Influences of precooling and silver thiosulphate on leaf abscission of two forms of rice flower

Posthart,est Biology and Technology, 2 (1992) 25-30

25

~ 1992 Elsevier Science Publishers B.V. All rights reserved 0925-5214/92/$05.00 POSTEC 00553

Influences of precooling and silver thiosulphate on leaf abscission of two forms of rice flower Margaret E. Johnston, J.G. Tisdell and D.H. Simons Gatton College, The Unil'ersity of Queensland. Lawes, QId. Australia (Accepted 21 January 19921

ABSTRACT Johnston, M.E., Tisdell, J.G. and Simons, D.H. (1992) Influences of precnoling and silver thiosulphatc on leaf abscission of two forms of rice flower. Postharz'est Biol. Teehnol. 2. 25-30.

Helich~'sum diosmifolium, commonly called rice or sago flower, is an Australian wildflower being exported to Japan. Leaf drop occurring 10, 12 and 14 days after harvest from flowering stems of both broad and fine-leafed forms was reduced by silver thiosulphate (STS) pulsing. The most severe leaf drop occurred when flowering stems were not precooled and were kept dry until the assessment stage of the experiment. Severe leaf drop occured 1(1, 12 and 14 days after harvest in flowering stems thai were kept in water during precooling. The vase life of the two forms behaved in different ways to the treatments. The fine-leafed form had its longest vase life when it was precooled and the stems kept dry during this treatment, ttowever, for the broad-leafed form the longest vase life was achieved by pulsing stems with STS (4 raM, 15 rain). followed by precooling with stems kept in water.

Key words: Flower we-cooling; Flower senescence: Helichrysum diosmff?~lium: Rice flower: Sagt~ flower: Silver thiosulphate

INTRODUCTION

Helichrysum d i o s m i f o l i u m , c o m m o n l y c a l l e d rice o r s a g o f l o w e r , is a n e r e c t s h r u b up to dense, spring Japan

5 m h i g h , w i d e l y d i s t r i b u t e d in Q u e e n s l a n d a n d N e w S o u t h W a l e s . It h a s t e r m i n a l h e a d s ( c a p i t u l a ) o f w h i t e , c r e a m o r p i n k f l o w e r s in l a t e w i n t e r , a n d o c c a s i o n a l l y in a u t u m n ( S t a n l e y a n d R o s s , 1986). It is b e i n g e x p o r t e d to as a c u t f l o w e r . P r o b l e m s w i t h l e a f b l a c k e n i n g a n d a b s c i s s i o n h a v e b e e n

reported. T h e m a t e r i a l is g r o w n in p l a n t a t i o n s o r h a r v e s t e d f r o m n a t u r a l l y o c c u r r i n g s t a n d s . T h i s s p e c i e is d i v e r s e , w i t h a r a n g e o f f o r m s o f l e a f a n d f l o w e r t y p e s .

Correspondence to." M.E. Johnston, Horticulture Section, Gatton ('o[lege, The University of Queensland, Lawes, Qld. 4343, Australia.

26

M.E. JOHNSTON ET AL

Although little selection has been done, a broad-leafed and a fine-leafed form have been identified. The fine-leafed form is preferred by commercial growers as the problems of leaf blackening and abscission are thought to be less severe in it. Kader (1985) reviewed the role of ethylene in inducing senescence and physiological disorders in harvested horticultural crops and reported that ethylene induced abscission of leaves of cabbage, chinese cabbage, cauliflower and foliage plants. Reid (1985) hypothesised that a gradient of auxin from the subtended organ to the plant axis maintains the abscission zone in a nonsensitive state. A reduction or reversal of the auxin gradient causes the abscission zone to become sensitive to ethylene. Hence, senescence and abscission could be accelerated by factors like shading and poor nutrition which alter auxin gradients by exposure to ethylene and by stresses which enhance ethylene production. Techniques used to avoid ethylene-induced abscission include avoiding exposure to ethylene, reducing the sensitivity of plants to ethylene by providing adequate nutrition and illumination, avoiding desiccation or treating plants with synthetic auxins (Reid, 1985). Silver thiosulphate (STS) is widely used in postharvest treatments of cut flowers as an inhibitor of ethylene action (Veen, 1983; Reid, 1985). Treatment of English holly with STS reduced leaf and berry abscission caused by a 5-day exposure to 2 ppm ethylene (Joyce et al., 1990). The objective of this study was to examine the influence of precooling and STS pulsing treatments on leaf abscission of two forms of harvested rice flower. MATERIALS AND METHODS

Flowering stems of both a fine-leafed and a broad-leafed form of rice flower were harvested early in the morning in October, from a commercial plantation at Flagstone Creek, Queensland. Flowering stem were graded and six long (86-120

j Dry, 4h ...- Not cooled - Water, 4 h / ~ - S T S , 1 mM Harvest I Graded I Fumigation t ~ ~

Precooled J ~ / / D r y 0°C, 2h ~ Water

STS 4 mM - 15 min, 25°C

Precooled 0°C, 2 h

-

Water

Fig. 1. Methods and treatments used for each form prior to vase life and leaf abscission assessment of rice flowers (Helichrysum diosmifolium ) when held at 20°C in water with chlorine.

