gamma irradiation for insect deinfestation damages native australian cut flowers

Scientia Horticulturae, 52 (1992) 343-355 343 Elsevier Science Publishers B.V., Amsterdam

Gamma irradiation for insect deinfestation damages native Australian cut flowers

K.A. Seaton a and D.C. Joyce b aDiviston of Horticulture, Western Australian Department of Agriculture, Baron-Hay Court, South

Perth, W..A. 6151, Australia "Division of Horticulture, CSIRO, 306 Carmody Road, St Lucia, Qld. 4067, Australia

(Accepted 28 April 1992 )

ABSTRACT

Seaton, K.A. and Joyce, D.C., 1992. Gamma irradiation for insect deinfestation damages native Aus- traliar, cut flowers. Scientia Hortic., 52: 343-355.

Gamma irradiation doses above 0.05 kGy for Geraldton wax, 0.1 kGy for banksia and 1.0 kGy for kangaroo paw caused significant (P < 0.05) reductions in flower and foliage vase lives. Doses of greater than 2 kGy and up to 10 kGy were required for immediate 100% kill of the bioassay insects (adult flour beetle, Mediterranean fruit fly adults and larvae, and spotted moth larvae ). Pretreating Geraldton wax shoots by cooling them or pulsing them with sugar lessened the detrimental effect of irradiation (0.1 kGy) on vase life. Pretreatment with silver thiosulphate had no positive effect. Irra- diation of Geraldton wax shoots in an inert atmosphere (nitrogen) exacerbated irradiation, induced reduction in vase life and increased flower abscission. None of the postharvest treatments tested were sufficiently ameliorative for irradiation to be considered a viable deinfestation treatment for Gerald- ton wax.

Keywords: Geraldton wax; banksia; kangaroo paw; vase life; postharvest; insects.

INTRO D U C T I O N

Freedom from insect infestation is essential for entry of cut flowers into countries with strict quarantine requirements, such as Japan and the USA (Seaton and Joyce, 1990 ). High energy gamma ray radiation is one of a number of postharvest deinfestation treatments that have been tested for cut flowers (Wit and Van de Vrie, 1985; Maughan, 1986; Joyce, 1988; Seaton et al., 1989). Gamma irradiation has successfully been used to deinfest papaya (Akamine and Goo, 1977), cherries (Burditt and Hungate, 1988; Jessup, ! 990 ) and mangoes (Spalding and Von Windeguth, 1988 ). Benefits of gamma

Correspondence to: K.A. Seaton, Western Australian Department of Agriculture, Baron-Hay Court, South Perth, W.A. 6151, Australia.

© 1992 Elsevier Science Publishers B.V. All rights reserved 0304-4238/92/$05.00

344 K.A. SEATON AND D.C. JOYCE

irradiation for deinfestation include deep penetration of tissue, its non-chemical nature and precise dose control.

Gamma irradiation can be used to sterilize insects or to kill them. The dose required to sterilize insects varies from 0.02 to 0.08 kGy depending on type of insect and its stage of development (Thomou, 1963; Anwar et al., 1975; Fisher, 1981 ). Doses of 1-2.5 kGy are required to kill insects (Hugue, 1963; Laviolette and Nardon, 1963; O'Brien and Wolfe, 1964).

Wit and Van de Vrie ( 1985 ) reported that cut flowers differ widely in their reaction to gamma irradiation, some varieties being damaged at only 0.05 kGy while others tolerated 0.5 kGy. Gamma irradiation caused blackening of Protea neriifolia, Protea compacta and Protea cynaroides flower bracts (Maughan, 1986). Doses of 0.1, 0.3 and 0.9 kGy suppressed the rate and degree of opening of P. compacta and Protea longiflora blooms, but not of Leucospernum cordifolium blooms (Haasbroek et al., 1973 ). Vase life of Ger- aldton wax was reduced by an irradiation dose of 0.1 kGy (Joyce, 1988 ).

