Management of Bacterial Diseases
Bacterial plant pathogens directly enter the host tissue either through natural openings or through wounds; therefore, it is difficult to manage them. Some of the general principles of managing the bacterial disease are as follows:
Exclusion of a disease entry either from a foreign nation or within the country, fro a diseased to a healthy tract is an effective measure for avoiding the disease. Quarantine measures are in vogue in several countries. E .g diseased managed: Citrus canker (Xanthomonas campestris pv. citri) in U.S.A.
Eradication is generally carried out for eliminating a well established pathogen and its host plant, collateral hosts, or insect vectors and some times use of cultural measures for starving out or killing the pathogen E. g of disease managed.
i) The complete distruction of all infected trees was successfully achieved the citurs canker in Florida, USA during 1914-1927.
ii) Pruning of the infected twigs is followed to reduce the inoculums in orchards for citrus canker.
iii) The destruction of volunteer plants and weed hosts brings down the inoculum level. e.g Brown rot of potato ( Pseudomonas Solanacearum).
iv)The crop residue may be burnt or ploughed deep into the soil with watering to ensure decomposition, which is helpful for the pathogens which cannot live saprophytically in the soil. E. g Bacterial blight of cotton (Xanthomonas campestris pv. malvacearum).
v) Crop rotation with cereals is advocated for the management of wilt of tobacco ( Pseudomonas solanacearum).
vi) The selected application of NPK , particularly low and split doses of N, helps to reduce the intensity of the bacterial leaf blight of rice ( Xanthomonas campestrsi pv. Oryzae).
vii) The control of insects is helpful in reducing the soft rot of vegetables ( Erwinia spp.) and the citrus canker ( Xanthomonas campestris pv. citri).
viiii) The avoidance of cultural mismanagement favourable to disease is important such as water logging in the nurseries ( against the bacterial leaf blight of rice), flooding or over irrigation in the field. ( against the soft rot disease)
ix) The sterilization of the cutting knife by flame or by 0.1 % KMNO4 solution while cutting the potato tuber for sowing is recommended against the potato wilt.
x) The seed certification programes to raise pathogen free seeds. E.g bean ( Xanthmonas campestris pv. campestris) are in practise in U.S.A.
xi) Elimaknation of the extremally and internally seed born pathogen by seed treatment.
E. g 1. Delinting of cotton seed with concentrated sulphuric acid for bacterial blight of cotton.
2. Hot water treatment of cotton seed at 560C for 10 minutes for bacterial blight of cotton.
3. Soaking of rice seeds in 0.025% strpetocyclic solution for leaf streak disease of rice.
xii) When tobacco is immediately grown after maize there is a considerable reduction in the incidence of Pseudomonas solanacearum on the later host.
xiii) There is some prospect of biological control with the application of organic matter in the form of compost and green manure and even inoculation of antibiotic micropropaganism, encouraging antagonism by the application of superphosphate, application of phages in seed plant and soil as well as by inoculating with bacteriocin- producing strains.
3. Plant Sanitation:
These measures are adopted so as to avoid the disease onset and also to prevent spread.
E.g. i) Removal of dead plant parts from fruit crops and protection of cut surface with suitable bactericides (E. g for citrus canker and fire blight of apple).
ii) Avoiding injuries to the plant parts at the time of cultural operations and during harvest, transport and storage.
iii) Collection and destruction of diseased fallen leaves, bolls etc. for bacterial blight of cotton.
4. Plant Protection:
These measures are adopted to prevent the onset and subsequent spread of plant diseases.
E. g i) Seed treatment of cotton and rice with antibacterial chemicals against bacterial blight and leaf streak diseases respectively.
ii) Treatment of vegetatively propagation material with bactericides e.g 0.02% stroptocycline for 30 minutes treatment of seed tubers of potato against brown rot disease.
iii) Foliar sprays with Bordeaux mixture and copperoxy – chloride against leaf spots and blights.
iv) Foliar sprays of streptomycin sulphate, 100 and 500 ppm against fire blight of apple and citrus canker.
v) Therapy: Pancillin and vancomycin are effective in the disintegration of the crow gall. The application of antibiotics for protection also involves therapy. The bacteriocines have also been demonstrated to be successful against bacterial disease E. g Agrobacterium radiobacter against crown gall of peach and tomato seedlings (Agrobacterium fumetaciens.)
vi) Immunisation: By screening under artificial epiphytic conditions, resistance source for bacterial pathogens can be known. Resistant varieties are evolved by selection, breeding and other methods. E. g HC-9, BJA-592, P-14, T-12, 101-102 B, Reba-B-50, Khandwa-2, DHY-286, B-1007, cultivars of cotton and N-22,IR-22 cultivars of rice resistant to bacterial blight disease of these crops.
vii) Disease Forecasting: Plant disease forecasting help in timely and economic management of bacterial diseases. Following basic principles are used for forecasting.
a. Forecasting by natural infection: This is based on observation of plants at regular intervals- both in the nursery as well as in the main field for the occurrence of the disease.
b. Forecasting by climatic condition: Effect of various metrological parameters on the incidence and spread of the disease in studied in detail and the congeneal meteorological parameters for these are workedout. Prediction model is prepared on the basis of these observations.
c. Forecasting by bacteriophage population: A correlation has been obtained between the occurrence of bacteriophage in the field (Soil, irrigation water, etc.) and disease outbreak in the case of bacterial leaf blight of rice. Prior to outbreak of the disease the phage population in soil and irrigation water increase. It is possible, to some extent to forecast the disease outbreak using the phage population as an index.