HortScience 31(6):1055-1056.  1996.

‘Maurine Blue’ Lisianthus [Eustoma grandiflorum (Raf.) Shinn.]
Brent K. Harbaugh and John W. Scott

Additional index words:  heat tolerant, high temperature, rosette, potted flowering plants

            Seedlings of commercial lisianthus cultivars form rosettes when grown at 25 to 28ºC (Harbaugh et al., 1992; Ohkawa et al., 1991).  Rosetted plants have a basal cluster of leaves; very short internodes, typical of biennials; and do not bolt or flower for 3 to 6 months without being exposed to 3 to 4 weeks at < 15 to 18ºC to reverse heat-inducing rosetting (Ohkawa et al., 1994; Pergola, 1992).  Semirosetted plants develop when seedlings are grown at a constant 22 to 25ºC or at <22ºC nights with >28ºC days.  Although semirosetted plants have one or more side shoots that many elongate and flower, they flower unpredictably and are of poor quality as cut flowers or potted plants.  Thus, commercial production of lisianthus for late spring or summer sales is limited by high temperatures in many areas of the United States and other countries.  Fall plug production, to produce flowering plants for early spring sales, also is difficult due to rosetting of plugs caused by the interaction of high temperatures and short days (Harbaugh, 1995).  ‘Maurine Blue’ is a heat tolerant lisianthus developed at the Univ. of Florida’s Gulf Coast Research and Education Center, Bradenton.  Seedlings have been produced at 28 to 31ºC without rosetting.

Origin

            ‘Maurine Blue’ is the F₁ hybrid resulting from crossing inbred lines GCREC-P76 and GCREC-9104 (Fig. 1). GCREC-P76 was an F₄ selection of a cross between GCREC-8-57 and ‘Yodel Pink’.  GCREC-8-57 was a self-pollinated plant (S₁) selected from ‘Tosen’ for its ability to flower in the summer (35ºC day) and for its basal and lower branching characteristics.  The ‘Yodel Pink’ plant was a selection that flowered after seedlings were exposed to 28ºC in a growth chamber.  In addition to its heat-tolerant characteristics, it was used because of its bell-shaped flowers and overlapping petals.  Growing conditions used to select F₁ to F₄ GCREC-P76 seedlings for resistance to heat-induced rosetting were 1) production during summer months under greenhouse conditions at > 35°C day in the F₁; 2) exposure of 3-to 4-week-old seedlings to 28ºC for 4 weeks in the F₂ and F₃; and 3) exposure of 17-day-old seedlings to 31ºC for 5 weeks in the F₄.  GCREC-9-104 was identified after 5 generations of self-pollination (S₅) from ‘Blue Poppy’.  Growing conditions used to select S₁ to S₅ generations for heat tolerance were 1) production of plants under summer greenhouse conditions in the S₁ and S₂; 2) exposure of seedlings to 28ºC for 4 weeks in the S₃ and S₄; and 3) exposure of seedlings to 31ºC for 5 weeks in the S₅.

Description

            ‘Maurine Blue’ tolerated greenhouse production temperatures year-round in Bradenton in 1994 with0% to 6% rosetting (Table 1) even though day maximum summer and fall readings reached 35ºC and nights were rarely below 22ºC (18ºC minimum).  During this evaluation, ‘Maurine Blue’ plants ranged from 38 to 58 cm in height (depending on planting date) and were 4 to 21 cm shorter than ‘Flamenco Blue’ and ‘Yodel White’.  ‘Maurine Blue’ flowered 87 and 120 days following sowing on 13 June and 13 Dec., respectively.  ‘Maurine Blue’ can be considered an early flowering cultivar since it flowered earlier than typical commercial cultivars, such as ‘Flamenco Blue’ or ‘Yodel White’.

            When seeds of ‘Maurine Blue’, ‘Blue Lisa’, and ‘Heidi Deep Blue’ were planted 5 Jan. 1995 at Bradenton and 17-day-old seedlings were grown at a constant 31ºC for 5 weeks, no ‘Maurine Blue’ plants rosetted.  However, all ‘Blue Lisa’ and ‘Heidi Deep Blue’ plants were semirosetted or rosetted (Table 2).  ‘Maurine Blue’ plants were intermediate in height when compared to ‘Blue Lisa’ (a dwarf cultivar) and ‘Heidi Deep Blue’ (for cut flowers).  There were more basal breaks (lateral stems forming from the first four to five leaf pairs before bolting) and lower breaks (lateral stems forming on the central flowering stem before the first flower bud) on ‘Maurine Blue’ plants compared to ‘Heidi Deep Blue’ or ‘Blue Lisa’.  ‘Maurine Blue’ had 40 + 6 open flowers and buds ≈ 1 week after the first flower opened.

