ALLOMETRICAL GROWTH OF THE QUANTITATIVE CHARACTERS OF PLANTS .2. THE INHERITANCE OF PLANT LEAF SHAPE AND LEAF SIZE OF TOBACCO

In this paper, six generation means of tobacco (Nicotiana tobacum) wer e used to study the genetic mechanism of leaf size and shape by the me thod of generation mean analysis. Four models were considered to estab lish a suitable one, namely: (1) a three-parameter genetic model (Mode l 1), (2) a six-parameter digenic interaction genetic model (Model 2), (3) a six-parameter synthetical genetic model (Model 3), and (4) a tw elve-parameter synthetical genetic model (Model 4). The data collected from six generations measuring three leaf positions and six growth pe riods of tobacco leaf shape index and leaf area were used for analysis . The results showed that additive and dominant gene effects, epistasi s, and their interactions with growth time (Model 4) are adequate to i llustrate the inheritance of leaf shape. Elongated leaf type is domina nt over oval leaf type; top leaf has more variability of leaf shape th an middle and lower leaves; dominant effect is negative and more influ ential than additive effect; additive, dominant and digenic interactio n effects may change during growth. The additive-dominant model (Model 1) may be used to illustrate the genetic mechanism of leaf size in th e third or fourth growth period for different leaf positions. Additive gene is negative and important to the leaf area. Dominant effect eith er has positive or negative value depending upon the leaf position. Sm all leaf size is dominant in top and lower leaves, but large leaf size is dominant in the middle leaves. It is still difficult to resolve th e genetic mechanism of leaf size by these models.