Selection among Haploid Sporophytes for Resistance to Black Shank in Tobacco

Black shank, caused by Phytophthora parasitica Dast var. nicotianae [Breda de Haan] Tucker, is a common disease of tobacco (Nicotinna tabacum L.). Selection for genetic resistance to black shank within an F1‐derived haploid population is more efficient than selection within an F2 diploid population. Our objectives were to identify black shank resistance in three segregating haploid tobacco populations and to verify that disease resistance assessed on haploids corresponded to that of doubled haploids (DHs). Population 1 was derived from ‘McNair 944’ × ‘ZA 692’, Populations 2 from ‘Coker 371‐Gold’ (C 371‐G) × ‘K 326’, and Population 3 from ‘VA 509’ × breeding line MDH 410. Haploids were transplanted into a disease nursery and disease incidence was recorded weekly throughout the growing season. We observed segregation for resistance in all three haploid populations. Rescue and chromosome doubling was successful for 85% of selected haploids. In the flue‐cured populations (1 and 2), all but one selected haploid was resistant as a DH. Transgressive segregation for resistance was identified in Population 1. The resistance of a population produced by Intel‐mating Population 1 DHs was equal to that of McNair 944, the resistant parent. Resistance of Population 2 DHs derived from selected haploids was equal to that of C 371‐G, the resistant parent. Selected DHs from Population 2 were significantly more resistant than both K 326 and an unselected DH population derived from the same cross. In Population 3, the hurley population, differences between parents and among DHs were difficult to detect and should be assessed in multiple environments.