Analysis of Flesh Thickness of Summer Squash by Using Mixed Major Genes and Polygene Inheritance Model

[Objective]The aim was to study the inheritance of flesh thickness,so as to provide a theoretical basis for breeding of thicker-flesh summer squash variety.[Method]Using mixed major genes and polygene inheritance model,a joint analysis of six generations from two crosses q-1×23-4G（Cross 1）and q-1×A-7（Cross 2）was conducted to investigate the inheritance of the flesh thickness of summer squash.[Result]The results showed that the flesh thickness was controlled by D-2 model（a pair of additive major genes plus additive-dominant polygene）;genetic effect of flesh thickness in the two crosses was mainly the dominant effect of polygene.Heritability values of the genes of F2 generation were relatively low,while the environmental effect was great.[Conclusion]To flesh thickness,the method of individual selection on high separated generations was effective in the breeding of summer squash with thick flesh.

Breeding of near-isogenic japonica rice lines with three major genes for resistance to bacterial blight

From 1986 to 1993, a set of near-isogenic japonicarice Iines with three major genes Xα-3, Xα - 4,and Xα-12 for resistance to bacterial blight(Xan-thomonas oryzae pv.oryzae)were developed anddesignated as CBB3, CBB4, and CBB12 respective-

Genetic Analysis on Plant Height in Rice in Different Growing Seasons

[Objective] The aim was to carry out the genetic analysis on plant height of rice（Oryza sativa L.）cultivated in different seasons.[Method] Three rice parents with great difference in plant height including CB1（83.1 cm）,CB4（105.5 cm）and CB7（115.6 cm）were chosen to construct two parental combinations：CB1×CB4 and CB7×CB4,and the corresponding filial generations P1,F1,P2,B1,B2 and F2 were obtained.The 6 populations were planted in middle and late seasons respectively to measure their height traits.The Akaike＇s information criterion（AIC）of the mixed major gene and polygene model was used to indentify the existence of major genes affecting quantitative traits in B1,B2,F2 populations.When the major genes existed,the genetic effects of the major genes and polygenes and their genetic variance were estimated through segregation analysis.[Result] One additive major gene plus additive-dominance polygenes was the most fitted genetic model for the trait in all B1,B2,F2 populations in two planting seasons.The heritability values of the major genes varied from 38.63% to 78.53% and those of polygenes varied from 1.72% to 36.04%,and the total heritability values were 45.52-92.93%.The additive effect d value of the two genetic populations under two planting seasons was-4.56,-9.16,-7.19,and-9.38,respectively,as suggested that additive effect of the major genes would decrease the express of the plant height trait.[Conclusion] The heritability of plant height trait was affected by planting seasons and the combinations clearly as a whole.

Genetic and genomic analyses for economically important traits and their applications in molecular breeding of cultured fish

The traits of cultured fish must continually be genetically improved to supply high-quality animal protein for human consumption.Economically important fish traits are controlled by multiple gene quantitative trait loci(QTL),most of which have minor effects,but a few genes may have major effects useful for molecular breeding.In this review,we chose relevant studies on some of the most intensively cultured fish and concisely summarize progress on identifying and verifying QTLs for such traits as growth,disease and stress resistance and sex in recent decades.The potential applications of these major-effect genes and their associated markers in marker-assisted selection and molecular breeding,as well as future research directions are also discussed.These genetic and genomic analyses will be valuable for elucidating the mechanisms modulating economically important traits and to establish more effective molecular breeding techniques in fish.