Cut flowers appear less tolerant of gamma irradiation than insects. How- ever, it may be possible to increase flower tolerance of irradiation by lowering their temperature (Maxie et al., 1971 ) or by purging with a nitrogen atmosphere to minimise free radicle formation in the presence of oxygen (Miiller and Zimmer, 1961; Leopold, 1964; Dharkar et al., 1966). It is also possible that pulsing flowers with sugar to protect mitochondria (Parups and Chan, 1973 ) and maintain membrane structure (Acock and Nichols, 1979; Paulin, 1985 ) may reduce irradiation injury. Similarly, pulsing with the ethylene- antagonist silver, as silver thiosulphate (Reid et al., 1980; Wit and Van de Vrie, 1985; Joyce, 1988), may be beneficial in ameliorating irradiation-induced senescence.

Microwave radiation may be an alternative to gamma irradiation for cut flower deinfestation. Microwave irradiation has been used against insects in- festing papaya to rapidly increase fruit temperature (Hayes, 1983; Hayes et al., 1984).

The objective of the present study was to assess the suitability of gamma irradiation, at doses required to sterilize and to kill insects as a deinfestation method for Geraldton wax, kangaroo paw and banksia. The effect of microwave irradiation on Geraldton wax was also determined.

M A T E R I A L S A N D M E T H O D S

Flowers

Flowering shoots of the native Australian cut flower exports Geraldton wax (Chamelaucium uncinatum Schauer. cultivars 'Purple Pride', 'Alba' and 'Newmarracarra', red and green kangaroo paw (Anigozanthos manglesii D. Don) and Hooker's banksia (Banksia hookeriana Meisn. ) were cut at com-

GAMMA IRRADIATION FOR INSECT DEINFESTATION 345

mercial maturity; viz. 30-60% of Geraldton wax flowers open, 20% of banksia florets open, one kangaroo paw flower open. Harvest was in the cool of the early morning. Cut shoots were placed immediately into buckets of water, transported to the laboratory, recut under water to length, and the lower leaves were removed. Shoots were placed into deionized water and held in 20°C laboratory until the following day when treatments were imposed.

Insects

Bioassay insects, adult confused flour beetle ( Tribolium confusum Koch. ), Mediterranean fruit fly adults and larvae (Ceratitis capitata Wiede.), and spotted moth larvae (Spodoptera litura F.) were raised as uniform popula- tions with which to assess the relative effects of different irradiation treatments Bioassay insects which do not naturally infest native Australian cut flowers were chosen, thereby avoiding potential quarantine implications. In- sects were reared at 25°C on prepared media. The media were 1:1 plain/ wholemeal wheaten flour for flour beetle, moist 2:1:1.2 paper pulp (un- bleached)/yeast (torula)/sucrose with mould inhibitors (sodium, methyl hydroxy and propyl hydroxy benzoate ) for Mediterranean fruit fly larvae and for spotted moth larvae, and autolyzed Brewers yeast and sucrose plus fresh water :solution for adult fruit fly. For experiments, flour beetles were 8-12 weeks ,old, Mediterranean fruit fly adults were 4 days old, Mediterranean fruit fly larvae were 5 days old (third interstar stage), and spotted moth larvae were 3 days old. Insect mortality was assessed following treatments until max- imum mortality counts were reached. Mortality was adjusted to allow for the natural attrition in the controls (Abbott, 1925 ).

Gamma irradiation

Dosing. - Flowering shoots were cut to 20 cm length and placed in 1 1 perspex flasks which fitted into the Gammacell 220 (Canada) 6°Co irradiation unit. 6°Co activity fell from 6.6 to 5.4 kGy h-1 during the 12 month experimental period, The gamma cell was calibrated by red-acrylic dosimetry. Doses at different positions in the cell did not vary by more than + 10% from the pre- scribedL dose. Doses of between 0.05 and 10 kGy were achieved by varying irradiation times from approximately 30 s to 2 h. The temperature in the cell did not: increase by more than 1 °C during 2 h of irradiation. Geraldton wax, kangaroo paw and banksia flowering stems were exposed to various irradiation doses. Insects were kept in 15 ml PVC vials for irradiation with the flowers.


