Browsing by Author "Veena, S S"

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Distribution of species of phytophthora affecting coconut and pepper in Kerala
(Department of Plant Pathology, College of Agriculture, Vellayani, 1996) Veena, S S; Peethambaran, C K
The present investigation was undertaken to correctly identify the species of Phytophthora causing bud rot of coconut and foot rot of pepper in Kerala and to find out their comparative role in causing diseases on coconut and pepper. The study also aimed at isolation of viable antagonistic agents against the pathogen, so as to utilize them in future for biological control. The study was conducted during 1992-96 at College of Agriculture, Vellayani and Indian Institute of Spices Research, Kozhikode. Detailed symptomatology of both the diseases at different locations were studied. Periodic collections were made from diseased coconut and pepper from seven districts of Kerala. The morphological characters of the isolates were studied in detail. The length, breadth, L/B ratio, pedicel length and caducity of sporangia of coconut isolates were smaller than pepper isolates. The sporangial shapes differed considerably between and among the isolates. All the isolates except those collected from Kannur and Kasaragod districts (C7 - C16), produced abundant number of sporangia on carrot agar. Phytophthora are either heterothallic or homothallic. Generally P. palmivora and P. capsici are heterothallic. But ten coconut isolates obtained from Kannur and Kasaragodu districts produced abundant number of sexual structures on carrot agar, indicating their homothallic nature and this is the first report of homothallic Phytophthora causing bud rot of coconut in Kerala. All other 52 isolates were mated with known A1 and A2 mating type and all the coconut isolates produced oospores with A1 and all the pepper isolates produced oospores when mated with A2. Zoospore production was induced from sporangia using cold treatment. The number of zoospores in sporangia ranged from 6-15 in number. Chlamydlospore production was a rare phenomenon in pepper isolates while all the coconut isolates and five pepper isolates produced chlamydospores. All the isolates were inoculated into pepper seedlings, coconut leaves, tender coconut and coconut seedlings and the time required for infection, variation in symptom expression by different isolates etc. were studied. All the sixteen coconut isolates produced foot rot in pepper. Fourty six isolates of pepper produced lesions on coconut leaves and nut rot in tender coconut, while, only six isolates of pepper produced bud rot in coconut plants. The cross infectivity of pepper isolates needed further confirmation to prove the point beyond doubt. Eight cultivated plants, 9 ornamental plants and 12 weed plants were tested for the host range of coconut and pepper isolates. Many plants belonged to the above three groups took infection successfully. The microorganisms found associated with healthy and diseased pepper and coconut plantations and microorganisms from soils of pepper and coconut gardens of different parts of Kerala were isolated. Out of more than 200 microorganisms, only 28 fungi inhibited the growth of Phytophthora in vitro. On pepper plant, 12 isolates had inhibitory action. Three organisms, viz., Verticillium chlamydosporium, Aspergillus terreus and Chaetomium sp checked the pathogen completely even after seven days of spraying with the organisms.
Etiology and management of powdery mildew disease of pumpkin (Cucurbita moschata Poir)
(Department of Plant Pathology, College of Horticulture, Vellanikkara, 1992) Veena, S S; Rema Devi, L
The present investigation was undertaken to correctly identify the causal organism of pumpkin powdery mildew disease in Kerala and to find out the environmental factors responsible for the occurrence of infection. Attempts were also made to screen different pumpkin lines to identify resistant ones to powdery mildew. The efficacy of different antifungal compounds against the disease were also tried. The study was conducted during 1990 -92 at College of Horticulture, Vellanikkara. Detailed symptomatology of the disease was worked out. The time taken for getting infection varied in resistant moderately resistant and susceptible plants. The fungus causing powdery mildew disease of pumpkin in Kerala was identified as Sphaerotheca fuliginea (Schlecht) Poll. Teleomorphic stage of the pathogen was not observed. From the cross inoculation studies it was clear that S. fuliginea from pumpkin cannot infect non-cucurbitaceous crops and weeds. Even in cucurbits it could infect only bittergourd and ivy gourd. The optimum temperature for germination of S. fuliginea was at 25°C followed by 20°C. The spores germinated at very high relative humidity while it was inhibited in water. Preliminary screening of 57 lines of pumpkin was conducted during 1990 season and 28 lines were selected from this for further studies. All the lines were found infected in both the seasons. But the degree of susceptibility and the age at which they became susceptible were varied. Only the line showed consistency in resistant reaction. Climatic factors like temperature, relative humidity, rainfall and sunshine hours were recorded for an year and was correlated with the disease severity. Incidence of the disease was indirectly correlated with rainfall. However, the influence of climatic factors were more pronounced during the initial stages of the crop. Laboratory and field experiments were conducted to find out the efficacy of five antifungal compounds and water on S. fuliginea. All the chemicals and water inhibited spore germination at varying concentrations. Effect of those chemicals and water were also tried under field conditions on line P. 46. At the end ofone week after spraying Carbendazim recorded maximum disease reduction. Disease at the time of harvest was least in Sulfex treated plants. Even water spray could reduce the disease considerably. Maximum yield was recorded from plants sprayed with Calixin. The best cost effective method to check powdery mildew infection of pumpkin was by spraying water.
