Incorporation of root-knot nematode (Meloidogyne javanica (Treub) Chitwood) resistance in the Zimbabwean elite Virginia tobacco (Nicotiana tabacum L.) germplasm: A review

Virginia tobacco (Nicotiana tabacum L.) is currently the most popular field cash crop grown in Zimbabwe. The farming of Virginia tobacco in Zimbabwe started during the late 19^th Century with introduced varieties which succumbed to most of the locally occurring pests and diseases. One major pest of tobacco that threatens the success of growing the crop has been the root-knot nematode [Meloidogyne javanica (Treub) Chitwood]. The pest attacks the root system of the crop from as early as the seedbed stage to such an extent that yield losses of above 90% can be realised if the nematode is not controlled. In Zimbabwe, the threat posed by the pest in the success of the tobacco farming industry was realised as early as the 1950s and one of the approaches used to contain it was breeding for resistance into the local tobacco germplasm among other methods such as chemical control and cultural practices like crop rotation. This paper is a review of the process that was followed in incorporating root-knot nematode resistance in flue-cured tobacco germplasm in Zimbabwe. It shows the sources/origin of the root-knot nematode (M. javanica) resistance currently present in the Zimbabwean Virginia tobacco (N. tabacum) germplasm and the methods used in transferring the resistance to elite germplasm currently used in modern breeding programmes. The current study also suggests the way forward for the future breeding research for root-knot nematode (M. javanica) resistance in continuity of the past 50 years of breeding effort for resistance to the pest.