Pretreatments

The following pre-irradiation treatments were compared for Geraldton wax cultivar 'Newmarracarra' using a gamma irradiation dose of 0.1 kGy: ambient 'storage' (20 ° C, control), overnight low temperature 'storage' (2.5 ° C, 18 h ), overnight sugar pulsing ( 5% w/v sucrose, 20 ° C, 18 h) and silver thiosulphate pulsing (4 mM Ag +, 20 min, 20 °C) followed by ambient 'storage' overnight. Non-irradiated 'controls' were maintained for each pretreatment.

During irradiation the 'low temperature storage' treatment, flowers were kept at 1.0 + 0.5 ° C by enclosing them in an ice water jacket within the gamma cell. All other pretreatments were irradiated at 20°C. The bioassay insects, flour beetles, were kept at the same temperature as the associated flowers.

Nitrogen atmosphere

Prior to irradiation ( 12 h ), Geraldton wax cultivar 'Purple Pride' flowering shoots and flour beetle and Mediterranean fruit fly larvae were held in cham- bers in water saturated pure nitrogen (N2) or ambient air atmosphere. At- mospheres were flushed at a rate of two exchanges per hour and flow rates q:ontrolled by fine metering valves (Nupro) and set using a bubble flow meter (Hewlett Packard). Stems stood in deionized water during this time. Cham- bers, with atmospheres maintained, were then placed in the gamma cell and the flowers and beetles irradiated at 0.1, 1 or 10 kGy.

Microwave irradiation

Flowering shoots (30 cm) of Geraldton wax cv. 'Alba' in vases were placed in a microwave oven (General Electric model M0703, 650 J s-1 ). The shoots and flour beetles were exposed to a range of energies (kJ) achieved by run- ning the oven at various power levels for varying times. The oven was allowed to cool to room temperature between treatments. Immediately on removal of the shoots from the oven a needle point thermocouple (Cu /Cn) was inserted into a flower and the temperature recorded. A break point of 51 ° C was iden- tified at 20 kJ, such that further increases in energy did not cause an apprecia- ble increase in flower temperature.

Flower and insect assessment

Immediately following irradiation, flowering shoots were re-cut under water (approximately 1 cm removed) and placed singly into individual 250 ml plastic vases containing 2% w /v sugar (sucrose) and 200 mg 1 -~ 8-hy- droxyquinoline sulphate. Vase life was assessed in a controlled environment


room: 20+2°C, 50+ 10% relative humidity, 12 h light period, 8 mmol m -2 s- 1 ligJat flux at flower height.

For Geraldton wax, end of vase life (days) for flowers was determined when half of the flowers on a shoot were 50% or more closed and for foliage when half of the needle-like leaves were desiccated for 50% or more of their length. For banksia, vase life for flowers was recorded when there was darkening of the stigmas, shrinkage of anther tubes of open flowers, and 'greying' of uno- pened florets and for foliage when half of the leaves were desiccated for 50% or more of their length. For kangaroo paws, end of vase life was noted when open flowers were wilted with loss of pollen from the anthers and when the tips of the fused corolla had dried out. A kangaroo paw flower was considered open if it appeared fresh with three or more tips of the mostly fused corolla of a flower bent back past 90 ° to the corolla tube. 'Total flower-open days' for kanga:roo paws was computed as the sum of the number of flowers open each day over the total vase life of each individual flowering shoot. Flower appear- ance was assessed daily, and flowering shoots and vases were weighed every second day. Shoot weight was expressed as a percentage of its initial weight (Day 1 ).

Insects were held after treatment in 80 ml screw top clear plastic vials fitted with nylon mesh lids and were kept in the controlled environment room for mortality assessment.

