Stem-end rot in major tropical and sub-tropical fruit species

Stem-end rot (SER) is one of the most destructive postharvest diseases affecting some tropical and sub-tropical fruits. The disease is caused by several fungal pathogens, including Botryosphaeriaceae species. In mango, Dothiorella dominicana, D. mangiferae, Lasiodiplodia theobromae, Phomopsis mangiferae, Cytosphaera mangiferae, Pestalotiopsis sp. endophytically colonize the inflorescence in the orchard or field. Fungi may occur endophytically in the stem tissue of the trees prior to inflorescence emergence. During the endophytic stage, the fungi colonize the phloem and xylem at stem-end and, after fruit ripening, some fungi become necrotrophic and colonize the fruit pulp causing SER. The SER pathogens in other fruit species, including ripe avocado or papaya, are not known to undergo an endophytic phase. Stemend rot is a disease that is difficult to control. Preharvest cultural practices and selection of resistant varieties are beneficial to reduce field infections. Studies have shown that numerous control options, involving cultural, chemical (fungicides, essential oils) and biological approaches, are available to manage SER through either direct inhibition of fungi or induction of host defenses. These may be used individually or integrated manner. The most common and effective practice for controlling the SER is preand postharvest application of synthetic fungicides. With the new tools that are currently available, and expected to emerge, there is a possibility of a better understanding the host–pathogen or host-microbiota interactions within the stem-end region, leading to newer technologies as alternatives to toxic synthetic fungicides for the management of SER in fruits.


INTRODUCTION
Production of fruits for human consumption is an important part of the market economy, requiring many investments. Any waste in the field or fruits after harvest, due to physical damage, disease or disorders incurs monetary losses. In fact, the monetary loss due to damage or loss of fruits after harvest is greater than losses in the field because the cost of harvesting, storage and transport etc. must be added to the cost of production.
Reduction of postharvest losses increases fruit availability and represent a critical component of ensuring food security. Most tropical fruits are highly susceptible to postharvest diseases. A larger portion of the postharvest fruit loss could be accounted for disease caused by fungal pathogens. Fruit susceptibility to postharvest diseases increases during ripening due to physiological changes and senescence favoring disease development (Prusky et al., 2002). Diseases of harvested fruits and mycotoxin contamination contribute to major economic losses to grower, wholesaler, retailer and consumer. Management of postharvest diseases is needed to avoid losses and increase revenues.
Anthracnose disease, caused by Colletotrichum species, and the stem-end rots often incited by a complex of fungi are considered most common and important postharvest diseases that limit the long-term storage of fruit commodities. The stem-end rots are affecting mostly the tropical and sub-tropical fruits. Mango (Mangifera indica L.), avocado (Persea americana), papaya (Carica papaya), citrus (Citrus sinensis), mangosteen (Garcinia mangostana), rambutan (Nephelium lappaceum L.) and carambola are fruits often affected by the stem-end rot disease.
Stem-end rots have been investigated extensively for understanding the cause/s, the process or the mode of infection and for formulation of disease management strategies. In most fruit species, fungal infection takes place in the field during flowering, fruit-set or at an early stage of fruit maturity. Understanding of the field infection process of stem-end rot and perhaps the epidemiology also is essential to help predict the disease risk during the fruit season. Predicting plant disease is not only challenging but requires major research efforts. In a complex handling system, cultural practices, safer fungicides and biological antagonists are integrated to manage postharvest diseases. The greatest challenge is to substitute synthetic fungicides with safer alternatives to sell a highest quality, residue-free produce to the consumer.
The review will focus on the research findings so far accumulated on the stem-end rot disease in tropical and sub-tropical fruit species, with emphasis on mango, avocado, papaya, banana and rambutan, including disease management strategies.

