, but minor, for controlling stem diameter. The high relative importance of the dominance component indicates that testcross evaluation of lines in early generations could identify lines for producing increased stem diameter in hybrids. Even though the three sources of sunflower with reduced height were different in morphologic and agronomic characteristics, they had similar genetic control of plant height and stem diameter. Each could be utilized in a breeding program to develop lines with reduced height and larger stem diameter.

Everyone makes comparisons. When we compare, we examine two or more items for likenesses, differences, or both. Comparison often helps us choose between alternative. Comparison also acquaints us with unfamiliar things.

6.1 Selecting items for comparison

Any item you compare must share some common ground. There’s simply no basis for comparison. Any valid