Studies were conducted from January to October 2005 to determine the effect of root-cutting length on adventitious shoot yield and the management practices necessary to produce nurseryquality primocane-fruiting blackberry plants. The first portion of the study measured the average number of shoots produced from 7.6 cm- and 15.2 cm-long root cuttings of APF-44 blackberry—a primocane-fruiting genotype from the University of Arkansas breeding program. Cuttings were forced in a shallow bin containing a soilless potting medium. The average number of shoots per root cutting from 7.6 cm- and 15.2 cm- long root cuttings averaged 1.6 and 2.7 shoots per root cutting, respectively. Rooting percentage for collected shoots was nearly 100% regardless of root-cutting length source. A qualitative comparison of shoots from the two roots lengths was similar. The latter part of the study included various treatments on the rooted shoots that might affect the productivity and quality of the final product intended for nursery sales in early fall. With the aim of producing a flowering/fruiting shrub by late September, three treatments were applied: pot dimension, fertilizer rate, and shoot tipping. Fertilizer rate had the greatest impact of all treatments with the higher rate producing larger and more attractive plants. Above-normal summer/fall temperatures may explain lack of fruiting on APF-44 blackberries, but the dimension and size of some plants provided a portion of the intended aesthetic

Clark, John R.

Dennis, Kimberley

Robbins, James A.

English

UARK (University of Arkansas )

Discovery, The Student Journal of Dale Bumpers College of Agricultural, Food and Life Sciences Volume 7 Article 8 Fall 2006 Adventitious shoot propagation and cultural inputs in nursery production of a primocane-fruiting blackberry selection Kimberley Dennis University of Arkansas, Fayetteville John R. Clark University of Arkansas, Fayetteville James A. Robbins University of Arkansas, Fayetteville Follow this and additional works at: https://scholarworks.uark.edu/discoverymag  Part of the Fruit Science Commons, Plant Biology Commons, and the Plant Breeding and Genetics Commons Recommended Citation Dennis, K., Clark, J. R., & Robbins, J. A. (2006). Adventitious shoot propagation and cultural inputs in nursery production of a primocane-fruiting blackberry selection. Discovery, The Student Journal of Dale Bumpers College of Agricultural, Food and Life Sciences, 7(1), 27-31. Retrieved from https://scholarworks.uark.edu/discoverymag/vol7/iss1/8 This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Discovery, The Student Journal of Dale Bumpers College of Agricultural, Food and Life Sciences by an authorized editor of ScholarWorks@UARK. For more information, please contact scholar@uark.edu. 27Adventitious shoot propagationand cultural inputs in nurseryproduction of a primocane-fruiting blackberry selectionKimberley Dennis*, John R. Clark†, and James A. Robbins§ABSTRACTStudies were conducted from January to October 2005 to determine the effect of root-cuttinglength on adventitious shoot yield and the management practices necessary to produce nursery-quality primocane-fruiting blackberry plants. The first portion of the study measured the aver-age number of shoots produced from 7.6 cm- and 15.2 cm-long root cuttings of APF-44 black-berry—a primocane-fruiting genotype from the University of Arkansas breeding program.Cuttings were forced in a shallow bin containing a soilless potting medium. The average numberof shoots per root cutting from 7.6 cm- and 15.2 cm- long root cuttings averaged 1.6 and 2.7shoots per root cutting, respectively. Rooting percentage for collected shoots was nearly 100%regardless of root-cutting length source. A qualitative comparison of shoots from the two rootslengths was similar. The latter part of the study included various treatments on the rooted shootsthat might affect the productivity and quality of the final product intended for nursery sales inearly fall. With the aim of producing a flowering/fruiting shrub by late September, three treat-ments were applied: pot dimension, fertilizer rate, and shoot tipping. Fertilizer rate had the great-est impact of all treatments with the higher rate producing larger and more attractive plants.Above-normal summer/fall temperatures may explain lack of fruiting on APF-44 blackberries,but the dimension and size of some plants provided a portion of the intended aesthetic.* Kimberley Dennis graduated in December, 2004 with a B.S. in horticulture.