Plant Pests and Pathogens

Table of Contents


Life Cycle.

Main Stage (Sexual reproduction).

Secondary Stage (Asexual reproduction).

Integrated Disease Management Program (IDM).

Disease Management Tables.

Disease Management in Organic Farming.

Environmental Issues.



Introduction to Apple Scab Analysis

Excluding lemon, bananas, and mango, Apple (Malus * Domestica) is the fourth extremely essential popular fruit variety, and one of the most economically relevant horticultural crops produced in temperate regions of the earth (Mansoor et al. 2019). It tends to grow well in India's valley zone at a height spanning from 1500 to 2700 m asl. Jammu & Kashmir's agro-climate environments in India are perfect for the growth of apple hybrids that account for almost 91% of its overall fruit production (Padder et al. 2011). It is susceptible to many viral infections with many pathogenic factors, such as fungi, bacteria, viruses, mycoplasmas, and nematodes. The biggest challenges impacting commercial apple cultivation in lowlands and moist locations are fungal outbreaks. It has been documented that over 70 chronic infections are available in apples, much of which is spread by pathogenic fungi.

Among the widespread fungal diseases in lowlands and moist areas of the globe, apple scab is the primary pathogenic infection in the mass cultivation of apples (Sandskar 2003). Apple scab is generated from the Venturia inaequalis pathogen (Gladieux et al. 2008). It is one of the most severe infections for the world's apple-growing zones (Tenzer & Gessler 1997). It is assumed one of the most significant challenges to the growth of agricultural apples, resulting in a decrease in fruit quality and weight, early fall of fruit, dethatching, and decrease in tree vigour over the period (Gao et al. 2009). The genus Malus is the primary host of Venturia inaequalis. The Apple scab incident was initially reported from Sweden in 1819 and Germany in 1833.

In the event of inadequate management of apple scab, financial consequences will boost the price of the production by up to 70%. Yield loss, on the first side, is influenced by direct contamination of the fruits and pedicels. Extreme leaves destruction on another side can lead to a diminished tree with a minimized development of flower buds. Therefore, to ensure effective pathogen control, a well-integrated strategy is typically required.

The main objective of this study is to determine how the Apple Scab pathogen influences an agriculturally relevant crop and coming up with concepts to control it. The report is focusing on different aspects: the Apple Scab disease cycle, an outline of an integrated disease management program, a table of an integrated disease management program, its role in farming, and environmental issues. Finally, it concludes the paper.

Life Cycle

Venturia inaequalis is a heterothallic ascomycetes pathogen that overwinters in the leaves sediment as pseudothecia while in areas with mild winter; it exists in sterile buds as conidia (Boehm et al. 2003).

The life cycle of V. inaequalis can be segmented into two stages, the sexual or main stage and the asexual or secondary stage (Figure 2). The main phases generally occur in winter and the asexual stage in summer.

Main Stage (Sexual reproduction)

Usually, this stage causes a primary disease. As a sexual fruiting organism, it grows during a short period of saprophytic seedlings production after leaves abscission in apple leaf waste. In the male, the sexual parts are divided into antheridia and ascogonia in the female unfertilized parent. Also, plasmogamy of the two gametangia can only be done if the ascogonium and antheridium come from sources of the contrary kind of breeding, i.e. carrying various breeding type alleles at the locus of the mating-type (MAT). In the asci, that in effect borne by the pseudothecium, the sexual seeds are developed. It has an inner and outer cell wall. Delicate and thin is the external cell membrane. The internal cell membrane, which prevents ascospores against winter, is flexible and thick (Jha et al. 2009).

Secondary Stage (Asexual reproduction)

It begins with the development of conidia. Spilocaea pomi is classified as V. inaequalis conidial phase. Conidia are singular-cells of olive or brown color with a breadth of 6-12μm and a length of 12-22μm. They are formed at the edge of small hyphae, called conidiophores, one after another (Biggs & Stensvand 2014). Conidia settle on an apple blooms or fruits and seeds, once spread by winds and wobbling rain. The germinating seeds of the hyphae spread across the cuticle and produce a unique disease.

Integrated Disease Management Program (IDM)

Effective management of apple scab pathogen includes an integrated methodology that relies on the objectives of the farmer. IDM is an integrative disease reduction approach that aims to achieve long-term feasibility, efficiency, and limited risk to the climate (Trumble 1998). It includes genetic tolerance, chemical implementation, cultural controls, and biological measures. Scab prevention IDM systems typically concentrate on decreasing main inoculums, or by employing predictive approaches to eliminate fungicidal sprays. It is the most powerful strategy to lessen yield deficiency due to scab.

By cultural strategies, successful horticultural activities such as identifying areas that offer more than six hours of sunshine per day can mitigate infection (Simon et al. 2006). Biological control is the process of regulating or eliminating plant disorders by including other microbes, like Microsphaeropsis ochracea (Carris & Rolland 2005). However, Beckerman (2009) discussed the chemical approach where, to protect the sensitivity of crops and to eliminate bacterial outbreak, sulphur, lime sulphur, and copper salts are necessary for successful scab management. Pruning has also proven to dramatically minimise leaf scab in conjunction with fungicide usage as it has increased spray accumulation in the canopy of the tree (Imre 2005).

Disease Management in Organic Farming

In organic farming, disease management is done by effective cultivation methods, biological control, and natural pests. IDM's role is to protect crops from achieving commercially harmful levels without causing environmental risk. The aspects that are included in effective IDM programs in organic farming are tracking pathogen crops, appropriately detecting pathogens, establishing commercial thresholds, introducing integrated disease control strategies, and maintaining and reviewing records (Edwards-Jones & Howells 2001).

