An Overview of the Biology of Sorghum Ergot

Synchronicity of pollination and inoculation with Claviceps africana and its effects on pollen–pistil compatibility and seed production in sorghum

“…Actually, callose formation would be a too late host reaction to stop C. africana infection progress. Previous results and ours demonstrate that the stigma is a niche for conidia germination (Bhuiyan et al 2002) and the main route for infection (Frederickson & Mantle 1988), as opposed to Ryley et al (2002) whom proposed that this pathogen penetrates directly through the style or ovary. This means that C. africana is a highly specific pathogen.…”

“…Male-sterile genotypes are more sensitive to infection than fertile ones (Meinke & Ryley 1997), and flowering is the vulnerable growth stage (Reed et al 2002). Hence, synchronous flowering among parental lines, deposition time of pollen and conidia on the stigma, and the relative growth rates of pollen tubes and conidia determines whether the ovary will be fertilized by the pollen nuclei or colonized by the fungus (Ryley et al 2002;Mendoza-Onofre et al 2006). Environmental factors may also predispose fertile sorghum genotypes to infection by decreasing pollen viability (Musabyimana et al 1995;McLaren 1997) or compatibility between pollen and the stigma (Moran et al 2002).…”

Efficacy, timing and method of application of fungicides for management of sorghum ergot caused by Claviceps africana

“…Possible explanations for this finding are that: (i) droplets leaving a cone nozzle have less momentum than those leaving a flat fan nozzle due to the swirling nature of the spray as it leaves the nozzle, hence they have less impact when they reach the panicles; (ii) cone nozzles produce a higher proportion of very fine droplets (< 100 µm diameter), which are susceptible to evaporation and drift; and (iii) droplets leaving the fan nozzles have greater exit velocities and reach the panicles sooner than those from hollow cone nozzles, making them less prone to drift and evaporation. In many situations, such as following rain periods when infection is likely to occur (Ryley et al 2003a), aerial application is the preferred option. The results of our trials suggest that applications of triadimenol as small droplets in low water volumes (50 L/ha) are as effective in reducing ergot severity as applications using larger droplets in higher water volumes (> 100 L/ha), thereby making aerial application a viable option.…”

“…Mature sclerotia of C. sorghi and C. sorghicola readily germinate (Bandyopadhyay et al 1998;Tsukiboshi et al 1999), but germination of C. africana sclerotia is poor (Frederickson et al 1991). Sclerotia of the latter species appear to have little or no role in the survival of the pathogen and, in Australia, C. africana can survive year-round on alternative and volunteer hosts (Ryley et al 2003a) and, for a limited period, on infected panicles (Bhuiyan et al 2002).…”

Patterns of release of the secondary conidia of Claviceps africana, the sorghum ergot pathogen in Australia

“…Ergot of grain sorghum ( Sorghum bicolor ) is caused by three pathogens, Claviceps africana , Claviceps sorghi and Claviceps sorghicola (Ryley et al ., 2002a). There have been reports on C. africana from the Americas, Africa, India, southeast Asia, Japan and Australia, on C. sorghi from India and neighbouring countries including Pakistan and Burma, and C. sorghicola in Japan only (Bandyopadhyay et al ., 1998; Tsukiboshi et al ., 1999).…”