Genetic Effect Analysis On Agronomic Characters, Construction Of A Genetic Mapping And Analysis On Genetic Diversity Of Summer Squash

By using six generation of two summer squash crosses, we studied the heterosis performance, the correlation between characters and the genetic mechanism of heterosis of summer squash. By using RAPD, the genetic map of summer squash was constructed. And RAPD analysis was applied to assess the genetic diversity and relationship in 47 summer squash germplasm.1. The result of heterosis analysis indicated that: there were different heterosis in yield characters; There were negative heterosis in two maturation characters and plant characters were improved. In yield composed characters, character of yield per plant and fruit number per plant showed the middle heterosis;Individual fruit mass of summer squash of hybrid F1 was both higher than their high parent; Ratio of fruit setting of summer squash of hybrid F1 showed the middle heterosis, and the heterosis of cross 1and cross 2 was separately 14.98%and 17.70%.The distinct heterosis in yield characters showed that hybrid F1 was higher yield than parents. In maturation characters, early flowering season of summer squash of hybrid F1 was more early than their early parent and node number of 1st female flower of summer squash of hybrid F1 was lower than their low parent; So hybrid F1 showed more early than parents. In the fruit composing characters, fruit length of cross 2 and fruit width of two crosses of hybrid F1 all showed different heterosis; Fruit uniformity of summer squash of hybrid F1 both were higher than that of high parent ;So the fruit shape characters of hybrid F1was better improved. In the plant composing characters, leaf number of summer squash of hybrid F1 decreased and was fewer than parents; Length of summer squash of hybrid F1 showed the middle heterosis, and the heterosis of cross 1and cross 2 was -32.26%and 37.21%; So plant characters of hybrid F1 were improved differently and were more compact.2. Correlation analysis indicated that: yield and yield composing characters had intimate relation with maturation characters, fruit characters and plant characters; maturation characters had intimate relation with fruit characters and plant characters. Yield per plant had positive significant relation with fruit number, individual fruit mass, and fruit setting ratio; While yield per plant had negative significant relation with early flowering season, node number of 1st female flower, fruit width and fruit stalk width; Ratio of fruit setting had significant relation with fruit stalk length, fruit length and fruit shape index; Node number of 1st female flowering had significant level with early flowering season, fruit stalk length, fruit length, plant length, leaf number and internode length; Fruit shape index had negative significant relation with fruit stalk width, but it had positive significant relation with fruit length, fruit uniformity, plant length, leaf number and internode length; So fruit characters had significant relation with each other and plant characters. Plant characters had significant relation with each other; Leaf number had negative significant relation with internode length.Yield composed characters, maturation characters, fruit characters and plant characters had significant relation and interacted with each other.3. Genetic analysis indicated that: fruit color was a qualitative character; green was dominant to white; Yield per plant of summer squash was D-2model, and additive effect played main role, but major gene played decisive role; Individual fruit mass accorded with B-1model, dominant effect and dominant×dominant epastasis mainly played role, and secondly additive effect played role; Fruit number per plant of summer squash fitted D-2 and was together controlled by major gene and polygene, and additive effect mainly played role on cross 1, while additive effect and dominant effect both played role on cross2; Genetic effect of fruit setting ratio of summer squash was mainly additive effect; Early flowering season of summer squash accorded with B-1model;dominant effect estimated value of summer squash was negative, so hybrid F1showed negative heterosis, and genetic effect of early flowering season of summer squash was mainly additive effect and additive×dominant epastasis; The result in node number of 1st female flowering showed that additive effect play main role on cross1 and additive effect and dominant effect together play main role on cross 2; Dominant effect estimated value of was negative, so hybrid F1showed negative heterosis; Fruit characters of summer squash accorded with B-1model or D-2 model, and fruit characters according with B-1model was controlled by major gene , but fruit characters that according with D-2 model was controlled by major gene and polygene, but polygene effect occupied higher percentage than major gene; Leaf number and internode length of summer squash both accorded with B-1model; Genetic effect of leaf number of summer squash was additive and dominant effect; Genetic effect of internode length of cross 1 was mainly additive effect and concurrently additive×additive epastasis,while genetic effect of internode length on cross 2 was mainly additive effect and concurrently dominant and dominant×dominant epastasis;Dominant effect estimated value of summer squash was negative, this made internode length shorten, so hybrid F1showed negative heterosis; Additive effect mainly played role on plant length of summer squash, and secondly additive×additive epastasis and dominant effect played role.So in the heredity of most character, dominant effect was positive, and dominant effect was the genetic basis of heterosis; In some other characters, dominant effect was negative and lower than of additive effect, this made hybrid F1 show negative heterosis like node number of 1st female flowering, early flowering season and internode length etc; epastasis widely existed in the heredity of summer squash characters.4.A 589 point map of summer squash was constructed from 93 F2:3 individuals each cross between summer squash q-1(vine/white) and23-4G(bush/green). The map delineated 20 linkage groups spanned 2060.9cM with an average distance of 3.50cM between the markers.5.RAPD analysis was to applied to assess the genetic diversity and relationship in 47 summer squash germplasm. Genomic DNA of 47 summer squash germplasms was amplified by RAPD. 30 polymorphic primers, screened out of 520 random Primers, were used and produced 367 reproducible bands. Of them, 302 bands (82.29%)were polymorphic. The cluster analysis divided the germplasm used in this study into 2 groups, which was not completely in agreement with the traditional taxonomy on summer squash. The first group was divided into four sub-groups. The second group was divided into five sub-groups. The similarity coefficient of 47 germplasms was between 0.63~0.89, so the genetic distance of summer squash was narrow; For growth habit, genetic relationship between cluster and half-sprawl was nearest.