Data analysis

For flowering shoots, replication was eight to ten-fold (i.e. eight to ten sin- gle stems). Vases were arranged in a randomized complete block design. For insect,;, replication was ten-fold. However, there were ten insects (samples) per cage (replicate). Data was evaluated by analysis of variance or by regression analysis using the method of least squares, as appropriate. Log transfor- mations of irradiation doses were used for Fig. 1 and Fig. 2, and of microwave energy for Fig. 3. Standard error of the means (SEM) are presented where appropriate.

R E S U L T S

Vase life and insect mortality

The vase life (y) of Geraldton wax cv. 'Purple Pride' flowers decreased markedly (y= 1.22-6.11 * logmx, n=40, r2=0.794) as the irradiation dose (x) was increased up to 0.2 kGy and then remained constant at 2.6 days (Fig. 1 (a)) . There was 51% loss of vase life for flowers following a 0.1 kGy dose. Foliage vase life appeared to decrease log-linearly (y= 3.53 - 4.28 * log~0x, n=50 r2=0.935) up to a 0.5 kGy dose. Vase life was reduced by 21% after a

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K.A. SEATON AND D.C. JOYCE

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Fig. 1. Effect of gamma irradiation on (a) vase lives of kangaroo paw flowers, banksia flowers and foliage and Geraldton wax cv. 'Purple Pride' flowers and foliage and (b) mortality of adult flour beetle, spotted moth larvae and adult Mediterranean fruit fly. See text for regression equations. Vertical bars indicate SEM except where smaller than symbol size.

dose of 0.1 kGy. The vase life o f banksia flowers and foliage also decreased log-linearly with increasing irradiation dose: y = 5.88 - 2.26 * logloX, n = 64, rZ=0.964 for flowers and y = 6.35 - 2.60 * log~oX, n = 64, rZ=0.946 for foliage (Fig. 1 ( a ) ) . Following irradiation at 0.1 kGy, vase lives of banksia flowers and foliage were shortened by 22% and 20% respectively. The magnitude o f reduction in banksia flower and foliage vase life was less than for Geraldton wax (Fig. 1 ( a ) ) . Kangaroo paw flowers were relatively tolerant of irradiation, there being no loss of vase life up to a dose of 1.0 kGy (Fig. 1 ( a ) ) . At higher doses up to 10 kGy, vase life o f kangaroo paw flowers decreased sub- stantially ( y = 15.9 - 11.6 * log~oX, n = 2 4 , r2=0 .986) . The vase life o f kangaroo paws was reduced by 74% on exposure to 10 kGy. 'Total flower open days' (data not shown) paralleled trends in vase life (Fig. 1 ( a ) ) . 'Total flower open days' was unaffected by irradiation up to a dose o f 1.0 kGy and was 24.6 days.


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Fig. 2. Effect of gamma irradiation applied in air or in nitrogen (100% N2, 12 h prior to and during irradiation) on (a) flower vase life and (b) flower abscission (measured 1 day after irradiation, percentage total initial flower count) for Geraldton wax cv. 'Purple Pride', and on (c) mortality of adult flour beetle and Mediterranean fruit fly larvae. The regression equations shown on panels (a ) - ( c ) refer to lines j oining three or more doses. Vertical bars indicate SEM except where smaller than symbol size.


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Fig. 3. Effect of exposure to microwave irradiation on (a) vase lives of Geraldton wax cv. 'Alba' flowers and foliage and (b) mortality of adult flour beetle. Regression equations are shown in the panels (a) and (b). Vertical bars indicate SEM except where smaller than symbol size.

Above 1.0 kGy 'total flower open days' decreased with increasing dose (i.e. y = 22.9 - 20.4 * logloX, n = 24, r 2 = 0.964. At a dose o f 2.0 kGy, 25% of flowers were darker in colour (i.e. changed from a bright red-green colour to a dull red-green colour) . Following exposure to a dose of 10 kGy, 75% of flowers were blackened.

