Environment Affects White Drupelet Disorder Expression on Three Blackberry Cultivars in South Mississippi.

White drupelet disorder (WDD) is a problem that occurs during the ripening stage in some blackberry (Rubus subgenus Rubus) cultivars. Although berries affected with a few white drupelets may taste fine, they are unpleasant aesthetically, and this may lead to negative consumer perceptions and economic ramifications. During 2 years of observational studies and field trials (2016 and 2017), we evaluated changes in three susceptible cultivars in Mississippi affected by WDD. 'Chickasaw', 'Kiowa', and 'Sweetie Pie' berries were harvested twice per week and assessed for WDD. Weather conditions differed substantially during harvest in 2016 and 2017, with 2017 being cooler and rainier which resulted in a lower incidence of WDD. Compared with 2016, in 2017, the overall percentage of berries exhibiting WDD dropped from 22% to 12% for 'Sweetie Pie', 6% to 3% for 'Chickasaw', and 8% to 3% for 'Kiowa'. The soluble solids concentration was highest in 'Sweetie Pie', 11.9% and 9.5% for 2016 and 2017, respectively. For all cultivars examined, the soluble solids concentration of extracted white drupelets was substantially lower than regular drupelets. The value for skin break force for white drupelets was higher than that for black drupelets, 0.99 N vs. 0.29 N, respectively. In 2017, an about 30% shadecloth treatment had a significantly positive impact by decreasing WDD symptoms in all cultivars by 63% when compared with non-shaded plants, but soluble solids concentration was lower. Our results indicate that rain and shadecloth decrease symptoms of WDD. Therefore, growers may be able to use overhead irrigation and shade to reduce WDD symptoms. [ABSTRACT FROM AUTHOR]