Based on the following information, answer the questions given below:

RNA interference (RNAi), is an evolutionarily conserved mechanism triggered by double-stranded RNA (dsRNA), causes gene silencing in a sequence-specific manner . This technique will be used to develop pest resistant plants . Several nematodes parasitise a wide variety of plants and animals including human beings. A nematode Meloidegyne incognitia infects the roots of tobacco plants and causes a great reduction in yield. A novel strategy was adopted to prevent this infestation which was based on the process of RNA interference. ( RNAi) takes place in all eukaryotic organisms as a method of cellular defense. This method involves silencing of a specific mRNA due to the complementary dsRNA molecule that binds to and prevents translation of the mRNA. Nematode-specific genes were introduced into the host plant by using Agrobacterium vectors. DNA produced both sense and anti-sense RNA in the host cells . These two RNA’s being complementary to each other formed a double stranded (dsRNA) that initiated RNAi and silenced the specific mRNA of the nematode.

Which part of the tobacco plant infects the nematode ?