† John R. Clark, faculty co-sponsor, is a professor in the Department of Horticulture.§ James A. Robbins, faculty co-sponsor, is extension ornamental-horticulture specialist, Arkansas Cooperative Extension Service.THE STUDENT JOURNAL OF THE DALE BUMPERS COLLEGE OF AGRICULTURAL, FOOD AND LIFE SCIENCESDISCOVERY VOL. 7, FALL 2006INTRODUCTIONBlackberries are a fruiting shrub in the genus Rubus,the same genus as raspberries; thus, cultivation of thetwo plants is very similar (Pritts and Handley, 1991).Traditional propagation methods of blackberries includetip layering, suckering, leaf-stem cuttings, tissue culture,and root cuttings (Caldwell, 1984). These techniques areoften used but all have some limitations for propagators.Root cuttings, of all options, can be the most economi-cal and timely way to propagate blackberries and theUniversity of Arkansas uses root cuttings for nearly allblackberry propagation (John R. Clark, personal com-munication). Based on a study by University of Arkansasundergraduate, Ellen Thompson (Thompson et al.,2004), a “simple modification” to the traditional root-cutting propagation method led to increased propaguleyield and rooting success. However, cultivar effects weresometimes significant. This modification of propagationtechnique allows for space-limited and/or greenhouseproduction and greatly decreases the time and monetaryinvestment associated with traditional methods.Thompson’s study was based on precedents of a SwissRubus propagation system, and the findings were sup-ported by the idea that forcing multiple adventitiousshoots from a single root cutting increases the successand number of blackberry daughter plants. Moreover,the closely related raspberry is propagated in this waywith similar results (Pritts and Handley, 1991).The advent of primocane-fruiting blackberries, firstintroduced by the University of Arkansas breeding pro-gram in 2004, provides for potential increases in fruityield and extends the growing season well into early fall(Clark et al., 2005). With this in mind, it might be possi-ble to produce a nursery-quality plant that could pro-duce fruit for home-gardeners into the autumn months.Moreover, the ornamental qualities of APF-44 blackber-ry specifically are conducive to a nursery’s aestheticrequirements; the plant is observed to have relativelyshort internodal length and a “bushy” mounded shape,and produces flowers and fruit in early Septemberthrough October (John R. Clark, personal communica-tion). Management practices to enhance these quali-ties—mid-summer tipping, fertilizer rates, and potdimension—are investigated in this study.MATERIALS AND METHODSExperiment I: Adventitious shoot propagationRoot cuttings of two sizes, 7.6 cm and 15.2 cm, wereevaluated in greenhouse conditions for propagule yieldfrom January to April 2005. The APF-44 blackberry rootcuttings used in propagation were collected from theUniversity of Arkansas Fruit Substation, Clarksville, inlate fall, 2004 (APF-44 is a breeding selection and is notreleased to the public nor is it an item of commerce).The diameter of the roots averaged approximately 5.3mm. After one month of cold storage, the root cuttingswere positioned in drainable plastic bins filled withLC1® soil-less potting mix (SunGro Horticulture;Alberta, Canada) to the fill line. Root cuttings were posi-28MEET THE STUDENT-AUTHORAfter graduating from Lee’s Summit NorthHigh School in Kansas City, Mo., I enrolled at theUniversity of Arkansas and graduated in the fall of2005 with a B.S. in horticulture and a minor inglobal agriculture, food, and life sciences. While incollege, I was involved in choir, a summer researchinternship in the Department of Plant Pathology, acommunity design project in Clarendon, Ark., andindependent student research such as this project.My undergraduate research has inspired me toattend graduate school, and I plan to apply for thespring semester of 2007. All of my undergraduateexperiences have contributed to my goals for thefuture, and I cannot wait to apply all I have learnedin a graduate program and a career. It has been anhonor to be involved in the University of Arkansas’thriving scientific community.Kimberley DennisTHE STUDENT JOURNAL OF THE DALE BUMPERS COLLEGE OF AGRICULTURAL, FOOD AND LIFE SCIENCEStioned horizontally at a depth of 2.5-3.5 cm below themedium surface. Greenhouse temperatures were main-tained at a minimum temperature of 20°C and a maxi-mum temperature of 25°C. Cutting bins were watered asneeded. The