Interactions between Peanut clump virus, Polymyxa graminis and cereal species unravelled through field and zoospores transmission assays

Peanut clump disease is a damaging disease on groundnut caused by two pecluviruses, Indian peanut clump virus (IPCV) and Peanut clump virus (PCV). Both viruses are transmitted to major crops such as peanut, pearl millet, sorghum, sugarcane and wheat by Polymyxa graminis, a protist endoparasite of roots belonging to the Plasmodiophorida - Cercozoa. Although the various actors of the disease have been extensively studied separately, little information are available on the interactions between them. The main objective of this study was to investigate the host-vector-virus interactions in soil-borne transmitted virus pathosystems, using peanut clump disease. A real time RT-qPCR targeting the 3’UTR extremity of both RNA1 and RNA2 was developed, allowing all PCV isolates to be quantified and increasing the sensitivity of PCV detection. A strategy based on using viruliferous zoospores produced on PCV-infected sugarcane was used to demonstrate the acquisition and virus transmission process. This allowed differences to be shown in PCV transmission efficiency depending on the formae speciales of Polymyxa, and in the independence of the multiplication of PCV and Polymyxa within the host. The study was complemented by measurements of yield, PCV infection rate and seed transmission, using pearl millet and sorghum accessions grown on a naturally PCV-infected field. Finally, the study looked at the impact of the seed, soil and vegetative transmissions of PCV on its spread and the implications in term of management. This thesis unravels the interactions occurring in peanut clump disease and shows the major role played by pearl millet and sorghum in the epidemiological development of the disease. It proposes innovative ways for managing the disease.(AGRO 3) -- UCL, 201

Etude du développement de pécluvirus sur Nicotiana benthamiana exprimant la protéine de capside virale du Peanut clump virus

L'arachide (Arachis hypogaea L.) est une plante couramment cultivée au Vietnam et dans la région de Hué. Si la présence de Pecluvirus n'a jamais été rapportée pour cette région, les risques liés à leur forte persistance dans le sol associé à la transmission par la semence implique une attention particulière. Dans ce travail, la capacité de développement de souches de l'Indian peanut clump virus et du Peanut clump virus dans des plantes transgéniques (Nicotiana benthamiana) exprimant le gène de la capside virale du IPCV-H a été étudiée. Les résultats obtenus montrent que les plantes inoculées avec les deux souches IPCV-L et IPCV-D multiplient le virus . Par contre, les plantes inoculées avec les souches IPCV-H , homologue et PCV-BF n'ont pas permis la détection du virus, indiquant une résistance dont le mécanisme reste encore à préciser. Un séquençage des souches présentes dans les échantillons testés semblent indiquer la présence de la souche de type IPCV-H dans les plantes testées positivement pour la présence du virus. Plusieurs hypothèses sont avancées pour expliquer ce phénomène, dont un possible synergie entre virus de stérotypes différents

Pecluviruses

Indian peanut clump virus (IPCV) and Peanut clump virus (PCV) cause significant losses in groundnut crops. IPCV and PCV infect also a wide range of dicotyledonous and monocotyledonous hosts. Virus infection often has few or no symptoms in other hosts, such as cereals and serological detection is hampered by the significant differences among the amino acid composition of pecluvirus coat proteins. The availability of non-serological, sensitive and broad-spectrum detection methods is therefore essential for the epidemiological studies and for the management of peanut clump diseases. Reverse transcription-polymerase chain reaction (RT-PCR) has been developed for the detection of both IPCV and PCV. The chapter describes pecluviruses and the molecular diagnostic techniques proposed for their identification and characterization, from serological to polymerase-based methods. It shows that pecluviruses can be present in graminaceous hosts, even when no symptoms are apparent, and highlights the risks of spreading disease by seed and soil movements

Characterization, diagnosis & management of plant virusesVolume 3. Vegetable and pulse crops : Chapter 5 - Pecluviruses