Environmental Issues

Pest management can be harmful to the environment, despite their advantages. Environmental factors like temperature and moisture influence the variability of soil, plants, or surface water that can persist for many months or weeks after the deployment of pesticides. The toxins in the environment can be distributed over large distances. Consequent environmental emissions may lead to the contamination of water bodies that will affect animals and humans (Bernardes et al. 2015).

Conclusion on Apple Scab Analysis

The biggest commercially destructive pathogen in lowlands and moist apple growing areas worldwide is the Apple scab, infected by the pathogen Venturia inaequalis. It has been concluded that to ensure improved and healthy apple growth, integrated management control of such disease is necessary. Such control can help in managing effective cultivation in organic farming. It has also been concluded that excessive use of IDM can affect the environment.

References for Apple Scab Analysis

Beckerman, J. (2009). Managing Scab-Resistant Apples, Disease Management Strategies for Horticultural Crops. USA. Perdue Extension.

Bernardes, M F F, Pazin, M, Pereira, L C & Dorta, D J 2015, Impact of Pesticides on Environmental and Human Health, Texicology Studies. 10.5772/59710

Biggs, A R & Stensvand, A 2014, Apple scab: Compendium of Apple and Pear Diseases and Pests, American Psychopathological Society Press, USA.

Boehm, E W A, Freeman, S, Shabi, E & Michailides, T J 2003, ‘Microsatellite primers indicate the presence of asexual populations of Venturia inaequalis in coastal Israeli apple orchards’, Phytoparasitica, Vol. 31, No. 3, pp. 236-251. 10.1007/BF02980833.

Carisse, O & Rolland, D 2005, ‘Effect of Timing of Application of the Biological Control Agent Microsphaeropsis ochracea on the Production and Ejection Pattern of Ascospores by Venturia inaequalis’, Phytopathology, Vol. 94, pp. 1305-14. 10.1094/PHYTO.2004.94.12.1305.

Delalieux, S, Aardt, J, Keulemans, W, Schrevens, E & Coppin, P 2007, ‘Detection of biotic stress (Venturia inaequalis) in apple trees using hyperspectral data: Non-parametric statistical approaches and physiological implications’, European Journal of Agronomy, Vol. 27, pp. 130-143.

Edwards-Jones, G & Howells, O 2001, ‘The origin and hazard of inputs to crop protection in organic farming systems: Are they sustainable?’, Agricultural Systems, Vol. 67, No. 1, pp. 31-47. 10.1016/S0308-521X(00)00045-7.

Gao, L, Berrie, A, Yang, J & Xu, X 2009, ‘Within- and between-orchard variability in the sensitivity of Venturia inaequalis to myclobutanil, a DMI fungicide, in the UK’, Pest management science, Vol. 65, No. 11, pp. 1241-9. 10.1002/ps.1816.

Gladieux, P, Zhang, X G, Afoufa-Bastien, D, Valdebenito Sanhueza, R M, Sbaghi, M, Le Cam, B 2008, ‘On the Origin and Spread of the Scab Disease of Apple: Out of Central Asia’, PLoS ONE, Vol. 3, No. 1.

Imre, H 2005, ‘Effect of Pruning on Apple Scab in Organic Apple Production’, Plant Disease, Vol. 89, No. 6, pp. 611-618.

Jha, G, Thakur, K & Thakur, P 2009, ‘The Venturia Apple Pathosystem: Pathogenicity Mechanisms and Plant Defense Responses’, Journal of Biomedicine and Biotechnology, pp. 1-10. 10.1155/2009/680160

Mac Hardy, W 1996, ‘Apple Scab Biology, Epidemiology and Management’, American Psychopathological Society Press.

Mansoor, S, Ahmed, N, Sharma, V, Jan, S, Nabi, S U, Mir, J I, Mir, M A & Masoodi, K Z 2019, ‘Elucidating genetic variability and population structure in Venturia inequalis associated with apple scab diseaseusing SSR markers’, PLOS ONE, Vol. 14, No. 11.

Padder, B A, Shah, M D, Ahmad, M, Sofi, T A, Ahanger, F A & Hamid, A 2011, ‘Genetic Differentiation among Populations of Venturia inaequalis in Kashmir: A North-Western State of India’, Asian Journal of Plant Pathology, Vol. 5, pp. 75-83.

Sandskar, B 2003, ‘AppleScab and Pests in Organic Orchards’, PhD, Thesis, Swedish University of Agricultural Sciences, Alnarp.

Simon, S, Lauri, P E, Brun, L, Defrance, H & Sauphanor, B 2006, ‘Does fruit-tree architecture manipulation affect the development of pests and pathogens? A case study in an organic apple orchard’, Journal of Horticultural Science and Biotechnology, Vol. 81, No. 4, pp. 765-7723. 10.1080/14620316.2006.11512135.

Tenzer, I & Gessler, C 1997, ‘Subdivision and genetic structure of four populations of Venturia inaequalis in Switzerland’, European Journal of Plant Pathology, Vol. 103, No. 6, pp. 565–571.

Trumble, J 1998, ‘IPM: Overcoming Conflicts in Adoption’, Integrated Pest Management Reviews, Vol. 3, No. 4, pp. 195-207. 10.1023/A:1009691223903.

Ziems, A D 2009 Apple scab: Plant disease. USA.

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