A Biostimulant Preparation of Brown Seaweed Ascophyllum nodosum Suppresses Powdery Mildew of Strawberry

Abstract

Strawberry, an important fruit crop, is susceptible to a large number of pathogens that reduce fruit quality and productivity. In this study, the effect of a biostimulant prepared from Ascophyllum nodosum extract (ANE) (0.1%, 0.2%, and 0.3%) was evaluated on powdery mildew progression under greenhouse and field conditions. In the greenhouse, application of 0.2% ANE showed maximum reduction in powdery mildew progression as compared to the control. Forty-eight hour post-inoculation, foliar spray of 0.2% ANE reduced spore germination by 75%. Strawberry leaves sprayed with ANE showed higher total phenolic and flavonoid content in response to powdery mildew infection. Furthermore, application of ANE elicited defense response in strawberry plants by induction of defense-related enzymes, such as phenylalanine ammonia lyase, polyphenol oxidase, and peroxidase activity. In field conditions, foliar spray of 0.2% ANE showed a reduction of 37.2% of natural incidence of powdery mildew infection as compared to the control. ANE sprayed plant also reduces the severity of powdery mildew infection under natural conditions. These results indicate that application of ANE induces the strawberry plant's active defense against powdery mildew infection by induction of secondary metabolism and regulating the activities of defense-related enzymes.

Keywords: Ascophyllum nodosum extract; Podosphaera aphanis; phenylalanine ammonia lyase; powdery mildew; strawberry.

Fig. 1

The effect of foliar spray with Ascophyllum nodosum extract (ANE) on spore germination of Podosphaera aphanis in detached strawberry leaves. (A) Microscopic view of germinated spores in Trypan blue stained strawberry leaves sprayed with control, 0.1% ANE, 0.2% ANE, and 0.3% ANE. (B) Percentage germination of P. aphanis on strawberry leaves sprayed with control (C), 0.1% ANE (T1), 0.2% ANE (T2), and 0.2% ANE (T3).

Fig. 2

(A) Foliar spray of Ascophyllum nodosum extract (ANE) reduces powdery mildew on detached leaves of strawberry placed on 2% water agar: control, 0.1% ANE, 0.2% ANE, and 0.3% ANE. This graph represents infected leaf area (B) and number of spores per mm² (C) of infected leaf of strawberry sprayed with control (C), 0.1% ANE (T1), 0.2% ANE (T2), and 0.3% ANE (T3).

Fig. 3

The effect of foliar spray of Ascophyllum nodosum extract (ANE) on powdery mildew of strawberry plants grown in green house conditions. (A) Powdery mildew infection on strawberry plants sprayed with control, 0.1% ANE, 0.2% ANE, and 0.3% ANE. (B) This graph represents disease severity on 7th and 15th day of post inoculation with spores of Podosphaera aphanis in strawberry plants sprayed with control (C), 0.1% ANE (T1), 0.2% ANE (T2), and 0.2% ANE (T3).

Fig. 4

The effect of Ascophyllum nodosum extract (ANE) on total flavonoid content (A), and total phenolic content (B) of strawberry leaves sprayed with control (C), 0.1% ANE (T1), 0.2% ANE (T2), and 0.2% ANE (T3), and strawberry leaves sprayed with control (C), 0.1% ANE (T1), 0.2% ANE (T2), and 0.2% ANE (T3) in response to powdery mildew infection.

Fig. 5

Defense-related enzyme activities in strawberry plants sprayed with different concentrations of Ascophyllum nodosum extract (ANE). (A) Phenylalanine ammonia lyase (PAL). (B) Polyphenol peroxidase (PPO). (C) Peroxidase (PO) activities in plants sprayed with control (C), T1 (0.1% ANE), 0.2% ANE (T2), and 0.2% ANE (T3), and strawberry leaves sprayed with control (C), 0.1% ANE (T1), 0.2% ANE (T2), and 0.2% ANE (T3) in response to powdery mildew infection.

Fig. 6

Natural incidence of powdery mildew on strawberry plants sprayed with control (C), 0.1% Ascophyllum nodosum extract (ANE) (T1), 0.2% ANE (T2), and 0.2% ANE (T3) under field conditions. Disease incidence (%)

Fig. 7

Disease severity of powdery mildew observed every 7 days for 1 month after the natural occurrence of disease on strawberry plants sprayed with control (C), 0.1% Ascophyllum nodosum extract (ANE) (T1), 0.2% ANE (T2), and 0.2% ANE (T3) under field conditions.