SER in mango
Mango (Mangifera indica L.) belongs to the dicotyledonous family Anacardiaceae. The genus Mangifera comprises of 62 species of which 15 are edible fruits. Mango originated in the Indo-Burma region and has been cultivated for at least 4,000 years in the Indian subcontinent and was spread from India to Asia, Africa, Australia, and other parts of the world by traders and missionaries (Kwee and Chang, 1985). Currently, mango is recognized as the most important fruit crop cultivated in 90 tropical and subtropical countries of the world.
Postharvest diseases of mango reduce fruit quality and cause severe losses resulting in completely unmarketable fruits. Stem-end rot is one of the most important diseases of mango posing a major threat to the industry, causing economic losses. The disease is a serious threat to the mango industry because it is difficult to control (de Oliveira Costa et al., 2010). It is more prevalent in fruit harvested from older trees (Coates et al., 1993). In Israel, SER causes 30-40% loss of harvested mango fruit during 2014 (Diskin et al., 2017a). In Sri Lanka postharvest losses of mango exceed 30 -40% of which a larger proportion of losses is due to extensive rotting of harvested fruits. Certain mango varieties show resistance to the stem-end rot (Karunanayake et al., 2014). The importance of the different fungi in causing mango stem-end rot is influenced by prevailing climatic conditions in the location.
Lasiodiplodia theobromae, Dothiorella spp. C. gloeosporioides, Phomopsis mangiferae and Pestalotiopsis mangiferae were identified as stem-end rot (SER) pathogens in mango in Sri Lanka with two more Ascomycota species namely Xylaria sp. and Nodulisporium sp. from the cv. 'Karuthacolomban' (Figure 1) in a more recent study using ITS sequence data (Karunanayake et al., 2014;Ekanayake et al., 2019). Botryosphaeriaceae and Diaporthaceae species, have been reported as pathogens of stem-end rot disease around the world, including Botryosphaeria dothidea, Diaporthe pseudomangiferae, Neoscytalidium dimidiatum (Marques et al., 2013;Serrato-Diaz et al., 2014). Diaporthe species were consistently isolated from mangoes showing stem-end rot in Japan (Ajitomi et al., 2020). The isolates reproduced the original symptoms in healthy mango fruits after inoculation and were re-isolated from the inoculated fruits. Based on morphology and a phylogenetic analysis of rDNA-ITS, CAL, H3, EF1-α, and TUB, the isolates were classified into two Diaporthe species (Clade I and Clade II) (Ajitomi et al., 2020).

SER in avocado, papaya and rambutan
The stem-end rot is recognized as a major postharvest disease in ripe avocado (Persea americana Mill.) fruit. Unripe fruits are usually free from visible symptoms or characteristic decay lesions develop during fruit ripening. Stem-end rot in avocado (Fig, 3) is caused by several fungi including Lasiodiplodia theobromae (Madhupani and Adikaram, 2017), Pestalotiopsis sp., Phomopsis perseae and Phoma spp. (Adikaram and Karunarathne, 1998) and occasionally by Colletotrichum acutatum as reported in New Zealand (Everett et al., 2005). The disease can result in heavy postharvest losses. Different causative agents are also reported to be associated with the disease. The fungus most commonly associated with SER in `Fuerte' avocado was Thyronectria pseudotrichia whereas in the variety `Edranol', it was Dothiorella aromatica. However, D. aromatica was found as the major causative agent of avocado SER in Australia (Darvas, 1981). SER of 'Hass' avocados in New Zealand is caused by Botryosphaeria  parva and Phomopsis spp. (Hartill and Everett, 2002). However, the pathogen most predominantly found causing the disease is L. theobromae.
Stem-end rot of papaya (Carica papaya L.) was initially attributed to Ascochya sp. (Hine et al., 1965). Later certain other genera including Botryodiplodia (Hunter and Buddenhagen, 1972;Abeywickrama et al., 2012), Phomopsis and occasionally Fusarium were found in diseased fruits (Hunter and Buddenhagen 1972). A stemend disease of papaya (Carica papaya L.) was reported to be caused by Mycosphaerella sp., the perfect stage of Ascochyta caricae-papayae (Chau et al., 1979). Initial symptom was a translucent zone that appears around the peduncle which follows slight browning of the region. When the disease advances the infected tissues become black, wrinkled and dry. White mycelium forms at the stem end.
Botryodiplodia theobromae also causes stem-end rot disease in papaya. The pathogen produces a wider margin of water-soaked tissue ( Figure 4) and a rough surface caused by an irregular pattern of erumpent pycnidia (Hunter and Buddenhagen, 1972). Later, the affected portion becomes shriveled and turns dark brown. The disease is found in certain papaya varieties in Sri Lanka. Stem-end rots of papaya occur when fungi invade the severed peduncle after harvest. Spores may invade through crevices between the peduncle and the papaya flesh or invade through small wounds that occur at harvest.
Rambutan (Nephelium lappacium Linn.) is a fruit native to South East Asia. The fruits are affected by postharvest stem-end rot caused by Gliocephalotrichum microchlamydosporum. The disease is reported from countries in Asia including Philippines, Thailand and Sri Lanka (Sivakumar et al., 1997). A dark brown lesion appears in the entire fruit 4-5 days after harvest. During latter stages of the disease, a dark color hyphal mass is developed on diseased tissues. The symptoms are most often observed in the stem-end region of the fruit. The flesh becomes soft, brown and semi-liquid (Sivakumar et al., 1997). The skin is softened, wrinkled and black in color with encrusted pycnidia of the fungus. G. microchlamydosporum infections take place only when a wound is present. Harvesting fruits with the stalk and avoidance of wounds on the fruit surface during harvest or handling could prevent the disease (Sivakumar et al., 1997).
Stem-end rot in ripe banana fruits is a minor disease and has not been reported from many regions in the world. The disease was recorded in Bangladesh (Rashid et al., 1999) and Thailand (Rattanakreetakul 2013) and the causal agent was identified as Lasiodiplodia theobromae (Syn. Botryodiplodia theobromae) in both the countries (Rashid et al., 1999;Rattanakreetakul, 2013). There is not much published information available on the disease. Synthetic volatile oils, linalool and eugenol, were found to be very effective in reducing the stem-end rot development (Rattanakreetakul, 2013) than the essential oils extracted from finger root (Bosenbergia rotunda) and lemon grass (Cymbopogon nardus) (Rattanakreetakul, 2013).
A fungal rot, observed in the rhizome of banana, caused by Ceratocystis paradoxa, was also described as a stemend rot. The rot forms brown color or water-soaked patches in the rhizome. The fruit stalks decay rapidly, the tissues become soft and blackened and have a characteristic sweet smell. The pathogen spreads to the fruit where it causes uneven black discoloration of the skin. The pulp is reduced to a dark brown soft wet mass and premature ripening of fruits.

