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Occurrence of Diseases in Floricultural Crops in and around Jorhat, Assam

Munmi Borah, Moyurtrishna Rajkhowa and Sakendar Ali

  • Page No:  054 - 063
  • Published online: 28 May 2019
  • DOI: HTTPS://DOI.ORG/10.23910/IJEP/2018.6.2.0294

  • Abstract
  •  mborah56@gmail.com

The objective of this study was to identify pathogenic diseases of economically important floricultural crops based on visual inspection and microscopic observation carried out during 2017-18 in and around Jorhat district of Assam. During the investigation, 3 diseases of chrysanthemum (2 fungal, 1 viral); 3 diseases of gladiolus (all fungal); 5 diseases of gerbera (all fungal), 2 diseases of rose (all fungal) and a fungal disease of marigold was identified. The diseases identified in chrysanthemum were alternaria leaf spot, sooty mould and mosaic disease. The diseases identified in Gladiolus were fusarium infection, alternaria leaf spot, curvularia leaf spot and corm rot. The diseases identified in gerbera were alternaria leaf spot, cercospora leaf spot, damping off, stemphylium infection and coniothyrium infection. Diseases identified in rose were alternaria leaf spot and cercospora leaf spot. In marigold, alternaria leaf spot was indentified causing infection to the crop. Overall pathogenic disease incidence of flower crops recorded as 60.41% in Chrysanthemum, 45.83% in Gladiolus, 55.55% in gerbera, 47.22% in rose and 45.83% in marigold. Area wise  maximum disease incidence (61.11%) was observed in Borbheta area followed by Bahona( 58.33%). Lowest disease incidence was recorded in Sungi (27.77%) in Jorhat district.

Keywords :   Disease incidence, floricultural crops, survey, pathogenic diseases, microscopic observation

  • Introduction

    Floricultural crops are vital component of the horticultural industry in India. India has an ancient heritage of floriculture from time immemorial due to its extensive use in religious rituals and occasions. Thus significance to this sector is given for its diverse uses in different events of our life. Essential oil extracted from flowers is use for manufacturing of perfumes.

    West Bengal, Karnataka, Maharashtra, Tamil Nadu, Odisha, Uttar Pradesh, Andhra Pradesh, Jammu and Kashmir and the North Eastern states are the major commercial flower growing states in India where marigold, roses, chrysanthemum, jasmine, tuberose etc. are commercially cultivated (Harisha et al., 2017). Floriculture industry is one of the most important commercial trades in horticulture as well as in Agriculture sector (Harisha et al., 2017). As the demand for cut flower in the market increases day by day in India growers emphasized on commercial export quality flower production. It is difficult to get good quality exportable blooms with higher yield and longer post harvest life of the cultivars under open conditions. Several factors have been found to be associated with this dwindling productivity of the flower crops. The most important factors associated are biotic and abiotic stresses. Among biotic stresses diseases caused by plant pathogens are prime factor.

    Chrysanthemum (Chrysos, golden; anthos, flower) is a popular flower crop of commercial importance. It belongs to the family Composite and has been commonly grown in gardens for more than 2500 years (Bose et al.,2003). Intensive production during the first half of the twentieth century resulted in devastating diseases, such as those caused by the fungi Ascochyta, Septoria, and Verticillium, along with bacterial infections, root rots, rusts, and viral and viroid infections which severely threatened the chrysanthemum industry (Trolinger et al., 2017).

    Gerbera (Gerbera jamesonii Bolus) is one of the beautiful cut flower being grown commercially under protected condition in Assam. It is considered a promising and valuable cut flower crop next to rose, ranks fifth among top ten cut flowers of world market (Saikia et al., 2018). In gerbera Powdery mildew, caused by Golovinomyces cichoracearum or Podosphaera sp., is the most common foliar disease of Gerbera daisies, but they are also plagued by Botrytis blight and Alternaria leaf spot. Gerbera is also susceptible to a host of root and crown rot diseases, including those caused by Fusarium, Phytophthora, and Pythium spp. (Brisco and Hausbeck, 2018).

    Gladiolus (Gladiolus grandiflorus L.) belongs to the family Iridaceae and native to Europe, Mediterrenean region and South Africa. It is also known as queen of bulbous ornamental plants and sword lily. It has fascinating spikes that contains attractive, elegant, dazzling and delicate florets that open in sequence over longer duration and hence having good keeping quality for cut spikes. It is mainly used for garden, interior decoration and for making bouquets (Singh et al., 2014). In gladiolus Fusarium corm rot, Gladiolus rust, and Curvularia spot are the most limiting fungal diseases, whereas Cucumber mosaic virus and Bean yellow mosaic virus emerge as the more threatening viral diseases affecting gladiolus (Elmer and Kamo, 2018).

