| Summary: | 碩士 === 國立中興大學 === 植物病理學系 === 84 === Rhizoctonia brown patch of turfgrasses caused by Rhizoctonia
spp. is commonly and seriously occurring in Taiwan. The main
causal agent is R. solani AG-4. Sixteen turfgrass seeds were
screened for quantitative baiting of this causal organism. The
criteria used to screen are conveniency of seed recovery from
soil, baiting efficiency, stability, easy to handle and shorter
time needed. Bahia grass seeds were found to be satisfied to
these requirements. The suitable conditions for bahia grass
seeds to bait R. solani are 12-15%(w/w) water content of the
soil incubated at 25℃. Bahia grass seeds were buried in soil
for 12 hr, and placed on tannic acid agar in dark for 12-16 hr.
Positive baiting is shown by brown color appeared beneath and
around the seeds. There is a good correlation between percent of
bahia seed baiting at 12 hr and density of propagules of R.
solani in soil assayed by multiple-pellet soil sampler method.
Bahia grass seed baiting also does well on other anatomosis
groups, i.e., AG-G(isolate WF2) and AG-F(TKS) but not WAG-O(
NP18). Two methods can be used to estimate the popagule density
of R. solani in soil by bahia grass seed baiting. Firstly
equation Y=4.53+17.69X obtianed from correlation analysis of
percent of bahia seed baiting and propagule density assayed by
multiple-pellet soil sampler can be used. Secondly based on
bahia grass seed could induce mycelial growth of R. solani in
soil for 0.25 cm length within 12 hr, this means that a single
bahia grass seed has ability to bait the pathogen in soil within
a radius of 0.25 cm in 12 hr. The soil weight of baiting range
of a single seed can be calculated from baiting range of soil
volumn, 4/3r3 =4/3 x 3.1416 x 0.25=0.065 cm3. Density of
propagules/g soil = number of positive baiting seeds/number of
seeds assayed x a single seed baiting soil range in g. The
second method can be used only when density of propagules is
low, or soil has to be properly diluted. If density of
propagules is too low, the sampling size of baiting seeds must
increase.
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