Postharvest diseases of avocados
Avocados (Persea americana) are affected by a number of plant pathogens in New Zealand, which exhibit symptoms either preharvest or postharvest. This review will consider postharvest pathogens only. The most prevalent fungi responsible for postharvest diseases are Colletotrichum acutatum, C. gloeosporioides, Botryosphaeria parva, Botryosphaeria dothidea and Phomopsis (Hartill 1991). Apart from Phomopsis, which is almost exclusively isolated from stem end rots, these fungi can cause both stem end rots and anthracnoses on ‘Hass’ avocados in New Zealand conditions. Botryosphaeria spp. are generally isolated in greater numbers from rots of avocados than are any of the other fungi.
Postharvest rots of ‘Hass’ avocados remain the most important problem of this crop. Ledger et al. (1993) found 23% of apparently healthy New Zealand ‘Hass’ avocados in the Sydney marketplace were affected with stem end rots, and 28% with anthracnoses. Altogether, over 40% of fruit were affected by rots. Under carefully controlled experimental conditions in New Zealand, despite the use of optimised postharvest storage regimes c.20% of ‘Hass’ fruit were affected by postharvest rots (Hopkirk et al. 1994).
In order to minimise postharvest diseases of avocados an integrated suite of strategies needs to be implemented, ie integrated disease management. Both preharvest and postharvest protocols and procedures are important in the ultimate control of plant pathogens responsible for postharvest diseases. A basic understanding of the infection processes and the periods of highest risk for infection to take place are required, in order to more effectively target pesticide applications. This will reduce costs for the grower, reduce the possibility of resistance developing in the target organisms, and will decrease residues on the surface of fruit and thus sustain market access. Preharvest and postharvest handling should be optimised to provide as little opportunity as possible for the pathogens to infect, to establish and to ultimately invade the avocado fruit. Temperature storage and ripening strategies need to be optimised for New Zealand conditions, and with future markets in mind. Therefore storage and shipment for 3-4 weeks also needs to be investigated, to prepare our industry for the future.
Caused by Glomerella cingulata, of which the conidial state is Colletotrichum gloeosporioides, is found in the USA, Israel (Prusky et al. 1983), Argentina (Oste & Ramallo 1974), Australia (Peterson & Inch 1980), New Zealand (Hartill 1991), India, South Africa (Rowell 1983) and Puerto Rico (Nolla 1926). Infection studies overseas have identified Colletotrichum gloeosporioides as a weak pathogen. Infection is enhanced by wounding, both artificially and by the fruit-spotting bug (Fitzell 1987), Cercospora spot or scab lesions (Nagy & Shaw 1980). On the tree during the season, spores of this fungus have been shown to germinate, form an appressoria and a short infection peg which penetrates c. 1.5 um into the skin (Coates et al. 1993). The fungus then remains quiescent until harvest, when antifungal dienes in the skin of avocado fruit break down due to degradation by lipoxygenase activity (Karni 1989; Prusky et al. 1988), the fungus resumes growth and invades the avocado fruit to cause postharvest rots (Prusky et al. 1988; Prusky et al 1990; Adikaram et al 1992; Neeman et al 1970; Prusky et al 1983; Prusky et al 1982; Prusky et al 1991; Sivanathan & Adikaram 1989; Prusky et al 1984). Breakdown of the antifungal dienes has been able to be delayed by CO2 (Prusky et al. 1991), hypobaric pressure (Prusky et al 1984) and by treatment with antioxidants (Prusky et al. 1995). These methods can be used as a control mechanism for anthracnoses. However, experiments have concentrated exclusively on ‘Fuerte’ avocados. ‘Hass’ avocados may have a different antifungal compound present in the skin, as these experiments were not able to be repeated in New Zealand conditions (White & Forbes 1994).
