Oomycete pathogens are common soil inhabitants and they can
infect the germinating seeds soon after planting. The germinating
seeds and growing roots release phenolic compounds that act as
growth stimulants and attractants for Pythium zoospores, allowing
the zoospores to grow quickly and infect roots, and these compounds
predispose the host to infection (Owen-Going et al. 2012).
Pythium spores germinate and penetrate feeder roots directly. In
pre-emergence damping-off, seed may be decayed or rot under the
soil surface soon after infection when moisture penetrates the
seed coat or when the radicle begins to extend, resulting in a poor
and uneven seedling stand (Howard et al. 1994). In postemergence
damping-off, cotyledons of the infected plant may break the soil
surface and soon wither and die, or healthy looking seedlings may
suddenly fall over (Howard et al. 1994). Infected seedlings will
discolor or wilt suddenly, or simply collapse and die. Weakened
seedlings also become vulnerable to attack by other soil-borne
pathogens. Pythium spp. can survive as thick-walled mycelia or
oospores for several years in soil and plant debris, and these are
the main source of disease inoculum in the soil (Martin and Loper
1999).
Oomycete pathogens are common soil inhabitants and they caninfect the germinating seeds soon after planting. The germinatingseeds and growing roots release phenolic compounds that act asgrowth stimulants and attractants for Pythium zoospores, allowingthe zoospores to grow quickly and infect roots, and these compoundspredispose the host to infection (Owen-Going et al. 2012).Pythium spores germinate and penetrate feeder roots directly. Inpre-emergence damping-off, seed may be decayed or rot under thesoil surface soon after infection when moisture penetrates theseed coat or when the radicle begins to extend, resulting in a poorand uneven seedling stand (Howard et al. 1994). In postemergencedamping-off, cotyledons of the infected plant may break the soilsurface and soon wither and die, or healthy looking seedlings maysuddenly fall over (Howard et al. 1994). Infected seedlings willdiscolor or wilt suddenly, or simply collapse and die. Weakenedseedlings also become vulnerable to attack by other soil-bornepathogens. Pythium spp. can survive as thick-walled mycelia oroospores for several years in soil and plant debris, and these arethe main source of disease inoculum in the soil (Martin and Loper1999).
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