Additional nitrogen application reduced white drupelet disorder in ‘Sweetie Pie’ blackberry

Authors: STAFNE, ERIC - Mississippi State Extension Service; RYALS, JENNY - Mississippi State University; Smith, Barbara

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2021
Publication Date: 11/9/2021
Citation: Stafne, E., Ryals, J., Smith, B.J. 2021. Additional nitrogen application reduced white drupelet disorder in ‘Sweetie Pie’ blackberry. HortTechnology. 31:(6)793-797. https://doi.org/10.21273/HORTTECH04931-21.
DOI: https://doi.org/10.21273/HORTTECH04931-21

Interpretive Summary: White drupelet disorder in blackberries is a tan-to-white discoloration of drupelets on the fruit that reduces the quality of berries making them unattractive to consumers. This disorder is affected by environmental conditions such as temperature and light intensity; however, we lack a complete understanding of other causes of the disorder. In this study we determined that blackberry plants receiving no extra nitrogen had the highest percentage of berries with white drupelets; plants that received additional nitrogen in 5 separate applications had fewer affected berries; and plants that received the same amount of nitrogen in one application had the fewest affected berries. The reduction in affected berries may be due to increased shading of berries due to more leaves on plants receiving higher levels of nitrogen applications. We also observed that the occurrence of white drupelets increased as the number of rainfall events increased. Blackberry growers can use this information to reduce the number of affected berries in their crop which will lead to a higher quality and better acceptance by the consumers.

Technical Abstract: White drupelet disorder in blackberry (Rubus subgenus Rubus) is an abiotic condition resulting from a genotype by environment interaction. While high temperatures and light intensities have been implicated, little is known why this disorder manifests. Other factors, such as overall plant stress, may be contributing influences. In this study, three treatments were applied to examine if addition of nitrogen can reduce white drupelet disorder on ‘Sweetie Pie’ blackberry over two seasons. Two nitrogen application treatments of 100 kg•ha-1 were applied at one time (1x) and five separate applications (5x) spaced one week apart. One control treatment of no additional nitrogen (0x) was also included. Berries were harvested and weighed as a total, then berries with white drupelets were separated out and weighed. The two values were divided to create a proportion and multiplied by 100 to make a percentage. Nitrogen application decreased the percentage of white drupelet berries from 12.1% to 9.4% (one application) and 8.6% (five applications). Occurrence of white drupelets by treatments 0x, 1x, and 5x was significantly correlated with cumulative number of rainfall events (r = 0.49, 0.47, 0.46, respectively). While it is likely that multiple factors are involved in development of white drupelets, additional nitrogen can reduce the problem. This may be due to increase in biomass resulting in more shading or by reducing inhibition of photosynthesis.