BA-Induced Offset Formation in Hosta Dependent on Cultivar

James M. Garner1, Gary J. Keever2, D. Joseph Eakes3, and J. Raymond Kessler4

Department of Horticulture, Alabama Agricultural Experiment Station, Auburn University, Alabama 36849-5408

Received for publication 26 Feb. 1996. Research conducted at Paterson Greenhouses, Auburn University, AL 36849. Use of trade names does not imply endorsement of products named or criticism of similar ones not named.

1Graduate Research Assistant.
2Professor.
3Associate Professor.
4Assistant Professor.

Additional index words: cytokinins, herbaceous perennials

Abstract

A foliar spray of 0, 1250, 2500, or 3750 mg benzyladenine (BA)/ liter was applied to 10 Hosta Tratt. (Funkia K. Spreng; Niobe Salisb.) cultivars. Response to BA treatment was cultivar dependent, with BA promoting offset formation in half of the cultivars. Compared to the control, increase in offsets produced by cultivars treated with 3750 mg BA/liter ranged from 116% in 'Francee' to 3500% in 'Frances Williams' at 30 days after treatment (DAT) and from 150% in 'Royal Standard' to 2250% in 'Frances Williams' at 60 DAT. Offset stage of development, as indicated by the number of unfurled leaves, was also cultivar- and BA-dependent. All cultivars treated with 3750 mg BA/liter had an average of three or more unfurled leaves at 60 DAT, while among control plants, 40% of cultivars averaged fewer than three unfurled leaves. No phytotoxic symptoms were noted in any cultivar, and plant size was either increased or not affected by BA treatment. Chemical name used: N- (phenylmethyl)-1H-purin-6-amine (benzyladenine, BA).

Hosta, herbaceous perennials in the lily family, are the most popular perennials for use in the shaded landscape (Rhodus, 1995). Hostas are conventionally propagated by crown division or tissue culture. However, division yields relatively few plants per clump, and is typically accomplished only annually (Walters, 1981). Tissue- cultured explants are costly and frequently may not be true to type (Meyer, 1980). Moreover, propagation of plants by tissue culture requires specialized techniques and facilities unavailable to most growers. Increasing the numbers of plants available and the introduction of new cultivars may be impeded by these factors.

Vegetative buds and roots of hosta grow from rhizomes, and the rhizomic apex appears to suppress outgrowth of axillary and rhizomic buds by apical dominance (Schmid, 1991). A primary factor in the mechanism of apical dominance is a hormonal interaction between auxins and cytokinins (Cline, 1988). Cytokinins, including benzyladenine (BA), can release lateral buds from inhibition when applied exogenously (Mok and Mok, 1994). Previous studies have demonstrated the effectiveness of BA in promoting the outgrowth of rhizomic and axillary buds in hosta (Keever, 1994). Furthermore, offsets formed from BA-induced buds can be removed from the mother plant soon after elongation and rooted under intermittent mist, with a higher percentage of rooting from offsets at a more advanced stage of development (Keever et al., 1995). Earlier studies were conducted using Hosta sieboldiana (Lodd.) Engl. only, yet considerable differences in response to BA application may be expected among the diverse hosta cultivars available, due to the large number of recombinations from which cultivars of this genus are derived (Schmid, 1991). The objective of this study was to determine differences among hosta cultivars in response to BA application.

Materials and Methods

On 20 Feb. 1995, dormant, bare-root divisions of 10 hosta cultivars were potted in 2.7-liter containers in a pine bark:sand medium (6:1 by volume). The medium was amended with 3 kg dolomitic lime, 0.9 kg Micromax (The Scotts Co., Marysville, Ohio), and 7.4 kg 24N-1.8P-10K (Polyon 12-month formulation, Pursell Industries, Sylacauga, Ala.) per m3.

Cultivars included Hosta fortunei (Bak.) L.H. Bailey 'Aureo-marginata' (AM), H. 'Big Daddy' (BD), H. 'Francee' (FR), H. 'Frances Williams' (FW), H. 'Gold Standard' (GS), H. 'Krossa Regal' (KR), H. montana (Maekawa) 'Aureo-marginata' (MA), H. 'Royal Standard' (RS), H. undulata (Otto & A. Dietr.) L.H. Bailey 'Albo-marginata' (UA), and H. 'Wide Brim' (WB). Plants were grown under 47% shade and irrigated by overhead rotary nozzles twice daily for 30 min per application, for a total volume of .30 mm/day.

On 7 July 1995, single-eye (no offsets) plants were selected for uniformity, and 10 single-plant replications of each cultivar were randomly assigned to each of four BA rates (0, 1250, 2500, or 3750 mg liter-1). Buffer-X (Kalo Agr. Chemicals, Inc. ) at 2 ml/liter was added to all BA solutions as a surfactant before foliar application at 0.2 liter/m2 or 5.4 ml/plant. Application was made with a CO2 sprayer fitted with a cone nozzle at 275 kPa. Temperature and relative humidity at the time of application were 27C and 85%, respectively.