Caused by Pseudocercospora purpurea causes spots on fruit, which at first form small greenish-white dots that expand into slightly sunken irregular brown blotches. Mature lesions are rarely larger than 0.5 cm, but the cracks and lesions formed provide entry for other fungi, particularly anthracnose fungi (Snowden 1990). This disease is found in Brazil (Albuquerque 1962), South Africa (Darvas 1982), Cameroon (Gaillard 1971), Japan (Hino and Tokeshi 1976) Mexico (Fucikovsky & Luna 1987) and USA (Nagy & Shaw 1980). Up to 69% preharvest fruit loss on some orchards in South Africa have been attributed to infection with this fungus (Darvas & Kotze 1987).
Is caused by Botryosphaeria ribis, of which the conidial state is Dothiorella gregaria in Israel, South Africa (Labuschagne & Rowell 1983), the USA (Stevens & Piper 1941), and parts of South America (Pinto et al. 1986; Zentmyer 1961). In New Zealand this disease is caused by Botryosphaeria parva (Hartill et al. 1986) or Botryosphaeria dothidea (Hartill 1991) and in Australia by Dothiorella aromatica (Muirhead et al. 1982). This disease can invade avocados through the body of the fruit or through the cut stem end (Snowden 1990). Symptoms usually only appear as fruit begin to soften after harvest, although this fungus has been isolated from lesions on hard unripe Californian avocados (Snowden 1990).
Are generally caused by Botryodiplodia theobromae in Australia (Peterson 1978), South Africa (Darvas et al 1987), the Ivory Coast (Frossard 1964) and the USA (Stevens & Piper 1941). Dothiorella spp., Phomopsis perseae (Peterson 1978) and Thyronectria pseudotrichia (Darvas et al. 1987) have also been implicated in stem end rots. Dothiorella spp. and Phomopsis spp. can cause latent infection in developing fruit (Peterson 1978). However, Botryodiplodia is a wound parasite, and most infections with this fungus probably take place at harvest. In New Zealand, Botryosphaeria dothidea, B. parva, Colletotrichum gloeosporioides, C. acutatum and Phompsis spp. have all been associated with stem end rots (Hartill 1991).
Caused by Spaceloma perseae, affects young developing fruit. Raised corky brown spots are produced on the skin which mar the cosmetic appearance of the fruit. Wound pathogens can gain entry to the fruit through lesions caused by this fungus (Ramallo 1969). Scab occurs in North, Central and South America, in the West Indies (Jenkins 1934), in New Zealand (Hartill 1991), and in South Africa and the Philipines (Snowden 1990).
Can cause postharvest diseases of avocado worldwide, but are rare in occurrence and are not perceived to be important. Amongst these are Alternaria sp. in Israel (Zauberman et al 1975), Penicillium expansum in the USA and the West Indies (Horne 1934; Wardlaw 1934), Fusarium spp. in Israel (Zauberman & Schiffmann-Nadel 1979), South Africa (Darvas & Kotze 1987), the USA (Horne 1934) and the West Indies (Wardlaw 1934), Pestalotiopsis versicolor in South Africa (Darvas & Kotze 1987), Phytophthora citricola which attacks fruit near the ground in Mexico (Fucikovsky & Luna 1987) and the USA (Koike et al. 1987), Trichothecium roseum in the USA (Horne 1934), and Rhizopus stolonifer in South Africa, the USA and Israel (Darvas & Kotze 1987; Zentmyer et al. 1965). In New Zealand species of Fusarium have also been isolated from anthracnoses (Hartill 1991).
In New Zealand Colletotrichum acutatum has been isolated from both stem end rots and anthracnoses of ‘Hass’ avocados (Hartill 1991). Some years, and on some orchards, anthracnoses are almost exclusively caused by this fungus (unpublished data). C. acutatum has not been reported from overseas, except for one record in Australia (Simmonds 1966). Therefore, information on the infection processes and epidemiology of this fungus cannot be obtained elsewhere. Studies of infection processes and epidemiology to date have targetted C. acutatum in New Zealand.