Endophytic colonization by SER pathogens
SER in mango is caused by diverse pathogenic fungi that endophytically colonize the inflorescence in the orchard or field. Dothiorella dominicana, Dothiorella mangiferae, Lasiodiplodia theobromae (Syn. Diplodia natalensis, Phomopsis mangiferae, Cytosphaera mangiferae, Pestalotiopsis sp. and Dothiorella 'long'), as well as other fungi, including Alternaria alternata, associated with the stem-end rot disease in mango, were found to occur endophytically in the stem tissue of mango trees prior to inflorescence emergence (Johnson et al., 1992). Endophytic colonization of inflorescence and pedicel tissue was found to be a primary route of infection for fruit which develops stem-end rot during ripening (Johnson et al., 2008). They enter the stem tissues through natural openings and wounds, mainly during inflorescence and flowering stages.
During the endophytic stage, the fungus colonizes the phloem and xylem of the fruit at stem-end and after fruit ripening, the fungus turns in to a necrotrophic lifestyle and starts colonizing the fruit parenchyma causing SER. Not all fungi present in the stem-end make the transition from endophytic to necrotrophic lifestyle and become pathogenic during fruit ripening. However, little is known about the fruit stem-end endophytic microbiome, which could contain new and existing biocontrol agents (Galsurker et al., 2018). At a plantation with a history of high stem-end rot levels, sequential monitoring of inflorescence tissue between flowering and harvest by plating out tissue pieces revealed that some of the pathogens, Dothiorella spp., P. mangiferae, Pestalotiopsis sp. and C. mangiferae, gradually colonised the inflorescence, reaching pedicel tissue of young fruit 8 weeks after flowering (Johnson et al., 1992).
During flowering and fruit set, colonization by A. alternata, Cladosporium cladosporioides, D. dominicana, D. mangiferae, Epicoccum purpurascens, Dothiorella sp. and Pestalotiopsis sp. is increased in Australia as the flowers undergoing senescence and young fruits are formed (Johnson et al., 1991a). Lasiodiplodia theobromae was isolated at high rates from flowers, peduncles, fruit-bearing shoots, and fruiting mother shoots in Japan (Takushi et al., 2019) In the third week after flowering, the incidence of D. dominicana and D. mangiferae with the fruit-pedicel connection tissue of mango declined in coincidence with early fruit-fall, suggesting that early infections by Dothiorella spp. may cause fruitlet abortion (Johnson et al., 1991b). After remaining low levels for the next six weeks, the incidence of Dothiorella spp. at 16 weeks after flowering, determined by isolation from fruit-pedicel connection tissue, was similar to the incidence of stemend rot, caused by Dothiorella spp., which developed in fruit harvested at that time. The results suggested that in fruit and fruit pedicel tissue, colonization might arise from Dothiorella spp. occurring endophytically in the peduncle. Using larger tissue pieces (1-2 mm thick TS or tissue 25 mm 2 x 3 mm) in isolations, endophytic colonization by Dothiorella spp. and P. mangiferae was detected in stem, inflorescence and pedicel tissues of mature fruit specimens from two different sites, one unsprayed, and the other regularly sprayed with copper. The fungi were detected more frequently in the samples from unsprayed trees (Johnson et al., 1992).
The earliest indicator of stem-end rot incidence at harvest was the infection level in peduncle tissue sampled 11 weeks after flowering (Johnson et al., 1991b). As the fruit ripens, some pathogenic fungi switch from endophytic colonization to necrotrophic stage and cause stem-end rot (Galsurker et al., 2020). Stem-end rot fungi are also found as endophytes in host tissue and can cause twig and branch dieback, cankers and fleck-spots on inflorescence and stem tissues. Hartill and Everett (2002) isolated SER pathogens from dead twigs and branches of avocado but appeared to be present as saprophytes and there was no evidence that they had killed the tissues. There are no records of B. theobromae to be an endophyte on avocado or papaya fruit.

