2.2. Assessment of plant growth promotion by CtHY
2.2.1. Inoculum preparation
CtHY was grown in mNB at 28 ◦C for 2 days. Yeast cells were
harvested by centrifugation at 10,000
×
g for 10 min, and the pellet
was washed twice and resuspended in distilled water. The resulting
suspension was diluted to
∼106 cfu mL−1 prior to inoculation.
2.2.2. Seed surface sterilization
Rice seeds (Oryza sativa cv. Reiziq) were surface sterilized by
soaking in 70% ethanol for 5 min and then in 0.5% mercuric chloride
solution for 30 s. Once drained, the seeds were rinsed with sterile
distilled water for five times (James et al., 2002).
2.2.3. Root elongation bioassay
Sterilized rice seeds were incubated with yeast suspension for
1 h with gentle agitation to allow the yeast to bind to the seed coat.
Sterile distilled water was replaced in control seeds. Coated seeds
were germinated on water agar in a growth chamber for 7 days at
25 ◦C. Shoot and root lengths were measured. The number of germinated
seeds was recorded and seedling vigor index was calculated
as given below (Jegathambigai et al., 2009). Ten plants of each water
agar plate were averaged and considered as one replicate.
Seedling vigor index
=
% Germination
×
(shoot length
+
root length)