In New Zealand, the current state of knowledge suggests that Colletotrichum acutatum spores released from infected dead twigs and fruit in the canopy, or possibly on the orchard floor, infect avocado fruit while hanging in the tree preharvest. Most infections are probably initiated from within the avocado tree, the influence of shelter belt infections does not seem to be important (Everett 1994). Timing of infection appears to be random throughout the year. Preliminary results tend to suggest that C. acutatum may be a wound pathogen, as only a few fruit became infected when unwounded fruit were artificially inoculated throughout the season in the orchard (Everett & Hallett 1994). When unwounded fruit were artificially inoculated immediately before, at, and after harvest, most fruit became infected at harvest (Everett & Hallett 1996). This was both through the side of the fruit and through the stem end. Therefore there must be some factor occurring at harvest that encourages infection. Damage caused by grading equipment was insufficient to aid infection (Everett & Hallett 1996). These results suggest that further research is required to investigate the amount of air-borne inoculum present in the packhouses during packing, in picking bags and picking bins, and for options for removing inoculum from all these sources to be investigated.
Epidemiology
Overseas, epidemiological studies have been limited to just one study (Fitzell 1987) in which it was shown that spores of Colletotrichum gloeosporioides were released from dead leaves entangled in the main canopy. The principle means of spread to avocado fruit was by rain-borne inoculum.
Knowledge of the effects of climate on infection periods preharvest is important for ultimate control of postharvest diseases. This avenue of research is essential to reduce the amount of preharvest sprays that need to be sprayed in the orchard. At the moment, our studies on C. acutatum have failed to identify an infection period. We are hoping that future studies of spore release in the orchard may provide more detailed information that should help further elucidate infective periods in the orchard, and thus allow more effective targetting of spray applications.
Preharvest sprays with copper have been shown to reduce postharvest diseases significantly (Hartill et al. 1990a). However, four sprays during the season were insufficient to reduce postharvest rots, twelve sprays were required before significant differences were obtained. In New Zealand, Benlate is also recommended as a preharvest treatment (AEC 1994), and has also been shown to reduce disease significantly when three sprays were applied during the season (Hartill et al. 1990b). Postharvest dipping with SportakR appears to be, at the current level of knowledge, unreliable. It appears that there may be a curing effect, or alternatively an infection period immediately after harvest that is not halted by a delayed application of prochloraz. Hartill (1988) found no difference in rots if prochloraz was applied within 24 hours of picking. However, recent results (unpublished) suggest that coolstorage for 24 hours before application of prochloraz may reduce the effectiveness of this fungicide. Current practices of harvesting and coolstoring may indeed result in avocado fruit being coolstored for up to three days before prochloraz is applied. It is important to investigate the effect of timing of application of prochloraz on its effectiveness, in combination with coolstorage. The results also suggest that postharvest pathogens of avocados should be tested for fungicide resistance, although resistance is unlikely to have developed as prochloraz is applied postharvest, and fruit exported. Therefore a resistant population of fungi is more likely to be present in Australia than in New Zealand.
Experimental results obtained in South Africa (Everett & Korsten 1996) have demonstrated the effectiveness of applying prochloraz either in wax or as an ultra low volume spray. Calculation of the residues of prochloraz on individual avocado fruit when applied at the rates used in South Africa showed that residues were just less than the maximum allowable for New Zealand export markets. Wax by itself also seemed to reduce levels of stem end rots. Other results obtained in South Africa demonstrated clearly that waxing increases the incidence of all postharvest diseases on ‘Fuerte’ avocados (Darvas et al. 1990). In the results of the experiment undertaken in South Africa (Everett & Korsten 1996), waxing increased the incidence of DCC. Waxes probably increase the humidity next to the skin of avocados, and may also increase the concentration of ethylene. Both these factors promote the germination and growth of anthracnose fungi (Darvas et al.1990; Flaishman et al. 1995). However, wax extended the shelf life of avocados when applied to ‘Fuerte’ avocados in South Africa (Darvas et al. 1990), therefore ethylene, which promotes ripening, is more likely to be inhibited by the wax coating. The same workers showed a correlation between shelf life and disease severity, thus extending the shelf life by applying wax has the effect of increasing disease (Darvas et al. 1990). The combination of these factors compound to result in an increase in postharvest diseases of waxed fruit, but it was shown that this effect could be negated by application of chemicals to the wax. The South Africans obviously consider the benefits of improved cosmetic appearance and extended shelf life outweigh the risk of increased disease as they continue to wax their fruit, despite postharvest chemical treatment no longer being acceptable in export marketplaces in Europe.