experimental design was a randomizedblock of 10 replications of three root cuttings per repli-cation. After the initial planting of root cuttings on 27Jan. 2005, shoots began to appear on 1 March, andshoots continued to be harvested every 3-4 days as theygrew to a length of approximately 5 cm with two partial-ly expanded leaves. This harvest continued until 4 Apr.One hundred-three total shoots from the two root-cut-ting treatments were transplanted into individual Jiffy®peat pellets (Jiffy Co., Batavia, Ill.), and were subse-quently placed under an intermittent mist system thatmisted  the cuttings for 8 s every 10 min until shoots hadrooted. Each shoot rooted in approximately 2.5 weeks.Shoot harvest continued until 4 Apr. when shoot pro-duction had significantly diminished. Data collectionincluded percent shoot production per week, total num-ber of shoots produced, shoot rooting success, and aver-age number of shoots per root cutting.Experiment II: Cultural inputs in nursery production ofAPF-44Shoot cuttings rooted in peat pellets were transplant-ed into black plastic pots with the same media volume(9,000 cm3) but different pot dimensions: a “tall” Classic1000-C® (25 cm top diam. x 23 cm tall) and a “squat”Classic 1200S-C® (28 cm top diam. x 19 cm tall)(Nursery Supplies Inc. (Chambersburg, Penn.).Transplanting began on 21 March and was completed on4 April. On 30 April, potted plants were randomlyarranged on an outdoor gravel pad. Plants were wateredas needed using overhead impact sprinklers. Fertilizerrate and tipping treatments began on 13 May. The designwas a randomized block of eight replications of eight ofthe following combination of treatments: 1) two potdimensions (described above); 2) PolyOn 18-6-12, 8-9month fertilizer topdress applied at a rate of 0.65 kgN/m3 or 1.31 kg N/m3; and 3) and the tipping treatmentapplied to half of the plants in mid-summer. On 13 May,all plants were tipped to 30 cm in preparation for thegrowing season, and the fertilizer treatments wereapplied. On 15 July, all flowers and developing berrieswere removed and the tipping treatment was applied tothe appropriate plants; these plants were again reducedto 30 cm in length by this tipping. By 12 Oct., the studywas concluded and the following data were collected: 1)shoot growth index (GI); 2) shoot fresh weight; and 3)qualitative measurements—flowering and fruiting, plantshape, internodal length, leaf color, etc.RESULTS AND DISCUSSIONExperiment I:Root length had a significant effect on the number ofadventitious shoots produced. The average number ofshoots per root cutting for short (7.6 cm) and long (15.2cm) root cuttings was 1.6 and 2.7, respectively. This find-ing supports results from an earlier study (Thompson etal., 2004). Shoot collection began approximately 4 weeksafter roots were placed in the medium. Shoot collectionwas greatest in the first 4 weeks of shoot emergence; afterthis point, shoot production was significantly decreased(Fig. 1). A total of 72.3% of shoots from the 7.6 cm rootswas harvested in the first 4 weeks. Similarly, 84.8% ofshoots from the 15.2 cm roots had been harvested in thesame time period. All shoots were of similar quality, andshoots were collected at the same point in development.The percent survival was nearly 100% (data not shown).Similar rooting percentages were reported previously(Thompson et al., 2004). These results suggest that thismethod also is successful for propagation of this black-berry genotype. The shoots grew vigorously in the peatpellets and rooted in approximately 1-2 weeks.Experiment II:Fertilizer rates of 0.65 kg N/m3and 1.31 kg N/m3 hada significant effect on all plant growth parameters. Shootfresh weights for plants grown at the low and high fertil-izer rates were 155 and 400 gm, respectively (Table 1).Fertilizer rate also had an effect on the height of theplants; on average the plants with the lower fertilizer ratewere 0.43 m tall versus 0.59 m for the higher rate (Table1). In a similar way, average plant widths of the high-fer-tilizer-rate plants were greater than for those receivingthe low fertilizer rate (Table 1). The plants that were nottipped averaged 0.47 m tall, whereas the plants thatunderwent the July tipping treatment were 0.55 m tall(non-signficant difference) (data not shown). All of theplants that were not tipped had a one-dimensionalgrowth habit, with shoots tending to fall over and growhorizontally, while the tipped plants were more spread-ing and attractive (data not shown). No