Phenotypic and pathogenic variability of sclerotium rolfsii sacc. infecting fruit crops and ornamentals
| dc.contributor.advisor | Beena, S | |
| dc.contributor.author | Hajara, P H | |
| dc.contributor.author | KAU | |
| dc.date.accessioned | 2017-08-05T09:46:57Z | |
| dc.date.available | 2017-08-05T09:46:57Z | |
| dc.date.issued | 2011 | |
| dc.description.abstract | The present study on “Phenotypic and pathogenic variability of Sclerotium rolfsii Sacc. infecting fruit crops and ornamentals” was undertaken in the Department of Plant Pathology, College of Horticulture, Vellanikkara during 2009-2011 with an aim to isolate the pathogen associated with the disease and to study the symptomatology of the disease, variability in phenotypic and pathogenic characters of isolates, compatibility of the different isolates, host range of the pathogen and estimation of IAA and total phenol content in mycelia, culture filtrate and sclerotia. Isolation of pathogen associated with the diseased specimens of selected ornamental plants viz., marigold and chrysanthemum and fruit crops viz., mango and banana yielded a total of 11 isolates of S. rolfsii from different locations. Among them, two isolates from marigold (MG-1, MG-2), four from chrysanthemum (CH-1, CH-2, CH-3, CH-4), three from mango (MN-1, MN-2, MN-3) and two from banana (BA-1 and BA-2) were obtained. The pathogenicity of the isolates was proved by artificial inoculation on their respective host. Symptomatology of disease revealed slight variation in the symptoms produced by the pathogen in different host plants. In marigold and chrysanthemum infection was observed on leaves and collar region. Flowers of marigold were also infected by the pathogen. Mango seedlings and grafts were infected by the pathogen on the collar region. In banana var. Kadali, infection was observed on pseudostem at the base of leaf petiole and pseudostem broken at the point of infection. Dark brown water soaked lesions were present on infected areas of all the plants. Later it was covered with thick white mycelial growth and brown sclerotia. Detailed study on the phenotypic characters of the isolates revealed variations in the cultural and morphological characters. All the isolates produced white coloured colony on all the selected media. Variation in the texture and type of mycelium, sclerotial initiation and maturation, number, position, weight of 100 sclerotia and production of exudates was recorded. Among the different media tested, Potato Dextrose Agar was found to be the best medium for the growth of pathogen. In all the isolates, hyphae are hyaline, branched, septate and the hyphal cell size 52.6-196.32 μm×4.25-8.93 μm. Sclerotia were dark brown, smooth and spherical, 0.5-2.00 mm diameter in size. The maximum size of sclerotia was recorded in MN-2 and minimum in BA-2. Cluster analysis of cultural and morphological characters revealed a degree of variability among the isolates. The lowest dissimilarity index was noticed between isolates CH-1 and BA-2. The isolates viz., MG-1, MG-2, CH-1, CH-2, CH-3, CH-4, MN-1 and MN-2 were found more similar and were grouped under the sub cluster A1 of cluster A. The isolates from banana stands separate and showed more dissimilarity with all other isolates. Mycelial compatibility between the different isolates of S. rolfsii was tested by dual culture method. Out of 55 combinations, eight Mycelial Compatibility Groups (MCG‟s) were identified. In the compatible reactions, intermingling of the mycelia and sclerotial formation was noticed at the site of interaction between isolates. Complete overgrowth of the mycelium of two isolates was not observed in compatible reactions. The isolates produced sclerotia with exudates in a line at site of interaction between the isolates. Sclerotial formation on the surface of both the cultures was also noticed. In the incompatible reactions, formation of inhibition zone of size 0.2 - 2.6 mm and development of sclerotia on either side of inhibition zone were observed. From the study, it was clear that the virulent isolate from marigold (MG-2) showed mycelial compatibility with virulent isolates from chrysanthemum (CH-2), mango (MN-2) and banana (BA-2). Cross inoculation studies revealed that all the isolates were pathogenic to other hosts but variation in the pathogenic character of these isolates was observed. Variation in the symptom expression was not noticed on the inoculated plants by different isolates obtained from the same host. All the isolates produced infection on the leaves of other hosts, but failed to produce collar infection on mango seedlings. The isolates BA-1 and BA-2 did not initiate infection on collar region of chrysanthemum. It was concluded that different isolates of S.rolfsii obtained from the selected fruit crops and ornamental plants showed variability in their pathogenic character. Host range of S. rolfsii was studied by cross inoculating different isolates of S. rolfsii on selected vegetables viz., tomato, amorphophallus and spices viz., black pepper, ginger. All the plants tested were found susceptible to the pathogen. Symptom appeared as small, water soaked brown discolouration on the inoculated leaves and collar region. Later it enlarged in size and covered with white mycelial growth of the pathogen in all the hosts except in the collar region of amorphophallus inoculated with MG-2 and MN-2. It was also observed that the initial infection was first noticed on leaves and collar region where pinprick have been given before inoculation. Variation among the isolates was observed in the production of sclerotia and was noticed that sclerotial development was completely absent in ginger and tomato on both the leaves and collar region. On the leaves of black pepper, white mycelial growth and sclerotial formation were noticed on the lower side of the leaves. The isolate BA-2 produced concentric zonations on the inoculated leaves of pepper. Estimation of IAA and total phenol in mycelia, culture filtrate and sclerotia of various isolates revealed that all the isolates produced highest IAA and total phenol in the sclerotia. Among the isolates, MG-1 and MG-2 recorded the highest IAA and total phenol in mycelia, culture filtrate and scloerotia of various isolates of the pathogen respectively. | en_US |
| dc.identifier.uri | http://krishikosh.egranth.ac.in/handle/1/5810027605 | |
| dc.keywords | Plant Pathology | en_US |
| dc.language.iso | en | en_US |
| dc.publisher | College of Horticulture, Vellanikkara | en_US |
| dc.sub | Plant Pathology | en_US |
| dc.subject | null | en_US |
| dc.theme | Phenotypic and pathogenic variability of sclerotium rolfsii sacc. infecting fruit crops and ornamentals | en_US |
| dc.these.type | M.Sc | en_US |
| dc.title | Phenotypic and pathogenic variability of sclerotium rolfsii sacc. infecting fruit crops and ornamentals | en_US |
| dc.type | Thesis | en_US |