Chemicals are becoming increasingly less acceptable in the marketplace. Furthermore, fruit treated with prochloraz, the only chemical available for use as a postharvest dip, cannot be exported to Asia, the USA and countries in Europe (AEC 1994). Therefore, refinement of application technology is a short-term solution to postharvest disease problems of avocados. It is highly probable that within 5 years prochloraz will no longer be able to be used. Therefore installation of ULV spray equipment and/or waxing equipment may not be economically viable in the long term. However, such equipment can be used for application of more environmentally friendly alternatives, such as biological control agents
Manipulation of postharvest storage regimes to decrease incidence of postharvest rots is a common strategy employed by a number of countries (Truter & Eksteen 1987; Young & Kosiyachinda 1975; Fitzell & Muirhead 1983; for example). However, the temperature regimes appear to be specific for each country, and indeed for regions within those countries (unpublished data). Therefore results of research obtained by overseas researchers should not be implemented in New Zealand without first testing under New Zealand conditions. Indeed, New Zealand ‘Hass’ avocados stored according to the most appropriate South African recommendations (‘Hass’ from KwaZulu/Natal) were affected by more rots than the standard New Zealand postharvest temperature regime, which is far from ideal (unpublished data). Hopkirk et al. (1994) have suggested a postharvest storage regime suitable for New Zealand ‘Hass’ avocados, and this regime should be adopted by the wider industry immediately. In New Zealand, CA storage of avocados has also been investigated (Hartill & Yearsley 1989). Although these fruit were stored at 12oC, not 15oC as has been recommended by Hopkirk et al. (1994), storage in 2%O2 /5% CO2 extended the effective storage of New Zealand ‘Hass’ avocados to 4 weeks in one trial, but rots were severe in an identical trial the following year. Overseas, higher concentrations of CO2 (10%) prevented development of anthracnose for 3-4 weeks in the varieties ‘Fuchs’ and ‘Waldin’ stored at 7.2oC (Spalding & Reeder 1975). For future long term storage and transport of New Zealand ‘Hass’ avocados, different storage strategies require further investigation.
Darvas et al. (1990) showed less stem end rots and more anthracnoses resulted from snap picking ‘Fuerte’ avocado fruit in South Africa. In his experiments, removing the pedicel delayed ripening, which may account for the increase in anthracnose rots. Tingwa and Young (1975) showed that removing the pedicel increased the rate of ripening in avocados in California. On ‘Hass’ fruit in New Zealand conditions, in two of three occassions more rots resulted in snap picked fruit (Hartill & Sale 1991).
Biological control of insects has attained a high degree of respectability and there are a large number of successful biological control programmes, based on release of predators, pheromones, sterile males, and application of Bacillus thuringiensis spores as a pesticide. There are also examples of biological control agents used to successfully control plant pathogens. One of the most successful is the biological control of crown gall, Agrobacterium tumefasciens, by a closely related bacterium, Agrobacterium radiobacter (Moore & Warren 1979). This biocontrol agent was isolated by an Australian researcher, Alan Kerr, and released worldwide, including New Zealand. A change in cultural practices of rose growing has reduced the importance of this biocontrol agent, but nonetheless it remains a commercial success story. Of equal success is the control of Heterobasidion annosum in British forests by spraying tree stumps with a species of Peniophora (Rishbeth 1963). This method of biological control has been used with almost 100% success for three decades. Currently there are over 40 biocontrol agents in commercial use worldwide (Appendix 1). Unfortunately some biological control agents have been marketed prematurely and have tended to reduce people’s faith in the technique. These BCAs have been insufficiently tested by independent researchers, and the idea has been sold rather than the tool. Examples of unscrupulous manipulation of new technology for commercial gain, before they have been properly tested, tends to bring the entire field into disrepute. Despite all this, I believe biological control is the next logical step in controlling plant diseases, if for no other reason than it is more consumer friendly than the use of pesticides, and therefore fruit treated with a BCA will be easier to market and sell than fruit treated with ‘nasty’ chemicals. BCAs also have the advantage that they are naturally occurring microorganisms, and their presence in a higher than natural concentration on the exterior of fruit such as avocados, in which the skin is not consumed, is unlikely to be harmful.
