The Bacterial Blight Abating Profitability of Pomegranate Growers

In Pakistan’s the agriculture sector playing an essential role in the economy of Pakistan, with 18.9 per cent share in GDP and providing about 42.31 per cent labor force. The climate of Pakistan is ideal for growing various fruits Pakistan has been blessed with immense agro-climatic conditions that favor the fabrication of a variety of Horticultural crops including various fruits like almond, apple, apricot, banana, ber, chiku, citrus, date palm, grapes, guava, litchi, loquat, mango, peaches, pomegranate, persimmon and etc. In Pakistan, fruits are being cultivated over an area of 0.77 million hectares with an annual production of 6.75 million tones.

 Pomegranate fruit plant has attracted consumers immense interest due to its health and nutritional properties. It is among the first five domesticated edible fruits (pomegranate, date palm, fig, olive and grapes). The plant was cultivated from 5000 BC documented two times in the Holy Quran with the name of Al-Ruman and extensively cultivating in Afghanistan, Iran, China, India, Turkey, Egypt, USA, Pakistan and Mediterranean countries (Spain, Morocco, Turkey, Tunisia). India is the world’s leading producer followed by China, Iran, Afghanistan, USA, Israel and etc. Turkey has the largest export share, followed by Egypt, India, and Spain. Pomegranates may be planted up to 1000 meters from sea level and show resistant to drought, salt, iron chlorosis, and active calcium carbonate. It can withstand temperatures as low as -10°C and as high as 45°C, although the finest fruit is produced around 38°C. It has been declared a super fruit globally due to the presence of vital compounds. Apart from the table consumption of pomegranate arils, the flowers fruit rind and vegetative parts of pomegranate plants are also good source of secondary metabolites such as Phenolic, anti-oxidants, tannins, dyes, alkaloids, protein, carbohydrates, vitamins, minerals, dietary fiber, bioactive compounds and some other phyto-chemicals as compared to other fruits. The edible portion of this fruit is up to 68 per cent with moisture contents (78%), phosphorus (70 mg/100g), protein contents (1.6%), calcium (10 mg/100 g), iron (0.3 mg/10g), riboflavin (0.10 mg/100g) and vitamin C (16 mg/100g of fruit weight.                                           

Pakistan is the 12^th largest producer of pomegranates while its cultivated area and production have been steadily declining since 2000. The total area of pomegranate fruit production in Pakistan during 2010 was 12952 with annual production 49997 tons (6.97 tons/Ha) which is decreased to 9434 during 2015 with annual production 42641tons (6.76 tons/Ha). Pomegranates are produced on 7330 hectares in Pakistan, with an output of 37.6 thousand tonnes per year. Balochistan province is making the most contribution (72%) followed by Punjab (21%) and Khyber Pakhtunkhwa (3%). In Punjab various districts like Rahim Yar Khan, Bahawalpur, Multan, Khanewal, and Vehari account for up to 80% of the total production of Punjabi (MNFSR, 2020). During 1980s, total area for pomegranate in Punjab was maximum at Alipur Tehsil. Alipur remained major pomegranate producing pocket with best quality in the South Punjab and city was considered as a brand name for pomegranate. The farmers from Alipur told that they got three times more profit as compared to other agronomic or fruit crops from Pomegranate orchards. But due to attack of Bacterial Blight, their orchards started to decline since last twenty years. Being the most profitable and superb fruit crop in the world it is going towards decline side in Pakistan. Pomegranate did not require so much inputs as compared to other fruit crops like wise Mango, Citrus, Litchi, Grapes, Apple, Pear, Apricot, Plum, Peach and etc. It can easily bear the harshly environment like shortage of water and fertilizers, salinity, high and low temperature and frost. But if proper care is given from selection of cultivar to orchard establishment, then our farmers can get maximum return from this ignored/ minor fruit crop. The cultivation of pomegranate always remained highly profitable for farmer. But unluckily since 2000 the profitability of pomegranate growers is continuously reducing due to various factors. Numerous stresses, such as bacterial blight, fungi, nematodes, nutritional deficiency, drought, excessive irrigation, high temperatures with solar radiations, a lack of improved cultivars, the production of offshoots (water shoots and suckers), etc., were to blame for the drastic decrease in its cultivated area and output. Problems including prolonged lack of appropriate cultivars, hot, dry spells, climatic change, nutritional inadequacies, physiological abnormalities, post-harvest losses, insect pests, and illnesses are all associated with unsustainable fruit output. Pomegranate production in South Punjab is taking its last breath due to several abiotic and biotic stresses.