            ‘Maurine Blue’ flowers acropetally with a “tier-type” display of some cut flowers that concentrate most of the flowers on top of the plant.  Flowers are bell-shaped when open with a petal length of 5.5 + 0.1 cm.  When flowers first open, petals are violet-blue [Royal Horticultural Society (RHS) violet-blue group 89C; RHS, 1966] on the adaxial petal surface, diffusing to a variegated 1.8 + 0.2-cm white band (RHS white group 155C) at the base of the petals.  As flowers mature, petal color darkens to violet (RHS violet group 86A) and the white band fades or completely disappears.  The abaxial petal surface is a lighter violet (RHS violet group 86B).  The center of the flowers (i.e., base of the petals surrounding the ovary) is a dark purple (RHS purple group 79A).

Characteristics and use

            ‘Maurine Blue’ ranged in height from 51 to 67 cm during 1994 and 1995 production trials in Bradenton and is intermediate in plant height when compared to commercial dwarf and cut flower cultivars.  To our knowledge, it is the first heat-tolerant lisianthus cultivar of this height.  ‘Florida Blue’, a semi-dwarf, heat-tolerant lisianthus cultivar, was released from our lisianthus breeding program in July 1995 (Harbaugh et al., 1996).

            Growth retardants are necessary for production of ‘Maurine Blue’ in pots 12 to 15 cm in diameter.  Plant height was 50 + 2.5 cm following foliar applications of butanedioic acid mono(2,2-dimethyllhydrazide) (daminozide) at 500 mg^.L^-1 3 weeks later.  These plants were produced in 11.5-cm square pots (0.65-L) provided with capillary mat irrigation.  Average plant height was 40 + 2 cm for ‘Maurine Blue’ plants treated with (2RS,3RS)-1-(4-cholorphenyl)-4,4-dimethyl-2-)1,2,4-triazol-yl)penten3-ol (paclobutrazol) at 0.25 mg a.i./pot applied as a soil drench when plants were ≈5 to 7 cm tall.

            While ‘Maurine Blue’ has more basal and lower branches than many commercial cultivars now forced in pots, three to four plugs per 12- to 15-cm-diameter pot are suggested for optimal marketing display.  Although this cultivar is intended to be used as a tall bedding plant or flowering potted plant, ‘Maurine Blue’ grown without growth retardants has a height suitable for the bouquet-cut flower market.

Availability

            Plugs of ‘Maurine Blue’ will be offered for sale through Earl J. Small Growers, Pinellas Park, FL.  Scientists interested in seed for research purposes can contact Dr. Harbaugh.

Literature Cited

Harbaugh, B.K. 1995. Flowering of Eustoma grandiflorum (Raf.) Shinn. Cultivars influenced by photoperiod and temperature.  HortScience 30:1375-1377.

Harbaugh, B.K., M.S. Roh, R.H. Lawson, and B. Pemberton.  1992.  Rosetting of lisianthus cultivars exposed to high temperatures.  HortScience 27:885-887.

Harbaugh, B.K., J.W. Scott, and D.B. Rubino.  1996.  ‘Florida Blue’ semi-dwarf lisianthus [Eustoma grandiflorum (Raf.) Shinn.].  HortScience 31:1057-1058.

Ohkawa, K., A. Kano, K. Kanematsu, and M. Korenaga. 1991.  Effects of air temperature and time on rosette formation in seedlings of Eustoma grandiflorum (Raf.) Shinn.  Scientia Hort. 48:171-176.

Ohkawa, K., T. Yoshizumi, M. Korenaga, and K. Kanematsu.  1994.  Reversal of heat-induced rosetting in Eustoma grandiflorum with low temperatures.  HortScience 29:165-166.

Pergola, G. 1992.  The need for vernalization in Eustoma russellianum.  Scientia Hort. 51:123-127.

Royal Horticultural Society.  1966.  Royal Horticultural Society colour chart.  Royal Hort. Soc., London.

Fig. 1. Pedigree of ‘Maurine Blue’ lisianthus.