HORTSCIENCE 26(10):1279-1280. 1991. determined by a micro-Kjeldahl procedure (Perrin, 1953); B by the azomethine-H col- Eustoma Quality is Adversely Affected orimetric method (Gaines and Mitchell, 1979); and P, K, Ca, Mg, Fe, Mn, and Cu by in- ductively coupled argon plasma spectropho- by Low pH of Root Medium tometry. There were two per experi- B.K. Harbaugh and S.S. Woltz mental unit and three replications of each treatment combination in the seedling stage Gulf Coast Research and Education Center, University of Florida, 5007 and seven replications of single- exper- 60th Street East, Bradenton, FL 34203 imental units in the stage. Additional index words. Eustoma grandiflorum, lisianthus, micronutrients Medium pH, microelements, and (Expt. 2). This experiment was a 5 (medium Abstract. Foliar chlorosis or bleaching, interveinal chlorosis, edge and tip necro- pH) × 2 (± microelements) × 3 (cultivar) sis, a poor root system, and stunted growth of Eustoma grandiflorum (Raf) Shinn factorial to determine if would re- seedlings were associated with a medium pH of 5.0 or 5.5 but not when the values spond similarly to medium pH and if symp- ranged from 6.4 to 7.5. The range in medium pH resulting in the best growth of toms associated with low medium pH would seedings and flowering plants was 6.3 to 6.7. Responses to medium pH were similar, increase with micronutrients in the fertilizer regardless of fertilizer solution pH or cultivar. Eustoma seedling and shoot fresh weights solution. Color variants have distinct growth for pH 5.0 and 5.5 were only 23% to 66% of corresponding values for plants grown habits, and cultivars were selected from sev- at pH 6.4. Leaf tissue Zn was extremely high (1050 mg·kg -l dry leaf tissue) at a medium eral seed companies in an attempt to rep- pH of 5.0, but other macro- and micronutrients in were not at abnormal levels. resent a broad genetic diversity of available seed. Eustoma grandiflorum (lisianthus) hybrids hydrated/calcitic lime regime were 5.0, 5.4, Seven-week-old Eustoma ‘Saga Pink’ have continued to gain acceptance as new 6.4, 7.1, and 7.5, respectively. (Takii and Co., Kyoto, Japan), ‘White’ (Sluis cut flowers, bedding plants, and potted flow- pH of medium and fertilizer solution (Expt. and Groot, Enkhuizen, Holland), and ‘Yodel ering plants since their introduction into the 1). This experiment was a 5 (medium pH) Mixture’ (blue, white, and pink blend; Sak- floriculture trade in the early 1980s (Halevy × 5 (fertilizer solution pH) factorial. The ata Seed Co., Yokohama, Japan) seedlings and Kofranek, 1984). As with most new crops fertilizer solution pH was adjusted with 1 M were potted into the five media and condi- with limited cultural information, commer- Ca(OH) 2 to 5.0, 5.6, 6.2, 6.8, or 7.5. Cal- tions of Expt. 1 for seedling evaluation. The cial producers have struggled with different cium chloride was used to provide equal fertilizer solutions were 300N-200P-600K aspects of the production and management amounts of Ca in each solution. The fertil- (mg·liter -1) with or without the following of this crop. We have observed many in- izer solution contained 500N-200P–600K– micronutrients: 25Fe-10Mn–5Cu-5Zn- -1 -1 stances when seedling production was vari- 175Ca (mg·liter ) from NH4H2PO4, KNO3, 1.6Mo (mg·liter ) from Fe-DTPA chelate, able, with small, poor-quality seedlings and NH4NO3 (62% NO3-N). MnSO4H2O, CUS04·5H20, ZnSO4·7H2O, and frequently being produced. In extreme cases, Six-week-old Eustoma ‘Saga Purple’ Na2MoO4·2H2O. There were three plants per seedlings had foliar chlorosis, leaf edge or seedlings were transplanted into 3.5 × 3.5 experimental unit and three replications of tip necrosis, and a stunted or poorly devel- × 6-cm pyramidal cell transplant flats (35 each treatment. oped root system. Initial investigations in- ml medium/cell) on 5 Mar. Fertilizer solu- The growing environment for both exper- dicated low medium pH (in the range of 5.0 tions were applied weekly at 6 ml/cell. Seed- iments was a fan-and-pad-cooled glass- to 5.8), now commonly recommended for ling width, shoot fresh weight, and medium house, where the air ranged from 18C night peat-based media (Joiner et al., 1983; Pe- pH were recorded 10 Apr. At this time, ad- to 33C day. Shade was provided by exterior terson, 1982), typically was associated with ditional seedlings were transplanted into 0.5- paint, and the midday photosynthetic photon these symptoms. Although no published data liter (10 cm) pots with the same medium and flux ranged from 600 to 800 µmol·m-2·s-1. on the effects of medium pH on Eustoma fertilizer treatments from which they were Experiment 1. Interactive effects between could be found, Roh and Lawson (1984) in- grown for seedling evaluations. Fertilizer so- medium pH and fertilizer solution pH were dicated a pH near neutral or 6.5 was satis- lutions were applied weekly at 100 ml/pot. not significant for any measured growth re- factory for Eustoma. The research reported Plant height, shoot fresh weight, number of sponse for either stage of growth. Fertilizer here was conducted to determine the influ- flowers and buds, and medium pH were re- solution pH had little effect on growth re- ence of medium pH on seedling production corded 4 June. Leaf tissue samples were also sponses, but medium pH had a significant and subsequent growth to flowering. taken at this time for elemental composition effect on all growth responses for both de-

The medium in two tests consisted of 4 analyses. Foliar N, excluding NO3-N, was velopmental stages (Table 1). Thus, data sphagnum peat : 2 horticultural vermiculite : 1 quartz sand : 1 perlite (by volume) amended with 3 kg single superphosphate (ON-9P-OK-22Ca)/m 3. To obtain a range in pH, the medium was amended with the fol- lowing hydrated : calcitic lime ratios (kg·m -3): 0.3:0.15, 0.9:0.45, 2.7:1.4, 5.4:2.7, and 8.0:4.0. Media were moistened and stored for 1 week before tests were in- itiated. After an additional week of daily ir- rigation for seedling establishment, pH values of saturated-paste medium extracts for each

Received for publication 21 Dec. 1990. Florida Agricultural Experiment Station Journal Series no. R-01444. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.

