Development of a Standardized Phenotyping Protocol for Blackberry

The beginnings of DNA-informed breeding for blackberry are underway, with a DNA fingerprinting method being developed for confirming identity by descent. With this movement towards molecular methods, the quality of phenotypic data must be high enough to complement genetic resolution and also be shared amongst breeding programs effectively. Previous protocols for phenotyping have been established under the USDA-Specialty Crop Research Initiative (SCRI)-funded RosBREED I project for apple, peach, strawberry, and sweet and tart cherry. Blackberry is one of several Rosaceous crops included in the SCRI-funded RosBREED II: “Combining Disease Resistance with Horticultural Quality in New Rosaceous Cultivars,” and phenotyping for quality is an objective of this project.  In an attempt to optimize commercial relevance, heritability, precision, and standardization with cost and labor efficiency, 17 traits were selected for analysis in this blackberry phenotyping protocol, with an emphasis on fruit quality. Plant traits include cane characteristics, presence or absence of thorns, plant health and vigor, flowering characteristics, and productivity. Fruit characteristics include berry weight, length and width, drupelet diameter, and firmness. Fruit compositional traits include soluble solids content (SSC), pH, and titratable acidity (TA). The phenotyping protocol was used to characterize seedling populations from the University of Arkansas (UA) and USDA-ARS, Oregon breeding programs. Preliminary data analysis of the implemented protocol revealed some findings, particularly in the area of compositional analysis. Analysis of SSC indicated that on average, the USDA-ARS populations had higher SSC compared to UA, with mean values ranging from 10.8 - 13.8% and 8.9 - 11.0%, respectively. In contrast, pH measurements indicated that USDA-ARS populations had lower pH than UA populations, pH mean values ranging from 3.6 - 3.9 and 3.95 - 4.2, respectively. TA in USDA-ARS material was more variable and generally higher, with mean values ranging from 0.9 - 2.0% compared to 0.6 - 1.2% for UA material. Crosses between UA and USDA-ARS parents were represented by three populations: two in Oregon (ORUS 4540 and ORUS 4674) and one in Arkansas (Ark_Pop1261). The greatest difference between these populations could be observed in average SSC, where ORUS 4540 and ORUS 4674 exceeded Ark_Pop1261 by 3.0 and 4.1%, respectively. The protocol will continue to be used and further refined in future phenotyping.