Studies On Physiological And Biological Methods For Heterosis Prediction In Watermelon

Watermelon is a universal horticultural crop originally planted in African tropical grassland. The using of heterosis brought revolution to watermelon breeding. During the breeding of heterosis, the selection and match of parents is key links for acquiring strong dominant combinations, which is time-consuming and operose. How to simplify the course was concerned. Breeding expert carried out research about heterosis prediction, from some aspects such as, colonial genetics, physiologic metabolism, molecular theory in order to found a simple, accurate, effective method to predict strong dominant hybridized combinations.In this assay, nine hybrid combinations and eighteen varieties were used as experimental materials. Through homogenizing, these hybridized combinations and their parents were used to select physiological and biochemical indexes tightly correlated to watermelon hybrid vigor. And the selected indexes were used to predict potential heterosis of 18 varieties, then field experiment tested the accurancy of the indexes. The results were as follows:1 The Oxidation activity of cotyledons mitochondrion of hybrid and homogenized parents had positive correlations with female parent . and the coefficient were 0.791 and 0.859, which were significant and very significant respectively, moreover hybrid F₁ had significant correlation with homogenized parents, and the coefficient was 0.803. The activity of euphylla glycolisome of hybrid and homogenized parents had significant positive correlations with male parent and the coefficients were 0.741 and 0.675, moreover hybrid F₁ had significant correlation with homogenized parents, and the coefficient was 0.815.So the two indexes conformed to the conditions for selecting indexes in this experiment.The threshold values of predicting in this experiment were defined as the maximum and minimum value of homogenized parents about the oxidation activity of cotyledons mitochondrion and the activity of euphylla glycolisome of the nine hybrid combinations. The threshold values as follows:Oxidation activity of cotyledons mitochondrion (unit:mgO₂/g fruit weight): 0.496-0.619 Activity of glycolisome of euphylla (unit: μmol glycollic acid /g fruit weight): 0.225-0.2752 Applying the indexes selected and threshold values to predict the hybrid vigor among the parents. 43 combinations were found to be promising heterosis in all and 15 combinations conformed to the two selected indexes in the same time.3 26 combinations had heterosis in yield, ten in early maturity and 35 in resistance amongthe 138 combinations, according to the field experiment.4 Field experiment verified: For the activity of euphylla glycolisome and mitochondrion oxidation activity of cotyledons, the heterosis prediction accuracy in yield and resistance were all above 50%. The prediction accuracies in yield were 66.67% and 55.88% respectively. Those in resistance were 55.56% and 76.47% respectively. The two indexes all could be used for predicting yield and resistance heterosis. But in yield the accuracy of the activity of euphylla glycolisome was higher and in resistance mitochondrion oxidation activity of cotyledons was higher. In early maturity, the accuracies of the two indexes were all below 50%, which were 11.11% and 20.59%So the two indexes could not be used for predicting early maturity heterosis.