Estimation of phenyl alanine ammonialyase (PAL) and some phytoalexins in Vicia faba plants infected with spot disease caused by Alternaria alternata

Abstract

Biological agents are an important approach to controlling many fungal phytopathogens; plants produce phytoalexins such as phenol, alkaloids and tannins as a response to the biotic stresses. The results showed that the addition of the biological control of Trichoderma harzianum to Alternaria alternata caused an increase in the activity of the enzyme phenylalanine ammonialyase (PAL) after 20 days from the start of the greenhouse experiment, which was 6.21 mmol/min in the Spinal variety, compared with the enzyme activity in the treatment with A. alternata alone, which was 5.51 mmol/min. The variety Netherland mulch recorded a lower phenolic content in all treatments, and the treatment with biological control T. harzianum in addition to A. alternata had the highest content as it reached 4.50 mg/g on day 20, Netherland mulch variety showed the most amount of alkaloids and tannins than others during different periods. The plants treated with the biological control of T. harzianum contained the most alkaloids on day 20, which was 5.15% It decreased to 3.65% on day 30. The most tannins in Netherland mulch variety were in the plants treated with biological control T. harzianum alone, which was 3.93% on day 20, compared to the plants treated with A. alternata alone, which was 0.71%. The addition of biological control of T. harzianum to A. alternata increased the plant amount of tannins, which was 2.01%. The study would help to understand the role of T. harzianum as a biological control to the response of the varieties to the formation of plant defenses, including phytoalexins.