Pomegranate Bacterial Blight: Abutilon indicum, Prosopis juliflora, and Acacia arabica as Antibacterial Agents for Xanthomonas axonopodis pv. punicae
Xanthomonas axonopodis pv. punicae causes bacterial blight disease in pomegranate. A complete range of symptoms of bacterial blight caused by X. axonopodis pv. punicae appear on various pomegranate plant parts, except roots. The present investigation was initiated to find a suitable alternative to synthetic antibiotics for the management of plant diseases caused by bacteria. The study was aimed to use wild plant species, viz., Abutilon indicum, Prosopis juliflora, and Acacia arabica as antibacterial agents against X. axonopodis pv. punicae. The aqueous extracts of A. indicum, P juliflora, and A. arabica plants has antibacterial activity against X axonopodis pv. punicae. The antibacterial activity was tested by a well diffusion assay, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC). The maximum activity was recorded by P. juliflora (MIC = 1.03 mg mL'1 and MBC = 0.15 mg mL'1) and A. arabica (MIC = 1.00372 mg mL'1 and MBC = 2.58 mg mL'1) against
X. axonopodis pv. punicae, while the lowest activity was recorded by A. indicum (MIC = 0.619 mg mL'1 and MBC = 0.923 mg mL-1). The largest zone of inhibition (ZOI) was shown by P jultflora, while the shortest ZOI was shown by A. indicum. The results infer that the extracts of P jtiliflora and A. arabica are highly sensitive to X. axonopodis pv. punicae. The plant extracts exhibited antibacterial activity with the potential to be used in the management of many plant diseases as an alternative to chemical antibiotics. A further phytochemical analysis is required to identify the bioactive compounds responsible for antibacterial activity.
Pomegranate (Ptinica granatum L.) is an ancient fruit, belonging to the smallest botanical family Punicaceae. Pomegranate is a native of Iran, where it was first cultivated in about 2000 BC but spread to the Mediterranean countries at an early date. It is extensively cultivated in Spain, Morocco, and other countries around the Mediterranean, Egypt, Iran, Afghanistan, Arabia, and Baluchistan. Pomegranate is a good source of carbohydrates and minerals such as calcium, iron, and sulfur. It is rich in vitamin C, and citric acid is the most predominant organic acid in pomegranate (Malhotra et al., 1983). Apart from the fleshy portion of the fruit, the crop residues are also finding a place in industries. The rind of the fruit is a good source of dye, which gives yellowish-brown color to khaki shades and is being used for dying wool and silk. The flower and buds yield light red dye, which is used for dying of cloths in India. The bark of the stem and root contains a number of alkaloids belonging to the pyridine group. The bark is used as a tanning material, especially in Mediterranean countries in the East (Bose, 1985). Pomegranate is regarded as the “Fruit of Paradise.” It is one of the most adaptable subtropical minor fruit crops, and its cultivation is increasing very rapidly. In India, it is regarded as a “vital cash crop,” grown in an area of 116,000 ha with a production of 89,000 million tons and an average productivity of 7.3 million tons (Srivastsva and Umesh, 2008). The successful cultivation of pomegranate in recent years has met with different traumas such as pests and diseases. Among the diseases, bacterial blight caused by X. axonopodis pv. Punicae is a major threat. Since 2002, the disease has reached an alarming stage and is hampering the Indian economy and the export of quality fruits. The disease accounted for up to 70-100% during 2006 in Karnataka and
Maharashtra, resulting in the wipeout of the pomegranate. During the year 2007, the total output of pomegranate production in India was down by 60% (Raghavan, 2007).
The causal organism of blight is X. axonopodis pv. punicae (Hingorani and Singh, 1959) Vauterin, Hoste, Kersters and Swings (Hingorani and Mehta, 1952; Vauterin et al., 1995). The plant is susceptible to a blight during all stages of growth and results in huge economic loss. Bacterial blight primarily affects the above-ground plant parts, especially leaves, twigs, and fruits. While the leaves how early water-soaked lesions to late necrotic blighting, the fruits show isolated or coalesced water-soaked lesions followed by necrosis with small cracks and splitting of the entire fruit (Petersen et al., 2010). Stems show lesions around nodes or injuries, forming cankers in later stages. Suspected symptoms on floral parts have also been reported (Chand and Kishun, 1991; Rani et al., 2001). It is also presumed that the stem canker could be an outcome of the systemic spread of bacterium from the leaf (Chand and Kishun, 1993). However, it is reported by Chand and Kishun (1991) and Rani et al. (2001) that attempts to reproduce the field symptoms of blight on detached leaves, twigs, and fruits were unsuccessful in artificial inoculations. The management of bacterial blight of pomegranate is a major concern. This disease could not be effectively managed by conventional antibiotics like streptocycline in field conditions. Thus, this investigation is carried out on the management of the disease by aqueous extracts of Abutilon indicum, Prosopis juliflora, and Acacia arabica plants. Continual and indiscriminate use of synthetic antibiotics to control bacterial diseases of crop plants has caused health hazards in animals and humans due to their residual toxicity (Raghavendra et al., 2006). A bioactive principle isolated from plants appears to be one of an alternative for controlling plant and human pathogens developing resistance to antibiotics. Plant-originated antibacterial compounds can be one approach to plant disease management because of their ecofriendly nature (Bollcan and Reinert, 1994).