At 30 and 60 days after treatment (DAT), visible offset counts and a growth index [(height + width at widest point+ width 90o to first width) ) 3] were determined for each plant . At 60 DAT, stage of development (SOD) was determined for each offset, with SOD 1= elongated bud with first leaf furled; 2 = one unfurled leaf; 3 = 2 unfurled leaves, etc. Data were tested by analysis of variance, using the SAS General Linear Model procedure, to test main effects and interactions. Comparison of controls to BA treatment and rate response to BA was determined by single degree of freedom orthogonal contrasts. Mean separation among cultivars was accomplished by Duncan's multiple range test (SAS Institute, 1988).

Results and Discussion

Offset counts. Offset formation in hosta in response to BA application was cultivar-dependent. At 30 DAT, more offsets were produced by treated plants than by controls for BD, FR, FW, KR, and RS (Table 1). Compared to controls, increases in offset counts at optimal BA rate ranged from 116% (FR) to 3500% (FW). Offset counts increased linearly with increasing BA rate in FR, FW, and RS, but in KR, optimal response to BA was achieved at the intermediate rate, 2500 mg BA/liter. For BD, offset counts were higher among treated plants compared to controls, and the highest number of offsets was formed in plants receiving 3750 mg BA/liter. Offset counts for treated plants were similar to controls in AM, GS, MA, UA, and WB at 30 DAT.

Offset counts generally increased between 30 and 60 DAT, but at 60 DAT, the response of most cultivars (AM, BD, FW, GS, KR, RS, UA, and WB) to BA was similar to that observed at 30 DAT. Offset counts for treated plants were higher than those of controls at 60 DAT in BD, FW, KR, MA, and RS. Compared to controls, increases in offset counts at optimal BA rate ranged from 150% (RS) to 2250% (FW). As observed at 30 DAT, offset counts increased linearly with increasing BA rate in FW and RS, and at 60 DAT, response in MA was also linear. With KR, optimal response to BA was again achieved with the intermediate rate, 2500 mg BA/liter. In BD, offset counts were again higher in treated plants, as compared to controls, and the highest number of offsets was formed in plants receiving 3750 mg BA/liter. In FR, a cultivar that readily forms offsets, sufficient offsets had formed in control plants at 60 DAT such that offset counts were similar to those of treated plants. In contrast to the response at 30 DAT, offset counts among BA-treated plants of MA were higher than those of controls at 60 DAT.

At 30 DAT, control plants of AM, FR, GS, RS, UA and WB had formed more offsets than other cultivars, indicating that these cultivars readily form offsets in the absence of BA. Among treated plants, BD, GS, KR, and RS formed more offsets at 30 and 60 DAT than other cultivars in the study. Cultivars BD, FW, and KR, which did not readily form offsets in the absence of BA, produced more offsets than other cultivars when treated with BA.

Stage of development. Influence of BA on offset SOD at 60 DAT was also cultivar-dependent. Offset SOD was more advanced for treated plants of BD and KR; yet, offset SOD lagged in treated plants of GS, RS, and WB as compared to controls (Table 2). With RS, the formation of more offsets in treated plants appeared to result in a slowing of development. There were no differences in offset SOD between BA-treated plants and controls in the remaining five cultivars.

Growth index. The growth index, measured at 30 and 60 DAT, generally increased or was not affected by BA rate (Table 3). At 30 DAT, the growth index was higher for treated plants than controls of BD, FR, and KR. The growth index of UA treated with BA was lower than that of control plants at 30 DAT, but similar to that of the controls at 60 DAT. The growth index in treated plants was similar to that of controls in the other cultivars at 30 DAT. At 60 DAT, the growth index was greater in treated plants than in controls for BD, KR, and MA, but similar to controls for all other cultivars. No phytotoxic symptoms were noted in any cultivar, and plant appearance was not adversely affected by BA. In many cases, plant appearance was enhanced by BA application. For example, the growth index increased for treated plants of KR at all BA rates between 30 and 60 DAT, while that for controls declined due to foliar necrosis in the mother plants. Expansion of BA-induced offsets appeared to enhance growth and appearance of KR, accounting for the increase in the growth index.