Indian peanut clump virus (IPCV) and Peanut clump virus (PCV) cause significant losses in groundnut crops . IPCV and PCV infect also a wide range of dicotyledonous and monocotyledonous hosts. Virus infection often has few or no sumptoms in other hosts, such as cereals and serological detection is hampered by the significant differences among the amino acid composition of pecluvirus coat proteins. The availability of non-serological, sensitive and broad-spectrum detection methods is therefore essential for the epidemiological studies and for the management of peanut clump disease. Reverse transcription-polymerase chain reaction (RT-PCR) has been developed for the detetion of both IPCV and PCV. The chapter describes pecluviruses and the molecular diagnostic tehniques proposed for their identification and charaterization, from serological to polymerase-based methods. It shows that pecluviruses can be present in graminaceous hosts, even when no symptoms are apparent, and highlights the risks of spreading disease by seed and soil movements

Detection of pecluviruses

Indian peanut clump virus (IPCV) and Peanut clump virus (PCV) cause significant losses in groundnut crops . IPCV and PCV infect also a wide range of dicotyledonous and monocotyledonous hosts. Virus infection often has few or no symptoms in other hosts, such as cereals and serological detection is hampered by the significant differences among the amino acid composition of pecluvirus coat proteins. The availability of non-serological sensitive and broad-spectrum detection methods is therefore essential for the epidemiological studies and for the management of peanut clump disease. Reverse transcription-polymerase chain reaction (RT-PCR) has been developed for the detection of both IPCV and PCV. The chapter describes pecluviruses and the molecular diagnostic techniques proposed for their identification and characterization, from serological to polymerase-based methods. It shows that pecluviruses can be present in graminaceous hosts, even when no symptoms are apparent, and highlights the risks of spreading disease by seed and soil movements

Acquisition and transmission of peanut clump virus by polymyxa graminis on cereal species

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

Peanut Clump virus transmission by Polymyxa graminis under controlled conditions.

More than fifteen soil-borne viruses belonging to the Beny-, Bymo-, Furo- or Pecluvirus, causing diseases on cereals and groundnut, are transmitted by the soil-borne protist root endoparasite Polymyxo graminis. Five special forms are distinguished within this species on the basis of their specific ecological and molecular characteristics, but the specificity of the transmission of the viruses by these forms has been Little investigated. In order to analyse the virus-vector interaction, the transmission assay of the Peanut clump virus by P. graminis f.sp. tropicalis has been conducted under controlled conditions. The major difficulty to be overcome was to combine high levels of PCV and vector infection in the same living plant. This was achieved by using cuttings of PCV-infected sugarcane (variety CP-89327) originating from Burkina Faso showing the typical red leaf mottle symptom as a source for the virus. A culture of P. graminis f.sp. tropicalis isolated from a PCV-infested soil from Niger was used as the vector. Systemic PCV infection in sugarcane at 25-30 degrees C allows plants with new young roots infected by the virus to be produced by placing cuttings of PCV-infected sugarcane in Hoagland nutrient solution for 21 days. These plants were inoculated with aviruliferous zoospores of P. graminis f.sp. tropicalis produced on infected pearl millet roots and maintained in an automatic immersion system. After 21 days' incubation at 25-30 degrees C with a 12 hour photoperiod, zoosporangia were observed in the roots of sugar cane. The zoospores released from these roots were used to infect healthy young pearl millet plants. Twenty days postinoculation, PCV was detected by RT-PCR in roots of inoculated plants. The vector was clearly identified in the roots by microscopy. This result reveals that a PCV isolate from red leaf mottle sugar cane is transmissible by a P. graminis f.sp. tropicalis isolate from a peanut clump infested field. This method should be helpful in the analysis of the specificity of pecluvirus transmission by P. graminis f.sp. tropicalis and P. graminis f.sp. subtropicalis

Seed, soil and vegetative transmission contribute to the spread of pecluviruses in Western Africa and the Indian sub-continent.

Peanut clump and sugarcane red leaf mottle diseases are caused by viruses of the genus Pecluvirus. Indian peanut clump virus occurs in the Indian sub-continent and Peanut clump virus in West Africa. A feature of these viruses is that they are both seed and soil transmitted. Both modes of transmission contribute to long-term persistence and field spread. Data on seed transmission in pearl millet, virus movement within the plant and virus diversity based on RNA-1 partial sequences are presented. This study emphasizes that pecluviruses are also viruses of cereals infecting sorghum and pearl millet, and highlights a correlation between the countries cultivating these two crops and the virus distribution. Ways of controlling pecluviruses and their vector, Polymyxa graminis, taking into account the virus dissemination routes, are proposed