LEAF ABSCISSION OF R1CE FLOWER

27

cm) and nine medium (60-85 cm) stems were selected for each treatment, giving 15 single flowering stems per replicate. A randomised complete block design with six treatments and two blocks was used. The handling sequence and treatments are shown diagramatically (Fig. 1) and the blocks were the broad and fine-leafed forms of rice flower. Before any treatments were applied, all flowering stems were placed in an enclosed room and fumigated for 2 h with an aerosol giving a concentration within the room of 0.015 g / m 3 pyrethrins, 0.024 g / m 3 piperonyl butoxide and 0.045 g / m 3 n-octyl bicyclo-. heptene dicarboximide to control lepidoptera larvae. Stems were then recut before they were put into water or STS. The flowering stems kept dry during the pulsing stage of the experiment were not recut until immediately prior to being measured and placed into deionised water with chlorine at 20°C for vase life and abscission determinations (Fig. 1). The precooling treatment was applied for 2 h at 0°C and was given within 4 h of harvest. No leaves were stripped from flowering stems prior to being placed into pulsing or precooling treatments. The STS treatment which was applied to precooled flowering stems was a 15-rain. pulse at a high concentration (4 raM): treated stems then were placed in water and moved into a cool room at 0°C for 2 h. The STS treatment applied to flowering stems that were not precooled was a 4 h pulse at a lower concentration (1 m M) and then treated stems were kept in water. After pulsing and precooling treatments were applied, the length of flowering stem without leaves, from the base of the stem to the lowest leaf, was measured and stems were placed in deionised water with 0.5 m l / l sodium hypochlorite and kept at 20°C. The length of the main stem without leaves was measured from the base of the stem to the lowest leaf, every 2nd day. The vase life (the number of days from harvest to when they were unsightly, due to wilting and discoloration of the pedicel) was recorded. These data were considered to be more objective than a rating system for leaf blackening, as the real problem with Hefichrysum diosmi)blium is that its leaves turn black and abscise. An analysis of variance of tk)rms and treatments was conducted for each time period. RESULTS

Stem length without leat,es. Leaf abscission occured throughout the holding period in both the broad and fine-leafed forms of rice flower (Fig. 2). The broad-leafed form of rice flower had a significantly longer length of flowering stem without leaves than the fine-leafed form at the start of the experiment (Fig. 2). During the experiment, leaves abscised from a further 10.5 cm of the flowering stem of the broad-leafed form and a further 18 cm of the flowering stem of the fine leaf form (Fig. 2). These data confirm our observations that leaf abscission occurs for both forms of rice flower; however, it is more obvious for the broad-leafed form because its leaves are larger. There was no significant interaction between treatments and forms for the length of flowering stem without leaves for any time period. The length of the flowering stem without leaves was not significantly influenced by any treatment for 8 days after harvesting. However, there were significant

28

M.E. J O H N S T O N ET AL.

70

l

E to 0) > 03

~ broad-leafed form -*- fine-leafed form

! ~ J

60

5

0 c--

12) c-"

50

E

O)

03 C -r-" Ill

40 i

LSD 5%!

i

0 ,q30

I

i

i

0

2

4

6

8

10

12

Days from harvest Fig. 2. Mean length of flowering stem without leaves for each form of rice flower averaged over all treatments. d i f f e r e n c e s b e t w e e n t h e t r e a t m e n t s , 10, 12 a n d 14 d a y s a f t e r h a r v e s t i n g ( T a b l e 1). A t 10 d a y s a f t e r h a r v e s t , w h e r e n o p r e c o o l i n g w a s a p p l i e d , t h e r e w a s s i g n i f i c a n t l y m o r e l e a f d r o p in f l o w e r i n g s t e m s t h a t w e r e k e p t d r y t h a n in t h a n t h o s e k e p t in w a t e r o r t h o s e t r e a t e d w i t h S T S (1 m M )

f o r 4 h, p r i o r t o b e i n g k e p t in w a t e r .

