Agarwal et al. (1989) reported that diseased plants at advanced stages of infection
showed collar infection followed by death within 14 to 42 days. However, in this experiment,
most of the infected seedlings died after 5 to 40 days, while other plants
survived until maturity but produced sterile, empty, and discoloured seeds. The first
72 h (3 days) during germination of the seeds appeared to be the most critical period
for the infection, mainly because of exudation of amino acids and sugars, acting as rich
energy substrates for the actively growing pathogen (Rajagopalan and Bhuvaneswari
1975). Therefore, the infected plants were taller than controls after 5 to 40 days. In addition,
heavily infected plants died within 10 to 40 days and statistical analysis showed
that the DSI was significantly (p ≤ 0.05) different between days and isolates.
Period of soaking the seeds in inoculum (conidial suspension) also assists the germinating
pathogen to penetrate into the seeds. Twelve hours exposure of seeds to
1.0 x 106 conidia/ml inoculum was selected following Rosmayati (1988) with slight
modifications. Ahmed et al. (1986) soaked the seeds for 24 h, but in less concentrated suspension. Concentrations of the inoculums could also affect the disease severity.
Normally, the disease severity becomes higher when higher concentrations of inoculum
are applied (Ahmed et al. 1986). Disease suppression was found to be less or
more dependent on the virulence of each isolate; different isolates showed different
levels of virulence. Ahmed et al. (1986) also reported that shoot elongation was
significantly higher at 3.1 x 104 conidia/ml or more for 48 h soaking and maximum
elongation of seedlings was attained when the seedlings were inoculated with 1.25
x 105 conidia/ml. Abnormal elongation was not observed if the inoculum levels were
lower than those concentrations.