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  • Author or Editor: R. A. Clark x
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Primocane-fruiting blackberry (Rubus subgenus Rubus Watson) selections have recently been developed by the University of Arkansas, but proper cane-management practices for the new germplasm have not yet been determined. It was observed in previous trials that primocane-fruiting selections flowered and fruited in late July and early August in Arkansas, which is often the hottest part of the summer and earlier than desired. Therefore, this study was conducted to determine the effects of primocane tipping on cane and fruit characteristics and to determine the effect of floricane presence on primocane performance. In Fayetteville, one-year-old plants of selections APF-8 and APF-12 were used to apply the four primocane-tipping treatments in combination with the two cane management treatments (presence or absence of floricanes). In Clarksville, the same genotypes were used to apply the two cane management treatments (presence or absence of floricanes). The tipping treatments had a significant effect on primocane yield and peak harvest as well as other parameters. The cane management treatments had a significant effect on total yield, but no other effects.

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Little research has been done to determine the chilling requirement for southern blackberry cultivars. However, field observations from areas where low amounts of chilling occur indicate that `Navaho' requires more hours of chilling than does `Arapaho'. The objective of the study was to determine a method for measuring chilling requirement using whole plants of two blackberry cultivars, Arapaho and Navaho. One-year-old bare-root plants of `Arapaho' and `Navaho' were field-dug and placed in a cold chamber at 3 °C. Ten single-plant replications of each cultivar were removed at 100-hour intervals up to 1000 hours. The plants were then potted and placed in a greenhouse (daily minimum temperature 15 °C) in a completely randomized design. Budbreak was recorded on a weekly basis. Data for budbreak was analyzed as a two-factor factorial (two cultivars and 10 chilling treatments) by SAS and means separated by lsd (P = 0.05). Data indicated that the chilling requirement for `Arapaho' is between 400 and 500 hours. This is evident as a 6-fold increase, which was the largest increase between two chilling treatments, occurred between 400 and 500 hours. For `Navaho', the largest increase (also 6-fold) occurred between 800 and 900 hours, which indicated a chilling requirement for `Navaho' of 800 to 900 hours. These data support previous observations and indicate the method used was successful in determining chilling requirement for blackberries.

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The University of Arkansas (UA) blackberry breeding program began in 1964, with the aim to provide high-quality fruit to the fresh market industry. One of the important traits for successful blackberry (Rubus subgenus Rubus Watson) postharvest handling is flesh firmness, so developing cultivars with high firmness is a top priority for the fresh market blackberry breeding programs across the world. In particular, the Arkansas blackberry program has a wide range of genotypes with exceptional firmness characteristics, including fruit with a unique crispy texture and firmness. During 2013 and 2014, fruit firmness measurements were done on 15 Arkansas genotypes including those with crispy and noncrispy textures. Firmness measurements consisted of fruit compression, skin drupelet penetration, and receptacle penetration. Confocal photos were taken on sections of berries of a subset of crispy and noncrispy genotypes, and color reversion was evaluated among these genotypes after storage. Compression force values differentiated crispy and noncrispy genotypes, with average values of 11.8 Newton (N) and 8.0 N, respectively. Drupelet penetration force was also higher for crispy genotypes averaging 0.23 N and noncrispy 0.15 N; similarly, receptacle penetration force averaged 0.20 N for crispy and 0.18 N for noncrispy genotypes. Visual inspection of fruit tissue revealed that drupelet mesocarp cells and receptacle cells and cell walls of crispy genotypes maintained their structure during ripening and did not break apart, whereas noncrispy genotypes did not maintain their structure and cellular integrity. Color reversion is a postharvest disorder in which drupelets of blackberry fruits turn red after being black at harvest. Therefore, it has a negative impact for growers, shippers, and consumers. After storage at 5 °C for 7 days, crispy genotypes expressed low levels of reversion compared with noncrispy genotypes. For crispy genotypes, 13.2% of drupelets developed color reversion, whereas a 41.0% developed this disorder in noncrispy genotypes, implying a better postharvest potential of this texture.

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Abstract

Salinity effects on yield and fruit quality of ‘Valencia’ orange (Citrus sinensis (L.) Osbeck) were determined in sand cultures artificially salinized with irrigation water applied twice daily. Yield reduction with increasing salinity during the 10-year study was attributed to a reduction in fruit number, not size. Salinity decreased rind thickness and delayed maturation but did not influence other fruit quality measures.

Open Access

Abstract

Salt tolerance of 10 shrub, 2 tree, and 4 iceplant species was determined in plots artificially salinized with NaCl and CaCl2.Tolerant species such as Texas sage (Leucophyllum frutescens (Berland) I. M. Johnst.), brush cherry (Syzygium paniculatum Gaertn.). Aleppo pine, (Pinus halepensis Mill.), European fan palm (Chamaerops humilis L.) and the 4 iceplants (Hymenocyclus croceus (Jacquin) Schwanter, Lampranthus productus (Haworth) N. E. Brown, Drosanthemum hispidum (L.) Schwart, and Delosperma alba Hort.) were affected little, if at all, by soil salinities of 7 mmho/cm (electrical conductivity of the saturation extract: ECe). Sensitive species like glossy abelia (Abelia grandiflora (Andre) Rehd.) Photinia (Photinia fraseri Dress.) Oregon grape holly (Mahonia aquifolium (Pursh) Nutt.) and Pyrenees cotoneaster (Cotoneaster congestus Bak.) were severely damaged or killed at ECe's of 4 mmho/cm. In general, leaves were injured only at levels that suppressed growth 50% or more.