Symptoms
The development of watery decay in ripe mangoes begins to appear around the stem-end which would rapidly expand through the pulp tissues, softening the entire upper half of the fruit (Figure 1), depending on the cultivar. The colonization extends ahead of symptoms along vascular tissue while colonization progresses into the fruit flesh and the seed coat. The symptoms produced during infection also vary with the pathogen. Fast moving dark lesions are produced by L. theobromae and Botryosphaeraceaeous fungi. Steel grey mycelium can develop over the surface on fruit affected by Neofusicoccum spp. Pycnidia may develop around the stem end particularly with infections caused by N. parvum (formerly D. dominicana) and (Johnson et al., 1991a). Symptom development is slower with Phomopsis mangiferae or Cytosphaera mangiferae and a dark lesion of more uniform radius develops at the stem end. Superficial mycelium does not usually develop (Johnson et al., 1991a). The occurrence of SER caused by P. mangiferae can be more frequent in fruit from dry areas.
In avocado also the SER symptoms develop only after harvest when the fruit starts to ripen. The earliest sign of infection is a slight shriveling around the stem button in the ripening fruit, and fungal mycelium may often be visible on the abscission scar when the button is removed. Conspicuous dark rot with a well-defined margin develops downwards from the stem-end. Rotting extends further with ripening covering most of the fruit which becomes shriveled. Affected fruit flesh becomes soft and pale in color (Figure 3), and the vascular strands running vertically turn brown to black.
Subsequently, rot develops from the stem-end of the fruit. Externally, the affected tissue becomes darkened and the area of rot has a well-defined and advancing margin. Internally, the flesh becomes darker, soften and the vascular strands may discolor in advance of the rotting flesh (Darvas, 1981).