HORTSCIENCE, VOL. 26(10), OCTOBER 1991 1279 fresh weight for both fertilization methods. Estimated optimum pH for seedling growth ranged from 6.3 to 6.7. If Zn toxicity due to high volubility at low medium pH was the cause of stunting of Eustoma seedlings, one might expect the ad- dition of Zn along with other micronutrients in the fertilizer solution to aggravate seedling growth problems. However, differences in seedling width and fresh weight due to low medium pH were greater when seedlings were grown without than when grown with mi- cronutrients (Table 3). Results from both ex- periments indicate the need for additional research on the requirements and balance of micronutrients for seedling growth, although the practical solution to the problem at this versely related to optimum pH levels for time appears to be to produce seedlings in growth (Table 2). This response is typical media with a pH near 6.4 (Biernbaum et al., when plants are stunted for various reasons 1988). but continue to take up nutrients. Only foliar In summary, medium pH had a dramatic levels of Zn (1050 mg·kg-1 dry leaf tissue) effect on seedling growth for all cultivars were at levels that might be toxic (Joiner et tested. The range of medium pH for maxi- al., 1983). Experience with geranium is sim- mum growth estimated for both experiments, ilar in that micronutrient levels, especially including all. measured responses, was from Mn and Fe, were enhanced by low medium 6.3 to 6.7. Perhaps more importantly, how- pH (Biernbaum et al., 1988). Eustoma ap- ever, was that at lower pH levels, which are parently can accumulate high concentrations commonly used in floriculture for peat-based of Zn at a low pH, levels that might cause media, Eustoma seedling and plant fresh the chlorosis and necrosis often observed. weights were only 23% to 66% of the fresh However, further research is necessary to weight of seedlings grown at a medium pH determine if Zn toxicity caused the plants to of 6.4. grow poorly or if other nutrient imbalances or additional factors associated with low me- Literature Cited dium pH inhibited growth, resulting in lux- Biernbaum, J., W. Carlson, C. Shoemaker, and uriant absorption of Zn. R. Heins. 1988. Low pH causes iron and man- Since Ca was introduced with lime sources ganese toxicity. Greenhouse Grower 6(3):92- for pH adjustment, medium Ca levels in- 93, 96-97. creased with increasing medium pH. How- Frett, J. J., J.W. Kelly, B.K. Harbaugh, and M. ever, 0.66 kg Ca/m3 of medium from single Rob. 1988. Optimizing nitrogen and calcium superphosphate, 175 mg Ca/liter in fertilizer nutrition of lisianthus. Commun. Soil Sci. & presented are main-effect means for effects solutions, and 30 mg Ca/liter in irrigation Plant Anal. 19(1):13-24. of medium pH on seedling and plant growth water probably would have supplied ade- Gaines, T.P. and G.A. Mitchell. 1979. Boron de- averaged over fertilizer solution pH treat- quate levels of Ca for growth in all media termination in plant tissue by the azomethine H ments. even though Eustoma requires relatively high method. Commun. Soil Sci. & Plant Anal. Regression analyses indicated quadratic levels of Ca (Fret et al., 1988). Foliar levels 10(8):1099-1108. relationships for the effect of medium pH on of Ca were higher at low than at high media Halevy, A.H. and A.M. Kofranek. 1984. Evalu- all measured growth responses (Table 1). pHs (Table 2), indicating that availability was ation of lisianthus as a new flower crop. HortScience 19(6):845-847. Seedlings and flowering plants grown with more important than absolute amount present a medium pH of 5.0 or 5.4 were only half in the media. Joiner, J. N., R.T. Poole, and C.A. Conover. 1983. the weight and width of seedlings grown at Experiment 2. Similar trends were evident Nutrition and fertilization of ornamental green- house crops, p. 317-403. In: J. Janick (ed.). pH 6.4. Symptoms of foliar chlorosis, a poor for effect of medium pH and micronutrients Hort. Rev. vol. 5. AVI, Westport, Conn. root system, and stunted plants were similar on growth of all cultivars. There was an in- Perrin, C.H. 1953. Rapid modified procedure for to symptoms associated with problems ob- teraction of micronutrient fertilization with determination of Kjeldahl nitrogen. Anal. Chem. served in commercial production of Eustoma medium pH, so regression analyses for the 25(6):968-969. seedlings. Maximum growth responses es- influence of medium pH on seedling growth Peterson, J.C. 1981. Modify your pH perspective. timated from quadratic equations were within were made for each fertilization method from Florists’ Rev. 169(4386):34-35, 92-93. a range of medium pH from 6.4 to 6.7, en- data combined for all cultivars (Table 3). Rob, M. and R. Lawson. 1984. The lure of lis- compassing all growth characteristics. Quadratic relationships were indicated for the ianthus. Greenhouse Manager 2:103, 104, 108, In general, foliar nutrient levels were in- effect of medium pH on seedling width and 110, 112-114, 116-121.

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