Studies On The Developmental Genetics Of Fruit And Seed Traits And Seed Quality In Sponge Gourd

Eight varieties(or breeding lines)of sponge gourd(Luffa cylindrical(L)Roem.Violales, Cucurbitaceae)were crossed in a diallel mating design with unbalanced data to generate F₁ generations.By randomized complete block design,parents and their F₁ generations were grown on the farm of Zhejiang University with two replications in 2004 and 2005,respectively.Fruit shape traits were determined in parents and F₁ generations;seedling stem dry weight,seedling leaf dry weight and the content of photosynthetic pigments of seedling cotyledon were evaluated in parents and F₂ generations.A genetic model including fruit direct effects and maternal effects was employed to evaluate the development of the fruit shape traits at different maturation times in sponge gourd.A genetic model for germinating traits of dicotyledon seed based on sponge gourd was proposed in the present study on the basis of the seed genetic models.Moreover, sponge gourd was used to study the changes of seed quality and seed testa pigments,and their relationships during seed development were analyzed.The main results were achieved as follows:(1)Genetic and correlation analysis of fruit shape traits in sponge gourd during development revealed the following results:The fruit shape is important quantitative trait closely related to the fruit quality.The results of variance analysis of fruit shape traits at economical(12d after anthesis)and physiological (60d after anthesis)maturation times indicated that fruit length and fruit perimeter were controlled by genetic effects of both fruit and maternal genetic systems.Fruit direct genetic effects were relatively more important for fruit shape traits at whole developmental period.The gene expression was most active at the economical maturation period(1-12d after anthesis)for two shape traits,and the activation of gene was mostly due to direct dominance effects at physiological maturation period(13-60d after anthesis).The coefficients due to different genetic effects,as well as the phenotypic correlation coefficients,varied significantly between fruit shape traits themselves at various maturation times.The results showed that it was relatively easy to improve fruit shape traits for industrial purpose by carefully selecting the parents at economical maturation time instead of that at physiological maturation time.Predicted genetic effects of sponge gourd showed that some parents such as 'Lifeng' and 'Fengyuan' were better than others for improving the fruit length and perimeter,respectively. Fruit length and perimeter were simultaneously affected by fruit direct genetic effects and maternal effects as well as GE interaction effects during four maturation times(3d,6d,9d and 12d after anthesis)under different environments.Fruit direct genetic effects were relatively more important for both fruit shape traits during the whole developmental period.The results of conditional variance components showed that gene expression was most active at early developmental periods especially for the first period(1-3d).The phenomena that some genes were spasmodically expressible among developmental periods were detected.Positive genetic correlations were significant between various maturation times in fruit length.Fruit additive correlation,additive×environment correlation and maternal×environment correlation between various maturation times were more important in fruit perimeter.(2)Genetic and correlation analysis of seed germinating traits in sponge gourd revealed the following results:Seedling stem dry weight and leaf dry weight were controlled by genetic effects of both embryo and maternal genetic systems,embryo genetic effects was more important.Environment of years would influence seedling stem dry weight and leaf dry weight,and embryo additive×environment effects played a leading role in genetic variation.The interaction heritability of seedling stem dry weight and leaf dry weight was the main heritability.After germinating for 7d and 14d,photosynthetic pigment of cotyledon including chlorophyll a,chlorophyll b,total chlorophyll and carotenoids was simultaneously affected by genetic effects of both embryo and maternal genetic systems and their interaction with environment effects(GE),the action of GE interaction was larger than main effects.Embryo additive×environment interaction effects mainly acted on the genetic variation of photosynthetic pigments.The analysis of genetic covariance components showed that there were closely relationships for most of genetic effects in the paired traits,and these relationships could be used in indirect selection of cotyledon photosynthetic pigment breeding,especially for paired traits with additive and/or maternal correlations.The interaction predictions of parents for most photosynthetic pigment traits were not in the same direction for both environments,indicating that environments could affect the performance of parents with different effects.(3)Analysis of seed quality during seed development revealed the following results:In the seed development process,seed dry weight increased gradually,the main accumulation period was 0-35d,accounting for more than 84%rate of maximum dry weight. Seed moisture content decreased gradually from 14-63d of seed development time.Activities of peroxidase(POD)and catalase(CAT),ascorbate peroxidase(APX)and the concentration of malondialdehyde(MDA)of seed remained high levels in early periods and declined during the latter developmental periods,It also observed that the contents of soluble protein and soluble sugar decreased rapidly during 14-21d and had no significant changes after 35d.The germination percentage,energy of germination,germination index and vigor index raised rapidly during 35-49d,and most of them reached the highest values in 49d,indicating that 49d was the optimal harvesting time with the highest seed quality.The changes of seed fresh weight,dry weight,moisture content,soluble protein and soluble sugar(y)on days after anthesis(x)could be simulated by regression equation y=a+bx+cx²(a,b and c were parameters).POD,CAT and APX activity had the linear(x)and \ or quadratic relation(x²)with days after anthesis.The stepwise regression analyses showed that there existed well correlation between seed quality parameters i.e germination percentage,energy of germination,germination index and vigor index,and the activities of antioxidant enzymes and MDA.Negative correlation was obeserved between APX activity and seed quality parameters.(4)Studies on seed testa pigment characters and their relation with seed quality paramaters in sponge gourd were conducted and some results were as follows:Contents of chlorophyll a,chlorophyll b,total chlorophyll and lutein were increased gradually during seed developing.Flavonoid content reduced firstly,then raised again,finally declined slowly.Polyphenol had a rapid decline in early developing period s,and then decreased slowly.Anthocyanin declined rapidly,then increased rapidly,the changes in the last period (57-63d after anthesis)were stabilized relatively.The content of melanin increased quickly from middle of developing time,respectively,and maintained high levels after 49d.Significant positive correlations were observed between flavonoids and melanin,flavonoids and chlorophyll a,anthocyanin and flavonoids,melanin and chlorophyll and melaninand and lutein.Polyphenol had negative correlation with chlorophyll,lutein and melanin,respectively. Melanin,flavonoids,chlorophyll and lutein had significantly positive correlation with seed quality parameters i.e germination percentage,energy of germination,germination index and vigour index,respectively.Negative correlation was found between polyphenol and seed quality parameters.The correlation results showed that if testa pigment characters in sponge gourd seed were realized,the performance of seed quality parameters could be predicted well.