Abstract
According to the seed defense theory, predation and pathogenicity should be lower in physically dormant (PY) seeds than those of no-dormant (ND). Thus, a study was conducted to determine the predation and pathogenicity of four tropical Fabaceae species to test the above hypothesis. Imbibition and germination of manually scarified (MS) and untreated (UT) seeds were tested using locally collected seeds. Pathogenicity and predatory rates of MS and UT seeds of each species was observed by keeping them separately in a woodland and a grassland for four weeks. Nutrient content and production of volatile compounds in seeds were determined. Germination and imbibition experiments confirmed the physical dormancy of two Senna spp., non-dormancy of Bauhinia variegata and physiological dormancy in Pterocarpus indicus seeds. Predation and pathogenicity were higher in the woodland than in the grassland. Lowest seed predation and pathogenicity were recorded in P. indicus and the highest in B. variegata. Pathogenicity and predation of MS seeds of Senna spp. were higher than that of UT seeds. No correlation was revealed between nutrient content and pathogenicity or predation. MS seeds released more volatile compounds than intact seeds as they were in imbibed state. Pathogenicity and predation depended on seed dormancy classes.
Highlights
The ‘plant defense theory’ explains the survival of seedlings and mature plants from pathogens and predators (McKey, 1974 and Herms and Mattson, 1992)
Physical defense syndrome is mainly adopted by seeds with physical dormancy, chemical and physical defense continuum by seeds with physiological dormancy, and microbial defense syndrome by non-dormant seeds (Dalling et al, 2011)
No significant mass increment was observed in the untreated fresh seeds of two Senna spp. during the imbibition whereas, manually scarified seeds of these two species increase in mass > 120 % (Figure 1)
Summary
The ‘plant defense theory’ explains the survival of seedlings and mature plants from pathogens and predators (McKey, 1974 and Herms and Mattson, 1992). Seed survival mainly depends on the seed size, nutrition and the structural or chemical traits that influence predation rates (Janzen, 1969; Grubb et al, 1998 and Moles et al, 2003). Considering all these facts, Dalling et al (2011) have put forward the ‘seed defense theory’ which explains the mechanisms of seed defense against pathogens and predators in the micro habitats of seeds. Physical defense syndrome is mainly adopted by seeds with physical dormancy, chemical and physical defense continuum by seeds with physiological dormancy, and microbial defense syndrome by non-dormant seeds (Dalling et al, 2011)
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