    Rose is one of the natures beautiful creations and is universally acclaimed as the queen of flowers due to its variety of shapes, sizes, colours and versatility. It is certainly the best known and most popular of all garden flowers throughout the world and has been growing for many million years (Gault and Synge, 1971). The crop is attacked by a number of diseases. Rose black spot, caused by Diplocarpon rosae F.A. Wolf [imperfect stage-Marssonina rosae (Lib.) Lind.] is the most important disease of the rose worldwide (Baker, 1948; Baskaran and Ranganathan, 1974) except in regions of low seasonal rainfall. Dieback, powdery mildew, rust, stem blight, alternaria leaf spot and black spot are some of the important fungal diseases of rose (Kakade et al., 2006).

    Marigold (Tagetes erecta L.) (Asteraceae) is a medicinal and ornamental plant. It is used for its nematocide, cosmetic and medicinal properties. The essential oil of the flower contains antioxidants (Perez Gutierrez et al., 2006). It is found in different colors and different fragrance. Yellow color is most common (Dixit et al., 2013). Alternaria spp., the cause of leaf spot and flower blight, and which are seed-and airborne in nature, are the major constraints in marigold cultivation (Chandel et al., 2010; Sen,1996; Qui et al., 2009). 

    Extremely limited information available about the prevalence of pathogenic diseases in flower crops of Assam. Therefore the study conducted to identify and record pathogenic diseases in some commercial flower crops in and around Jorhat district of Assam.


  • Materials and Methods

    2.1.  Disease survey

    For present study, a few locations in and around Jorhat district were selected for the survey. The locations selected were Borbheta, Kenduguri, Bahona, Dhekiajuli, Sungi and Dergaon (Table 1 and 2). The diagnostic field survey was conducted during 2017-2018 in selected localities in order to find out the status of disease incidence in commercial flower crops. For sampling purposes, within a field a roving survey was conducted following a zig-zag sampling pattern each of the fields. Nearly 6 plants plot-1 were selected randomly and observations were made as % incidence of diseases. Plant samples were taken to the laboratory and pathogens were confirmed using compound microscope. For different diseases  incidence was estimated as a % age of individual plants expressing symptoms of a disease within the field section. Thus, % disease incidence was calculated in all the six locations surveyed along with disease incidence in all five flower crops that were considered for the study (Table 1 and 2).


    Percent disease incidence= (No. of infected plants/Total number of plants)×100

    2.2.  Symptomatology and microscopic study of the pathogen

    Symptoms of different diseases of flower crops were studied in the field and laboratory condition. Sampling survey conducted in different areas aided in observing symptom development in the plant and microscopic study of the pathogen done in laboratory condition. Collected samples of the diseased plants were stored in moist condition for further microscopic study. The microscopic observation of the pathogens was done through light microscope. Morphological characters of the fungal pathogens were studied viz., type of mycelium, branching pattern, type of spores, their shape and presence of sexual structures of the pathogen (Table 3). Microphotographs of the pathogen were taken.


  • Results and Discussion

    In this study, overall pathogenic disease incidence of flower crops recorded as 60.41% in Chrysanthemum, 45.83% in Gladiolus, 55.55% in gerbera , 47.22% in rose and 45.83 % in marigold (Table 1). It was found that the  Alternaria leaf blight disease was found to be more severe in surveyed areas followed by cercospora leaf spot. Area wise  maximum disease incidence (61.11%) was observed in Borbheta area followed by Bahona( 58.33%). Lowest disease incidence was recorded in Sungi ( 27.77%) (Table 2). Data presented in Table 1, shows the incidence of different pathogenic diseases in flower crops of Jorhat, Assam. The details of the results obtained are presented below:

    3.2. Symptomatology and identification of pathogen of surveyed crops

    3.2.1.  Chrysanthemum

    a) Alternaria blight: Symptoms consisted of spots on the leaves as well as on petals. These spots were at first yellowish, and then became dark brown and black surrounded by yellow halo. Later defoliation of leaves occured and plant died (Figure 1). The causal organism of the disease  was  Alternaria spp. The fungus produce muriform conidia having  both  transverse and longitudinal septa. Conidia observed under microscope  attached in the conidiophores in chain. Conidia and conidiophores were coloured (Figure 2)(Table 3). The results were in conformity with the study of Kumar et al. (2011), Trolinger et al. (2018), Dominguez-Serrano et al. (2016), Farhood and Shervin (2019). 


    b) Sooty mould: Black superficial fungal growth on the aerial parts of plants were observed particularly on upper leaf surface of the leaves (Figure 3). The disease was caused by Cladosporium spp. The fruiting body of the fungus observed under microscope which resembled perithecia (Figure 4) (Table3). The results were in conformity with the study of Chomnunti et al. (2014).

    c)Mosaic of chrysanthemum: Infected plant has shown stunted growth. The leaves of infected plants were deformed, small and leathery and exhibit mosaic and mottling with raised dark green areas. Blisters were formed on the leaves and size of leaves reduced (Figure 5).The aphid vector of the viral disease was is also observed in some of the surveyed locations. The mosaic virus infection was confirmed by sap inoculation assay (Figure 6). The results were in conformity with the study of  Keller (1950) and Noordam (1952).