treatmentresulted in plants with consistently different numbers offlowers or fruits (data not shown). Qualitatively, theplants with the best shape, leaf color, and size were thetwo tipped treatments and the higher fertilizer rate; potdimension did not cause any aesthetic disparity (datanot shown).The main objective of these studies was to determinethe propagation and production methods necessary toproduce nursery-quality plants of APF-44 in a timelymanner. As previous studies have concluded, root lengthplays a significant role in forcing adventitious shoots.29Longer roots produce more shoots – this is expected asthey are simply longer. On the other hand, analysis ofthese values indicates that per 15.2 cm of root length, theshorter root produces more shoots on average for a sim-ilar length of space (i.e. 2 – 7.6 cm roots can produce 3.2shoots per 15.2 cm, whereas the 15.2 cm roots produced2.7 shoots in this study). This finding is of potentialvalue to propagators, who need thousands of shoot cut-tings. For instance, 2000 7.6 cm roots cuttings with atotal root cutting length of 15,200 cm should yield 3200shoots. Likewise, 1000 15.2 cm of root cuttings with thesame 15,2000 cm total should yield 2700 shoots. On theother hand, shoot quality was the same for the two rootlengths. In fact, shoot quality was maintained at anexcellent level throughout the first portion of the exper-iment: all shoots rooted and indicated no nutrient defi-ciency. Thompson et al. (2004) noted the same observa-tion with ‘Apache’, ‘Arapaho’, and ‘Ouachita’ blackberrycultivars.Building upon an efficient propagation method, thisstudy is the first to investigate plant management tech-niques that might create a nursery-quality, primocane-fruiting blackberry marketable to homeowners duringautumn. After shoots had been rooted and potted andtreatments were applied, disparities began to appearamong the plants. Plants that were tipped in mid-sum-mer and fertilized with the higher fertilizer rate dis-played the intended mounded shape and short intern-odal lengths. On the other hand, the main objective ofthis portion of the experiment was not met; at the con-clusion of the study, no plants had plentiful berry orflower displays. The negative effects of heat on floweringhave been observed for APF-44, and this may explain theproblem (John R. Clark, personal communication).Also, plants remaining in a juvenile state due to pruningmay be less likely to flower (John R. Clark, personalcommunication). In this particular study, flowers wereplentiful before the May flower/bud removal; after thistime, plants rarely produced buds. Blackberry plantswithout berries in September are not marketable as anursery-quality ornamental intended for autumn sale.Fortunately, it is possible that additional breeding mightachieve more abundant blooming and increased heattolerance for flowers and fruits.Further studies might include use of an adult second-year plant, a different genotype identified with moreabundant flowering in heat, or simply moving the studyto a more temperate climate. The root cutting methodwas successful, and no improvements are suggested.LITERATURE CITEDCaldwell, J.D. 1984. Blackberry propagation.HortScience 19:193-195.Clark, J.R., J.N. Moore, J. Lopez-Medina, P. Perkins-Veazie, and C.E. Finn. 2005. Prime-Jan (APF-8) andPrime-Jim (APF-12) primocane-fruiting blackber-ries. HortScience 40:852-855.Pritts, M. and D. Handley. 1991. Bramble productionguide. Northeast Regional Agricultural EngineeringService, Ithaca, N.Y.Thompson, A.E., J.R. Clark, and C.R. Rom. 2004.Propagation of thornless blackberries utilizingadventitious shoots from root cuttings. Inquiry, TheUniversity of Arkansas Undergraduate ResearchJournal. 5:101-104.30 DISCOVERY VOL. 7, FALL 2006Table 1. Effect of fertilizer rate on nursery plant shoot and plant growth parameters of APF-44 blackberry (APF-44is a breeding selection and is not released to the public nor is it an item of commerce).Fertilizer rate (kg N/m3) Shoot fresh weight (g) Shoot height (m) Plant width 1 (m) Plant width 2 (m) GIz (m3)0.65 155.3 by 0.431 b 0.658 b 0.292 b 0.076 b1.31 400.3 a 0.586 a 1.200 a 0.729 a 0.428 az GI = growth index. Calculated by the formula hr2, where h is shoot height, r=0.5d, and d is the mean of two diametermeasurements taken at 90° angle from each other.yMean separation by LSD, P<0.05.THE STUDENT JOURNAL OF THE DALE BUMPERS COLLEGE OF AGRICULTURAL, FOOD AND LIFE SCIENCES 31Fig. 1. Dates of adventitious shoot collection from APF-44 blackberry.

