Study On Physiological And Genetic Analysis Of Storability In Broccoli Florets

Broccoli is a very popular vegetable due to its high value of nutrients and varieties of health promoting compounds in our daily diet. However, the respiratory metabolism of broccoli is very strong because its edible parts are immature florets and branchlets. Broccoli is easy to senescence and unfavorable for storage after harvest, its storage life is only 2-3 days when stored at room temperature. Although various storage techniques have been widely applied to delay senescence of broccoli, that still can not satisfy the increasing demand on broccoli, as more people pay high attention to food safety, nutrition and health care. So it has important significance to breed broccoli varieties with good storability and high nutrient content.First of all, broccoli resources provided by our group were used to identify the storability, and then we selected two significant different storability broccoli inbred lines as our materials. We analyzed the change rules of nutrient content and the relative expression levels of chlorophyll degrading genes during 4℃ storage; Six generations(P1, P2, F1, BC1, BC2 and F2) derived from the two materials were used for genetic analysis of storability trait. We also used F2 population for QTL mapping study.All those studies can provide reference and guidance for broccoli breeding in order to select high nutritional content and good storability broccoli varieties, and improve the efficiency of breeding.The main results were as follows:1. 38 broccoli materials were stored at 4℃, 22 materials were stored at 20℃, We investigated the storage life of those materials reference Ku’s method. Results showed that there were 6 inbred lines of materials whose storage life were more than 50 days during 4℃ storage. And 20℃ storage test showed that the storage life of 3 materials up to 96h(4 days).2.We used ’13B32’ and ’13B33’ as our test materials, whose storabilities were significant difference in 4℃storage. The contents of chlorophyll, carotenoid, soluble protein, soluble sugar and polyphenol were measured in the two materials when harvested. Results showed that the contents of chlorophyll, carotenoid and soluble sugar decreased during the storage, while it declined slowly in ’13B32’ whose storage life was longer. The changes of soluble protein showed different in the two materials, it decreased first, increased suddenly and then decreased at last in ’13B32’, while it decreased in ’13B33’ during the whole storage. Polyphenol contents of the two materials increased first, then decreased and reached the peak at 7th day, but the increase in ’13B32’ was larger than in ’13B33’.3.The analysis of the expression of chlorophyll degrading genes in the two significant different storability broccoli heads indicated that the expression of BoCLH1 showed the same behavior in the two materials, it was detected a higher expression before storage, then decreased to a low level during the storage. The expression of Bo CLH2 changed slightly in ’13B32’, however it changed largely in ’13B33’, and the expression level was higher than ’13B32’. The expression of BoPPH declined in ’13B32’ during the whole storage, but it had a evident increase at the 14 th day in ’13B33’. The expression of BoPaO had a sharp increase in both of them,but the day appeared in ’13B32’ was later than ’13B33’. The obvious expression peak of BoRCCR appeared at the 21 th day in’13B33’, but it changed slightly in ’13B32’.4. Six generations were used for the genetic analysis of broccoli storability trait. The results showed that the storability trait was controlled by two major genes plus polygenes, The major genes heritability was higher in F2 population, it was 86.43%, but the dominant effect values(-10.50) and the additive with additive interaction effect values(-16.31) were negative, and they were lager than the additive effect values(8.40). The heritability of polygenes were higher in backcross populations, they were 62.17% and 56.25% in BC1, BC2 populations respectively.5.We used F2 as mapping population,and constructed a linkage genetic map successfully. The map covered 830.2cM with an average interval of 4.83 cM, it included 9 linkage groups, 157 SSR makers and 15 Indel makers. The analysis of QTL mapping showed that a total of 8 QTLs that controlling the storability trait of broccoli were tested. There were 2 QTLs whose distance from the markers Ra2G09 and Scaffold36127 were less than 1cM.