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Gerardo H. Nunez, James W. Olmstead and Rebecca L. Darnell

Vaccinium arboreum (VA) is a wild blueberry species that exhibits wider soil pH tolerance and greater ability for iron and nitrate uptake than cultivated Vaccinium species, including southern highbush blueberry (SHB, V. corymbosum interspecific hybrids). The ability of VA and SHB to respond to iron deficiency by rhizosphere acidification was investigated. Rooted cuttings of the VA genotype FL09-502 and SHB ‘Emerald’ were transplanted to a hydroponic system filled with complete nutrient solution. After 14 days of acclimation at 45 µm iron, plants were transferred to unbuffered nutrient solutions containing 90 or 10 µm iron. ‘Emerald’ and FL09-502 plants grown in 10 µm iron exhibited less iron uptake and lower chlorophyll, total iron, and active iron contents than plants grown in 90 µm iron. Generally, there were no species-level differences in iron or nitrate uptake. Neither FL09-502 nor ‘Emerald’ acidified the rhizosphere in either the nutrient solution or in a gel-based assay, regardless of external iron concentration. A screen of 18 additional genotypes of VA and SHB confirmed that this response is absent in these taxa. Thus, rhizosphere acidification is not part of the iron deficiency response of SHB and VA. In addition, the ability to acidify the soil is not likely to be responsible for the wider soil pH tolerance of VA.

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Gerardo H. Nunez, Alisson P. Kovaleski and Rebecca L. Darnell

Consumer perception plays an important role in the decision to purchase organic vs. conventional produce. A web-based survey was used to evaluate perceptions and purchase behavior toward organic produce in a sample population of college-aged students. The effect of formal education on this perception was also investigated. Most subjects in this sample population were aware of and had positive perceptions of organic produce and organic agriculture. The likelihood of being an organic consumer was similar across genders, ages, and fields of study. Subjects who reported to be organic consumers associated less risk with organic produce than those who reported to never have purchased organic produce. A 50-minute lecture about organic agriculture altered the perception students had about organic produce. After the lecture, students expressed bleaker perceptions about the health benefits and ethical soundness of organic agriculture. On the other hand, after the lecture students expressed a more positive perception of the policies and regulations that govern the organic foods market. Overall, data suggest that students’ perception of organic produce and agriculture is based on anecdotal evidence and that formal education on the topic of organic agriculture can affect this perception.

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Christopher S. Imler, Camila I. Arzola and Gerardo H. Nunez

Unlike most horticultural crops, blueberry (Vaccinium spp. section cyanococcus) prefers low-pH (4.2–5.5) soils. Other plants can acidify their rhizosphere to create a hospitable microenvironment. Southern highbush blueberry (SHB; Vaccinium corymbosum interspecific hybrids) plants do not acidify their rhizosphere in response to Fe deficiency, but other factors that affect rhizosphere pH have not been elucidated. We report results from two hydroponic experiments exploring N uptake effects on the rhizosphere pH of ‘Emerald’ SHB. Ammonium (NH4 +) uptake led to rhizosphere acidification, whereas nitrate (NO3 ) uptake led to rhizosphere alkalization. When grown in a split-root hydroponic system, roots that took up NH4 + acidified the rhizosphere to a greater extent that roots not exposed to NH4 +. Rhizosphere acidification was observed even in a nontreated control. These results suggest that NH4 + uptake is the main driver of rhizosphere pH in SHB. N form effects suggest that fertilization with NO3 might lead to undesirable rhizosphere alkalization.

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Gerardo H. Nunez, Hilda Patricia Rodríguez-Armenta, Rebecca L. Darnell and James W. Olmstead

Root growth and root system architecture (RSA) are affected by edaphic and genetic factors and they can impact plant growth and farm profitability. Southern highbush blueberries [SHBs (Vaccinium corymbosum hybrids)] develop shallow, fibrous root systems, and exhibit a preference for acidic soils where water and ammonium are readily available. The amendments used to create these soil conditions negatively affect the profitability of SHB plantations. Hence, breeding for RSA traits has been suggested as an alternative to soil amendments. Vaccinium arboreum is a wild species that is used in SHB breeding. V. arboreum exhibits greater drought tolerance and broader soil pH adaptation than SHB, and—according to anecdotal evidence—it develops deep, taproot-like root systems. The present study constitutes the first in-depth study of the RSA of Vaccinium species with the intention of facilitating breeding for RSA traits. Root systems were studied in rhizotron-grown seedling families. In separate experiments, we tested the effect that growth substrate and family pedigree can have on root growth and RSA. Subsequently, a genotyping by sequence approach was used to develop single nucleotide polymorphism (SNP) markers that could be used along with the phenotyping method to investigate the heritability of RSA traits and look for marker-trait associations. We found that RSA is affected by growth substrate and family pedigree. In addition, we found that V. arboreum exhibited greater maximum root depth and a lower percentage of roots in the top 8 cm of soil than SHB, and interspecific hybrids generally exhibited intermediate phenotypes. Also, we found that RSA traits exhibit moderate to low heritability and genetic correlations among them. Finally, we found 59 marker-trait associations. Among these markers, 37 were found to be located in exons, and 16 of them were annotated based on protein homology with entries in National Center for Biotechnology Information (NCBI) GenBank. Altogether, the present study provides tools that can be used to breed for root architecture traits in SHB.