There was no effect o f irradiation up to a dose of 0.1 kGy on mortality of the three bioassay insects, flour beetles and Mediterranean fruit fly and spotted moth larvae (Fig. 1 ( b ) ) . At 2 kGy some insects were killed. However, 2 kGy caused considerable damage to Geraldton wax and banksia. At 2 kGy, mortality was 19.4%, 20.7% and 26.7% for moth larvae, fruit fly and flour beetles, respectively. At 10 kGy, the dose required to kill all beetles (Fig. 2 ( c ) ) , dramatic loss in vase life was recorded for kangaroo paw (Fig. 1 ( a ) ) .

GAMMA IRRADIATION FOR INSECT DEINFESTATION

Low temperature, and sugar and STS pulse pretreatments

351

Pretreatments of low temperature, and sugar or STS pulses extended the vase life of non-irradiated Geraldton wax 'Newmarracarra' flowers by 2-3 days over the control (Table 1 ). For non-irradiated foliage, which had a vase life 4 days shorter than the flowers, exposure to low temperature or sugar pretreatment increased vase life, although not to the extent that it equalled flower vase life (Table 1 ). Pulsing flowering shoots with STS extended foliage vase life beyond flower vase life.

Vase life of control flowers exposed to an irradiation dose of 0.1 kGy was reduced by 42% (Table 1 ). For shoots pretreated at low temperature or sugar pulsed, there was an extension of vase life for flowers of 63% (cold) and 68% (sugar) and for foliage of 31°/o (cold) and 14% (sugar) (Table 1 ). Pulsing

TABLE l

Effect on exposure to 0.1 kGy gamma irradiation on (a) vase life of flowers and foliage and (b) loss in stem fl'esh mass (%) of Geraldton wax cv. 'Newmarracarra' following various pretreatments of low temperature or sugar or STS pulsing

Pretreatraent (a) Vase life (days)

Flowers Foliage

Non-irradiated Irradiated Non-irradiated Irradiated

Control1 10.2b 2 5.9b 2 6.52 8.3c Low teml9erature a 12.8a 9.6a 8.8b 10.9b Sugar pu) se 4 13.0a 9.9a 9.2b 9.5bc STS pulse 5 12.8 5.6b 14.2a 13.3a

Pretreatment (b) Loss in stem fresh mass at 14 days (%)

Non-irradiated Irradiated

Control 2 56.7a 2 54.2a 2 Low temperature 3 40.0b 46.4a Sugar pulse 4 37.7b 46.3a STS pulse 5 12.3c 25.3c

INo pretreatment. 2LSD (P < 0.05, pretreatment X irradiation treatment) for flowers = 1.8 days and for foliage = 1.9 days (replication ten-fold) and for loss in stem mass= 11.7%. For data within columns, means followed by a common letter do not differ significantly (P < 0.05, Duncans Multiple Range Test ). 32.5 o C for 18 h, including during irradiation. 4Pulsed with 5% w/v sucrose at 20°C for 18 h immediately before irradiation. 5Pulsed with 4 mM silver thiosulphate at 20°C for 20 min and then held for 18 h at 20°C before irradiation.

3 5 2 K.A. SEATON AND D.C. JOYCE

with STS offered no protection of flowers from irradiation, but gave 60% extension of vase life for foliage (Table 1 ).

There were no significant differences (P< 0.05 ) among losses in flowering stem fresh mass during vase life for the non-irradiated and the irradiated control, low temperature and sugar pulse treatments. STS pulsed non-irradiated shoots lost less fresh mass (P< 0.05) than irradiated shoots (Table 1 ). The STS pulse was the treatment most effective in minimizing loss in fresh mass during vase life. To a lesser extent, low temperature or sugar pulse pretreatments tended to reduce loss in fresh mass for non-irradiated shoots (Table 1 ). Visual observation made during vase life assessment suggest that the main effect of the STS pulse was to prevent flower and leaf drop.

