The objective of this study was to investigate the specificity of the interactions between Polymyxa graminis, Peanut clump virus (PCV), and cereals, particularly the acquisition and the transmission of the virus by three P. graminis formae speciales. A new strategy has been developed: it involves using sugarcane as the common host for both the virus and its vector in order to produce the viruliferous zoospores of P. graminis f. sp. subtropicalis, temperata, and tropicalis that were then inoculated on cereal species. This experiment enabled the role of P. graminis f. sp. tropicalis and subtropicalis zoospores in PCV transmission to be demonstrated. The efficiency of this transmission was shown to vary, depending on the P. graminis special forms. Interestingly, the high transmission of the PCV isolate from Burkina Faso by an isolate of P. graminis f. sp. tropicalis from Niger on pearl millet suggests that there is a coevolution mechanism in this pathosystem. The study also provides evidence that the host plant species in which Polymyxa zoospores are produced could affect the infectivity of the vector. Finally, using Polymyxa quantitation by quantitative reverse-transcription polymerase chain reaction and in situ observations of the virus, the study demonstrates the independence of the development of PCV and its vector in the host plants.

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The 3'-end region of many virus isolates has been shown to possess conserved sequences in addition to the presence of numerous genomic and subgenomic RNAs. Utilizing these sequences, a broad-spectrum reverse transcription-polymerase chain reaction protocol has been developed to detect all the known Indian peanut clump virus and Peanut clump virus isolates, that cause peanut clump diseases in West Africa and India. The primers were targeted at the highly conserved 3'-untranslated regions of the PCV RNA-1 and RNA-2. The conservation was confirmed by sequencing these untranslated regions of RNA-1 for six isolates and RNA-2 for one isolate. The conserved structure of the RNA-1 and RNA-2 was observed and the importance of this region for the virus survival was confirmed. The primers were also designed for virus quantitation using a Taqman(®)-based real-time RT-PCR. The use of RT-PCR and real-time quantitative RT-PCR improved the sensitivity of PCV detection compared to ELISA. RT-PCR also led to the detection of IPCV and PCV on two new natural hosts: Oldenlandia aspera and Vigna subterranea. Real-time RT-PCR is considered to be an ideal tool for identifying resistant sources to both IPCV and PCV.

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