Assessment of genetic diversity among different indigenous Xanthomonas isolates via RAPD and ISSR

The genetic diversity among seven Xanthomonas isolates representing four species was assessed using RAPD and ISSR PCR-based techniques. Both techniques revealed high degrees of polymorphisms among the studied isolates. A cluster dendrogram based on the combined data of RAPD and ISSR showed that genetic diversity exists in local isolates of Xanthomonas. In terms of percentage similarity values, the genomic variation was found to be in the range of 29.29% - 100% among the isolates. X. campestris (Mangifera indica) remained unclustered in cluster dendrogram and revealed a unique genomic profile compared to other isolates used in this study

In vitro control of Alternaria citri using antifungal potentials of Trichoderma species

The antifungal potential of five species of Trichoderma viz., Trichoderma viride, Trichoderma aureoviride,  Trichoderma reesei, Trichoderma koningii and Trichoderma harzianum was investigated in vitro against  Alternaria citri, the causal agent of the black rot disease on a broad range of citrus cultivars. Cultural filtrates of Trichoderma species were obtained by growing them on different media. The effect of different filtrate  concentrations revealed that aqueous extracts of all Trichoderma species significantly reduced the fungal  biomass of the target fungal pathogen. Generally, 100% culture filtrate of the test Trichoderma species  significantly reduced the growth of fungus. On each medium, a different response was observed. Culture filtrate of T. harzianum was found highly effective in suppressing growth (up to 93%) of the test fungal species  grown on malt extract medium. T. harzianum and malt extract medium were therefore selected for fraction  analysis. There was 68% reduction in growth of the A. citri due to 1% concentration of ethyl acetate fraction of cultural filtrate of T. harzianum when grown in malt extract broth.Key words: Citrus, Alternaria citri, ethyl acetate fraction, Trichoderma harzianum, viride, aureoviride, reesei, koningii

Tree dieback in Punjab, Pakistan

Survey of 10 districts of Punjab viz. Sialkot, Gujranwala, Lahore, Faisalabad, Sheikhupura, Gujrat, Jehlem, Rawalpindi, Sargodha, and Hafizabad were undertaken from March 2003 to March 2004 to study the present status of tree dieback incidence in these areas. A total of 21 tree species were found victim of the dieback disease. The disease incidence, however, varied in different tree species. Furthermore, there was also difference in disease severity in different surveyed districts of the province. Dalbergia sissoo Roxb. and Acacia nilotica (Lam) Willd. ex Delile., were found to be the most affected species in all the districts. Among the commonly grown trees Mangifera indica L., Eucalyptus citriodora Hook., E. camal-dulensis Dehnh., Populus hybrida M. Bieb., Ficus religiosa L., F. bengalensis L., Bombax ceiba L., Syzygium cumini (L.) Skeels., Psidum guajava L., and Albizia lebbeck Benth. were found affected with dieback. The less commonly cultivated species like Toona ciliata (Roxb.) M. Roemer, Heterophragma adenophyllum Seem. ex Benth. & Hook., Ficus glomerata Roxb., Mimosup elengi, Terminalia arjuna Wight & Arn., Grevillea robusta Cunn., Ehretia acuminata R. Br., Platanus  orientalis L. and Barringtonia acutangula (L.) Gaertn. were also found victims of the dieback.  Termites and fungi were found to be the most common biotic factors responsible for the disease. Among the abiotic factors generally drought and environmental pollution seemed to be the main causes for dieback initiation and severity

In vitro biological control of Fusarium solani – cause of wilt in Dalbergia sissoo Roxb.

Five species of Trichoderma viz. Trichoderma viride Pers. Ex Gray, T. harzianum Rifai, T. koningii Oudem, T. aureoviride Rifai and T. pseudokoningii Rifai, and three species of Aspergillus viz. Aspergillus fumigatus Fresenius, A. glaucus Link and A. oryzae (Ahlb.) Cohn were evaluated for their in vitro antagonistic potential against Fusarium solani (Mart.) Sacc., the cause of wilt disease in Shisham (Dalbergia sissoo Roxb.). Among the Trichoderma species T. harzianum showed the best performance followed by T. viride, T. aureoviride, T. koningii and T. pseudokoningii, respectively, resulting in 52.4, 24,13.7, 9 and 2% reduction in colony growth of the test pathogenic fungus. Similarly there was 23, 20 and 7.5% reduction in colony growth of F. solani due to antagonistic effects of A. fumigatus, A. glaucus and A. oryzae, respectively

