Dirty panicle pathogens inoculation
Pure cultures of Bipolaris oryzae, C. lunata and Alternaria padwickii
isolated from discolored rice seeds were used for rice plant
inoculation. Each pathogen was grown on autoclaved rice seeds
contained in a plastic bag and incubated under near ultraviolet
light for 10 d or until the spores could be observed (modified from
Chamswarng and Intanoo, 2002). Spore suspensions were prepared
and the spore concentration was adjusted to 1 104 spores/
mL using a haemacytometer. Inoculation was performed by
spraying the spore suspension on the whole rice plants at the early
stage of panicle formation.
Sample collection and data acquisition
Rice growth, disease incidence and yield components of each
treatment were recorded from 60-day-old and 120-day-old rice
plants. These included the height (the length from the base of tiller
to the terminal of the flag leaf) and the number of tillers per rice
hill. The severity of dirty panicle disease on whole panicles of rice
plants was determined twice at 2 and 4 wk after the third Trichoderma
spray by sampling 25 whole panicles from each replication
and four replications per treatment (modified form
Chettanachit et al., 2009). Disease severity from 10 g of panicledetached
seed in each replication (four samples per replication)
was further determined as the percentages of healthy seed, dirty
panicle infected seed and empty seed (unfertile or undeveloped
seeds). For the yield assessment, rice panicles were collected and
the moisture content of the rice seed was reduced to 14%. All seed
samples were detached from the panicles, then the total rice yield,
1000-healthy seed weight, and 1000-seed weight were recorded.
The quality of milled brown rice was determined by sampling
paddies from each treatment (1 kg per replication, four replications
per treatment) for the brown rice milling process. The
weights of healthy seed or whole kernels plus head rice and