A cDNA library enriched with differentially expressed transcripts was constructed from Pratylenchus coffeae challenged resistant banana cultivar (Karthobiumtham-ABB) through suppression subtractive hybridization (SSH) technique to elucidate the nematode resistance mechanisms. A total of 256 unique genes of this SSH library were sorted into eight functional categories. Of these, 26.8% were unigenes involved in defense and/or signal transduction including resistant gene homologues, disease resistance response proteins and transcripts associated with disease related proteins and protein kinase signaling. These findings imply that invasion of nematode triggers multiple signaling pathways both through tissue damage caused by nematode invasion and recognition of nematode elicitors by R genes. Confirmation of defense specific representative genes through semi quantitative RT-PCR revealed their increased expression levels in resistant than in susceptible cultivar and the resistant cultivar triggered response much earlier than the susceptible cultivar.

Resistance gene analogues (RGAs) were isolated from two banana cultivars viz., Karthobiumtham and Rose using degernate primers designed from the conserved motifs of different plant resistance genes.A total of 40 sequences were hit with various R genes, of which 20 sequences were having uninterrupted open reading frame (ORFs).Based on the conserved domains like P loop, internal kinase 2, kinase 3a and hydrophobic domain motifs of the deduced amino acid sequences were grouped as NBS-LRR class of resistant genes.The phylogentic analysis of RGAs showed that all the Musa RGAs are grouped under non-TIR branch and grouped into six distinct Musa RGA cluster.To investigate the expression profile of the RGAs, specific primers were designed for one representative RGA from each RGA cluster and it was found that C1 and C5 were induced upon root lesion nematode infection in the resistant (cv.Karthobiumtham) and not in susceptible (cv.Nendran) cultivar.C6 was expressed only in resistant cultivar not in susceptible one.But there was no change in the expression of C2 and C3 in both resistant and susceptible cultivars.These results indicate that in depth study on C1, and C5 RGAs will be helpful for further improvement of P. coffeae resistance in banana.

Understanding of molecular mechanisms underlying host-nematode interactions is of primary importance in devising strategies to control nematode. Cultivars with differential reactions to nematode and the optimum time of sampling are the important criteria to study the host-nematode interactions. Based on the investigation on rate of P. coffeae population buildup in the roots, root lesion index, root weight and percentage of healthy root, Karthobiumtham and Nendran were identified as the most resistant and susceptible cultivars respectively among the ten cultivars used in this study. The phenol-metabolizing enzymes, viz., peroxidase and polyphenol oxidase as well as total phenols content and pathogenesis related protein, viz., beta-1,3-glucanse were assessed in the roots of P. coffeae inoculated resistant and susceptible banana cultivars. The activities of peroxidase, beta-1, 3-glucanase and content of total phenol were higher in the roots of uninoculated resistant cultivar than susceptible one. In post-inoculation stage, a steady increase in enzymes activities was noticed from 2 Days After Inoculation (DAI) onwards with maximum activity on 6 DAI for peroxidase and polyphenol oxidase, 4 DAI for total phenols content and 8 DAI for beta-1,3 glucanase. Except total phenols content, the level of enzyme activities was higher even up to 12 DAI than the uninoculated control plants of both cultivars. The PPO activity was again reconfirmed by estimating the time course expression of PPO transcript level. Based on the time course studies on enzyme assays and mRNA level the present study suggested that the samples should be collected within 8 DAI of nematode for understanding the molecular mechanism of Musa-nematode interaction.