ntified as already having a significant impact. Virus-resistant crops are under development. These include maize resistant to the African endemic maize streak virus and cassava resistant to African cassava mosaic virus. Parasitic weeds such as Striga attack the roots of crops such as maize, millet, sorghum and upland rice. Field trials in Kenya using a variety of maize resistant to a herbicide have proven very successful. Drought-tolerant crops are also under development as are improved varieties of local African crops such as bananas, cassava, sorghum and sweet potatoes.