Adventitious shoot propagation and cultural inputs in nursery production of a primocane-fruiting blackberry selection

ScholarWorks@UARK

Discovery, The Student Journal of Dale Bumpers College ofAgricultural, Food and Life SciencesVolume 7 Article 8Fall 2006Adventitious shoot propagation and cultural inputsin nursery production of a primocane-fruitingblackberry selectionKimberley DennisUniversity of Arkansas, FayettevilleJohn R. ClarkUniversity of Arkansas, FayettevilleJames A. RobbinsUniversity of Arkansas, FayettevilleFollow this and additional works at: https://scholarworks.uark.edu/discoverymagPart of the Fruit Science Commons, Plant Biology Commons, and the Plant Breeding andGenetics CommonsThis Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Discovery, The Student Journalof Dale Bumpers College of Agricultural, Food and Life Sciences by an authorized editor of ScholarWorks@UARK. For more information, pleasecontact scholar@uark.edu, ccmiddle@uark.edu.Recommended CitationDennis, Kimberley; Clark, John R.; and Robbins, James A. (2006) "Adventitious shoot propagation and cultural inputs in nurseryproduction of a primocane-fruiting blackberry selection," Discovery, The Student Journal of Dale Bumpers College of Agricultural, Foodand Life Sciences. University of Arkansas System Division of Agriculture. 7:27-31.Available at: https://scholarworks.uark.edu/discoverymag/vol7/iss1/827Adventitious shoot propagationand cultural inputs in nurseryproduction of a primocane-fruiting blackberry selectionKimberley Dennis*, John R. Clark†, and James A. Robbins§ABSTRACTStudies were conducted from January to October 2005 to determine the effect of root-cuttinglength on adventitious shoot yield and the management practices necessary to produce nursery-quality primocane-fruiting blackberry plants. The first portion of the study measured the aver-age number of shoots produced from 7.6 cm- and 15.2 cm-long root cuttings of APF-44 black-berry—a primocane-fruiting genotype from the University of Arkansas breeding program.Cuttings were forced in a shallow bin containing a soilless potting medium. The average numberof shoots per root cutting from 7.6 cm- and 15.2 cm- long root cuttings averaged 1.6 and 2.7shoots per root cutting, respectively. Rooting percentage for collected shoots was nearly 100%regardless of root-cutting length source. A qualitative comparison of shoots from the two rootslengths was similar. The latter part of the study included various treatments on the rooted shootsthat might affect the productivity and quality of the final product intended for nursery sales inearly fall. With the aim of producing a flowering/fruiting shrub by late September, three treat-ments were applied: pot dimension, fertilizer rate, and shoot tipping. Fertilizer rate had the great-est impact of all treatments with the higher rate producing larger and more attractive plants.Above-normal summer/fall temperatures may explain lack of fruiting on APF-44 blackberries,but the dimension and size of some plants provided a portion of the intended aesthetic.* Kimberley Dennis graduated in December, 2004 with a B.S. in horticulture.† John R. Clark, faculty co-sponsor, is a professor in the Department of Horticulture.§ James A. Robbins, faculty co-sponsor, is extension ornamental-horticulture specialist, Arkansas Cooperative Extension Service.THE STUDENT JOURNAL OF THE DALE BUMPERS COLLEGE OF AGRICULTURAL, FOOD AND LIFE SCIENCESDISCOVERY VOL. 7, FALL 2006INTRODUCTIONBlackberries are a fruiting shrub in the genus Rubus,the same genus as raspberries; thus, cultivation of thetwo plants is very similar (Pritts and Handley, 1991).Traditional propagation methods of blackberries includetip layering, suckering, leaf-stem cuttings, tissue culture,and root cuttings (Caldwell, 1984). These techniques areoften used but all have some limitations for propagators.Root cuttings, of all options, can be the most economi-cal and timely way to propagate blackberries and theUniversity of Arkansas uses root cuttings for nearly allblackberry propagation (John R. Clark, personal com-munication). Based on a study by University of Arkansasundergraduate, Ellen Thompson (Thompson et al.,2004), a “simple modification” to