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

Abstract

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