Pomegranate production is associated with many problems like long dry spells, non-availability of suitable varieties, climate changes, nutritional deficiencies, physiological disorders, post-harvest losses, pests and diseases. Among these constraints, losses due to pests and diseases are very high. Although, 25 to 30 per cent of total cost of production is being spent on plant protection especially pesticides, to manage biotic constraints. Among various biotic constraints, the huge loss by pomegranate grower is faced due to bacterial disease popularly known as ‘bacterial blight’ caused by Xanthomonas axonopodis pv. punicae. The occurrence of leaf spot of pomegranate for the first time in India during 1952 while in Pakistan it was reported first time in 1995. The bacterial blight is also known as nodal blight, black spot, oily spot, Telya and Hudda disease in various Pg producing regions. The bacterial blight of pomegrante is a notorious disease for economic point of view. It affects almost all commercial cultivars including Baidana, Sawa kaghzi, Sandhura, Kalehar, Ternab and Sandhuri. Severity of infection varies with type of cultivars grown and prevailing climatic conditions.

 Morphological Characteristics of Bacterium

            The XaP appeared as short rod with rounded ends, single or in pairs, monotrichous, gram negative, non-endospores with capsule with measuring 0.75 to 3.0μm in length and 0.45 to 0.5μm in width. The optimum temperature required for the growth of XaP is 30^oC. The maximum and minimum temperature required for the growth is about 40 to 10^oC and thermal death point was 52^oC.

Symptoms of BB ; 

The symptoms as irregular spots of 2 mm to 5 mm in diameter. Initially small spots were observed on lower side and adjacent spots combined and covered larger areas of leaves. The spots were initially light brown in colour, surrounded by water-soaked margin and later turned into dark brown as disease progressed. The initially spots on leaves were small, circular with yellowish border and brown center. Tissue necrosis and defoliation occurred in serious cases of infection. Fruits and flowers also infected with water-soaked spots in the earlier stages and later became dark brown with oily appearance after 4-7 days after infection. The disease symptoms on stem appeared as brown to black colour spots around the nodes leading to girdling and cracking of nodes. Brown to black, ‘L’ or ‘Y’ shaped cracks spots also occurred on fruit pericarp.

On flower buds, small water-soaked lesions, appeared which later on turned to brown to black coloured spots leading to dropping of buds under severe incidence. Symptoms on fruits were very conspicuous with small pin head sized lesions surrounded by diffused water-soaked margin as a mark of bacterial infection. The lesions later on developed into brownish black coloured, medium to big sized spots (2–10 mm in diameter). One to many such spots could be seen on the single fruits. In severe case of infection, the affected fruits split opens with L/Y/ star shaped cracks on the pericarp. Infected fruits did not develop further nor dropped but dried up and hanged in the plant itself.  Later on, spots turned dark brown, coalesced and covered the larger areas of leaf lamina led to the shedding of leaf at the final stage. They did not notice any symptoms on twigs/branches and fruits.

Primary sources of inoculum (Fallen leaves and Wounds on Stomata)

            The fallen leaves play crucial role in the survival of the XaP where it survives. The pathogen, XaP survive in the infected fallen leaves reserved protected under field condition upto 210 days and in canker lesions upto 80 days. The pathogenic bacterium causing leaf spot of pomegranate contaminated through wounds and stomatal openings and shows water-soaked lesions, which later build up into irregular spots.

Source of spread

The infected plant residues of pomegranate, such as leaf, stem and fruit, which are left out in the field after the harvest of the crop serve as a primary source of inoculum for subsequent season to initiate the disease. The vital role of infected fallen leaves in the survival of pathogenic bacterium causing leaf spot of various crops is well established.

