Monilinia fructicola intercepted on Prunus spp. imported from Spain into South Africa between 2010 and 2020

The international trade of plants and their products, such as fresh fruits, can facilitate the introduction and spread of foreign pests and diseases. We examined South Africa’s import of stone fruits ( Prunus spp.) as a pathway for introducing Monilinia fructicola (G. Wint.) Honey and document recommended phytosanitary measures to deal with the risk associated with its exportation into the country . Fresh fruits of Prunus spp. are imported from various countries. The current study provides a report on 10 years (2010–2020) importation of Prunus spp. from Spain to South Africa with associated cases of M. fructicola. We also detail the current management measures for imported stone fruits from Spain to South Africa. We report 18 M. fructicola detections that were found during the study period. The number of detections presents enough trends to determine the level of phytosanitary concerns regarding the importation of Prunus spp. fresh fruit from Spain, which cannot be neglected. M. fructicola is an economically important brown rot on many fruit hosts and potentially threatens agricultural and horticultural industries, the environment, and biodiversity in South Africa. The importation of Prunus spp. requires intensive management strategies for M. fructicola, as pathogens may pose a major phytosanitary concern because it could thrive and reproduce in various environmental conditions and on various host plants in South Africa. Therefore, if M. fructicola establishes in South Africa, its impacts will have consequences for different key socio-economic sectors, including the agricultural industry.


Introduction
International movement of plant products such as fresh fruits through trade is a pathway by which foreign pests can be transported and introduced to new areas. Plant pests are known to affect infrastructure, agriculture, and biodiversity negatively. 1 Due to climate change and variability, the impacts associated with invasive pests are likely to increase steadily, leading to more stringent trade restrictions and border inspection rates by trading partners. 2 Moreover, challenges are perceived when the pests are detected in countries that largely depend on economic structure, such as agricultural exports and other industries and ecosystems. 3 One of the most economically important pests of Prunus spp. is Monilinia spp., which results in blossom blight and brown fruit rot. 4,5 Amongst the various variants of brown rot, Monilinia fructicola (G. Wint.) Honey is regarded as the most destructive disease host plant belonging to subfamilies Prunoideae and Pomoideae globally. [6][7][8] However, this pest is more common on ripening stone fruits and less common on pome fruits. [9][10][11] Its direct economic impact is through destroying and/or significantly reducing a crop yield at pre-and post-harvest stages by eliminating blossoms or rotting mature fruits. 12 The disease also infests the leaves and shoots of host plants. 13 Importing fresh fruit poses a prospective risk to local host plants through extremely dispersible, abundant spores of M. fructicola from reused packaging and disposal sites for discarded fruit. 14 M. fructicola subsists on mummified fruits. 15,16 The yellowish exogenous stromata display the principal symptom on peaches, pears, and apples approximately 15 days after ripening. 15,17 The impact of M. laxa and M. fructigena on fruits is considered minimal compared to that of M. fructicola. 16 Studies have indicated that the latter pest is more aggressive and hard to control due to its anastomosis behaviour and sexual recombination. 18 It is also known to contain a tremendous genetic change, making and possessing a higher potential to overcome genetic barriers. [19][20][21][22][23][24] Of all the stone fruits' pests, M. fructicola is also considered the most highly transmissible pest known to infect the plants at different growth stages, including flowers, twigs, and fruits. [19][20][21][22] Over the past 70 years, trade disputes have been raised concerning the classification pertaining to the official status of the presence of M. fructicola in South Africa. Currently, the National Plant Protection Organisation of South Africa lists M. fructicola as a quarantine pest for South Africa on phytosanitary import requirements of fresh fruits and propagation materials for Prunus spp., Pyrus spp., Cydonia spp., Malus spp. and Vitis spp. The International Plant Protection Convention (IPPC) defines pests as 'any species, strain or biotype of plant, animal or pathogenic agent injurious to plants or plant products' 25 . It further defines quarantine pests as 'a pest of potential economic importance to the area endangered thereby and not yet present there, or present but not widely distributed and being officially controlled'. M. fructicola is not known to occur in South Africa, although it was mistakenly declared. [26][27][28][29][30][31][32] The introduction of M. fructicola into South Africa could have an undesirable impact on the country's stone and pome fruit production. Stone fruit production in South Africa is the largest in Africa, accounting for 16% of southern hemisphere output and 1% of global production. 31 Of the stone fruit produced in South Africa, 20% is exported and the rest is locally consumed. The value of the stone fruit industry in South Africa is ZAR2 billion annually. South Africa produces about 1.3 million tonnes of apples and pears per year. 31 The value of the pome fruit industry in South Africa is ZAR8 billion annually. We aimed to provide a report on a 10-year period (2010-2020) of importation of Prunus spp. from Spain to South Africa with associated cases of M. fructicola and to recommend additional phytosanitary measures to deal with the risk associated with its exportation in South Africa.