The avocado industry in South Africa has been committed to biological control over the past eight years, and have been trail blazing for the rest of the world (Korsten 1995). The best way to use BCAs, especially in the South African example, is as a preharvest spray. This precludes the necessity for postharvest treatments of the fruit. The South Africans aim to have a commercial product registered for use by the end of 1996.
Coates et al. (1995) also isolated antibiotic producing BCAs for testing. The avocado industry (Rod Dalton, pers. comm.) ceased funding this programme because Coates et al. (1995) failed to demonstrate postharvest efficacy when the BCA was applied as a dip. In contrast, work in New Zealand (Everett 1996) has demonstrated that two BCAs tested as postharvest dips significantly reduced anthracnose.
In order to reduce postharvest rots of avocados to manageable levels to improve the quality of New Zealand avocados to become the "world’s finest", immediate, short term and long term strategies need to be put in place.
Of immediate benefit is implementation of knowledge already gained. To this end, rationalisation of the harvest by forming co-operatives to ensure New Zealand avocados are picked and packed in as short a time as possible is an imperative requirement. Overseas this has proved a successful strategy for overcoming the problems associated with a large number of small growers (Free, 1995). Perhaps the use of smaller packhouses, specifically designed for avocados would be of benefit. At the moment some grower groups appear to be more successful at managing harvesting, packing and the cold chain than others. Wide application of successful management strategies would benefit even those grower groups currently ahead of the rest, by creating demand for a superior product consistently obtainable from New Zealand.
Refining prochloraz application technology is short term in benefit only. Increasing consumer resistance to the use of postharvest chemicals will ultimately require prochloraz applications to cease.
Of longer term benefit is the investigation of biological control as an alternative control strategy. The advantage of this technology is that it can be used preharvest, to counter any attempts by our markets to restrict postharvest treatments completely, as is currently the situation with export kiwifruit.
Continued investigation of the plant pathogens is also required for a successful long term control strategy. Knowledge of the periods when avocado fruit are most at risk of infection is also essential for long term effective control strategies to be implemented. Increased sanitation in the packhouse may be found to be necessary in the future. Development of prediction models in the orchard for calculation of periods of infection risk will also be an invaluable tool in the future, to enable growers to more effectively target spray applications and thus reduce costs, and reduce the risk of resistance to chemicals, especially benlate, to develop in the populations of target organisms.
Adikaram, N.K.B., Ewing, D.F., Karunaratne, A.M. and Wijeratne, E.M.K. (1992). Antifungal compounds from immature avocado fruit peel. Phytochemistry 31: 93-96.
AEC (1994). Quality Manual for the 1993/94 Season.
Albuquerque, F.C. (1962). Mancha parda do abacate. Revista de la Sociedad de Agronomia e Veterinaria de Para (Brazil) 8: 35-41.
Coates, L.M., Muirhead, I.F., Irwin, J.A.G. and Gowanlock, D.H. (1993). Initial infection processes by Colletotrichum gloeosporioides on avocado fruit. Mycol. Res. 97: 1363-1370.
Coates, L.M., Stirling, M., Pegg, K., Hayward, C., Cannon, K., Cooke, T., and Dean, J. (1995). Biological control of anthracnose in avocado. Final Report Project Number: AV207. Queensland Dept. of Primary Industries.
Darvas, J.M. (1982). Chemical control of Cercospora spot disease of avocados. South African Avocado Grower’s Association Yearbook 5: 58-59.
Darvas, J.M. and Kotze, J.M. (1987). Avocado fruit diseases and their control in South Africa. South African Avcoado Grower’s Association Yearbook 10: 117-119.
Darvas, J.M., Kotze, J.M. and Wehner, F.C. (1990). Effect of treatment after picking on the incidence of postharvest fruit disease of avocado. Phytophylactica 22:93-96.