Evaluation of bacterial strains for the induction of plant biochemicals, nutritional contents and isozymes in barley

The controlled placement of gold nanoparticles (AuNPs) in poly­(styrene-<i>b</i>-isoprene-<i>b</i>-styrene) [SIS] triblock copolymer thin films was achieved by tuning the surface chemistry of the AuNPs. Facile thiol ligand exchanges permitted quick and thorough exploration of the surface chemistry effects on AuNP segregation behavior. By using thiol-functionalized polystyrene (PS-SH) or 1-dodecanethiol (C₁₂SH) ligands to tune nanoparticle surface chemistry, AuNPs were selectively incorporated into either the polystyrene (PS) or the polyisoprene (PI) domains. Nanocomposite polymer films were characterized by atomic force microscopy, transmission electron microscopy (TEM), and TEM tomography. AuNPs synthesized with a C₁₂SH capping ligand preferentially segregated into PI-rich domains. However, after exchanging C₁₂SH with PS-SH ligands to a C₁₂SH:PS-SH molar ratio of approximately 5:1, AuNPs showed an affinity for PS-rich domains. The C₁₂SH:PS-SH transition ratio was much higher than expected, based on molecule-averaged surface energy arguments that predicted a ratio of 0.4:1 to 0.8:1. The unexpected transition ratio was rationalized according to the area-averaged enthalpic contributions of the capping ligands. Furthermore, mixing and incorporating PI- and PS-preferential AuNPs created a well-mixed nanocomposite, which highlights the versatility of the AuNPs

Foliar application of liquiritin protects Chinese flowering cabbage against cucumber mosaic virus and increases health-promoting compounds

Decades of research have revealed notable similarities between the immune systems of the plant and animal kingdoms. Liquiritin has long been used to stimulate the body immunity in animals against an array of diseases. Considering the homology of some induced immune responses between animals and plants, we examined the effects of exogenously applied liquiritin to stimulate defense responses in Chinese flowering cabbage plants against cucumber mosaic virus (CMV) infection under greenhouse and field conditions. Foliar application of liquiritin (200 ppm) effectively suppressed the development of CMV symptoms by not less than 40% compared with the control in cabbage plants in both greenhouse and field trials along with the significant increases in the marketable yield and nutritional quality of cabbage. Liquiritin application enhanced the production of phenolic compounds and different defense-related enzymes in treated plants. Moreover, quantitative real-time PCR analysis revealed that liquiritin significantly up-regulated the expression of different defense-related genes upon pathogen inoculation, indicating an induction of the salicylic acid-mediated defense system. Collectively, the findings of this study indicate that liquiritin can effectively control CMV in cabbage plants.This study was supported by funding from the Science and Technology Foundation of Guangdong Province (Project No: 2020B0202090002); Guangdong Agriculture Department of China (2020KJ122) and Science and Technology Foundation of China (Project No: QN2020013006).Peer reviewe

Identification of a Potential ISR Determinant from Pseudomonas aeruginosa PM12 against Fusarium Wilt in Tomato

Biocontrol of plant diseases through induction of systemic resistance is an environmental friendly substitute to chemicals in crop protection measures. Different biotic and abiotic elicitors can trigger the plant for induced resistance. Present study was designed to explore the potential of Pseudomonas aeruginosa PM12 in inducing systemic resistance in tomato against Fusarium wilt. Initially the bioactive compound, responsible for ISR, was separated and identified from extracellular filtrate of P. aeruginosa PM12. After that purification and characterization of the bacterial crude extracts was carried out through a series of organic solvents. The fractions exhibiting ISR activity were further divided into sub-fractions through column chromatography. Sub fraction showing maximum ISR activity was subjected to Gas chromatography/mass spectrometry for the identification of compounds. Analytical result showed three compounds in the ISR active sub-fraction viz: 3-hydroxy-5-methoxy benzene methanol (HMB), eugenol and tyrosine. Subsequent bioassays proved that HMB is the potential ISR determinant that significantly ameliorated Fusarium wilt of tomato when applied as soil drench method at the rate of 10 mM. In the next step of this study, GC-MS analysis was performed to detect changes induced in primary and secondary metabolites of tomato plants by the ISR determinant. Plants were treated with HMB and Fusarium oxysporum in different combinations showing intensive re- modulations in defense related pathways. This work concludes that HMB is the potential elicitor involved in dynamic reprogramming of plant pathways which functionally contributes in defense responses. Furthermore the use of biocontrol agents as natural enemies of soil borne pathogens besides enhancing production potential of crop can provide a complementary tactic for sustainable integrated pest management