Data collection
The data in the current study were obtained from 702 samples from the imported consignments of fresh fruit of Prunus spp. from Spain to South Africa, based on convenience sampling (also known as haphazard sampling or accidental sampling). These samples were collected from three ports of entry in South Africa: (1) OR Tambo International Airport, (2) Cape Town, and (3) Port Elizabeth Harbour. Consignments were inspected by the quarantine inspectors from the Department of Agriculture, Land Reform and Rural Development (DALRRD) between 2010 and 2020, to determine if pests were present and/or to determine compliance with phytosanitary regulations. International Standard for Phytosanitary Measures (ISPM) No. 31 describes procedures for inspecting consignments of plants, plant products and other regulated articles at import and export. 33 It is focused on determining compliance with phytosanitary regulations, based on visual examination, documentary checks, and identity and integrity checks. A confidence level of 95% is commonly used during inspection and sampling. 34 A 95% confidence level means that the conclusions drawn from the sampling results will detect a non-compliant consignment, on average, 95 times out of 100. Therefore, it may be assumed that, on average, 5% of non-compliant consignments will not be detected. If the inspector has grounds to believe that the consignment contains brown rot, a sample will be extracted and sent to the DALRRD laboratory for additional examination and identification. All fruits suspected to be infested with brown rot were collected and identified using the diagnostic protocol for Monilinia species. [35][36][37] Data analysis Records

Monilinia fructicola interception via fruit imports
We aimed to report on 10 years' of importation of Prunus spp. to South Africa from Spain and their associated cases of M. fructicola. The introduction of M. fructicola into South Africa could negatively impact stone and pome fruit production in the country. Over a period of 10 years, we recorded 18 M. fructicola detections across the three ports of entry investigated. The highest number of M. fructicola interceptions were recorded between 2010 and 2015 ( Table 1) (Table 1).
M. fructicola has been reported in various countries around the globe. However, unless extra phytosanitary measures are taken in South Africa, transmission to local orchard trees through highly dispersible, profuse spores from recycled packaging materials and fruit disposal sites may not necessarily happen. 40 In Spain, the first report of M. fructicola on plums was recorded in the southwestern part of the country. 41 During that period M. fructicola was a quarantined pathogen in Europe and was reported on imported apricot, nectarine and peach in several European countries. 41 The number of detections presents enough trends to determine the level of phytosanitary risk associated with the importation of Prunus spp. fresh fruit from Spain. Brown rot has been officially recognised in orchards in Austria, Spain, Czech Republic, Italy, and Germany since it was initially discovered in French orchards in 2001. In Switzerland, M. fructicola has also been reported on imported fruit in Hungary and Switzerland. 43 Peaches with brown rot were discovered in a 5-year-old orchard in Gorika, western Slovenia, in 2009. Fruit lesions and mummified fruits were among the symptoms. 44 Two imported peach isolates came from Greece and Spain, one nectarine isolate came from Greece, and the local plum isolate originated from Spisk tiavnik (Serbia). 45 Brazil is an importer of stone fruits from Spain, Chile, the USA and Argentina. M. fructicola was originally detected in the nation due to imported stone fruit, and several isolates are able to adapt to the environment of Brazil's primary fruit producing regions. All Monilinia isolates studied were pathogenic to peaches, whereas isolates from Chile and the USA were able to induce brown rot in both wounded and unwounded apples and pears 46 , presenting a high risk of Monilinia spp. in stone fruit production in Brazil.
In 2017, brown rot symptoms were seen on the fruit of Japanese apricot, peach, apricot, Japanese plum, and sweet cherry with 2-5% incidence levels in Korea. 47 This was the first confirmed report of brown rot caused by M. fructicola, resulting in early symptoms that eventually destroyed entire fruit crops in the country. 47 M. fructicola is also a significant pest on Malus spp. (apples). In Italy, the first report of M. fructicola was recorded on apple. 48 In Mongolia, the highest interception rate of brown rot of apple fruit (37-41%) occurred in imported apples from China. About 12-19% of brown rot of apple was recorded in imported apples from the USA, while 11-29% was detected in imported apples from Russia. 49 This led to widespread brown rot through the imported apples.
Therefore, the South African apple industry also needs to be protected against invasion of M. fructicola through application of phytosanitary measures during import. In South Africa, the apple industry plays a significant role in the economy, considering their foreign exchange earnings, employment creation and linkages with support institutions. 50

