Date of Graduation

8-2017

Document Type

Thesis

Degree Name

Master of Science in Horticulture (MS)

Degree Level

Graduate

Department

Horticulture

Advisor/Mentor

John R. Clark

Committee Member

M. Elena Garcia

Second Committee Member

Renee T. Threlfall

Third Committee Member

Ioannis E. Tzanetakis

Keywords

Blackberry, Fruit

Abstract

There are two major public blackberry (Rubus L. subgenus rubus Watson) breeding programs in the United States: one at the University of Arkansas (UA) and another at the U.S. Department of Agriculture Agricultural Research Service Horticultural Crops Research Unit (USDA-ARS HCRU) based in Corvallis, OR. The germplasm and breeding objectives of these two breeding programs are diverse, but frequent collaboration necessitated a standardized method of characterizing plant and fruit traits. A phenotyping protocol for blackberry was developed at UA and implemented for two years on UA seedling populations. The protocol included plant traits (health, vigor, estimated crop load, peak bloom date, and number of canes) and fruit compositional traits (firmness by compression, berry weight, soluble solids content, pH, and titratable acidity). Multivariate analysis indicated that quantitative measurements, rather than qualitative, were best for phenotypic resolution, particularly for specific traits contributing to larger overall characteristics. Fruit compositional traits were evaluated on juice from one year from populations of blackberries grown at UA and UDSA-ARS HCRU, and included soluble solids content, pH, titratable acidity, and organic acids and sugars. Analysis of variance of fruit compositional traits indicated that population means in UA material had more significant differences for several attributes when compared to USDA-ARS HCRU material. Generally, UA seedlings had lower soluble solids content, higher pH, and lower titratable acidity as well as acid content than USDA-ARS HCRU seedlings. Another interesting attribute of fresh-market blackberries is red drupelet reversion, a postharvest phenomenon in which drupelets on the berry turn red. Nine UA advanced selections and cultivars were harvested at different times of days and evaluated for weight lost by berry, change in firmness, and incidence of red drupelet reversion after storage. Results indicated that a novel “crispy” genotype performed better than other genotypes in regard to red drupelet reversion. However, for both change in firmness and incidence of reversion, a significant genotype and harvest time interaction effect was observed. Overall, it is suggested that growers harvest blackberries at earlier, cooler times to avoid the postharvest disorder, regardless of genotype.

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