Browsing by Author "Kaveriappa, K.M."
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Item Effect of pre- and post-inoculation factors on infection of cocoa by Colletotrichum gloeosporioides(2007-02-08) Chandra Mohanan, R.; Nambiar, K.K.N.; Kaveriappa, K.M.Five-day old cultures of Colletotrichum gloeosporioides were more virulent. The, infection increased linearly with the increase in time of exposure to high RH and exposure to high humidity for 72 h was ideal. Oat meal agar was the best medium for sporulation. Conidia produced in this medium showed higher germination and degree of infection. Conidia germination was maximum in tap water as also the degree of infection. Disease development was the highest on 18-day old cocoa seedlings.Item Efficacy of fungicides to control three virulent isolates of Colletotrichum gloeosporioides on cocoa(2007-02-08) Chandra Mohanan, R.; Kaveriappa, K.M.The widespread occurrence of Colletotrichum disease of cocoa in India warrants the study on the control of the disease. Symptomatology of this disease revealed that besides pod rot, there are three kinds of foliar symptoms namely, blight, shot hole and irregular spot caused by Colletotrichum gloeosporioides Penz. The relative efficacy of nine fungicides on the growth of three virulent isolates of C. gloeosporioides causing blight, shot hole and irregular spot symptoms on cocoa leaves was studied in the laboratory. Out of the nine fungicides tested in vitro Carbendazim (Bavistin WP=0.05-0.10 per cent) mancozeb (Dith-ane M-45=0.20 and 0.30 per cent) and ziram (Liquid Cuman=0.3 per cent) inhibited the growth of all the three isolates completely. There was considerable variation in growth among the three isolates at different concentrations of the various fungicides tested. The effect of the above three fungicides in controlling the foliar infection caused by the three isolates, when applied as pre- and post-inoculation sprays was studied. In both pre- and post-inoculation sprays, the leaf blight and irregular spots caused by the respective isolates were controlled effectively by Bavistin WP (0.05 per cent) followed by Dithane M-45 (0.2 per cent) whereas the shot hole symptom was effectively controlled by Dithane M-45 followed by liquid cuman (0.3 per cent). Thus Bavistin WP and Dithane M-45 were found to be promising fungicides to control C. gloeosporioides disease of cocoa.Item Epidemiological studies of Colletotrichum gloeosporioides disease of cocoa(2007-02-08) Chandra Mohanan, R.; Kaveriappa, K.M.; Nambiar, K.K.N.The intensities of foliar infection (leaf blight and shot hole) and pod rot, caused by Colletotrichum gloeosporioides, were recorded from a cocoa-areca mixed garden and a cocoa-monocrop garden during 2 years. The intensity of pod rot was recorded from both the gardens. The intensities of leaf blight and shot hole gradually increased from July, reached a peak during September-November, decreased thereafter and reached the lowest level during April-June. Increase in leaf infection was associated in both plantings and in both years with the period of rain (June-November). The phylloplane population of C. gloeosporioides also increased during June-November when the temperature tended to be low and constant with high rainfall and relative humidity. During this period there were few susceptible stages of pods (cherelles and young pods) and pod infection was very low. Nearly mature pods were free from infection. In both years, pod infection was more in the cocoa-areca mixed garden than in the cocoa-monocrop; it was observed during January-May, when the susceptible stages were mostly prevalent but when the C. gloeosporioides population was low and the climatic factors appeared to be relatively unfavourable. This may be one reason for the lesser incidence of pod rot when compared to foliar disease.Item Epidemiological studies on inflorescence dieback of arecanut caused by Colletotrichum gloeosporioides(2007-02-08) Chandra Mohanan, R.; Kaveriappa, K.M.The inflorescence dieback of areca palm occurs mainly during the months of March - May. Areca inflorescences immediately after shedding of male flowers are highly susceptible to the disease. The infection usually starts from the tip of inflorescences and spreads towards the base leading to shedding of female flowers. The scars left by the male flowers at the time of shedding and the dew water deposits during night are believed to be the favourable factors for the germination, penetration and infection by the fungus on the rachille of inflorescences. It has been observed that the areca fruits which are resistant when green become susceptible when they ripen. The epidemiological studies have shown that the incidence of the disease becomes higher and higher during February-March, reaches a peak during April-May and subsequently becomes insignificant during July-January. The high relative humidity (86-99%) and low temperature (18-29°c) in the early hours of the morning (2.00 hr to 8.00 hr) followed by high temperature (28-34. 5°c) and low ft H (30-70yo) in the afternoon (12.00 hr to 16.00 hr) and the availability of inflorescences of the susceptible stage appear to favour disease development during March-May. The relationship between per cent inflorescence produced and disease incidence was found to be highly significant (r=0. 