These results indicate a cultivar-dependent response to BA for the hosta cultivars evaluated. Offset counts were higher in treated plants of BD, FW, KR, and RS at both 30 and 60 DAT. The same was true for FR at 30 DAT and for MA at 60 DAT. Stimulation of offset formation by BA application concurs with previous research (Keever, 1994). Offset counts in treated plants were similar to those of the controls in AM, GS, UA, and WB. Compared to controls, offset SOD for treated plants increased in BD and KR, decreased in GS, RS, and WB, and was similar in the remaining five cultivars. Ninety percent of all BA x cultivar combinations showed an average SOD greater than or equal to 4 at 60 DAT, and with all cultivars, some level of BA treatment resulted in an average SOD more or less than 4. However, among offsets that formed in the control treatment, 40% of the cultivars averaged < 4. Results from previous studies indicated a higher rooting percentage for SOD 4 than for less advanced stages (Keever et al., 1995). The SOD of most cultivars, when treated with BA, was so advanced at 60 DAT that well developed roots were present on most offsets; these offsets would likely require minimal care for establishment. Generally, the growth index either increased or was not affected by BA rate. Plants displayed no phytotoxic symptoms as a result of BA application, and plant appearance was often enhanced by the outgrowth and development of BA-induced offsets.

BA application to hosta may decrease production time of a wide range of cultivars, including certain cultivars that are otherwise slow to produce offsets, possibly increasing efficiency and decreasing production costs. Among the cultivars evaluated in this study, BA application to BD, FR, FW, KR, MA, and RS resulted in the largest increase in offset production. Understanding the cultivar-dependent response to BA application appears to be a key factor in capitalizing on BA-induced offset formation and development during hosta production.

Literature Cited

Cline, M.G. 1988. Apical dominance. Bot. Rev. 57:318-358.

Keever, G.J. 1994. BA-induced offset formation in hosta. J. Environ. Hort. 12:36-39.

Keever, G.J., D.J. Eakes, and C.H. Gilliam, 1995. Offset stage of development affects hosta propagation by stem cuttings. J. Environ. Hort. 13:4-5.

Meyer, M.M., Jr. 1980. In vitro propagation of Hosta sieboldiana. Hortscience 15:737- 738.

Mok, D.W.S. and M.C. Mok. 1994. Cytokinins. CRC Press. Boca Raton, Fla.

Rhodus, T. 1995. Top twenty perennials. Greenhouse Grower. 13:80.

SAS Institute. 1988. SAS/SAT user's guide, release 6.03. SAS Institute. Cary, N.C.

Schmid, W.G. 1991. The genus Hosta. Timber Press. Portland, Ore.

Walters, J. 1981. Propagation of herbaceous perennials. Comb. Proc. Intl. Plant Prop. Soc. 32:583-588.

Table 1. Offset counts of hosta cultivars
at 30 and 60 days after treatment (DAT) with four BA ratesz
___________________________________________________________________________________
Offset counts
___________________________________________________________________________________
Cultivary
___________________________________________________________________________________
BA rate
(mg.L-1)
AM BD FR FW GS KR MA RS UA WB
___________________________________________________________________________________
30 DAT
0 2.1cx 0.4d 1.9c 0.1d 3.9a 0.5d 0.2d 2.9abc 2.5bc 3.4ab
1250 3.1bc 4.7ab 2.5cd 1.0de 5.9a 5.2a 0.1e 6.3a 2.2cd 2.7cd
2500 3.2bc 4.1b 2.9bc 1.6c 3.4bc 6.9a 1.5c 8.6a 2.2bc 2.7bc
3750 2.6de 4.8c 4.1cd 3.6cd 4.6c 5.4b 0.7e 10.4a 3.3cd 2.5de
0 vs. BA NS *** * ** NS *** NS *** NS NS
BA rate NS Q** L** L*** NS Q*** NS L*** NS NS
60 DAT
0 3.4a 0.5b 3.7a 0.2b 4.4a 0.8b 0.5b 4.4a 4.0a 3.7a
1250 3.7bc 5.4ab 2.9cd 0.9de 5.6ab 5.7ab 0.5e 6.7a 5.0ab 2.9cd
2500 4.6b 4.3b 4.6b 1.9d 4.6b 7.7a 2.4cd 9.0a 5.5b 3.9bc
3750 3.0cd 5.6b 4.5bc 4.7bc 4.2bc 5.7b 2.1d 11.0a 5.1bc 3.1cd
0 vs. BA NS *** NS ** NS *** * *** NS NS
BA rate NS Q* NS L*** NS Q*** L*** L*** NS NS
___________________________________________________________________________________ Cultivar x BA interaction significant (P is less than or equal to 0.01) at 30 and 60 DAT.

yAM = Hosta fortunei 'Aureo-marginata', BD = H. 'Big Daddy', FR = H. 'Francee', FW = H. 'Frances Williams', GS = H. 'Gold Standard', KR = H. 'Krossa Regal', MA = H. montana 'Aureo-marginata', RS = H. 'Royal Standard', UA = H. undulata 'Albo-marginata', WB = H. 'Wide Brim'.

xMean separation within rows by Duncan's multiple range test, P is less than or equal to 0.05.

wNS,*, **, ***: nonsignificant, or significant at the P is less than or equal to 0.05 (*), 0.01 (**) or 0.001 (***) level; control included in regression analysis.

