Physiological and Anatomical Responses of Faba Bean Plants Infected with Chocolate Spot Disease to Chemical Inducers

Abstract

Plant diseases are biotic stresses that restrict crop plants' ability to develop and produce. Numerous foliar diseases, such as chocolate spots, can cause significant production losses in Vicia faba plants. Certain chemical inducers, including salicylic acid (SA), oxalic acid (OA), nicotinic acid (NA), and benzoic acid (BA), were used in this study to assess efficacy in controlling these diseases. A foliar spray of these phenolic acids was used to manage the impacts of the biotic stress resulting from disease incidence. All tested chemical inducers resulted in a significant decrease in disease severity. They also enhanced the defense system of treated plants through increasing antioxidant enzyme activity (Peroxidase, polyphenol oxidase, β-1, 3-glucanase, and chitinase) compared to the corresponding control. Healthy leaves of faba plants recorded the lowest (p < 0.05) values of all antioxidant activities compared to those plants infected by Botrytis fabae. Moreover, the separation of proteins using SDS-PAGE showed slight differences among treatments. Furthermore, foliar spray with natural organic acids reduced the adverse effects of fungal infection by expediting recovery. The SA (5 mM) treatment produced a pronounced increase in the upper, lower epidermis, palisade thickness, spongy tissues, midrib zone, length, and width of vascular bundle. The foliar application with other treatments resulted in a slight increase in the thickness of the examined layers, especially by benzoic acid. In general, all tested chemical inducers could alleviate the adverse effects of the biotic stress on faba bean plants infected by Botrytis fabae.

Keywords: Botrytis fabae; antioxidant enzymes; chocolate spot disease; faba bean; protein banding and anatomy.

Figure 1

Effect of spraying faba bean plants with varying concentrations of organic acids on the severity of chocolate spot disease under greenhouse conditions. Letters a to k represent significant levels (p < 0.05), i.e., a treatment with the letter “a” is significantly different from “b”, and “b” is significantly different from “c”, and so forth. If two treatments have the same letter, they are not significantly different from each other.

Figure 2

Effect of spraying faba bean with various concentrations of organic acids on the development of chocolate spot disease in field conditions in the two successive seasons. Letters a to k represent significant levels (p < 0.05), i.e., a treatment with the letter “a” is significantly different from “b”, and “b” is significantly different from “c”, and so forth. If two treatments have the same letter, they are not significantly different from each other.

Figure 3

Activity of peroxidase (Unit/g fresh wt./min) in faba bean leaves infested with B. fabae plants treated with chemical inducers. LSD 5% for healthy and infected plants at 0, 6, 12, 24, and 48 h are 0.012, 0.012, 0.021, 0.004, 0.018, 0.005, 0.00.016, 0.010, and 0.021, respectively. Letters a to k represent significant levels (p < 0.05), i.e., a treatment with the letter “a” is significantly different from “b”, and “b” is significantly different from “c”, and so forth. If two treatments have the same letter, they are not significantly different from each other.

Figure 4

Activity of polyphenol oxidase in faba bean leaves infested with B. fabae plants treated with chemical inducers. LSD (5%) for infected and healthy plants at 0, 6, 12, 24, and 48 h are 0.009, 0.008, 0.062, 0.044, 0.099, 0.010, 0.039, 0.011, 0.014, and 0.037, respectively. Letters a to k represent significant levels (p < 0.05), i.e., a treatment with the letter “a” is significantly different from “b”, and “b” is significantly different from “c”, and so forth. If two treatments have the same letter, they are not significantly different from each other.

Figure 5

Activity of β-1,3-glucanases in faba bean leaves infested with B. fabae treated with chemical inducers. LSD (5%) for infected and healthy plants at 0, 6, 12, 24, and 48 h are 0.096, 0.096, 0.104, 0.061, 0.122, 0.099, 0.083, 0.012, 0.011, and 0.060, respectively. Letters a to k represent significant levels (p < 0.05), i.e., a treatment with the letter “a” is significantly different from “b”, and “b” is significantly different from “c”, and so forth. If two treatments have the same letter, they are not significantly different from each other.

Figure 6

Activity of chitinase in leaves of faba bean infested with B. fabae plants treated with chemical inducers. LSD 5% for infected and healthy plants at 0, 6, 12, 24, and 48 h are 0.011, 0.011, 0.120, 0.101, 0.103, 0.066, 0.079, 0.086, 0.105, and 0.049, respectively. Letters a to k represent significant levels (p < 0.05), i.e., a treatment with the letter “a” is significantly different from “b”, and “b” is significantly different from “c”, and so forth. If two treatments have the same letter, they are not significantly different from each other.

Figure 7

Separation of soluble proteins (SDS-PAGE) in faba bean plant leaves treated with chemical inducers against B. fabae.

Figure 8

Effect of foliar application with chemical inducers on the anatomical characteristics of faba bean (Vicia faba L.) terminal leaflet under chocolate spot disease stress.

Figure 9

Transverse-sections through blade of the terminal leaflets of faba bean (Vicia faba L.) under chocolate spot disease: (a) Untreated plant (Control), (b) Plant treated with benzoic acid and (c) Plant treated with salicylic acid. Abbreviations: Le = Lower epidermis; P = Palisade tissue; St = Spongy tissue Ue = Upper epidermis and Vb = Vascular bundle.