Stem-end microbiome
Traditionally, Plant Pathologists have focused on the species of the pathogen and its function at a time. In recent times, studies have been broadened to the concept of 'microbiome', the entire community of microorganisms within a habitat and its surrounding environmental conditions. A holistic approach is endorsed to explore how microbiomes influence the ecosystem and pathosystem function and their dependence on each other because of its complex nature.
The microbiome consists of all the microorganisms (fungi, yeasts and bacteria) inhabiting the plant tissue. The advances in high-throughput sequencing of DNA have been applied to study the plant microbiome. In apples, variety and rootstock modulate the endophytic microbiome, suggesting coevolution of a specific genotype with its microbiome (Liu et al., 2018). When these methods were used to study the mango stem-end microbiome during postharvest storage and disease development, healthier stem-ends (with a lower incidence of SER) showed more diverse microbial communities (Diskin et al., 2017b). In contrast, an increase in SER incidence was correlated with a reduction in microbiome diversity and an expansion of one or several fungal pathogen families, such as Pleosporaceae and Botryosphaeriaceae. In addition, the increase in fungal abundance and SER was correlated with an increase in the chitin-degrading, Chitinophagaceae bacteria and a reduction in biocontrol agents (Diskin et al., 2017b). This implies that the stem-end microbiota is a dynamic system that can be modified to control SER-causing pathogens.
Today, the genomes of most of the hosts and SER pathogens are available, which will enable transcriptome analysis that could open new insights for better understanding the host defense response and the switching of pathogenic fungi from endophytic to pathogenic stage. This transcriptome analysis could lead to the development of new control methods.

Management of SER
SER can be controlled by good field sanitation, optimal cultural and harvesting practices coupled with prompt cold storage after harvest. In warm and humid tropics, however, the use of refrigeration is costly. Most of the commercially available synthetic fungicides are toxic and can bring about adverse effects on human health and environment. Therefore, due to consumer concerns, alternative methods aimed at preventing, suppressing, or delaying disease symptoms have been investigated (Sommers, 1985). More attention is therefore required to be focused on other control methods. In situations where the SER is a serious problem, the use of synthetic fungicides may be necessary.

Chemical control
Control of SER has been traditionally achieved using synthetic fungicides (Singh and Sharma, 2007) which can be applied preharvest or at postharvest stage. Considering the fact that most SER pathogens infect the flower first (Johnson et al., 1992;Diskin et al., 2017a) and later invade the fruit pedicel residing endophytically, targeting of the flowering stage for application of fungicides seems appropriate. Although environmentally unsound, the more common practice for controlling SER is by postharvest fungicidal treatments.
Good control of avocado stem-end rot was achieved with the fungicides that contain Ethyl hydrogen phosphonate and Copper oxychloride as active ingredients (Darvas, 1981). Preharvest spray application of copper oxychloride, combined with commercial dicarbamic fungicides, containing manganese and zinc, from flowering until harvest, controls most postharvest diseases of mango (Lonsdale and Kotze, 1993). Diskin et al. (2017) also report that, application of the chemical fungicide that contain the active ingredients fluopyram and pyrimethanil or fludioxonil and cyprodinil during flowering, significantly reduces the incidence and severity of postharvest SER and side decay in mango fruits as it reduces early colonization by pathogenic fungi.
However, Peterson et al. (1991) state that a significant reduction in SER was not achieved by preharvest fungicide treatment. Benzimidazole fungicides, are effective against SER caused by Lasiodiplodia theobromae on mango, whereas imidazoles are not (Estrada et al., 1996, Plan et al., 2002. Dipping mango fruits in warm carboxamide fungicides has been found effective (Johnson et al., 1990;Sangchote, 1991;Swart et al., 2006) or partially effective (Muirhead et al., 1982) in the past. In a comparative study, the efficacy of six commercial fungicides was assayed by artificially inoculation of mango with L. theobromae. This study showed that benzimidazoles fungicides were the most effective in inhibiting the mycelial growth of L. theobromae (Syed et al., 2014).
The use of some of the fungicides mentioned above in early literature was banned from use globally in 2001 (List of banned pesticides and pesticide watch list, 2015) or are to be banned from Europe at the end of 2021 (Shimshoni et al., 2019). Recent work suggests that azoxystrobin fungicides or electrolyzed oxidizing water instead of fungicides are effective in controlling SER of avocado (Hassan and Dann, 2019). Prochloraz fungicides are to be banned at the end of 2021 from Europe due to their unfavourable toxicological properties and Fludioxonil, a relatively safer, wide spectrum fungicide has been found to be a suitable alternative for avocado (Shimshoni et al., 2019) and as a postharvest treatment for mango.