Nitrogen atmosphere

Purging for 12 h in N2 reduced the flower vase life of non-irradiated shoots by 66% (Fig. 2 (a ) ) . Gamma irradiation treatment in addition to N 2 treatment reduced flower vase life following 0.1, 1.0 and l0 kGy doses by 63%, 66% and 81%, respectively as compared with irradiation in air. The N2 atmosphere had a negligible effect on flower abscission (Fig. 2 (b) ) . However, flower abscission increased with increasing irradiation doses in air to 6.0% and 32.3% for 1.0 and 10 kGy, respectively. Abscission was even higher for 0.1, 1.0 and 10 kGy doses in N2, the levels being 16.3%, 24.5% and 87.6%, respectively. Gam ma irradiation doses of 0.1 to 1.0 kGy did not kill adult flour beetles or Mediterranean fruit fly larvae irradiated in air nor Mediter- ranean fruit fly larvae irradiated in N 2 (Fig. 2 (c)) . However, irradiation of adult flour beetles at 0.1 and 1.0 kGy in N2 achieved 47.4 and 73.7% mortality, respectively. All insects were killed at 10 kGy whether irradiated in air or in N2.

Microwave irradiation

Vase life of Geraldton wax cv. 'Alba' flowers was reduced by 81% on exposure to 10 kJ microwave energy (Fig. 3(a) ). There was no vase life after a 68 kJ dose. Similar losses of vase life were recorded for foliage as for flowers. Mortality of insects was only slightly increased by 10 kJ microwave dose, and was only 9.7% after exposure to 68 kJ microwave energy (Fig. 3 (b) ).

D I S C U S S I O N

Geraldton wax flowers were more sensitive to damage by gamma irradiation than banksia flowers and foliage (Fig. 1 (a) ) . Geraldton wax and banksia foliage were about equally sensitive to gamma irradiation (Fig. 1 (a) ) . Kan-

G A M M A l R R A D I A T I O N F O R INSECT DEINFESTATION 3 5 3

garoo ipaw was most tolerant of gamma irradiation, being unaffected by a 1 kGy dose. In contrast with the flowering shoots, the bioassay insects were relatively insensitive to gamma irradiation. Only 19-27% were killed by a 2 kGy dose. A dose of l0 kGy was required for 100% kill in 1 day (Fig. 3(c) ). Ten kGy is 200 times greater than the dose above which reduction occurred in the vase life of Geraldton wax. Huqhe ( 1963 ) reported that 2.5 kGy was required to kill Rhizopertha dominica instantly. For a lesser dose of 1.0 kGy it took 12-30 days to kill Sitophilus oryzae L. and Tribolium castaneum (Viado and Manoto, 1963; O'Brien and Wolfe, 1964). For gamma irradiation to be considered a practical quarantine treatment for cut flowers, insects must be killed within 1-3 days at most. The present study shows that for a range of insect types and stages this short time frame necessitates doses in the order of 2-10 kGy. Such high doses damage Geraldton wax, banksia, and, to a lesser extent,, kangaroo paw.

Gamma irradiation doses of 0.02-0.08 kGy are required to sterilize insects (Thomou, 1963; Anwar et al., 1975; Fisher, 1981 ). In the present experiments there was up to 63% and 20% loss of vase life of Geraldton wax and banksia, respectively, at a dose of 0.1 kGy. However, there was no loss of vase life of kangaroo paw at 0.1 kGy. Thus, in the longer term, and assuming even- tual acceptance by importing countries, sterilization of insects may be a practical insect deinfestation measure for kangaroo paw.

Pretreatments of low temperature 'storage' (2 ° C ) or sucrose or STS pulsing prolonged the vase life of Geraldton wax. However, the positive effects of pretreatment did not fully overcome the deleterious effects of irradiation (Table 1 ). There was no beneficial effect of purging flowering Geraldton wax shoots in an inert (N2) atmosphere for 12 h. N2 was injurious, presumably because of anaerobis.

