Ecological and genetic evaluation of morphological and biochemical characters of quality in Brassica rapa L. accessions from VIR collection

Peculiarity of chemical composition of Brassica rapa L. crops (high water content and low content of fats) determine their low-calorie character. They are notable for relatively high content of carbohydrates and proteins, including all essential amino acids. Biochemical composition varies greatly among B. rapa members. We are the first to carry out a multifactor evaluation of valuable morphological and biochemical traits of B. rapa accessions from the core collection of Vavilov Institute of Plant Genetic Resources (VIR, 96 samples) in eco-geographical study (South China and Leningrad region of Russia) under field trials and under a greenhouse conditions. By means of the developed SSR (simple sequence repeats) markers which are in linked disequilibrium with QTL of morphological and biochemical traits, the molecular genetic analysis was firstly carried out in leafy, rooted, and oilseed B. rapa genotypes from the VIR core collection. As a result, new genetic sources for quality parameters have been found among the samples investigated. In average, the samples did not differ noticeably on plant morphology (leaf length, leaf width, petiole size, hairiness, colour) in field tests when growing in South China and in Leningrad region, whereas in a greenhouse at higher plant density the leaf size decreased, e.g. in Chinese cabbage, pak-choi, wutacai, and turnip the leaves were 5-12 cm longer and wider in the field tests. Under field trials, we revealed the significant and high significant correlations between dry matter (DM) and ascorbic acid (AA) level ( r = 0.51, p < 0.05), DM and chlorophyll a (Chla) content ( r = 0.59, p < 0.05), DM and carotenoids (Cd) ( r = 0.55, p < 0.05), DM and carotins (Cn) ( r = 0.67, p < 0.05), DM and b-carotene (b-C) ( r = 0.59, p < 0.05), DM and protein (P) level ( r = -0.49, p < 0.05); Chla and Chlb ( r = 0.93, p < 0.001), Chla and Cd ( r = 0.59, p < 0.05), Chla and Cn ( r = 0.49, p < 0.05), Chla and b-C ( r = 0.99, p < 0.001); Chlb and b-C ( r = 0.92, p < 0.001); Cd and Cn ( r = 0.49, p < 0.05), Cd and b-C ( r = 0.63, p < 0.05); Cn and b-C ( r = 0.49, p < 0.05). In the greenhouse, the significant and high significant r values were as follows: r = -0.59 (p < 0.05) for DM and AA, r = 0.58 (p < 0.05) for DM and Chlb, r = -0.53 (p < 0.05) for DM and Cd, r = 0.71 (p < 0.001) for DM and Cn; r = -0.59 (p < 0.05) for AA and Chlb, r = 0.83 (p < 0.001) for AA and Cd, r = 0.58 (p < 0.05) for AA and P; r = 0.74 (p < 0.001) for Chla and Chlb, r = 0.67 (p < 0.05) for Chla and Cn, r = 0.95 (p < 0.001) Chla and b-C; r = -0.48 (p < 0.05) for Chlb and Cd, r = 0.87 (p < 0.001) for Chlb and Cn, r = 0.64 (p < 0.05) for Chlb and b-C; r = 0.63 (p < 0.05) for Cn and b-C. The semi-headed Chinese cabbage Syaobaikou and Dunganskaya, pak-choi Mayskaya, and especially Ching Pang Yu Tsain with a distinctly high level of chlorophylls and carotene, are indicated as new promising genetic sources for valuable biochemical parameters under both field and greenhouse conditions. Their indices in the field trials and greenhouse tests were 5.44-7.03 and 4.20-5.40 %, respectively, for DM (that is higher as compared to mean value for the crop), 12.61-24.66 and 24.12-33.23 % for P, 32.56-46.46 and 30.00-61.47 mg/100 g for AA, 33.35-110.64 and 53.82-95.99 mg/100 g for Chla, 12.20-53.80 and 17.89-44.78 mg/100 g for Chlb, and 1.80-6.75 and 3.00-6.04 mg/100 g for b-C. It is confirmed that the SSR markers BRMS051, KS51082, BRMS043 and KS50200 may effectively screen collection accessions and breeding material for desired morphological and biochemical traits. Our original data allow to practically implement an association mapping strategy and identify genetic determinants of morphological and biochemical quality characteristics using unique B. rapa collection preserved in VIR.