65**).Item Foliar diseases caused by Colletotrichum species(2007-02) Chandra Mohanan, R.; Kaveriappa, K.M.Item Susceptibility Of Cocoa Pods To Colletotrichum Gloeosporioides Infection(1989) Chandra Mohanan, R.; Kaveriappa, K.M.; Nambiar, K.K.N.Cocoa pods of different sizes and ages were inoculated by spraying a conidlal suspension of Colletotrichum gloeosporioides Penz. with and without injury. Although all types of inoculations caused infection of cherelles and young pods, severity of infection depended upon the method of inoculation and age of pods. The cork borer method of inoculation was preferred on account of the highest percentage of infection and uniformity in the development of lesions, which facilitated the measurement of lesions and proper assessment of the disease. For the measurement of lesion size seventh day of inoculation of cherelles is ideal. When pods were inoculated without wounds, infection was initiated mostly from the stalk end indicating that the stalk end was more vulnerable for infection than other parts. The susceptibility of pods decreased with increase in age of pods, the cherelles being more susceptible. Nearly mature pods did not take up infection. There was a significant variation in the lesion size between different age groups.Item Symptomatology of Colletotrichum disease of cocoa in India(1983) Chandra Mohanan, R.; Kaveriappa, K.M.Item Variability In Growth Of Colletotrichum Gloeosporioides Isolates Pathogenic On Cacao In Response To Fungicides, Antibiotics And Detergent(1991) Chandra Mohanan, R.; Kaveriappa, K.M.; Nambiar, K.K.N.Growth rates of three virulent isolates of Colletotrichum gloeosporioides Penz. causing foliar diseases viz., blight, shot hole and irregular spot on cacao were compared on potato dextrose agar medium containing different concentrations of fungicides (Carbendazim and Mancozeb), antibiotics (Nystatin and Actidione) and a detergent (Cetavlon). The three isolates varied markedly from each other in their growth response in the presence of these chemicals. Of the two fungicides tested, the isolates were more sensitive to Carbendazim than Mancozeb. The growth of all the three isolates was completely inhibited in the presence of Carbendazim at 5 and 10 u g/ml medium, whereas the growth of irregular spot isolate was completely inhibited even at 3 ug/ml medium. The isolates were found to be sensitive to Nystatin and Actidione though complete inhibition of growth was not observed at any of the concentrations tested. All the three isolates also showed marked variation in growth in response to Cetavlon. The irregular spot isolate was more sensitive to Cetavlon than the other two.Item Variation In Cultural And Morphological Characters Within Cocoa Isolates Of Colletotrichum Gloeosporioides(2007) Chandra Mohanan, R.; Kaveriappa, K.M.; Nambiar, K.K.N.Isolates of Colletotrichum gloeosporioides Penz. causing infection on leaves and pods of cocoa were collected from various cocoa gardens in the southern states of India. The isolates were grouped into three groups based on the symptoms produced on cocoa leaves, viz., leaf blight, shot hole and irregular spot. Cultural and morphological characters of 299 isolates causing leaf blight (210 isolates), shot hole (77 isolates), and irregular spot (12 isolates) symptoms were studied. When the isolates were grown on potato dextrose agar medium for 10 days, they showed great variability in colour and consistency of the mycelium, growth rate, degree of sporulation and size of conidia indicating that there is considerable amount of genetic heterogeneity. The isolates from each of the three symptom groups were classified into white, dark and light types based on the colour of the colony. The light type isolates showed the highest degree of sporulation. Rate of growth was the highest in white and dark types, whereas sporulation was the lowest in these groups. Out of a total of 299 isolates collected from various symptom groups, 249 isolates were of light type indicating the predominance of this group among the population of C. gloeosporioides. There was significant negative correlation between rate of growth and degree of sporulation among the isolates. The white, dark and light types could be further classified into groups and subgroups based on the marked variation in the rate of growth, sporulation, presence of acervuli and conidia size. Of the 299 isolates, 28 produced acervuli on 10-day-old cultures of which 26 belonged to light type. There was marked variation in the size of the conidia. Seven isolates of the light type culture group produced perithecia with asci ascospores in 10 to 20-day-old cultures. Isolates belonging to light type have been reported as more pathogenic than the other two groups. There appeared to be marked interrelationship between colony colour, rate of growth, sporulation and virulence. The higher rate of sporulation coupled with more pathogenic nature of the light types appears to help them to perpetuate and predominate under natural condition.Item Variation In Pathogenicity Among The Isolates Of Colletotrichum Gloeosporioides On Cocoa In India(2007) Chandra Mohanan, R.; Kaveriappa, K.M.Colletotrichum disease of cocoa (Theobroma cacao L.) occurs in most of the cocoa growing regions in India. Symptomatology of the disease reveals that besides pod rot there are three kinds of foliar symptoms, viz., blight, shot hole and irregular spot. The leaves, pods and seedlings showing various symptoms of the disease were collected from 101 cocoa gardens including nurseries in the states of Kerala, Karnataka and Tamil Nadu. Isolation of the pathogen from infected plant parts invariably yielded Colletotrichum gloeosporioides Penz. A total of 312 isolates of the pathogen were collected, of which 198 were from leaves, 82 from pods, and 32 from seedlings. Based on the colour of the colony when grown on potato dextrose agar medium the isolates under each symptom group were classified into light (gray), dark (olive gray to black) and white types. Disease index was calculated by inoculating 18-day-old cocoa seedlings. Of the 312 isolates, 299 were pathogenic, of which 210 incited blight, 77 incited shot hole and only 12 isolates incited irregular spot. The most virulent isolate among blight, shot hole and irregular spot group was found in Kanyakumari, Cannanore and Chikmagalur districts respectively. The study further showed that most of the isolates of C. gloeosporioides were pathogenic and among them leaf blight group of isolates were predominant and wide-spread. Inoculation trials also revealed a great variation in pathogenicity among the isolates under each symptom group. In general isolates of light type were found to be most virulent. From the results it may be concluded that while screening for disease resistance it is desirable to select light type of isolates covering a wide range of collections.Item White thread blight of Cacao in India(1983) Chandra Mohanan, R.; Kaveriappa, K.M.