Pretreatment effects suggest, however, that irradiation damage to Gerald- ton wax flowers and/or foliage is less under conditions of: ( 1 ) low metabolic rates (beneficial effect of cold conditions); (2) abundant soluble carbohy- drate (beneficial effect of sugar pulse); (3) ethylene 'inactivation' (beneficial effect of silver thiosulphate pulse). Conversely, more damage occurred where very low oxygen presumably resulted in reduced ability of cells to re- pair irradiation damage (detrimental effect of N2 atmospheres). The detrimental effect of irradiation under N2 overrode the potentially beneficial effect of low oxygen in reducing sites for free radical formation (Dharkar et al., 1966).

Microwave irradiation was damaging to Geraldton wax and had no appre- ciable effect on insect mortality (Fig. 4). General interest exists within the Australian cut flower export industry for deinfestation by irradiation. Irradia- tion, particularly electron beam, is seen as a potentially quick, effective, and clean method of killing insects. The present study shows, however, that irradiation is not practical for the three major native Australian cut flower export


lines, Geraldton wax, banksia, and kangaroo paw. While pretreatments for Geraldton wax, such as sugar pulsing, partially ameliorate the deleterious effects of a 0.1 kGy dose, such a low exposure is not sufficient to kill insects.

ACKNOWLEDGMENTS

This project was funded by an Innovative Agricultural Marketing Pro- gramme grant from Austrade. Appreciation is expressed to K.T. Fisher for access to the gamma irradiation cell, T.J. Enright for technical assistance, and to W.M. Woods and R.N. Emery for provision of the insects. Australian Flower Exports provided the flowers.

REFERENCES

Abbott, W.S., 1925. A method of computing the effectiveness of an insecticide. J. Econ. Ento- tool., 18: 265-267.

Acock, B. and Nichols, R., 1979. Effect of sucrose on water relations of cut, senescing, carnation flowers. Ann. Bot., 44: 221-230.

Akamine, E.K. and Goo, T.S., 1977. Effects of gamma irradiation on shelf life extension of flesh papayas (Carica papaya L. var. Solo). Res. Bull. 165. Hawaii Agric. Exp. Station, Univ. Hawaii, 23 pp.

Anwar, M., Chatha, N., Ohinata, K. and Harris, E.J., 1975. Gamma irradiation of melon fly: laboratory studies of the sexual competitiveness of flies treated as pupae 2 days before celo- sion or as 2-day-old adults. J. Econ. Entomol., 68: 733-735.

Burditt, A.K. and Hungate, F.P., 1988. Gamma irradiation as a quarantine treatment for cherries infested by Western cherry fruit fly (Diptera:tephrifidae). J. Econ. Entomol., 81: 859- 862.

Dharker, S.D., Savagaon, A.N., Srirangarajan, A.N. and Sreenivasan, A., 1966. Irradiation of mangoes: I. Radiation induced delay in ripening of Alphonso mangos. J. Food Sei., 31: 863- 869.

Fisher, K.T., 1981. Fruit fly under attack from the sterile-insect-technique. J. Agric. West. Aust., 22: 51-52.

Haasbroek, F.J., Rousseau, G.G. and de Villiers, J.F., 1973. Effect of gamma-rays on cut blooms of Protea compacta R.Br., P. longiflora Lamarck and Leucospernum cordifolium Salisb. Ex Knight. Agroplantae, 5: 33-42.

Hayes, C., 1983. Disinfestation with microwaves. Proc. 19th Annual Hawaii Papaya Ind. Ass. Conf., 30 September-1 October, 1983, Kauai, HI, pp. 28-30.

Hayes, C.F., Chingon, H.T.G., Nitta, F.A. and Wang, W.J., 1984. Temperature control as an alternative to ethylene dibromide fumigation for the control of fruit flies (Dip- tera:Tephritidae) in papaya. J. Econ. Entomol., 77: 683-686.

Huque, H., 1963. Preliminary studies on irradiation of some common stored - - grain insects in Pakistan. In: Radiation and Radioisotopes Applied to Insects of Agricultural Importance. Proc. IAEA and FAO Syrup., 22-26 April 1963, Athens, Greece, pp. 455-463.