    3.2.2.  Gerbera

    a)Cercospora leaf spot: Small round water soaked lesions developed on leaves and stems. Later those spots coalesced and blighted the entire leaf (Figure 7). Cercospora  spp.cause Cercospora leaf spot disease of gerbera. The conidiophores of the fungus   geniculat  type , septate , dark coloured.  Conidia were observed as septate and needle shaped (Figure 8)(Table 3). The results were  in conformity with the study of Singh and Kumar (2012).

    b)Stemphylium and coniothyrium infection: Necrotic lesions were coalesce to form large canker like area on leaf (Figure 9). Coniothyrium  pycnidia observed  with pycniospores (Figure 10). Spores emerging from pycnidia were observed under microscope (Figure 11)(Table 3). Stemphylium spore were single oval, muriform, constricted at central septum (Figure 11)(Table 3). The results were in conformity with Nishi et al. (2009).


    c) Alternaria leaf spot: Characteristic symptom leaf spots with concentric rings observed on infected leaves. The spots were mostly irregular and coalesce to cover large areas of the leaf blade. Brown specks form on florets and the leaves. Centers became white on the leaf spots (Figure 12). Fungal pathogen Alternaria  alternate cause Alternaria leaf spot of Gerbera . Under the microscope  we observed  obclavate  conidia with short  beak at tip . Conidia had 2 transverse and  8 longitudinal septa , conidia were  colored (Figure 13)(Table3). The results were  in conformity with the study of Farhood and Hadian (2019).


    d)Rhizoctonia rot: Symptom consisted of blackening of the petiole of  leaves at  the base as the plant. Later the infected plants collapsed (Figure 14).Causal organism of the disease was Rhizoctonia  spp. Hyphae  of the pathogen showing the distinguishing right angles and had constriction at the point of swelling .Hyphae were septate(Figure 15)(Table 3).The results were in conformity with the study of Wick and Dicklow (2013).


    3.2.3.  Gladiolus

    a)Fusarium yellow: Older leaves became yellow and stunted growth of plants observed. Flower size, shape and color became abnormal. Flowers not developed while stalks were curved. Corms rotted from the center outward. Oval, sunken spots on the corm surface were brown and had concentric rings. Centre of the corm turned black and rotted completely (Figure 16, 17). Pathogen Fusarium spp cause fusarium yellow of gladiolus .Under the microscope sickle shaped  macroconidia, were observed (Figure 18)(Table3). Conidia of the fungus were septate and coloured. The results were in conformity with the study of Riaz et al. (2010).


    b)Alternaria Blight: The most pronounced symptom  brownish circular spot with yellow  margins was observed on leaves , later spot coalescing and cover large area of plant (Figure 19).Alternaria blight of gladiolus caused by Alternaria spp. The conidia were observed under miocroscope  as  coloured, obclavate  having both longitudinal and transverse septa on it (Figure 20)(Table3). The results were in conformity with the study of Bhagat et al. (2018).


    c)Curvularia leaf spot: Symptom consisted of brown  colour oval to circular spot surrounded by yellow halo. Later the spot emerged and necrotic lesions were observed on leaves (Figure 21). Casual organism of the disease was Curularia spp. The conidiophores were geniculate, Conidia were ellipsoidal, often curved, rounded at end. Conidia tapering slightly at ends (Figure 22)(Table 3).  The results were in conformity with the study of Torres et al. (2013), Riaz et al. (2010).

    3.2.4.  Rose

    a)  Alternaria leaf spot: Characteristic leaf spot symptom with concentric ring were observed on leaves. The spots were mostly irregular and coalesce to cover large areas of the leaf blade. Small dark circular spots with light brown centers surrounded by concentric ring (Figure 23). The Causal organism was identified as Alternaria spp. through microscopic observation. The Conidia were observed as coloured, obclavate  having both longitudinal and transverse septa and they attached with conidiophores on chain (Figure 24)(Table 3). The results were in conformity with the study of Abbas et al. (2017).

    b)Cercospora leaf spot: Circular spots appeared on leaf later coalesced to form large necrotic area (Figure 25). The disease was caused by Cercospora spp .Truft of Conidiophores developed from stoma. The conidia were observed under microscope as cylindrical and having septa (Figure 26)(Table 3). The results were in conformity with the study of Kang et al. (2019).


    3.2.5.  Marigold

    a)Alternaria leaf spot:The first symptom observed as circular  brownish spot on  leaf.  Later the spots turned blackish, coalesced and it covered entire leaf and reduced the flower quality (Figure 27). The Causal organism of the disease was identified as Alternaria alternata. The conidia were coloured and obclavate. The conidia having both longitudinal and transverse septa and its attached to the conidiopohore in chain (Figure 28)(Table 3). The results were in conformity with the study of Tomioka et al. (2000) and Hotchkiss and Baxter (1983).


  • Conclusion

    After carrying out the survey for disease incidence in floricultural crops of Jorhat district an nearby areas, we could draw the conclusions that most of the floricultural crops found to be disease stressed. Management of diseases is based upon identification of the diseases to take up management strategies. Recognition and control of these diseases is vital and therefore this research will help increase the current understanding for growers and researchers on identification and determining disease  incidence levels in field.


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