| Melon（Cucumis mlo L.）is an annual plant of Cucumis genus in Cucurbitaceae family.Sugar content is an important factor of fruit quality and commodity value in melon.It is of importance to explore the inheritance and accumulation characteristics of sugar in melon fruit.In this paper,the sugar components of 14 melon varieties and 1 cucumber variety were analyzed and compared.‘Huapicaigua’,‘XLH’and‘Baizhuogua’were selected as the materials to explore the relationship of sugar accumulation and sucrose metabolism-related enzymes activities.‘Huapicaigua’with low sugar content and‘XLH’with high sugar content were selected as parents,and their six generations（P1,P2,F1,F2,B1,B2）were used to analyze the genetic characteristics of sugar content in melon.This study was intended to provide references for melon quality breeding,genetic classification and fruit sugar accumulation regulation,also,to shed light on elucidating the genetic rules of sugar content in melon fruits.The main results are as follows:1.In the same cultivation condition,there were some differences in fructose,glucose,sucrose and total sugar content in different melon varieties.The proportion of 3 kinds of sugar contents was also different.The varieties of crisp melons and serpent melons had the lowest sugar content,which were like cucumber cultivar‘Daiduoxing’,and the difference between its content and other melon varieties was mainly observed in the sucrose and total sugar content.The sucrose and total sugar contents of cantaloupe,netted melon and honeydew melon were relatively higher than that of striffen melon.‘Yongtian No.5’and‘Cuixue No.5’had the highest sucrose content,total sugar content and relative sweetness index,which were about twice higher of‘HJG’,‘SWX’and‘Baizhuogua’.There was a significant positive correlation between fructose and glucose content in melon fruits.Sucrose content might be the key factor affecting the total sugar content.The content and proportion of sugar components could be used as a reference basis for melon classification.2.Study on sugar accumulation and related enzyme activities in different melon fruits showed that the accumulation of fructose and glucose was the main sugar change in‘Huapicaigua’,while the minor accumulation of sucrose were only observed in the mature period of fruits.The content of fructose and glucose in fruits of‘XLH’and‘Baizhuogua’fluctuated in a certain range,and sucrose accumulation showed an obvious turning point,like a‘S’curve.The beginning point of sucrose accumulation were at the fruit veraison stage.The sucrose accumulation in melon fruits was affected by sucrose phosphate synthetase（SPS）,invertase（AI and NI）and sucrose synthase（SS）activities.The sucrose accumulation of‘XLH’and‘Baizhuogua’fruits was mainly related to the increase of SPS activity and the decrease of AI and NI activity.The activities of SPS,SS,AI and NI in‘Huapicaigua’were stayed in a low level in the development.3.‘Huapicaigua’with low sugar content and‘XLH’with high sugar content as parents,their six generations（P1,P2,F1,F2,B1,B2）were used to analyze the genetic characteristics of sugar content in melon.The results showed that the fructose content of melon fruit was controlled by two pairs of additive-dominance-epistasis major genes and additive-dominant-epistasis polygenes（MX2-ADI-ADI model）.The glucose,sucrose and total sugar content were controlled by two pairs of additive-dominance-epistasis major genes and additive-dominant polygenes（MX2-ADI-AD model）.The soluble solids content was controlled by one pair of additive-dominance major gene and additive-dominant-epistasis polygenes（MX1-AD-ADI model）.The fructose,glucose,sucrose and total sugar content were all controlled by two pairs of major genes and polygenes genetic model,and the major genes had negative enhancement.The interaction existed commonly between major genes.The major genes controlling fructose,glucose and total sugar content had the strongest dominant and dominant interaction.The major genes controlling sucrose content had the strongest dominant and additive interaction.The negative additive effect of polygenes controlling sucrose and total content was obvious.The heritability of major genes of fructose,glucose,sucrose and total sugar content was over than 0.850 in F2 group,and the environment showed very little effect,so it would be more efficient to be selected in the early generation. |