Jessup, A.J. 1990. Gamma irradiation as a quarantine treatment for sweet cherries against Queensland fruit fly. HortScience, 25 (4): 456-458.

Joyce, D.C., 1988. Postharvest characteristics of Geraldton wax flowers. J. Am. Soc. Hort. Sci- ence, 13(5): 738-742.

GAMMA IRRADIATION FOR INSECT DEINFESTATION 3 5 5

Laviolette, P. and Nardon, P., 1963. Influence of irradiation on the adults ofSitophilus sasakii takahashi (Curculionidae) and their offspring. In: Radiation and Radioisotopes Applied to Insects of Agricultural Importance. Proc. of IAEA and FAO Symp., 22-26 April 1963, Ath- ens, Greece, pp. 431-441.

Leopold, A.C., 1964. Radiation. In: Plant Growth and Development. McGraw-Hill, NY, pp. 353-368.

Maxie, E.C., Sommer, N.F. and Mitchell, F.G., 1971. Chemical, economic physical and phys- iological limitations to irradiation of fruits. In: Disinfestation of Fruit by Irradiation. Proc. of Panel on the Use of Irradiation in the International Fruit Trade, 7-11 December 1970, IAEA Vienna, pp. 93-100.

Maughan, J., 1986. Postharvest treatment ofprotea cut flowers to eradicate arthropods. Protea National, June 1986, pp. 13-17.

Mtiller, A. and Zimmer, K.G., 1961. Studies on radiation-produced free radicals in biological systems. In: M.S. Blois et al. (Editors), Free Radicals in Biological Systems. Academic Press, New York, pp. 325-335.

O'Brien, R.D. and Wolfe, L.S., 1964. Radiation, radioactivity and insects. American Inst. Biol. Sciences and US Atomic Energy Commission. Monograph Series on Radiation Biology. Ac- ademic Press, 211 pp.

Parups, E. and Chan, A., 1973. Extension of vase life of cut flowers by use of isoascorbate containing preservative solution. J. Am. Soc. Hort. Sci., 98: 22-26.

Paulin A., 1985. Influence of exogenous sugars on the evolution of some senescence parameters of petals. Acta Hort., 181: 183-193.

Reid, M.S., Paul, J.L., Farhoomand, M.B., Kofranek, A.M. and Staby, G.L., 1980. Pulse treat- merits with silver thiosulphate complex extend the vase life of cut carnations. J. Am. Soc. HoiSt. Sci., 105: 25-27.

Seaton, K.A. and Joyce, D.C., 1990. Report on marketing, quarantine and postharvest handling of Australian cut flower exports to Japan, 1989. J. Int. Protea Assoc., 20: 45-64.

Seaton, K.A., Joyce, D.C. and Enright T.J., 1989. Quarantine insect disinfestation of cut flowers: a short review. In: The Production and Marketing of Australian Flora., Proc. Symp., 13- 14 J uly 1989, The University of Western Australia.

Spalding, D.H. and von Windeguth, D.L., 1988. Quality and decay of irradiated mangos. HoitScience, 23:187-189.

Thomou, H., 1963. Sterilization ofDacus oleae Gmel. by gamma irradiation. In: Radiation and Radioisotopes Applied to Insects of Agricultural Importance. Proc. IAEA and FAO Symp., 22-26 April 1963, Athens, Greece, pp. 413-424.

Viado, G.B. and Manoto, E.C., 1963. Effect of gamma irradiation on three species of Philippine insect pests. In: Radiation and Radioisotopes Applied to Insects of Agricultural Importance. Pro z. IAEA and FAO Symp., 22-26 April 1963, Athens, Greece, pp. 443-453.

Wit, AK.H. and van de Vrie, M., 1985. Gamma irradiation for postharvest control of insects and mites in cut flowers. Med. Fac. Landbouww. Rijksuniv. Gent., 50/2b, pp. 697-704.

gamma irradiation for insect deinfestation damages native australian cut flowers

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