Essential oils with fungicidal properties
Plant extracts have gained much importance in recent years as safe and effective alternatives to synthetic fungicides. Moringa oleifera, Syzygium aromaticum and Cinnamomum zeylanicum (Alam et al., 2017) extracts of Datura stramonium and Eucalyptus camaldulensis (Ullah et al., 2017), basil oil (Ocimum basilicum), cardamom oil (Elettaria cardamomum) and citronella oil (Cymbopogon nardus L.) (Kulasinghe et al., 2019) have shown significant antifungal activity against mycelial growth of SER pathogens and also a reduction of SER development in mango. Dip treatment of mango fruits cv 'Karuthacolomban' in vivo with cardamom oil in warm water (45 ˚C) significantly reduced SER development with little effect on sensory properties (Kulasinghe et al., 2019). Similarly, spray and fumigation treatments using basil, clove, cinnamon leaf and cinnamon bark oils, followed by storage at 12 -14 ºC for 8 days, enabled effective control of the SER of mango cv 'Karuthacolomban' (Kodituwakku et al., 2020). Similarly, another study involving fumigation treatment with thyme oil, clove oil and cinnamon oil vapors resulted in inhibition of Colletotrichum gloeosporioides and L. theobromae growth in vitro (Perumal et al., 2016). Papaya cultivars, 'Rathna' and 'Red Lady', stored at 12-14 ˚C following treatment with 1% (w/v) alum (sodium aluminium sulphate) or 1% alum and 0.16% (v/v) basil oil and enclosed in styrofoam sleeves were found free of postharvest diseases including SER (Abeywickrama et al., 2012). No residues of basil oil could be detected on fruit peel by gas chromatography at the end of the experimental period of 14 days (Abeywickrama et al., 2012).

Biological control
Biocontrol is another less common yet environmentally friendly method of controlling SER. Application of a cell suspension of Aureobasidium pullulans at the stemend of harvested unripe avocado fruit delayed incidence of stem-end rot by two days compared to controls which had either stalk intact or not. Retention of stalk reduced the progression of symptoms in both treated and control avocado fruits but did not significantly affect disease incidence. Aureobasidium pullulans reduced conidia germination and mycelial growth of L. theobromae, (Madhupani and Adikaram, 2017). Normally, chitinase, β-1,3-glucanase and antifungal activity of the peel of avocado fruit (control) declined during ripening. In A. pullulans-treated fruits, however, the activity of chitinase and β -1,3-glucanase was increased when fruits were inoculated with L. theobromae after treatment with A. pullulans. β-1,3-glucanase activity increased only slightly in fruits that was inoculated with L. theobromae without treatment. Greater preformed antifungal activity was retained in A. pullulans-treated fruits during ripening. Enhanced activity of chitinase and β-1,3glucanase and greater retention of preformed antifungal activity may have contributed to the delayed stem-end rot incidence in A. pullulans-treated avocados. Application of A. pullulans, two days prior to inoculation and retention of stalk at harvest, allowed better establishment of A. pullulans on the treated site (Madhupani and Adikaram, 2017).
Pestalotia neglecta, a non-pathogenic surfaceinhabitant, most commonly encountered on the avocado fruit, exhibited strong antagonistic properties against Phoma species, a major stem-end rot pathogen in Sri Lanka. Application of conidia of P. neglecta on to the stem-end region of harvested avocados, pre-inoculated with Phoma species, delayed stem-end rot development by four days, compared to the control. A similar effect was not observed with B. theobromae. In vitro studies confirmed that P. neglecta was antagonistic to Phoma species, but not B. theobromae. The antagonism appears to be due to a heat-labile extracellular factor. Dipping avocado fruits in a suspension of conidia of P. neglecta delayed both anthracnose and stem-end rot development (Adikaram and Karunaratne, 1998).
Bacillus subtilis (isolate B246), Bacillus cereus and Bacillus licheniformis (isolate B248) were inhibitory to avocado postharvest pathogens. B. cereus isolate B249 actually stimulated development of Lasiodiplodia theobromae. Diffusible metabolites from the four antagonists impeded growth of C. gloeosporioides, D.aromática, P. perseae, L. theobromae, but not of T. pseudotrichia. B. subtilis (B246) mode of action was determined using an in vitro spore-germination assay. In vitro the antagonist effectively reduced percentage spore germination of C. gloeosporioides, D. aromática, P. perseae, L. theobromae, F. solani, P. versicolor and D. setariae. In addition, bulb formation and lysis of hyphae were observed, as well as bacterial movement towards germinating spores and subsequent attachment to the spores (Korsten and Jager, 1995;Korsten et al. 1988;. When applied in the field, B. subtilis was found to get attached to and colonize avocado flowers and interfere with SER-causing pathogen colonization (Demoz and Korsten, 2006). Postharvest application of B. licheniformis reduced mango anthracnose and SER (Govender et al., 2005) and Trichoderma viride was reported to control SER caused by L. theobromae in mango fruit (Kota et al., 2006).
Trichoderma harzianum isolated from soil of Rambutan orchards were found to be effective biocontrol agents against Botryodiplodia, Colletotrichum and Gliocephalotrichum spp. causing postharvest diseases of Rambutan in Sri Lanka (Sivakumar et al., 2012).

