Sympatric occurrence of sibling Phytophthora species associated with foot rot disease of black pepper in India.

Foot rot disease caused by Phytophthora capsici is a serious threat to black pepper cultivation in India and globally. High diversity exists among the Phytophthora isolates of black pepper and hence detailed investigations of their morphology and phylogenetic taxonomy were carried out in the present study. In order to resolve the diversity, 182 isolates of Phytophthora, collected from different black pepper-growing tracts of South India during 1998-2013 and maintained in the National Repository of Phytophthora at ICAR-Indian Institute of Spices Research, Kozhikode, were subjected to morphological, molecular and phylogenetic characterization. Morphologically all the isolates were long pedicellate with umbellate/simple sympodial sporangiophores and papillate sporangia with l/b ranging from 1.63 to 2.55 µm. Maximum temperature for the growth was ~ 34 °C. Chlamydospores were observed in "tropicalis" group, whereas they were absent in "capsici" group. Initial molecular studies using internal transcribed spacer (ITS) marker gene showed two clear cut lineages-"capsici-like" and "tropicalis-like" groups among them. Representative isolates from each group were subjected to host differential test, multilocus sequence typing (MLST) and phylogeny studies. MLST analysis of seven nuclear genes (60S ribosomal protein L10, beta-tubulin, elongation factor 1 alpha, enolase, heat shock protein 90, 28S ribosomal DNA and TigA gene fusion protein) clearly delineated black pepper Phytophthora isolates into two distinct species-P. capsici and P. tropicalis. On comparing with type strains from ATCC, it was found that the type strains of P. capsici and P. tropicalis differed from black pepper isolates in their infectivity on black pepper. The high degree of genetic polymorphism observed in black pepper Phytophthora isolates is an indication of the selection pressure they are subjected to in the complex habitat which ultimately may lead to speciation. So based on the extensive analysis, it is unambiguously proved that the foot rot disease of black pepper in India is predominantly caused by two species of Phytophthora, viz. P. capsici and P. tropicalis. Presence of multiple species of Phytophthora in the black pepper agro-ecosystem warrants a revisit to the control strategy being adopted for managing this serious disease. The silent molecular evolution taking place in such an ecological niche needs to be critically studied for the sustainable management of foot rot disease.

Comparison of dimensional accuracy of four different die materials before and after disinfection of the impression: an in vitro study.

BACKGROUND: This study was conducted to compare the linear dimensional accuracy of die materials before and after disinfection of the impression. Type IV and V conventional dental stone, type IV-resin impregnated and copper-plated die materials were studied. MATERIALS AND METHODS: A stainless-steel master die analogs to a complete veneer crown preparation with three scribed lines (I: vertical, II and III: horizontal) was machined and measurements were made from these scribed reference lines. Impressions were made with monophase addition silicone impression material for each of the specimens. 2% glutaraldehyde was used as a disinfectant. The fabricated dies were measured to the nearest 0.0001 mm. ANOVA and post hoc was carried out using Scheffe multiple comparison test at significance level of 0.05. RESULTS: Type IV resin-impregnated dental stone and copperplated dies approximated the dimensions of the master die. Type IV and V conventional dental stone dies showed greater variation in measurements. Statistically significant differences were observed for type IV resin-impregnated and copper-plated dies in dimension I and III. For dimension II no significant differences were found for dies fabricated from four die materials. A one-way analysis of variance indicated no statistical significant differences among the two groups of dies fabricated from disinfectant treated impressions and those fabricated from nondisinfectant treated impressions. CONCLUSION: Type IV resin-impregnated dental stone and copper-plated dies are dimensionally more accurate than type IV and V conventional dental stone die materials. No significant linear distortion in the dies fabricated from the disinfected impressions was observed.