Darvas, J.M., Kotze, J.M. and Wehner, F.C. (1987). Pathogenicity of fungi causing pre- and postharvest diseases of avocado fruit. Phytophylactica 19: 489-493.
Everett, K.R. (1994). Isolation and testing of fungi from three shelter belt species (Casuarina cunninghamiana, Cryptomeria japonica and Salix sp.) adjacent to two avocado orchards. HortResearch Client Report No. 94/123.
Everett, K.R. (1996). Testing potential biological control agents using an intact fruit test and a postharvest dip. HortResearch Client Report No. 96/129.
Everett, K.R. and Hallett, I.C. (1994). Infection of `Hass' avocado fruit by Colletotrichum acutatum. p. 82 in NZ Society for Microbiology and NZ Society for Biochemistry and Molecular Biology Joint Annual Conference, 9-12 May, Conference paper and poster abstracts
Everett, K.R. and Hallett, I.C. (1996). Infection of avocados by Colletotrichum acutatum. NZSHS/NZIAS Convention, Ruakura, August 26th-29th. in press.
Everett, K.R. and Korsten, L. (1996). Postharvest rots of avocados: improved chemical control by using different application methods. pp. 37-40 in: Proceedings of the 49th New Zealand Plant Protection Conference.
Fitzell, R.D. (1987). Epidemiology of anthracnose disease of avocados. South African Avcoado Grower’s Association Yearbook 10: 113-116.
Fitzell, R.D. and Muirhead, I.F. (1983). Reducing post-harvest disease in Fuerte avocados by temperature management. Aust. J. Exp. Agric. Anim. Husb. 23: 331-336.
Flaishman, M.A., Hwang, C.S. and Kolattukudy, P.E. (1995). Involvement of protein phosphorylation in the induction of appressorium formation in Colletotrichum gloeosporioides by its host surface wax and ethylene. Physiol. Mol. Plant Pathol. 47: 103-107.
Free, V.V. (1995). Cooperatives as a focal point for post-harvest handling and marketing. Proceedings of the International conference on Harvest and postharvest technologies for fresh fruits and vegetables. 20-24 February, 1995, Guanajuato, Mexico.
Frossard, P. (1964). La pourriture pedonculaire des avocats en Cote d’Ivoire. Influence de la temperature sur le devleoppement de Diplodia natalensis. Fruits 19: 401-403.
Fucikovsky, L. and Luna, I. (1987). Avocado fruit diseases and their control in Mexico. South African Avocado Growers Association Yearbook 10: 119-120.
Gaillard, J.P. (1971). Lutte contre le Cercospora de l’avocatier au Careroun. Fruits 26: 225-230.
Hartill, W.F.T. (1991). Post-harvest diseases of avocado fruit in New Zealand. New Zealand Journal of Crop and Horticultural Science 19: 297-304.
Hartill, W.F.T. and Sale, P.R. (1991). Report to the avocado growers research committee on a comparison of the incidence of post-harvest rots in plucked and clipped fruits. 5pp.
Hartill, W.F.T., Manning, M.A. and Allen, D.J. (1986). Control of postharvest diseases of avocado. Proceedings of the 39th New Zealand Weed and Pest control Conference, pp. 158-161.
Hartill, W.F.T., Fowler, M., Sale, P.R. and Sawden, D. (1990a). Report to the avocado growers research committee on the effects of copper sprays and dead wood removal on the incidence of post-harvest rots. 10pp.
Hartill, W.F.T., Sale, P.R. and Sawden, D. (1990b). Report to the avocado growers research committe on the use of benlate orchard sprays to control post-harvest rots of avocado. 6pp.
Hino, T. and Tokeshi, H. (1976). Varietal ressitance of avocado to cercosporioisis and some observations on the disease cycle. Summa Phytopathologica 2: 127-132.
Hopkirk, G., White, A., Beever, D.J. and Forbes, S.K. (1994). Influence of postharvest temperatures and the rate of fruit ripening on internal postharvest rots and disorders of New Zealand ‘Hass’ avocado fruit. New Zealand Journal of Crop and Horticultural Science 22: 305-311.