Economic consequences and recommended phytosanitary measures
M. fructicola has been categorised as a quarantine pest based on its potential economic importance to the South African Prunus spp. fruit industry and it is currently not present in the country. M. fructicola is one of the most economically important diseases affecting stone and pome fruits in the orchards and after harvest by destroying or reducing a crop yield by killing blossoms or by rotting mature fruits. 5,51-56 Post-harvest losses of 80-85% may occur under favourable conditions for brown rot development. 16 In Indiana, the brown rot of apples was discovered on the fruit of 'pristine' apples, causing 50% crop loss in 2015. 57 Other apple growers reported a significant loss of 5-20%. 57 Among the species causing brown rot and blossom rot in the genus Monilinia, M. fructicola is regarded as the most highly infectious pathogen at different stages of plant growth. 21,23,24 It caused severe post-harvest yield losses, sometimes in excess of 30%, in California's Central Valley. 58 Brown rot fungal infections can begin early in the growth season on blooms and/or young shoots. 16,59,60 While blossom blight outbreaks may not be severe enough to cause a serious decrease in fruit production, they still pose a risk. 59 At harvest, healthy fruit may be contaminated with spores, which then cause decay in storage and during marketing. Green fruits may harbour latent infections. 61 Fungi that infect such fruit remain dormant until the fruit begins to ripen. 62 M. fructicola may be a major phytosanitary concern to the South African fruit industry because it could find favourable conditions for survival, development, reproduction and dispersal ( Table 2). The importation of Prunus spp. from Spain should require intensive application of phytosanitary measures for M. fructicola both in export and port of entry through regular inspections. The environmental conditions in South Africa are diverse. Therefore, if M. fructicola is established in the country, impacts could lead to socio-economic consequences in various key agricultural sectors and biodiversity in general and loss of export markets by restricting trade by importing countries. This pest has never been reported on any of these plant species in South Africa, presenting a high risk if detected in the country through stone fruit import from Spain (Table 2).
South Africa is a major producer and exporter of Prunus spp. and pome fruits, which are major hosts of M. fructicola. As a consequence of introduction, this pest may pose a major restriction to trade by importing countries. Approximately 16% of the stone fruit grown in the southern hemisphere comes from South Africa. 32 About 20% of stone fruit produced in South Africa is for the export market, leaving the rest for local consumption. It is important to note that the value of the stone fruit industry in South Africa is ZAR2 billion. The country produces approximately 1.3 million tonnes of apples and pears per annum, with a value of ZAR8 billion. 50 M. fructicola is not known to occur in South Africa and is regarded as a quarantine pest listed on various phytosanitary import requirements of many export countries. However, M. fructicola is endemic to North American countries, although it is also found in Asia and Oceania. 63 The introduction of M. fructicola into European countries has raised concerns about the possible impact on stone fruit production in the region. 64 The European and Mediterranean Plant Protection Organization regarded M. fructicola as a quarantine pest up until 2001 across Europe. 15 Recently, stone fruit growing countries across Europe reported the presence of M. fructicola; as a result, it has been declared a regulated harmful pest in the European Union. 65,66 In terms of geographic distribution, M. fructicola is known to occur in Europe, Africa, North America, South America and Oceania. 67 Risk analysis per the US Animal and Plant Health Inspection Service -Plant Protection and Quarantine guidelines was conducted for M. fructicola ( Table 2). Because of its vast host range, significant economic effect, widespread dissemination, and extensive geographic distribution, M. fructicola has a high pest potential.

