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Incidence of Cereal Viruses in Primary Grain-Producing Regions of Asiatic Russia between 2001 and 2003

K.A. Mozhaeva, *L.L. Domier, T.B. Kastalyeva, **N.N. Kakareka, N.V. Girsova

Russian Research Institute of Phytopathology, B. Vyazyomy, Moscow Region, 143050, Russia, *United States Department of Agriculture-Agricultural Research Service, Urbana, IL  61801, USA, **Institute of Biology and Soil Science, Far East Branch RAS, Vladivostok, 690022, Russia

Barley yellow dwarf (BYD) is the most economically important and widely distributed disease of cereals throughout the world.  In Russia, a causal agent of BYD, Barley yellow dwarf virus (BYDV), was first identified in the Krasnodar Territory in 1961. In 1995, the virus was first found in Asiatic Russia. There have been reports of eight additional virus species damaging cereals in Asiatic Russia. In 2001-2003, leaves of cereal crops and cereal wild grasses with visible symptoms of BYD and those of other virus damage such as stripes, streaks and dwarfing were collected during field inspection or received from Provincial Stations for Plant Protection. BYDV and Cereal yellow dwarf virus (CYDV-RPV) were checked by ELISA using specific commercial antibodies against the viruses or monoclonal antibodies prepared in collaboration with T.N. Erokhina from the Institute of Bioorganic Chemistry of the Russian Academy of Science. Furthermore, eight other viruses, namely, Barley stripe mosaic virus (BSMV), Brome mosaic virus (BMV) Northern cereal mosaic virus (NCMV), Oat pseudorosette virus (OPV), Soil-borne wheat mosaic virus (SBWMV), Wheat dwarf virus (WDV), Wheat spindle streak mosaic virus (WSSMV), and Wheat streak mosaic virus (WSMV) were checked, using Agdia Inc. and Loewe diagnostics, in samples showing  corresponding symptoms. This work was conducted as part of an ISTC project. All known BYDVs (-PAV, -MAV, -SGV and -RMV) as well as CYDV-RPV were detected in samples from crop-producing territories and provinces of Asiatic Russia including Ural, Western and Eastern Siberia and the Far East. As a rule, cereal crops were damaged by several BYDVs or by BYDV(s) and CYDV. On average, for 3 years 45% of ELISA-positive samples contained BYDV-PAV, 50% of the samples contained BYDV-MAV, the latter percentage was true for BYDV-SGV and CYDV-RPV; BYDV-RMV was present in 60% of the samples. So, all viruses occurred as a mix infection of five (rarely), four, three or two viruses. Sometimes only one virus was present. Some differences were observed in BYDVs and CYDV incidence among the regions as well as within a region among years. In 2001, BYDV- MAV predominated in Ural and West-Siberian regions, while BYDV-PAV was predominant in Eastern Siberia.  In 2002, BYDV-PAV, -RMV and CYDV-RPV occurred equally in the samples from Ural region, the same was true for BYDV-PAV, -MAV, and -SGV in Eastern Siberia. In 2003, BYDV-RMV was found in 65-70% of the samples from all four regions. In Western Siberia, BYDV-SGV was predominant (75%) in 2003. BMV, BSMV and WSMV as well were detected in all mentioned regions, but there was no evidence for the presence viruses that are transmitted by soil-borne fungus Polymyxa graminis such as SBWMV and WSSMV. Of the viruses causing dwarfing, NCMV was found in the samples from Western and Eastern Siberia and the Far East, whereas OPV was detected only in West-Siberian and Far-Eastern samples. WDV was not found.

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Peanut clump virus is seed transmitted in pearl millet (Pennisetum glaucum)

Otto1, G., De Herthog1 P., Delfosse2, P. & C. Bragard1

1 Unité de phytopathologie, Université catholique de Louvain (UCL), Croix du Sud, 2bte3, 1348 Louvain-la-Neuve, Belgium, 2 International Crops Research Institute fro the Semi-Arid Tropics, ICRISAT-Sadoré, BP 12 404,  Niamey, Niger

Since 1990, the harvested groundnut area has almost doubled in Africa, reaching 10.472.600 ha for an estimated production of 8.969.190 Mt of groundnuts in shell in 2003. Along with the increasing importance of groundnut in the livelihood of small scale farmers, growing health concerns have raised throughout groundnut cultivated area. Yield losses due to pests, fungi or viral diseases such as groundnut rosette or peanut clump became a significant problem. The clump disease produces symptoms characterized by a bushy aspect of the shoots and roots due to an internode reduction, leading to yield loss up to 60%. The viral agent responsible for the disease in Africa is the Peanut clump virus (PCV), transmitted by the root endoparasite Polymyxa graminis. Currently, the clump disease of groundnut has been detected in Burkina Faso, Chad, Ivory Coast, Mali, Niger, Nigeria, Senegal and Sudan.

A less documented aspect of infection by PCV is the transmission through seed. Initiated in the roots through the infection by P. graminis, the viral infection moves throughout the plant and reaches the embryonic axis of the seed. The plantlet raised from a groundnut infected seed will display typical symptoms of the disease but with a stunting often less severe than early soil-infected plants. Transmission through seed is of critical importance for epidemiology as it can play a crucial part in the perpetuation and dissemination of the virus. Seed transmission of PCV to groundnut has already been demonstrated but its epidemiological significance was considered as low, due to the unability of the vector to produce numerous viruliferous resting spores dicotyledonous plants. This work focused on the study of seed transmission of the virus in two important monocotyledonous crops, pearl millet and sorghum. These cerals are often used in rotations with groundnut and are execllent hosts for P. graminis. The seed transmission rates under field conditions were assessed for ten pearl millet cultivars and ten sorghum cultivars. Grow-out tests highlighted the occurrence of PCV transmission in pearl millet seeds, with rates ranging between 0.19% and 2.45%. None of the ten cultivars tested showed a complete resistance to seed transmission but significant differences appeared between cultivars. The virus could be detected by DAS-ELISA in the roots of all the infected plants arisen from infected seeds. Moreover, the virus was always located near the apex of all the developing roots. The study underlines the risk of dissemination of the disease to healthy fields through the use of infected sowing material. The co-existence of non-viruliferous P. graminis and infected pearl millet roots may lead to the establishment of the disease in previously healthy areas. It also shows the potential for breeding cultivars with limited seed transmission of the virus.

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