Effect of the absence of condensed tannins in faba beans (Vicia faba) on resistance to foot rot, Ascochyta blight and chocolate spot

Abstract

The effect of breeding for the absence of condensed tannins in the testa of Vicia faba L. on resistance to foot rot, Ascochyta blight and chocolate spot diseases was investigated in 1988-92 at Wageningen, The Netherlands. For this purpose the disease development in tannin-free and tannin-containing partners of six near-isogenic pairs was compared after exposure to causative pathogens. Except for one near-isogenic pair, in which both partner lines showed a relatively high resistance, the tannin-free lines were more susceptible to foot rot than the tannin-containing partners of the same pair. This observation indicates that the presence of condensed tannins in the testa prevents infection of the plant by the causative pathogens. Fusarium oxysporum and F. solani, isolated from faba bean tissues showing foot rot symptoms, were shown to be primary foot rot pathogens, while F. avenaceum caused wilting of young plantlets. No pathogenic isolates were obtained from F. tabacinum. Resistance to Botrytis fabae (chocolate spot disease), scored on leaves and stems under glasshouse and field conditions in 1992, was not influenced by selection for the absence of condensed tannins which occur in the testa of mature seeds. Under the same environmental conditions, leaves, stems, pods and seeds of tannin-free lines showed similar levels of damage due to Ascochyta fabae (Ascochyta blight) as the tannin-containing partner lines of the same near-isogenic pair. These results indicate that condensed tannins do not play a role in resistance to both B. fabae and A. fabae, probably because, except for the seeds, these polyphenols do not accumulate in the tissues affected by these pathogens.

Rapid deployment of allelochemicals in exudates of germinating seeds of Sesbania (Fabaceae): roles of seed anatomy and histolocalization of polyphenolic compounds in anti-pathogen defense of seedlings

“…Pathogen attacks occur in the first hours of seedling development (Harman 1983;Nelson 1990), at a stage when the seedling is highly vulnerable because most resources are allocated to growth and are thus unavailable for defence (Sprent & Thomas 1984;Herms & Mattson 1992). These environmental pressures have shaped the structure of the seed coat, helping to ensure that dormant seeds remain viable during long periods of storage in pathogen-rich soils (Anderson & Baker 1983;Halloin 1983;Harman 1983;Graaff & Van Staden 1984;Kremer et al 1984;Cabrera & Martin 1986;Helsper et al 1994).…”

“…Artificial selection has favoured seeds that are palatable, low in anti-nutritional compounds and quick to germinate upon planting (Powell et al 1986;Cabrera & Martin 1986, 1989Pascual Villalobos & Gellis 1990). These selection pressures have led to lower levels of proanthocyanidins and other phenolics, and have resulted in increased susceptibility to pathogens (Halloin 1983;Harman 1983;Graaff & Van Staden 1984;Kremer et al 1984;Cabrera & Martin 1986, 1989Pascual Villalobos & Gellis 1990;Helsper et al 1994;Gao & Shain 1995). As a result, high levels of proanthocyanidins in seed coats clearly represent the ancestral state of this character.…”

“…These interactions may be antagonistic (e.g., with pathogens) or positive (e.g., the symbiosis between legumes and rhizobia). Because pathogenic fungi, bacteria, viruses and nematodes are abundant in soil, seeds with long periods of dormancy require defence for their persistence in soil (Anderson & Baker 1983;Halloin 1982Halloin , 1983Harman 1983;Graaff & Van Staden 1984;Kremer et al 1984;Cabrera & Martin 1986;Helsper et al 1994). Upon germination of the seed, these pathogens may quickly kill young seedlings or weaken them at a critical and highly vulnerable stage of growth.…”

“…Given the high incidence of attack by soil pathogens, selection should have favoured the evolution of defences against rhizosphere pathogens. Numerous studies document the production by germinating seeds of exudates that function as chemical defences against soil pathogens (Kraft 1977;Short & Lacy 1976, 1978Graaff & Van Staden 1984;Kremer et al 1984;Paszkowsky & Kremer 1986;Pascual Villalobos & Jellis 1990;Warr et al 1992;Helsper et al 1994).…”

“…The future defences of seedlings may simultaneously be the present defences of dormant seeds. Previous studies have focused on the chemical nature of exudates (Kraft 1977;Short & Lacy 1978;Graaff & Van Staden 1984;Paszkowsky & Kremer 1986;Warr et al 1992;Helsper et al 1994) and to a lesser extent on their histological localization within the seed (Halloin 1982;Venere 1980;Graham 1991). No study exists, however, that examines seed structure in relation to release of exudates, or that attempts to integrate morphological, histological and biochemical aspects of the release of allelochemicals by germinating seedlings.…”