16 research outputs found
Identifying New Sources of Resistance to Brown Stem Rot in Soybean
Brown stem rot (BSR), caused by the fungus Phialophora gregata f. sp. sojae (Allington & D.W. Chamberlain) W. Gams (syn. Cadophora gregata), causes yield losses up to 38%. Three dominant BSR-resistant genes have been identified: Rbs1, Rbs2, and Rbs3. Additional BSR resistance loci will complement breeding efforts by expanding the soybean [Glycine max (L.) Merr.] genetic base. The objective of this research was to determine if PI 594637, PI 594638B, PI 594650A, and PI 594858B contained novel BSR resistance genes. The accessions were crossed to three genotypes with known BSR resistance genes and populations were developed for allelism studies. A minimum of 60 F2:3 families tracing to individual F2 plants in each population were used, and six seeds from each F2:3 family were tested. Resistant and susceptible controls and parents were also included. The BSR symptoms were assessed under growth chamber conditions 5 wk after inoculation by measuring foliar and stem severities and recovery of P. gregata from stem sections. Allelism tests of F2:3 plants from crosses of PI 594638B, PI 594858B, and PI 594650A with the resistant sources fit a 15:1 ratio, indicating that the resistant gene possessed by each of the PIs was nonallelic to Rbs1, Rbs2, and Rbs3. The three PIs contain at least one novel BSR resistance gene and have the potential to serve as donors to elite germplasm, increasing stability of host resistance to P. gregata. Allelism tests of PI 594637 segregated in a 3:1 ratio and no significant difference was found between PI 594637 and the susceptible controls, indicating that PI 594637 is susceptible to BSR
RB56-178 Streak Mosaic of Wheat in Nebraska and Its Control
A mosaic of wheat was first observed in Nebraska by Peltier in 1922. Peltier found diseased plants in a large number of winter and spring wheat varieties at Lincoln, and in some instances, he successfully inoculated wheat and corn from the juice of infected plants. The temperatures under which Peltier maintained his inoculated plants are unknown and other criteria now employed to characterize the viruses were not utilized. It is probable, however, that he was working with what is now known as wheat streak mosaic virus.
This bulletin reports the results of studies on the epidemiology of wheat streak mosaic under Nebraska conditions. Particular attention is given to the occurrence and certain characteristics of the mite vector of the virus, the relation of weather and other factors to some of its activities, a correlation of certain mite situations with epidemics of the disease, and recommendations for disease control