H o w e v e r , f l o w e r i n g s t e m s k e p t in w a t e r w h i l e t h e y w e r e p r e c o o l e d h a d signific a n t l y m o r e l e a f d r o p t h a n t h o s e in w a t e r n o t h a v i n g b e e n p r e c o o l e d o r e v e n t h o s e

TABLE 1 Influence of treatments on the mean length of stem without leaves at 10, 12 and 14 days after harvest, combining results from both flower forms Days from harvest 10 12 14

Not precooled 1

Mean n Mean n Mean n

Precooled i

SED

Dry

Water

STS

Dry

Water

STS

Max z

Max-Min 3

56.0 bc 30 61.2 bc 27 65.7 b 11

46.6 ~' 29 49.5 " 28 52.9 5, 22

44.1 ~ 30 46.9 ~ 28 50.1 ~ 25

49.9 ,~b 30 53.4 ~b 29 60.3 b 28

54.4 hc 30 58.9 bc 30 63.2 b 25

49.1 ~,h 27 50.4 ~,b 27 53.1 ~ 23

3.63

3.73

3.56

3.63

3.56

4.61

i Numbers within each 'days to harvest' followed by the same letter are not significantly different (P = 0.05) (Duncan's Multiple Range Test). 2 SED to be used for comparing two treatment means each with maximum replication, n. 3 SED to be used for comparing two treatment means where one has maximum and the other minimum replication.

I,EAF ABSCISSION OF RICE FLOWER

_~t)

Broad-leafed form

~

Fine-leafed form

16 15 cd

~-~

14

-

13

I

LSD 5%

c6

>

12 11 dry

water

STS

Not Precooled

dry

water

STS

Precooled

Fig. 3. Mean vase life of rice flower for each treatmen! and form. treated with 1 m M STS and not precooled but placed in water afterwards. Similar results were obtained 12 days after harvest. At 14 days after harvest, significantly less leaf drop occurred from flowering stems treated with STS at either concentration or those kept in water without precooling compared to all other treatments (Table 1).

Vase lifO. When flowering stems of rice flower were not precooled the vase life of the broad-leafed form was improved by pulsing stems with STS (1 m M , 4 11). However, for the fine-leafed form kept without precooling, the longest vase life was obtained when flowering stems were kept in water (Fig. 3). The vase life of the fine-leafed form was significantly greater than the broad-leafed form when they were kept in water, However, when kept dry or treated with STS, there was no significant difference for vase life between the forms (Fig. 3). When flowering stems were precooled, the vase life of the broad-leafed lk)rm of rice flower was longer when an STS (4 m M , 15 min) pulse was given prior to precooling. However, when flowering stems of the fine leafed form were procooled, there were no differences in vase life of flowering stems kept dry, in water or those pulsed with STS (Fig. 3). The vase life of the broad-leafed form was significantly longer when pulsed with STS and then precooled than any other of the treatments tested (Fig. 3). The vasc life of the fine-leafed form was little influenced by treatments other than not precooling and keeping dry which significantly reduced their life. CONCLUSIONS These results showed clearly that flowering stems of rice flower that werc not precooled and kept dry or without STS showed the most severe leaf abscission and

30

M.E. JOHNSTON ET AL.

the shortest vase life. Leaf abscission is a problem in both the broad and fine-leafed forms of rice flower used in this experiment and material needs to be collected and assessed to determine whether or not genetic variability exists for this character. In both leaf forms, vase life was the shortest when stems were kept dry and not precooled, so this handling system can not be recommended. Keeping stems in water, pulsing with STS and precooling all improved the vase life of the fine-leafed form but there were no clear differences between these treatments. With the broad leafed form, precooling was of benefit in all cases and when combined with STS pulsing it resulted in the longest vase life. Further research is required to develop a harvesting and handling system for commercial growers of rice flower to minimise the leaf abscission problems. ACKNOWLEDGEMENTS

This research was funded by the Gatton College research fund. The flowering stems used in this experiment were generously donated by Mr Graham Cook, Flagstone Creek, Queensland. The authors acknowledge the technical and clerical assistance of Mr S. Vuthapanich, Mrs M. Eisemann, Mr G. Beech, Mrs L. Fischer and Ms J. Webber. REFERENCES

Joyce, D.C., Reid, M.S. and Evans, R.Y. (1990). Silver thiosulphatc prevents ethylene induced abscission in holly and mistletoe. HortSciencc 25, 90-92. Kader, A. (1985). Ethylene induced senescence and physiological disorders in harvested horticultural crops. HortScience 20, 54-57. Reid, M.S. (1985). Ethylene and abscission. HortScience, 20, 45-49. Stanley, T.D. and Ross, E.M. (1986). The Flora of South East Queensland, Vol. 2. Queensland Department of Primary Industries, Brisbane, Qld. Veen, H. (1983). Silver thiosulphate: An experimental tool in plant science. Sci. Hortic. 20, 211-224.