Temperature and pH requirement

The optimum temperature required for the growth of Oily spot disease causing bacterium was 30ºC with maximum tolerance limit at 40°C. Minimum temperature required for the growth of pathogen was about 5- 10°C and the thermal death point at 52ºC. The pathogen, Xanthomonas axonopodis pv. punicae, grew at a wide temperature range of about 20°C to 40°C and recorded maximum number of colonies when inoculated plates were incubated at 27°C Manjula (2002). The growth of pathogen was not observed at 10°C. An optimum pH of 7.2 was found to be good for growth with a range between 5.5 to 8.0. Giri (2009) reported that, the 20°C was optimum for Ramatala, Gulaganjikoppa,

H. B. Hally, Uthnal, Bardol, Shravanagere, Bennehally, Mudol, Hulihyder, Talkal, Kurubara Ramanahally isolates, while 30°C was found to be optimum for the remaining isolates. However, these isolates showed good growth even at 20°C. All the isolates of X. axonopodis pv. punicae required pH 5.0 for maximum growth. The growth of almost all the isolates decreased as the pH of the medium gradually increased to 8.0, while Ramatala and Mudol isolates showed good growth even at pH 8.0. Yenjerappa (2009) evaluated the varied temperature and pH levels for the growth of X. axonopodis pv. punicae and noticed that temperature of 30°C and pH of 7.0 to 7.5 were found optimum for the good growth of the pathogen. The over and below these levels the growth was decreased.               

The Risk Period for BB Disease in Pomegranate

The risk period for Bacterial blight in pomegranate can be divided into three groups; Low Risk period, medium risk period and High-risk period.

Low Risk period;

No bacterial blight disease in field of pomegranate but climate conditions is suitable.

Use of bio cards of Trichoderma, Pseudomonas and Bacillus as a bio control agent.

Use of plant nutrients (K, Mg and Ca) and apply preventive n=bactericides ().

Medium Risk Period;

Suitable climatic condition. Availability of pathogen history without diseases infection symptoms. Use preventive bactericides as it takes 10 to 15 days to develop disease symptoms.

High Risk Period;

Climatic conditions suitable befor 8 days. Pathogen history avaialabel. Symptoms of BB disease have been seen. Use Copper oxychloride + Antibiotics.

Disease Severity triangle

Methods for Bacterial blight Management

The integrated approach must be adopted for effective management against bacterial blight in pomegranate. The farmers should adopt following strategies to get rid from bacterial blight.

1. Avoid Pomegranate plantation in very light soil where chance of BB increased.
2. Selection of healthy planting material that must be disease free. Keep proper planting distance (minimum 14*10 feet). High density cause BB. The recommended spacing between the plant and rows is 4.5×4.5 m. Many farmers accommodate more plants per unit area. Hence, there is more possibility of spread of disease.
3. Use of organic manure, cakes, slurry, biofertilizers and Slurry (without urine).
4. Use of organic mulch to reduce soil temperature and improving soil moisture.
5. Improve white root development.
6. Disinfect pruning tools before pruning a new plant (Dettol @ 20ml per liter of water).
7. Avoid from Hard pruning.
8. Use live fencing.
9. Use of live fencing.
10. Do not use nitrate based nitrogenous fertilizers (Potassium nitrate, Magnesium nitrate, Ammonium nitrate Calcium nitrate and etc.).
11. Application of 4% copper-based dust or 1% Bleaching powder under plant canopy during rainy season.
12. Good and sustainable harvest should be only after 4 years of planting but many farmers take crops soon after 1 year or 1 ½ year of planting. This practice makes the plants become weak and more prone to the disease.
13. Sanitation of the orchard: farmers are unaware of role of sanitation in management of bacterial blight of pomegranate. Diseased leaves and fruits which are fallen on the surface of soil are simply left as it is in the orchard. This situation helps to build up more disease. Also use disinfectants like hydrogen peroxide (H₂O₂) during high-risk period.
14. Insect management: many insect infesting pomegranates are causing damage to the fruit, hence entry of bacteria will be very easy. This insect menaces increase the severity of disease.
15. Try to reduce maximum biotic and abiotic stress.
16. Immediately spray just after pruning with Bordeaux mixture @ 1% or Streptocycline @ 0.25 gm plus COC @ 2gm per liter of water.
17. Reduced the no of spray to avoid chemical stress and physical injury. Unnecessary spraying: frequent and unnecessary spraying leads to the deposition of water drops on the diseased parts and this will be helpful for release of bacterial cells hence there are more chances of spreading of disease.
18. Application of COC and Streptocycline just after thunder storm.
19. Clean cultivation. Collect the infected materials (diseased fruits, fallen leave, water shoots and suckers) and fired them.
20. Do not disposed off the diseased fruits in canal or water course.
21. Dot takes any fruits from young plant for three years.
22. Application of Salicylic acid @ 0.3gm/ Liter of water.
23. Use deficient irrigation strategy during fruit development stages.
24. Use of systemic and non-systemic bactericides.
25. Movement of workers in the orchard: many a times there is chance of movement of workers from a diseased field into healthy fields without any change of dress and uncleaned condition.
26. No visitor or unknown person to allow in your orchard as it may be carrier of BB disease.

