Bacterial leaf blight (BLB) of rice caused by Xanthomonas oryzae pv. oryzae (Xoo) is a major disease in rice and Pseudomonas fluorescens is known as a successful bioagent against the pathogen. The present investigation was carried out to study the effect of micronutrients, viz. boron (B), iron (Fe), zinc (Zn), and molybdenum (Mo) on the efficacy of the bioagent and induction of defense mechanism in rice. The study revealed that P. fluorescens strain PfAs1 enriched with 50 ppm Zn could suppress the blight pathogen by 45.92% compared to control and other micronutrients under in-vitro condition. The results also demonstrated a reduction of 82.99% disease intensity in rice due to application of Zn enriched PfAs1. Further study was made to understand whether the Zn enriched PfAs1 (Zn PfAs1) induces defense response in rice. The levels of expression of defense related genes, viz. OSPR1a, OSPR1b, OSPR10a, Xa1 and Xa26 against Xoo was quantified by quantitative PCR (qPCR). During the interaction of rice with Zn PfAs1, a 20 fold increase in the expression of rice BLB resistance gene Xa26 and pathogenesis related (PR) gene OsPR1b, was observed when compared with controls. Similarly, 14 and 10 fold increase in levels of expression of OsPR1a and OsPR10a genes was recorded, respectively. An 8 fold increase in the level of expression of Xa1 gene was also recorded in the study. This is the first report on enhanced defense response in rice due to the antagonistic potential of Zn enriched P. fluorescens strain against BLB pathogen.

A transmission study was conducted to identify and confirm the insect vectors of viral diseases of king chilli Capsicum chinense Jacquin, at the Virology Laboratory, Assam Agricultural University, Jorhat. The study reveals that Cucumber Mosaic Virus (CMV), Potato Virus Y (PVY) and Chilli Leaf Curl Virus (ChLCV) were the viral diseases transmitted by Aphis gossypii (Glover), Myzus persicae (Sulzer) and Bemisia tabaci (Gennadius), respectively. The detection of CMV and PVY were done through DAS-ELISA assay and ChLCV was done through PCR technique. The results showed that A. gossypii and M. persicae were successfully transmitting the CMV and PVY (40% each). DAS-ELISA revealed that 57.14% of the plant and 66.67% of A. gossypii samples were found to be positive to CMV. While, 42.17 and 60.00 % of PVY detection was observed from plant and M. persicae samples, respectively. B. tabaci also successfully transmitted ChLCV with 80% of the tested plant and the PCR results revealed that the primer pair ChLCV F1 and ChLCV R1 successfully yields 550bp at annealing temperature of 48oC from the infected plant as well as from B. tabaci samples and fail to detect from healthy plants, aphids, and leafhoppers samples.

The pumpkin leaf curl disease is an emerging disease of pumpkin in Assam, India. Symptomatic pumpkin leaf samples from different locations were immunologically tested using Begomovirus specific antibody. PCR with the ELISA-positive samples, using Geminivirus universal primers amplified 1.4 kb virus-specific fragments. Sequence of these amplicons showed around 95% identity with squash leaf curl China virus-[Pumpkin: Varanasi] (SLCCV-Pumpkin: Varanasi EU573715). To investigate the possible functions of the viral proteins present in the fragment, the full-length C2 and C3 genes were conceptually translated and were subjected to in silico proteomic analyses. The phylogenetic analysis of both the proteins divulged the relationship of our isolate with related viruses and isolates. Multiple sequence alignment (MSA) of the proteins revealed the presence of the known viral conserved motifs, viz., zinc-finger (ZNF) motif [ 36 CXCX(7)CX(6)H 53 ], the arginine-rich nuclear localization signal (NLS) motif ( 28 RRRR 31 ) as well as the minimal activation domain in C2 protein. In the C3 protein, the 91 LKYLD 95 and the replication enhancer motif ( 30 YFK 32 ) were found to be conserved. Finally, 3-D models of the two proteins were predicted via ab initio approach and subsequently, the models were validated. To our knowledge, this study is a pioneering attempt to construct the ab initio 3-D models of two begomoviral proteins taking a SLCCV isolate as a model.

Tomato leaf curl disease, caused by the begomovirus tomato leaf curl virus (ToLCV) that is transmitted by whitefly (Bemisia tabaci), restricts the production of tomatoes in major tomato-growing countries. Yield losses of tomatoes attributable to leaf curl virus species/ strains differ from country to country. For instance, yield losses in the USA account for 20%, Nigeria (23%), Lebanon (40%), Mediterranean region (50%), Sudan (50%), Malawi (63%), Kenya (75%) and Tanzania (80%); in the Caribbean Islands, South, Central and North America between losses of between 30% and 100%, and in India, losses of up to 100% have been estimated (Maruthi et al., 2003;Polston et al., 2002;Singh et al., 2015).The management of leaf curl diseases can be accomplished by limiting the vector population through the use of insecticides and a combination of other available approaches. However, the repeated use of the same active ingredient in insecticides has led to the development of pesticide-resistant populations of B. tabaci (Horowitz et al., 2004;Palumbo et al., 2001); in addition, pesticide usage is discouraged because it is hazardous to the environment and human health. The use by growers of resistant cultivars developed through breeding techniques would offer a long-lasting, environmentally friendly and sustainable approach. Unfortunately, most commercially grown cultivars are susceptible to tomato-infecting begomoviruses, although some resistance has been identified in wild relatives of tomato that could be used for the development of hybrid lines.A practical approach to the identification in wild relatives of these genes conferring resistance to leaf curl viruses is the continuous screening of tomato germplasm.