Plant growth promoters mediated quality and yield attributes of milk thistle (Silybum marianum L.) ecotypes under salinity stress

Abstract

Silybum marianum (L.) Gaertn (Astraceae) is a well-reputed medicinal plant mostly utilized for silymarin (Sily) content and oil production, however, the information about Sily contents in achene part is still fragmented under different climatic conditions. In this study four milk thistle ecotypes from Faisalabad (FSD), Gujranwala (GUJ), Quetta (QTA), and Kallar kahar (KK) having an altered achene color were analyzed under salt stress. Application of plant growth promoters (PGPs) is one of the solution for ameliorating the effect of salinity and increasing the quantity and quality traits of milk thistle, so ascorbic acid (AsA), thiourea (TU), and moringa leaf extract (MLE) were soil supplied after developing salinity stress (120 mM with irrigation) at germination stage. Predetermined levels were selected for PGPs such as AsA (500 µM), MLE (3%), and TU (250 µM). Results revealed that all yield related attributes were significantly decreased, while secondary metabolites, pericarp epidermis, pericarp parenchyma, and pericarp seed integument increased under salinity stress. Data suggested that PGPs treatment was helpful to alleviate the deleterious effects of salinity stress and enhance the milk thistle quality and quantity parameters. The ecotypic variations with altered achene color patterns represent an advantage for QTA ecotypes for higher Sily extraction under salt stressed conditions.

Figure 1

(a) Main panicle length, (b) short panicle length per plant, (c) capitulum diameter, and (d) number of flowers per plant of milk thistle under control and salinity stress conditions. The plants were soil supplemented with different plant growth promoters during 2017 and 2018.

Figure 2

(a) No. of achene per capitulum, (b) no. of achene per plant, (c) 1000 achene weight (d) achene length, and (e) achene width of milk thistle under control and salinity stress conditions. The plants were soil supplemented with different plant growth promoters during 2017 and 2018.

Figure 3

(a) Total soluble phenolics content, and (b) flavonoid content of root and shoot of milk thistle under control and salinity stress conditions. The plants were soil supplemented with different plant growth promoters during 2017 and 2018.

Figure 4

(a) Silymarin content, and (b) oil content achene of milk thistle under control and salinity stress conditions. The plants were soil supplemented with different plant growth promoters during 2017 and 2018.

Figure 5

Elucidation of salinity stress treatment on the achene color and achene P.par and P.epi and SI length in different milk thistle ecotypes. Co, cotyledon; SI, seed integument; P-Par, pericarp parenchyma; P-epi pericarp epidermis.

Figure 6

Pearson’s correlation matrix between different growth and yield parameters under control and salt stress conditions during 2017 and 2018. Correlation matrix of different dependent variables with independent variables (ecotypes) under control stress conditions during 2017. SI seed integument epidermis, P-Par pericarp parenchyma, P-epi pericarp epidermis, Sily silymarin, Flavo flavonoids, Phe Phenolics, AW achene width, AL achene length, A.P achene/plant, TAW thousand achene weight, A.C achene/capitulum, CD capitulum diameter, NOF number of flowers, SPL short peduncle length, MPL main panicle length. Blue box represents negative correlation, while red for positive correlation.