Horne, W.T. (1934). Avocado diseases in California. Bulletin of California Agricultural Experiment Station No. 585: 72pp.
Karni, L., Prusky,D., Kobiler, I., Bar-Shira,E. and Kobiler,D. (1989). Involvement of epicatechin in the regulation of lipoxygenase activity during activation of quiescent Colletotrichum gloeosporioides infections of ripening avocado fruits. Physiological and Molecular Plant Pathology 35, 367-374.
Koike, S.T., Ouimette, D.G. and Coffey, M.D. (1987). First report of avocado fruit rot caused by Phytophthora citricola. Plant Disease 71: 1045.
Korsten, L. (1995). Status of research on biological control of avocado pre- and post-harvest diseases: an overview. South African Avocado Growers’ Association Yearbook 18: 114-117.
Jenkins, A.E. (1934). Sphaceloma perseae the cause of avocado scab. Journal of Agricultural Research 49: 859-869.
Labuschagne, N. and Rowell, A.W.G. (1983). Chemical control of post-harvest diseases of avocado by pre-harvest fungicide application. South African Avocado Growers’ Association Yearbook 6: 46-47.
Ledger, S.N., Campbell, T.P., Banks, A.G., Atkinson, I., Kernot, I.I. and Fullelove, G.D. (1993). Internal quality of avocados in retail shops. Queensland Department of Primary Industries Report, 27pp.
Moore, L.W. and Warren, G. (1979). Agrobacterium radiobacter strain 84 and biological control of crown gall. Annual Review of Phytopathology 17: 163-179.
Muirhead, I.F., Fitzell, R.D., Davis, R.D. and Peterson, R.A. (1982). Post-harvest control of anthracnose and stem-end rots of Fuerte avocado with prochloraz and other fungicides. Australian Journal of Experimental and Animal Husbandry 22: 441-446.
Nagy, S. and Shaw, P.E. (1980). p. 127 in Tropical and Subtropical Fruits. Composition, Properties and uses. AVI Publishing, Westport, Connecticut. 570pp.
Neeman, I., Lifshitz, A. and Kashman, Y. (1970). New antibacterial agent isolated from the avocado pear. Applied Microbiology 19: 470-473.
Nolla, J.A.B. (1926). The anthracnoses of citrus fruits, mango and avocado. Journal of the Dept. of Agriculture of Porto Rico 10: 25-50.
Oste, C. A. and Ramallo, N.E.V. de (1974). Podredumbre apical de la palta producida por Colletotrichum gloeosporioides Penz. Revista industrial y Agricola de Tucuman 51: 37-40.
Peterson, R.A. (1978). Susceptibility of Fuerte avocado fruit at various stages of growth to infection by anthracnose and stem-end rot fungi. Australian Journal of Experimental and Animal Husbandry 18: 158-160.
Peterson, R.A. and Inch, A.J. (1980). Control of anthracnose on avocados in Queensland. Queensland Journal of Agricultural and Animal Sciences 37: 79-83.
Pinto, de T.A., Alvarez, A.M. and Tobar, C.G. (1986). Pudricion de frutos y cancros en ramas de palto, causados por Dothiorella sp. en la V Region de Chile. Agricultura Tecnica 46: 499-501.
Prusky, D., Keen, N.T., Sims, J.J. and Midland, S.L. (1982). Possible Involvement of an Antifungal Diene in the Latency of Colletotrichum gloeosporioides on Unripe Avocados. Phytopathology 72, 1578-1582
Prusky, D., Keen, N.T. and Eaks,I. (1983). Further evidence for the involvement of a preformed antifungal compound in the latency of Colletotrichum gloeosporioides on unripe avocado fruits. Physiological Plant Pathology 22, 189-198.
Prusky, D., Ascarelli, A. and Jacoby, B. (1984). Lack of Involvement of Nutrients in the Latency of Colletotrichum gloeosporioides in Unripe Avocado Fruits. Phytopathology 110, 106-109.
