Assertion : Black rust of wheat is a hazardous disease which is caused by Puccinia fungus. Reason : Aflatoxin is produced in the groundnut by the infection of a bacterium.

Step-by-step solution

Stem rust, also known as black stem rust is caused by Puccinia graminis tritici, a fungus. It primarily infects wheat, but also causes minor infections on cultivars of barley and rye. Groundnut production is reduced by Aspergillus species, a fungus, which causes quantitative losses and produces highly toxic and carcinogenic chemical substance known as aflatoxins.