Incidence of Soybean vein necrosis virus in Alabama Soybean Fields

Soybean vein necrosis virus (SVNV) was first reported in the United States during 2008 and has since rapidly spread to all major soybean-producing regions of North America. In 2013, a 4-year study was initiated to determine the distribution and incidence of the virus in Alabama soybean fields and potential weed hosts in the state. The weed host survey focused on populations of morning glory growing adjacent to maturing soybeans fields, along with additional commonly occurring weed species found in Alabama. SVNV was detected throughout Alabama (27 of 28 counties tested) and was most common in the northern region of the state. The average incidence of SVNV in fields in northern Alabama increased from 31.8% in 2013 to 82.6% in 2016. Average incidence of the virus in central Alabama soybean fields ranged from 5.1 to 14.8%, and southern Alabama fields ranged from 0 to 8.8% over the 3-year period. Only one population of morning glory tested positive for SVNV during the 3-year survey of this potential weed host. None of the 15 additional weed species screened tested positive for SVNV. This study has demonstrated that SVNV is found in Alabama soybean fields throughout the state and that soybeans grown in northern Alabama are at greater risk for infection.

The wound pathogen Chondrostereum purpureum, its history and incidence on trees in North America

Since Percival's inoculation studies in 1902 with the wound pathogen Chondrostereum purpureum (Pers.�:�Fr.) Pouz. on plum trees in England, this fungus has become well known as the cause of silver-leaf disease of rosaceous fruit trees. However, its pathological impact on forest trees has been little studied and appreciated. Therefore, the question is raised about the pathogenic role and incidence of C. purpureum on other trees in damaged forests. A survey of 561 collections of this fungus in herbaria of Canada and the United States found that the highest incidence occurred in the Betulaceae (45%), especially Betula (27%) and Alnus (15%). The second-most favoured host family was the Salicaceae (20%) with a 15 and 5% occurrence on Populus and Salix, respectively. The third-most favoured substrate was apparently the Rosaceae at 11%, but this reflected a bias of agricultural research in orchards. A 6% incidence was found in the Fagaceae, 4% in the Aceraceae and 3% in the Ulmaceae. From 1 to 3% of the collections occurred for each of the Cornaceae, Juglandaceae, Magnoliaceae and Pinaceae. Incidences <1% were indicated for each of the Aquifoliaceae, Caprifoliaceae, Cupressaceae, Grossulariaceae, Hamamelidaceae, Hippocastanaceae, Myrtaceae, Oleaceae, Rhamnaceae and Tiliaceae. The host survey data indicate that C.�purpureum is an important pathogen with epidemic potential in forest trees, especially species in the Betulaceae and Salicaceae. The silvering symptom is inconspicuous in birch and other non-rosaceous trees. Forests with greatest vulnerability are those subjected (1) to physical forces that cause stem injuries to susceptible trees, (2) to environmental conditions conducive for infection and (3) to high levels of basidiospore inoculum from fruiting bodies on hardwood slash that result from timber harvesting and storm damage. Silver-leaf is an important fungal disease of many tree species in North America and is largely responsible for the birch dieback in North American forests. Control data from several mycoherbicide experiments support this conclusion.