Infection process and host range of Colletotrichum capsici
1995
Pring, R.J. | Nash, C. | Zakaria, M. | Bailey, J.A.
The pathogenicity, host range and infection process of three isolates or Colletotrichum capsici, from cowpea (Vigna unguiculata), bean (Phaseolus vulgaris) and betle vine (Piper betle), are described. The location and morphology of infection hyphae of C. capsici within hypocotyls of cowpea were investigated by light, transmission and cryo-scanning electron microscopy. All isolates attacked a similar range of legumes, but other legumes were resistant. Wounding increased their pathogenicity on susceptible hosts. All susceptible tissues were completely rotten within 8-10 days, with acervuli present over the entire surface of the hypocotyls. Initial infections occurred after production of appressoria. Infection hyphae penetrated cuticles and initially grew beneath the cuticle in the anti- and periclinal walls of epidermal cells causing extensive wall degradation. Subsequently, hyphae grew in and destroyed the walls of underlying cortical cells. This was associated with extensive death of adjacent cells, which led to production of water-soaked lesions. When tissues were extensively rotted, hyphae entered sclerenchymatous fibres by direct growth through their walls. Freeze-substituted preparations revealed vesicles and plasmatubules in infection hyphae. It is proposed that successful pathogenesis is based on suppression or host defence responses through rapid killing of infected tissues. A comparison of this infection strategy with those of other Colletotrichum species indicates that knowledge of a pathogen's infection process may be used to predict whether it has a narrow or wide host range.
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