Answer :

(a)
• Meloidegyne incognitia
• Roots
(b) By using Agrobacterium vector, Nematode specific genes were introduced into host plant, introduction of DNA produced both sense and anti-sense RNA in the host cells these two RNAs being complementary to each other form a double stranded RNA (ds RNA), that initiated RNAi and thus silenced the specific mRNA of the nematode hence parasite could not survive in host.