Field management and postharvest practices
There is a variation in susceptibility to SER among cultivated mango varieties. Studies done in Thailand reveal that cultivars 'Okrong' and 'Tong dum' had higher disease incidence compared to 'Khaew' (Sangchote, 1991). This variation in susceptibility is due to the higher sucrose content in susceptible cultivars (Sangchote, 1991). Karunanayake et al. (2014) report that there is a correlation with antifungal compounds; especially those in mango latex that contribute to cultivar differences in susceptibility to SER. Chitinase activity was highest in cultivars 'Rata' and 'Kohu' that are resistant to SER and lowest in cultivars 'Gira' and 'Karuthacolomban' that are susceptible to SER (Karunanayake et al., 2014). Further, this is possibly the underlying reason for reduced SER in fruits that are not de-sapped after harvest. The simple practice of harvesting fruits with intact pedicels as opposed to detaching the fruit pedicel at its base which the common practice had a major and significant impact on reducing SER incidence in mango and avocado fruit (Diskin et al., 2017a;Sangchote, 1991). A negative correlation was observed between pedicel length and SER development in 'Karuthacolomban' mangoes (Karunanayake et al., 2015). Fruits harvested with pedicel, thereby retaining the latex, developed SER later compared to the fruits which were detached from the pedicel. Sangchote (1991) reported similar findings where fruits with longer pedicels developed SER later and those with longer pedicels had the lowest disease incidence opposed to those without pedicel that had the highest disease incidence. The fruit peel in which latex was retained had greater chitinase activity. The reduction of anthracnose and SER could be due to the greater antifungal resorcinols and chitinase activity respectively in latex-retained fruit (Karunanayake et al., 2015). Similarly, 'Kensington Pride' mango fruit stored with 2-to 3-cm long stems had significantly more resorcinol in their peel and smaller anthracnose lesions than de-sapped fruit (Hassan et al., 2007). Therefore, it seems that when harvesting fruit with stems, more sap that contains antifungal compounds is left in the fruit stem and peel, leading to decreased postharvest side decay and SER (Galsurker et al., 2018).
Applying high doses of potassium fertilizer to the soil, during fruit development significantly reduced SER development in mango fruit cv. 'Karuthacolomban' at the postharvest stage. The effective dose of fertilizer was 2055 g x 3/ tree/ year which was three times the recommended dose (Karunanayake et al., 2016). The elicitors Salicylic acid (Karunanayake, 2008) and Kasil (Sinniah, 2010) were more effective in controlling anthracnose than SER of mango fruit.
A combination of hot water with gamma irradiation at the postharvest stage significantly reduced mango SER and anthracnose (Spalding and Reeder, 1986). UV-C controls fungal pathogens, including SER-causing pathogens (Stevens et al., 1996) by inducing fruit resistance (Romanazzi et al., 2016). Similarly, red mango fruit that was exposed to sunlight in the orchard accumulated anthocyanin and was more resistant to SER than fruit that developed within the tree canopy (Diskin et al., 2017a). Therefore, pruning and exposure of fruit to sunlight could be a good method for reducing postharvest SER. Hotwater dips and different heat-treatment such as rinsing, hot vapor and dry-air treatments have been suggested to reduce postharvest diseases including SER of mango (Alvindia and Acta., 2015;Coates et al., 1993).
Considering the mode of infection and colonization, a combination of control measures is needed to be employed in the control SER, if fungicides are not used. These practices should commence at the time of flowering and continue through fruit development to the postharvest stage until it reaches the consumer especially in fruits such as mango.

DECLARATION OF CONFLICT OF INTEREST
The authors declare no conflict of interest.