Field Assessment of Black Spot Resistance In Roses Iin a Hot Humid Climate

A replicated rose evaluation trial was planted in the spring of 2006 at the Texas A&M University Horticulture Farm in College Station, Texas (USA). This trial was systematically evaluated for black spot resistance and landscape quality over 3 years. The roses evaluated included a wide range of classes including Hybrid Teas, Polyanthas, Shrub roses, Chinas, Teas, and ground covers as well as various experimental breeding lines. Among the roses evaluated, some maintained excellent health and good landscape quality such as Belinda’s Dream and Knockout. Unfortunately, there were also some roses, most notably New Zealand, that were so highly susceptible to black spot that they died within the first year. It is noteworthy to mention that a German line 91/100-5, a rose genotype with the Rdr1 black spot resistance gene, initially appeared very resistant to black spot but by the third year showed considerable black spot infection whereas breeding lines involving Rosa wichurana ‘Basye’s Thornless showed no black spot development beyond an occasional infected leaf.