Table 2:
Risk ratings and scores from intercepted Monilinia fructicola generated from the imported Prunus spp. fresh fruit from Spain. The numeric value for the ranking that is used to generate the cumulative risk rating is the number in brackets following the risk rating. Each risk factor is assigned a score of high, medium, or low.

Consequences of introduction
Climate/host interaction High (3) Host range High (3) Dispersal potential High (3) Economic impact High (3) Environmental impact Medium (2) Likelihood of introduction Quantity imported High (3) Survive post-harvest treatment High (3) Survive shipment High (3) Not detected on entry Medium (2) Moved to suitable habitat Medium (2) Find suitable host High (3) Pest risk potential (risk score) 30 To manage diseases in exporting countries, growers are encouraged to remove and destroy mummified fruits and infected tissues to reduce the inoculum potential during winter months. The residues of pruning must be destroyed or inactivated. After blossoming, infected or symptomatic twigs and branches must be removed. Any infected fruit must be destroyed. Growers are encouraged to improve ventilation and insulation by green pruning and herbicides to avoid excess moisture.
Pre-harvest treatments include a minimum of three sprays of fungicide during bloom and a further three sprays 28 days before harvest, with the last application not more than 10 days before harvest. Resistance against the benomyl, dicarboximides and demethylation-inhibiting fungicides (Cyproconazole, Difenoconazole, Fenbuconazole, Tebuconazole) have been reported in countries where fungicides have been used regularly. 68 All isolates of M. fructicola tested from Spain showed resistance to benzimidazole fungicides and a few of these isolates showed resistance to dicarboximide fungicides. 69 An anti-resistance strategy must be implemented to prevent the development of pesticide resistance. 70,71 Exporting countries are encouraged to inspect each registered production site for M. fructicola at least 6 weeks before harvest. A sample of 600 fruits must be withdrawn from each production site Fruit that has been thinned and left on the orchard floor can be a substantial inoculum source for secondary infections. 12 Brown rot should be reduced in nectarine and potentially other stone fruit orchards by removing or destroying thinned fruit. Quiescent fungal infections can affect green, immature, and mature sweet cherry fruit, and they can be apparent or invisible. 71,73 Even if the inoculum is consistently high and the environmental conditions are favourable in an orchard, the risk of fruit brown rot at different developmental stages may vary due to seasonal changes in fruit susceptibility. 59,74 M. fructicola is an economically important pathogen, causing brown rot symptoms on several plant hosts. 75

Conclusion
The reported interceptions of M. fructicola were all found on stone fruits imported to South Africa from Spain. This species of fungus is a quarantine pest for South Africa and is currently listed in various phytosanitary import requirements for the importation of fresh fruits and propagation materials to South Africa.
The phytosanitary concern is that M. fructicola could survive, develop, reproduce, and spread under favourable conditions. Furthermore, various host plants in South Africa are associated with the disease. We recommend that fresh fruits of Prunus spp. samples should undergo a systems approach in the exporting country to minimise the risk of transport of M. fructicola. In addition, a visual inspection should be conducted, but it should not be the only phytosanitary intervention. Recommended phytosanitary measures should include pre-harvest control in the orchards, pest free areas/places of production, a preharvest inspection of fruits and testing, post-harvest inspection and testing, and cultural practices including removal and destruction of mummified fruits and infected tissues.