the traditional root-cutting propagation method led to increased propaguleyield and rooting success. However, cultivar effects weresometimes significant. This modification of propagationtechnique allows for space-limited and/or greenhouseproduction and greatly decreases the time and monetaryinvestment associated with traditional methods.Thompson’s study was based on precedents of a SwissRubus propagation system, and the findings were sup-ported by the idea that forcing multiple adventitiousshoots from a single root cutting increases the successand number of blackberry daughter plants. Moreover,the closely related raspberry is propagated in this waywith similar results (Pritts and Handley, 1991).The advent of primocane-fruiting blackberries, firstintroduced by the University of Arkansas breeding pro-gram in 2004, provides for potential increases in fruityield and extends the growing season well into early fall(Clark et al., 2005). With this in mind, it might be possi-ble to produce a nursery-quality plant that could pro-duce fruit for home-gardeners into the autumn months.Moreover, the ornamental qualities of APF-44 blackber-ry specifically are conducive to a nursery’s aestheticrequirements; the plant is observed to have relativelyshort internodal length and a “bushy” mounded shape,and produces flowers and fruit in early Septemberthrough October (John R. Clark, personal communica-tion). Management practices to enhance these quali-ties—mid-summer tipping, fertilizer rates, and potdimension—are investigated in this study.MATERIALS AND METHODSExperiment I: Adventitious shoot propagationRoot cuttings of two sizes, 7.6 cm and 15.2 cm, wereevaluated in greenhouse conditions for propagule yieldfrom January to April 2005. The APF-44 blackberry rootcuttings used in propagation were collected from theUniversity of Arkansas Fruit Substation, Clarksville, inlate fall, 2004 (APF-44 is a breeding selection and is notreleased to the public nor is it an item of commerce).The diameter of the roots averaged approximately 5.3mm. After one month of cold storage, the root cuttingswere positioned in drainable plastic bins filled withLC1® soil-less potting mix (SunGro Horticulture;Alberta, Canada) to the fill line. Root cuttings were posi-28MEET THE STUDENT-AUTHORAfter graduating from Lee’s Summit NorthHigh School in Kansas City, Mo., I enrolled at theUniversity of Arkansas and graduated in the fall of2005 with a B.S. in horticulture and a minor inglobal agriculture, food, and life sciences. While incollege, I was involved in choir, a summer researchinternship in the Department of Plant Pathology, acommunity design project in Clarendon, Ark., andindependent student research such as this project.My undergraduate research has inspired me toattend graduate school, and I plan to apply for thespring semester of 2007. All of my undergraduateexperiences have contributed to my goals for thefuture, and I cannot wait to apply all I have learnedin a graduate program and a career. It has been anhonor to be involved in the University of Arkansas’thriving scientific community.Kimberley DennisTHE STUDENT JOURNAL OF THE DALE BUMPERS COLLEGE OF AGRICULTURAL, FOOD AND LIFE SCIENCEStioned horizontally at a depth of 2.5-3.5 cm below themedium surface. Greenhouse temperatures were main-tained at a minimum temperature of 20°C and a maxi-mum temperature of 25°C. Cutting bins were watered asneeded. The experimental design was a randomizedblock of 10 replications of three root cuttings per repli-cation. After the initial planting of root cuttings on 27Jan. 2005, shoots began to appear on 1 March, andshoots continued to be harvested every 3-4 days as theygrew to a length of approximately 5 cm with two partial-ly expanded leaves. This harvest continued until 4 Apr.One hundred-three total shoots from the two root-cut-ting treatments were transplanted into individual Jiffy®peat pellets (Jiffy Co., Batavia, Ill.), and were subse-quently placed under an intermittent mist system thatmisted  the cuttings for 8 s every 10 min until shoots hadrooted. Each shoot rooted in approximately 2.5 weeks.Shoot harvest continued until 4 Apr. when shoot pro-duction had significantly diminished. Data collectionincluded