Fusarium verticillioides is an insidious fungal pathogen of maize associated with diseases such as ear rot and kernel rot. It attacks the phyllosphere region of the maize plant especially on inflorescence and cobs. Thus, this study was conducted to isolate potential phyllosphere colonizing antagonistic microbes for the management of Fusarium ear rot. Four phyllosphere colonizing antagonistic bacteria were found to be effective in suppression of the growth of Fusarium verticillioides. Based on 16S rDNA analysis, these bacterial isolates were identified as Pseudomonas aeruginosa isolate 1, P. aeruginosa isolate 2, Bacillus subtilis isolate and B. amyloliquefaciens. Among these four phyllosphere bacteria tested against F. verticillioides, the maximum inhibition of mycelial growth of F. verticillioides and production of volatile compounds was exhibited by P. aeruginosa isolate 1. Application of P. aeruginosa isolate-1, as seed treatment @ 10 g/kg of seeds, soil application @ 5 g/pot and foliar spray @ 0.2 per cent, recorded the minimum PDI with the maximum disease reduction over control. Thus, the present study showed that P. aeruginosa isolated from agricultural ecosystem could be a potential phyllosphere antagonistic bacterium for the management of maize ear rot disease.

One of the most destructive citrus diseases in the world is called citrus Huanglongbing (HLB). For effective HLB associated ‘Candidatus liberibacter spp.’ prevention, sensitive and precise diagnostics are essential. Candidatus Liberibacter asiaticus (CLas), Candidatus Liberibacter africanus (CLaf), and Candidatus Liberibacter americanus (CLam) are among the ‘Candidatus liberibacter spp.’ that infect citrus. The most common of these is the species known as Las. To assess the impact of citrus greening disease in the citrus orchard, leaf samples exhibiting greening symptoms were picked up from 210  mandarin orange trees from nine localities in four districts  and among them 189 plants showed HLB positive and leaf samples are picked up from 216 acid lime trees from nine localities in six districts of Tamil Nadu where citrus is cultivated in a larger area and among them 202 plants showed HLB positive. A “conventional singleplex polymerase chain reaction (PCR) Nested PCR and Q-PCR (Quantitative PCR)” was performed on the extracted DNA samples to detect Ca. Liberibacter asiaticus. Among all the mandarin orange growing localities from “Kanalkadu and Thandikudi in Dindigul district” and among the acid lime fields, the samples from  “Sankarankoil from Tirunelveli district and Kallar from Nilgiris district” showed consistent amplification of 1160 base pairs fragment by using specific primers OI1 and OI2C and also 703 base pairs fragment with gene-specific primers A2 and J5  targeting beta-operon (rpiKAJL-rpoBC) gene which is a  ribosomal protein gene of Ca. Liberibacter asiaticus, these results showed that these districts are exclusively positive to Clas . The nested PCR method significantly increased the sensitivity to identify Las up to 10 times and 100 times, respectively, compared to qPCR and conventional PCR in this study. A set of nested PCR primer pairs were examined to diagnose Las. Nested PCR was used to analyse 14 samples from 2 different citrus cultivars in 2 different districts. Among those again kanalkadu orchard for mandarin orange and Sankankoil orchard for acid lime showed more disease incidence and consistent amplification.  The findings indicate that all the  samples tested positive for HLB; the samples of blotched and chlorotic leaves from the acid lime field at Sankarankoil (thirunelveli district) and mandarin orange field at kanlakaadu (Dindigul district)  had the highest positive detection rate (100%).  The outcomes show that the nested PCR primer pairs are capable of detecting Las in a variety of symptomatic tissues, citrus cultivars, and geographical locations. The set of nested PCR primers used in the current work will be a very helpful addition to the existing methods for Las detection.

No abstract