Chromosomal karyotype analysis of ‘four seasons shuidong sweet crisp’ mustard

Brassica juncea was one of the important leaf vegetables which had important edible value, and was popular with consumers. Brassica juncea cv. four seasons shuidong sweet crisp mustard had characteristics of flesh crispy, tasted sweet and delicious. And have high resistance to disease, rain and heat. It also have advantages of not easy to bolting in the growth process, high yield, and can be planted throughout the year. Therefor it had been widely cultivated in many places of China. In this study, we measured and calculated seven chromosome parameters of ’four seasons shuidong sweet crisp mustard’: chromosome length, relative length index, relative length type, arm ratio, centromere index and centromere type. Chromosomal analysis was carried out. The experiment results showed that the karyotype formula was 2n=36=24m+12sm and the maximum chromosome length was measured 3.70 µm and max arm ratio was determined 2.39, relative length ranged between 3.28% to 7.84%. There are four types of relative length, including long (L), medium long (M2), medium short (M1) and short (S) chromosomes. In addition, the maximum centromeric index was measured in 45.82%, centromere type were metacentric (m) and submetacentric chromosomes (sm), while the number of m was more than sm. Karyotype asymmetry index was 62.04%, and the karyotype characteristics was type 2B according to Stebbins’s classification criteria. According to the above information, we can drawn a conclusion that ’four seasons shuidong sweet crisp mustard’ is a relatively primitive mustard variety. The findings revealed its karyotypic characteristics of ’four seasons shuidong sweet crisp mustard’ from the cytogenetic aspects.