percent shoot production per week, total num-ber of shoots produced, shoot rooting success, and aver-age number of shoots per root cutting.Experiment II: Cultural inputs in nursery production ofAPF-44Shoot cuttings rooted in peat pellets were transplant-ed into black plastic pots with the same media volume(9,000 cm3) but different pot dimensions: a “tall” Classic1000-C® (25 cm top diam. x 23 cm tall) and a “squat”Classic 1200S-C® (28 cm top diam. x 19 cm tall)(Nursery Supplies Inc. (Chambersburg, Penn.).Transplanting began on 21 March and was completed on4 April. On 30 April, potted plants were randomlyarranged on an outdoor gravel pad. Plants were wateredas needed using overhead impact sprinklers. Fertilizerrate and tipping treatments began on 13 May. The designwas a randomized block of eight replications of eight ofthe following combination of treatments: 1) two potdimensions (described above); 2) PolyOn 18-6-12, 8-9month fertilizer topdress applied at a rate of 0.65 kgN/m3 or 1.31 kg N/m3; and 3) and the tipping treatmentapplied to half of the plants in mid-summer. On 13 May,all plants were tipped to 30 cm in preparation for thegrowing season, and the fertilizer treatments wereapplied. On 15 July, all flowers and developing berrieswere removed and the tipping treatment was applied tothe appropriate plants; these plants were again reducedto 30 cm in length by this tipping. By 12 Oct., the studywas concluded and the following data were collected: 1)shoot growth index (GI); 2) shoot fresh weight; and 3)qualitative measurements—flowering and fruiting, plantshape, internodal length, leaf color, etc.RESULTS AND DISCUSSIONExperiment I:Root length had a significant effect on the number ofadventitious shoots produced. The average number ofshoots per root cutting for short (7.6 cm) and long (15.2cm) root cuttings was 1.6 and 2.7, respectively. This find-ing supports results from an earlier study (Thompson etal., 2004). Shoot collection began approximately 4 weeksafter roots were placed in the medium. Shoot collectionwas greatest in the first 4 weeks of shoot emergence; afterthis point, shoot production was significantly decreased(Fig. 1). A total of 72.3% of shoots from the 7.6 cm rootswas harvested in the first 4 weeks. Similarly, 84.8% ofshoots from the 15.2 cm roots had been harvested in thesame time period. All shoots were of similar quality, andshoots were collected at the same point in development.The percent survival was nearly 100% (data not shown).Similar rooting percentages were reported previously(Thompson et al., 2004). These results suggest that thismethod also is successful for propagation of this black-berry genotype. The shoots grew vigorously in the peatpellets and rooted in approximately 1-2 weeks.Experiment II:Fertilizer rates of 0.65 kg N/m3and 1.31 kg N/m3 hada significant effect on all plant growth parameters. Shootfresh weights for plants grown at the low and high fertil-izer rates were 155 and 400 gm, respectively (Table 1).Fertilizer rate also had an effect on the height of theplants; on average the plants with the lower fertilizer ratewere 0.43 m tall versus 0.59 m for the higher rate (Table1). In a similar way, average plant widths of the high-fer-tilizer-rate plants were greater than for those receivingthe low fertilizer rate (Table 1). The plants that were nottipped averaged 0.47 m tall, whereas the plants thatunderwent the July tipping treatment were 0.55 m tall(non-signficant difference) (data not shown). All of theplants that were not tipped had a one-dimensionalgrowth habit, with shoots tending to fall over and growhorizontally, while the tipped plants were more spread-ing and attractive (data not shown). No treatmentresulted in plants with consistently different numbers offlowers or fruits (data not shown). Qualitatively, theplants with the best shape, leaf color, and size were thetwo tipped treatments and the higher fertilizer rate; potdimension did not cause any aesthetic disparity (datanot shown).The main objective of these studies was to determinethe propagation and production methods necessary toproduce nursery-quality plants of APF-44 in a timelymanner. As previous studies have concluded, root lengthplays a significant