Prusky, D., Kobiler, I. and Jacoby, B. (1988). Involvement of Epicatechin in Cultivar Susceptibility of Avocado Fruits to Colletotrichum gloeosporioides after Harvest. Journal of Phytopathology 123, 140-146.
Prusky, D., Karni, L. Kobiler, I. and Plumbley, R.A. (1990). Induction of the preformed antifungal diene in unripe avocado fruits: effect of challenge inoculation by Colletotrichum gloeosporioides. Physiological and Molecular Plant Pathology 37: 425-435.
Prusky, D., Plumbly, R.A. and Koblier, I. (1991). Modulation of natural resistance of avocado fruits to Colletotrichum gloeosporioides by CO2 treatment. Physiological and Molecular Plant Pathology 39, 325-334.
Prusky, D., Ohr, H.D., Grech, N., Campbell, S., Kobiler, I., Zauberman, G. and Fuchs, Y. (1995). Evaluation of antioxidant butylated hydroxyanisole and fungicide prochloraz for control of post-harvest anthracnose of avocado fruit during storage. Plant Disease 79: 797-800
Ramallo, N.E.V. de (1969). Sarna o verrugosis del palto en Tucuman. Revista industrial y Agricola de Tucuman 46: 27-30.
Rishbeth, J. (1963). Stump protection against Fomes annosus. III. Inoculation with Peniophora gigantea. Annals of Applied Biology 52: 63-77.
Rowell, A.W.G. (1983). Post-harvest disease control in avocados usign prochloraz. South African Avocado Growers’ Association Yearbook 6: 19.
Simmonds, J.H. (1966). Host index of plant diseases in Queensland. Queensland Dept. of Primary Industries.111 pp.
Sivanathan, S. and Adikaram, N.K.B. (1989). Biological activity of four antifungal compounds in immature avocado. J. Phytopath. 125: 97-109.
Snowden, A.L. (1990). A Colour Atlas of Post-Harvest Diseases and Disorders of Fruits and Vegetables. Vol. 1: General Introduction and Fruits. Wolfe Scientific. 302pp.
Stevens, H.E. and Piper, R.B. (1941). Avocado diseases in Florida. Circular of the United States Department of Agriculture No. 582: 46pp.
Tingwa, P.O. and Young, R.E. (1975). Studies on the inhibition of ripening in attached avocado (Persea americana Mill.) fruits. American Society of Science Journal 100: 447-449.
Towsen, E., van Wyngaardt, S., Verschoor, J.A. and Korsten, L. (1995). The importance of monitoring antagonists survival for efficient biocontrol. South African Avocado Growers’ Association Yearbook 18: 121-123.
Truter, A.B. and Eksteen, G.J. (1987). Controlled and modified atmospheres to extend storage life of avocados. South African Avocado Growers’ Yearbook 10: 151-153.
Wardlaw, C.W. (1934). Preliminary observations on the storage of avocado pears. Tropical Agriculture 11: 27-35.
White, A. and Forbes, S.K. (1994). Summary of postharvest avocado research undertaken by DSIR and HortResearch. HortResearch Client Report No. 94/297. 8pp.
Young, R.E. and Kosiyachina, S. (1975). Low temperature storage of ripe avocado fruit. Yearbook of the Californian Avocado Society 1975-76, pp. 73-76.
Zauberman, G. and Schiffmann-Nadel, M. (1979). Physiological response of avocado fruit to infection by different Fusarium species. Phytopath. Z. 89: 359-365.
Zauberman, G., Schiffmann-Nadel, M., Fuchs, Y. and Yanko, U. (1975). La lutte contre les pourritures de l’avocat et son effet sur le changement de la flore des chmpignons pathogenes des fruits. Fruits 30: 503-504.
Zentmeyer, G.A. (1961). Avocado diseases in the America. Ceiba 9: 61-79.
Zentmeyer, G.A., Paulus, A.O., Gustafson, C.D., Wallace, J.M. and Burns, R.M. (1965). Avocado diseases. Circular of Californian Agricultural Experiment Station No. 534: 11pp.