Abstract
Mathematical relationships were investigated between above-ground dry weight (W1), below-ground dry weight (W2) and total dry weight (W3) and linear dimensions of height (H) and stem diameter (D) of 275 container-grown sour orange seedling rootstocks, in order to develop regression models for estimating W1, W2 and W3. There were significant correlations between H and D and the three weight categories. There was also colinearity between H and D. The formulae recommended for estimating W1, W2 and W3 for rootstocks greater than 10 cm in height and stem diameter greater than 1.50 mm were W1 = 0.523 + 0.242D2, W2 = -0.167 + 0.0911D2, and W3 = -0.689 + 0.333D2. Alternatively, W2 can be estimated with greater accuracy by subtracting W1 from W3 (W2 = W3 – W1). W1, W2 and W3 are in grams; D is in millimetres. Plots of observed dry weight versus dry weights that were estimated from the three regression models above, showed linear relationships. These three regression models provide an accurate, non-destructive method of estimating W1, W2 and W3 at minimal cost using simple linear non-destructive measurements. Regression studies conducted on 79 seedlings that were less than 10 cm in height and less than 1.50 mm in stem diameter, produced models that had poor predictive abilities (R2 < 0.61). This can be attributed to the lag phase in growth and development of the above-ground parts of the plant, following germination during the first 10 to 12 weeks of the seedling's life.