role in forcing adventitious shoots.29Longer roots produce more shoots – this is expected asthey are simply longer. On the other hand, analysis ofthese values indicates that per 15.2 cm of root length, theshorter root produces more shoots on average for a sim-ilar length of space (i.e. 2 – 7.6 cm roots can produce 3.2shoots per 15.2 cm, whereas the 15.2 cm roots produced2.7 shoots in this study). This finding is of potentialvalue to propagators, who need thousands of shoot cut-tings. For instance, 2000 7.6 cm roots cuttings with atotal root cutting length of 15,200 cm should yield 3200shoots. Likewise, 1000 15.2 cm of root cuttings with thesame 15,2000 cm total should yield 2700 shoots. On theother hand, shoot quality was the same for the two rootlengths. In fact, shoot quality was maintained at anexcellent level throughout the first portion of the exper-iment: all shoots rooted and indicated no nutrient defi-ciency. Thompson et al. (2004) noted the same observa-tion with ‘Apache’, ‘Arapaho’, and ‘Ouachita’ blackberrycultivars.Building upon an efficient propagation method, thisstudy is the first to investigate plant management tech-niques that might create a nursery-quality, primocane-fruiting blackberry marketable to homeowners duringautumn. After shoots had been rooted and potted andtreatments were applied, disparities began to appearamong the plants. Plants that were tipped in mid-sum-mer and fertilized with the higher fertilizer rate dis-played the intended mounded shape and short intern-odal lengths. On the other hand, the main objective ofthis portion of the experiment was not met; at the con-clusion of the study, no plants had plentiful berry orflower displays. The negative effects of heat on floweringhave been observed for APF-44, and this may explain theproblem (John R. Clark, personal communication).Also, plants remaining in a juvenile state due to pruningmay be less likely to flower (John R. Clark, personalcommunication). In this particular study, flowers wereplentiful before the May flower/bud removal; after thistime, plants rarely produced buds. Blackberry plantswithout berries in September are not marketable as anursery-quality ornamental intended for autumn sale.Fortunately, it is possible that additional breeding mightachieve more abundant blooming and increased heattolerance for flowers and fruits.Further studies might include use of an adult second-year plant, a different genotype identified with moreabundant flowering in heat, or simply moving the studyto a more temperate climate. The root cutting methodwas successful, and no improvements are suggested.LITERATURE CITEDCaldwell, J.D. 1984. Blackberry propagation.HortScience 19:193-195.Clark, J.R., J.N. Moore, J. Lopez-Medina, P. Perkins-Veazie, and C.E. Finn. 2005. Prime-Jan (APF-8) andPrime-Jim (APF-12) primocane-fruiting blackber-ries. HortScience 40:852-855.Pritts, M. and D. Handley. 1991. Bramble productionguide. Northeast Regional Agricultural EngineeringService, Ithaca, N.Y.Thompson, A.E., J.R. Clark, and C.R. Rom. 2004.Propagation of thornless blackberries utilizingadventitious shoots from root cuttings. Inquiry, TheUniversity of Arkansas Undergraduate ResearchJournal. 5:101-104.30 DISCOVERY VOL. 7, FALL 2006Table 1. Effect of fertilizer rate on nursery plant shoot and plant growth parameters of APF-44 blackberry (APF-44is a breeding selection and is not released to the public nor is it an item of commerce).Fertilizer rate (kg N/m3) Shoot fresh weight (g) Shoot height (m) Plant width 1 (m) Plant width 2 (m) GIz (m3)0.65 155.3 by 0.431 b 0.658 b 0.292 b 0.076 b1.31 400.3 a 0.586 a 1.200 a 0.729 a 0.428 az GI = growth index. Calculated by the formula hr2, where h is shoot height, r=0.5d, and d is the mean of two diametermeasurements taken at 90° angle from each other.yMean separation by LSD, P<0.05.THE STUDENT JOURNAL OF THE DALE BUMPERS COLLEGE OF AGRICULTURAL, FOOD AND LIFE SCIENCES 31Fig. 1. Dates of adventitious shoot collection from APF-44 blackberry.

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Adventitious shoot propagation and cultural inputs in nursery production of a primocane-fruiting blackberry selection

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