Recurrent selection is being used to improve Fusarium oxysporum f. sp. vasinfectum race 4 (FOV4) resistance in Upland (Gossypium hirsutum L.) and Pima (G. barbadense L.) cotton using naturally infested fields and artificially inoculum-greenhouse sites. Our primary objective is to introduce a known FOV4 dominant gene that has shown resistance in Pima into the Upland species. In 2013, 2014 and 2015, we evaluated 1155 entries for resistance. These entries were exposed to FOV4 pressure in naturally infested fields and rated. Selected entries were then self- and cross pollinated. Parental lines and F1 populations were then inoculated with FOV4 and grown under greenhouse conditions for rating and reselection. This research will provide additional germplasm to broaden the genetic base for FOV4 resistant cotton.
In California, Fusarium wilt of cotton is a serious fungal disease that is caused by Fusarium oxysporum f. sp. vasinfectum (FOV). Practices that have reduced the effects include not planting in sandy or sandy-loam textured soils that have a high infestation of root knot nematode and use crop rotation to help manage soil inoculum levels. This has been useful with FOV races 1 and 3, but Fusarium oxysporum f. sp. vasinfectum (FOV4) has been found to cause substantial damage in the absence of root knot nematode (Meloidogyne incognita) and persists even when crop rotation is practiced. Thus, the only long-term management of FOV4 is developing resistant cultivars. One objective of this study is to evaluate a known resistant FOV4 dominant gene from Pima (PS6) for potential introgression into Upland germplasm. The second objective is to identify and develop Upland germplasm…