Please mention the plant in which you are working. Eventhough Green plant regeneration through organogenesis is reported in many species, it may not be applicable in all plants.Yellow callus is a good sign in some plants where you can induce embryos and develop somatic plants.I think media manipilations can help.Even black calli can regenerate in to plantlets if it is put in right media.

Please let me know the crop (plant) on your research work?. Please check and make sure of media composition especially in the hormones, alter the hormone concentration which may give good result. Even temperature in the growth chamber also will cause the blackening of callus (you can check the temperature by keeping thermometer inside the growth chamber with regular interval).

Note: I have faced the problem and I did the same I suggested above.

Also, it could be something wrong with the medium components, and not related to using CRISPR-Cas9 method per se. To test this, you can include several plates of callus without treatments as CONTROLs. If even the controls cannot grow, then your plant-tissue culture procedure has problem. As mentioned by other posters, you should let us know which plant species you are working on.

Hi Mhummed,

To be able to help you to do resolve your problem, I need to know not only which plant you use, but also wich genotype you use on your research? There are many parametrs that may affect the regeneration and regenarion rate depending on the used species based on many years of experience in vitro culture and transgenic plants production of many differents species. In addition to light and tempertaure that you should check, others factors can affect deeply regeneration such as: 1) the genotype, 2)hormones rate (cytok, auxine), 3) Hormone concentrations, 3) sucrose concentration, kinds of vitamins.

thanks for your kind suggestion. i am working on Rapeseed (Brassica napus).