Cultural and preventive Management of B. Blight

            Several management options have been investigated, involving the application of antibiotics, chemicals and other cultural practices. For the successful management of any disease under normal conditions, clean sanitation, eradication of primary source and chemical protection at initial stages are some of the measures recommended. Hence, thorough understanding of disease epidemiology and concrete package is necessary to address bacterial blight effectively and to save the crop at early stages. Now, it is the established fact that, weather factors play an important role in the inhibition and spread of the disease.

Biocontrol agents

The inhibitory effect of Pseudomonas fluorescens on the growth of Xanthomonas citri was recorded by Unnamalai and Gnanamanickam (1984). Sivamani et al., (1987) studied the toxicity of Pseudomonas fluorescens against bacterial plant pathogens of banana (Pseudomonas solanacearum) and rice (Xanthomonas campestris pv. oryzae). They discovered that native strains of Pseudomonas fluorescens could be the efficient biocontrol agents against Pseudomonas solanacearum and Xanthomonas oryzae. Chand et al., (1991) studied the antimicrobial activity of Erwinia herbicola and Bacillus subtilis against Xanthomonas campestris pv. viticola in vitro.

Chemical Methods

Chlorination of drinking water has been used since long to purify microbial contamination. Stable bleaching powder a cheap chemical has been effectively used for the control of some bacterial plant diseases like black rot of garden stocks, black rot of cabbage Bordeaux mixture 5:5:50, 1% perenox 1:50 lime sulphur controlled the bacterial disease on pomegranate caused by the infection of Xanthomonas axanopodis punicae. The use of bleaching powder (2 kg/ha) on the standing paddy crop, when the crop is 74 days old, in controlling the bacterial leaf blight efficiently and this is very effective with five sprays of streptocycline + copper oxychloride. Chand et al., (1981) evaluated that the stable bleaching powder (250 ppm) was very efficient in decreasing the number of colonies of Xanthomonas campestris pv. campestris. The results obtained on inhibition were effective with streptocycline (100 ppm) and exhibited significantly remarkable to Agrimycin-100 (100 ppm), Agallol-3 (10,000 ppm) and plantvax 20 EC (500 ppm). Bordeaux mixture (5:5:50) in combination with either streptocycline (500 ppm) or plantomycin (500 ppm) was very powerful in controlling the citrus canker caused by Xanthomonas citri. Spraying of Bordeaux mixture alone also reported the lower canker incidence in comparison with bavistin at 0.1%. The significant effect of bactrinashak, streptocycline or bacterimycin at 0.05% concentration in combination with COC 0.25 % against bacterial blight of pomegranate under field conditions. During an investigation it was found that the lowest percent disease incidence (PDI) of 14.07 with the spray of streptocycline (0.5 %) in combination with COC (02%) against bacterial blight of pomegranate under field condition.

Ghulam Mustafa
PhD Scholar
MNS- University of Agriculture, Multan