You can try following 4 suggestions

1. Overnight Soaking of the seed not needed always, if you are using freshly harvested seed it already contains the desired moisture.

2. sterilize the seed before dehusking.

3. You have to keep your inoculated culture continuosly in dark for atleast 7-10 days.

4. Sometime Nonembryonic part of the seed also prevents callus cultuture, so try some seeds with  embryo part only.(remoove non embronic part.

Best of luck...

Is there any existent protocol that everyone follows for rice tissue culture?

Have you seen this 2015 paper:

Title: "Proline and Glutamine Improve in vitro Callus Induction and Subsequent Shooting in Rice"

MATERIALS AND METHODS

Rice materials

For callus induction, sterilized seeds were cultured on Murashige and Skoog (MS) medium (Murashige and Skoog, 1962) supplemented with 3% sucrose, 0.8% agar and different concentrations of 2,4-dichlorophenoxy acetic acid (2,4-D) (Table 1). All cultures were maintained at (28 ± 2) °C under a 16 h photoperiod provided by cool white fluorescent lamps. Additionally, to investigate the effects of proline and glutamine on callus induction.

The calli were induced from rice seeds. From Fig.1 and fig.2, it seems that the higher concentration of 2,4-D (up to 2 mg/L in their exp), the more calli was induced. Proline and Glutamine further improved callus induction. Did you use the same genotype as one of the 4 genotypes they used? How much 2,4-D did you use? You can consider adding proline and glutamine into medium too.

Dear Yau,

I just read the article.I'll talk to my supervisor about this findings. I'm using different genotypes(Swarna & Kasalota) right now. I used 0.5,1,1.5,2,2.5,3,3.5,4 mg/l level of hormonal concentration.

Thank you very much for your contribution

Hi Niloy,

If nobody has done callus induction from these genotypes (Swarna and Kasalota), probably you have to try on different 2,4-D concentration and find out which conc. is the best one for your varieties, as you have done above. And make sure your seeds are not very old.

Embryogenic callus of rice has proved most successful for plant regeneration in vitro. This be kept in mind while doing your experiment. 

Dear Niloy Kumar Das ,

I suggest this protocol for Japonica and indica, instead of Ms used 

N6 salts and N6 vitamins, 1.5 mg/ L 2,4-2,4-D, 0.7 g /L L-proline, 68.4 g /L sucrose, and 36 g/ L glucose (pH 5.2).

with best regards

khaled

try to use 2 mg.l-1 of 2,4-D in combination with 0.5 mg.l-1 of NAA and 2x of MS media (double strength of MS SALT/L ) .

BEST REGARDS