Table 2. Offset stage of development (SOD) at 60 days after treatment (DAT)
of hosta cultivars with four BA ratesz
________________________________________________________________________________
Offset stage of development
________________________________________________________________________________
Cultivary
________________________________________________________________________________
BA rate
(mg.L-1)
AMBD FR FW GS KR MA RS UA WB
________________________________________________________________________________
0 0.58bcx 1.8d 5.8bc 1.4d 9.0a 3.1cd 1.8d 9.7a 8.1ab9.2a
12505.4bc 4.4cd 4.3cd 2.3de 8.2a6.1abc 1.5e7.9ab 6.0abc 6.3abc
25005.3abc 4.0cd4.7abcd2.7d5.7abc 6.0abc4.4bcd6.4ba6.8a5.0abc
37504.6d5.0cd7.2abc4.9d7.1abc7.4ab5.3bcd8.3a8.9a7.3ab
0 vs. BANS*** NS NS* *** NS *** NS *
BA rateNS L***Q* L*L** L*** L** Q*** NSQ**

zCultivar x BA interaction significant (P is less than or equal to 0.01) at 60 DAT; SOD 1 = elongated bud, first leaf furled, 2 = 1 unfurled leaf, 3 = 2 unfurled leaves, etc.

yAM = Hosta fortunei 'Aureo-marginata', BD = H. 'Big Daddy', FR = H. 'Francee', FW = H. 'Frances Williams', GS = H. 'Gold Standard', KR = H. 'Krossa Regal', MA = H. montana 'Aureo-marginata', RS = H. 'Royal Standard', UA = H. undulata 'Albo-marginata', WB = H. 'Wide Brim'.

xMean separation within rows by Duncan's multiple range test, P is less than or equal to 0.05.

wNS,*, ***: nonsignificant (NS) or significant at the P is less than or equal to 0.05 (*) or 0.001 (***) level.

vNS, L, Q: nonsignificant, linear, or quadratic response, respectively, at the P is less than or equal to 0.05 (*),

0.01 (**), or 0.001 (***) level; control included in regression analysis.

Table 3. Growth index of hosta cultivars
at 30 and 60 days after treatment (DAT) with four BA ratesz
Growth index
_____________________________________________________________________________________
Cultivary
_____________________________________________________________________________________
BA rate
(mg.L-1
AMBD FR FW GS KR MA RS UA WB
30 DAT
0 28.1bx 21.5c 27.4b32.8a32.6a22.1c 26.9b34.9a32.0a25.1bc
125029.7b25.3d26.7bcd34.3a 35.5a29.1bc25.6cd34.9a28.2bcd25.5cd
250030.5cd25.0f31.3cd32.7bc37.2a 33.2bc28.8de34.7ab30.0cde27.1ef
375023.8e25.6de31.3b33.4ab 32.9ab31.8b27.9cd35.0a32.0bc27.2d
0 vs. BANS** * NSNS *** NSNS * NS
BA rateQ** L** L***NS Q* Q** NS NS Q* NS
60 DAT
030.0bc22.7d30.6bc33.0ab32.3ab 21.7d27.2c35.6a33.1ab27.0c
125030.4c26.8d27.0d35.2a35.0ab31.7bc27.2d35.9a32.6abc25.0d
250030.4def27.1f31.7cde35.2bc34.3bcd 36.2b31.3cde40.4a34.0bcd28.2ef
375027.1f27.0f34.7bc36.3ab 31.8cd34.4bc30.8de38.6a34.4bc28.2ef
0 vs. BANS *** NSNSNS ****NSNS NS
BA rateNS Q*Q*NSQ*Q** L**L*NSNS

zCultivar x BA interaction significant (P is less than or equal to 0.01) at 30 and 60 DAT; growth index = (height + width at widest point + width 90o to first width) + 3, in cm.

yAM = Hosta fortunei 'Aureo-marginata', BD = H. 'Big Daddy', FR = H. 'Francee', FW = H. 'Frances Williams', GS = H. 'Gold Standard', KR = H. 'Krossa Regal', MA = H. montana 'Aureo-marginata', RS = H. 'Royal Standard', UA = H. undulata 'Albo-marginata', WB = H. 'Wide Brim'.

xMean separation within rows by Duncan's multiple range test, P is less than or equal to 0.05.

wNS,*, **, ***: nonsignificant (NS) or significant at the P is less than or equal to 0.05 (*), 0.01 (**) or 0.001 (***) level. vNS, L, Q: nonsignificant, linear, or quadratic response, respectively, at the P is less than or equal to 0.05 (*),

0.01 (**), or 0.001 (***) level; control included in regression analysis.

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