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Abstract

Boron (B) tolerance of 25 ornamental shrub species was determined in large, outdoor sand cultures. Tolerant species such as Natal plum (Carissa grandiflora (E. H. Mey.) A. D. C.), Indian hawthorn (Raphiolepis indica (L.) Lindl.), Chinese hibiscus (Hibiscus rosa-sinensis L.), oleander (Nerium oleander L.), Japanese boxwood (Buxus microphylla Siebold and Zucc.), bottlebrush (Callistemon citrinus (Curtis) Stapf), ceniza (Leucophyllum frutescens (Berland.) I. M. Johnst.), and blue dracaena (Cordyline indivisa (G. Forst) Steud.) were affected little, if at all, by 7.5 mg B/liter in the irrigation water. Sensitive species like yellow sage (Lantana camara L.), juniper (Juniperus chinensis L.), Chinese holly (Ilex cornuta Lindl. and Paxt.), Wax-leaf privet (Ligustrum japonicum Thunb.), laurustinus (Viburnum tinus L.), thorny elaeagnus (Elaeagnus pungens Thunb.), xylosma (Xylosma congestum (Lour.) Merrill), photinia (Photinia ☓ Fraseri Dress.), and Oregon grape (Mahonia aquifolium (Pursh) Nutt.) were severely damaged or killed by 7.5 mg B/liter and moderately damaged by 2.5 mg B/liter in the irrigation water. B tolerance and B accumulation in the leaves were not correlated and no correlation was found between B tolerance and salinity tolerance.

Open Access

Abstract

Three grape cultivars (Vitis vinifera L.) were sprinkler-irrigated to determine if they would absorb sufficient sodium and chloride through their leaves to attain toxic levels. The concentration of both Na and Ca within the leaves increased linearly with sprinkling time. Both ions were approaching known tolerance levels after 54 hours of sprinkling. The counter ion of the 3 salt species tested (NaCl, CaCl2, and Na2SO4) had no effect on the amount of sodium or chloride accumulated.

Open Access

Previous work by our group has detected the presence of a heterogeneous population of Ty1-copia-like reverse transcriptase retrotransposon sequences in the sweetpotato genome. Recently, we detected the presence of putatively active Ty1-copia-like reverse transcriptase sequences from a virus-infected `Beauregard' sweetpotato clone. In the current study, we report the differential detection of putatively stress-activated sequences in clones from seedling 91-189. The clones were infected with different combinations of virus isolates followed by extraction of leaf RNA samples at three sampling dates (weeks 2, 4, and 6) after inoculation. After repeated DNAse treatments to eliminate contaminating DNA, the RNA samples were subjected to first strand cDNA synthesis using random decamer primers followed by PCR analysis utilizing Ty1-copia reverse transcriptase-specific primers. Through this approach, we detected amplified fragments within the expected size range (280-300 bp) from clones infected with isolates of sweetpotato leaf curl (SPLC) and feathery mottle viruses (FMV) (week 2 and 6) and FMV (week 4). We were unable to detect PCR products from the noninfected clones or the other infected samples. The data suggests that specific viruses may be involved in the expression of these Ty1-copia-related reverse transcriptase sequences. It also appears that sampling at various dates is necessary to detect putative activity over time. This preliminary information is essential before proceeding to the construction and screening of cDNA libraries to isolate and fully characterize the putatively active sweetpotato Ty1-copia-like retrotransposon sequences. Through the partial or complete characterization of sweetpotato Ty1-copia elements, sequences that correspond to cis-regulatory element(s) can be identified and further studied for their roles in responding to specific stress factors.

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A planting of sawdust-mulched highbush blueberries (cv. Bluecrop) was established on a Captina silt loam at the Univ. of Arkansas Research and Extension Center, Fayetteville, in 1994. Nitrogen rate and method of delivery treatments were begun that year and continued through the first two fruiting years (1996 and 1997). Rates included 0, 67, 134, 201, and 268 kg·ha-1 N using ammonium sulfate during the fruiting years (one-half and two-thirds these rates in 1994 and 1995, respectively), and methods of delivery included dry, surface-applied, and fertigation. Total N for the year was applied in three applications for the dry application and in 12 applications using fertigation. Neither yield nor berry mass were statistically significantly affected by N rate or method of delivery. Also, method of delivery had little effect on foliar levels of any macro- and microelements. Rate of N influenced foliar N most years, with the highest N rate increasing foliar N the greatest. The N rate required to consistently achieve adequate foliar N levels (minimum of 1.6% N) was 134 kg·ha-1. Foliar levels >2.0% were common with the two highest N rates. Foliar Mg and Mn were also influenced by N rate, with the lowest Mg level found for the highest N rate, while excess foliar Mn (800 to 100 ppm) was common with the higher N rates in 1997.

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DNA isolated from Fusarium lateritium Nees: Fr.-infected `Jewel' sweetpotato [Ipomoea batatas (L.) Lam.] plants was compared to F. lateritium-free `Jewel' plants for differences in random amplified polymorphic DNA (RAPD) marker products. Differences in RAPD marker products were detected. Amplified DNA isolations from F. lateritium-infected `Jewel' plants generated additional, unique DNA fragments not found in amplified DNA isolations of F. lateritium-free `Jewel' plants. These unique amplified DNA fragments were consistent with those obtained from amplified DNA isolations of the F. lateritium isolate, 91-27-2, used for inoculation. We found that F. lateritium DNA successfully competes with sweetpotato DNA in the polymerase chain reaction for priming sites in a 3: 1 ratio of sweetpotato DNA to F. lateritium DNA. Our results indicate the importance of avoiding plant material infested with pathogens to avoid spurious marker bands.

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