Expression of pathogenesis related proteins by plant growth promoting rhizobacteria in controlling taro leaf blight
(Department of Plant Biotechnology, College of Agriculture, Vellayani, 2020) Rajalakshmi, R; Veena, S S
Molecular characterization of pathogens associated with post harvest diseases in elephant foot yam
(Department of Plant Biotechnology, College of Agriculture, Vellayani, 2018) Adithya, V; Veena, S S
Morphological, biochemical and molecular characterization of Trichoderma isolates from tuber crop ecosystems
(Department of Plant Biotechnology, College of Agriculture,Vellayani, 2019) Linet K Joseph; Veena, S S
Elephant foot yam (Amorphophallus paeoniifolius (Dennst.) Nicolson) is an important tuber crop popular as a food security crop and as a remunerative cash crop. Collar rot caused by Sclerotium rolfsii is the most destructive and predominant disease causing great crop loss in elephant foot yam. Application of Trichoderma spp is being recommended as the eco-friendly strategy to combat the crop loss. The present study, ―Morphological, biochemical and molecular characterization of Trichoderma isolates from tuber crop ecosystem‖ was conducted at the Division of Crop Protection, ICAR- Central Tuber Crops Research Institute (CTCRI), Sreekariyam, Thiruvananthapuram during October 2018 – August 2019. The study was performed to evaluate 43 Trichoderma isolates obtained from tuber crop ecosystem for their bio-control potential against S. rolfsii, to characterize the isolates using morphological, biochemical and molecular approaches and to analyse the molecular diversity. The differential antagonistic potential of the isolates were assessed by adopting three in vitro screening methods. The screening methods executed were dual culture/ direct confrontation method, antibiosis test for production of diffusible metabolites and volatiles. Based on the additive effect of each mode of inhibition, it was concluded that the isolates viz., T38, T36, T32, T40 and T6 have excellent antagonistic potential. Twenty six best isolates were selected for further study based on the ranking of additive result. The efficiency of 26 isolates for induction of chitinase and β-1,3-glucanase was studied against the cell wall of S. rolfsii as carbon source. There was no direct correlation observed between antagonistic potential of isolates and induction of chitinase enzyme. Whereas, positive correlation was observed between antagonistic potential and induction of β-1,3-glucanase enzyme. The effect of volatile organic compounds (VOCs) on plant growth was studied using mustard seeds. The isolates 94 showed differential response to various growth parameters like fresh weight, number of leaves, root length, shoot length and number of shoot lets. For morphological characterization, the macro and micro morphological characters such as growth rate, colony color, reverse colony color, odor of culture and branching pattern of conidiophore, size of conidia and phialides of isolates were studied. Morphological identification of Trichoderma isolates up to species level was found difficult due to the overlapped expression of these characters. The molecular characterization was done by amplifying and analyzing the sequences of ITS gene 1 and 2 and tef1 gene. The six different species identified are T. asperellum, T. virens, T. hamatum, T. reesei, T. longibrachiatum and T. erinaceum. The variability was studied using SSR markers and it was found that Jaccard’s similarity coefficient of 10 SSR primer banding patterns varies from 0.31 to 1.00. Fourteen T. asperellum isolates (T1, T2, T3, T5, T11, T13, T15, T16, T17, T18, T19, T20, T42, T43) were clustered in cluster A and the remaining three T. asperellum isolates (T32, T34 and T41) were clustered into cluster B. It showed the significant variability even within the same species. Considering the antagonistic potential, high chitinase and glucanase production and plant growth promotion, isolates T2, T15, T32, T34 (T. asperellum) and T40 (T. erinaceum) were selected as effective bio-control agents. The present study helped in identifying the Trichoderma isolate with high antagonistic potential against S. rolfsii and the entire process ensured more précised and targeted application of Trichoderma isolate in field condition. The outcome of the study will be a key factor in developing appropriate management strategy to mitigate collar rot disease in elephant foot yam.
Piriformospora indica mediated response in taro (Colocasia esculenta (L.) Schott) with special emphasis to growth and leaf blight incidence
(Department of Plant Biotechnology,College of Agriculture, Vellayani, 2016) Lakshmipriya, P; Veena, S S