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Potato leafroll virus (PLRV) is a serious aphid transmitted virus disease of potato (Solanum tuberosum L.). Field observations suggest that the cv. BelRus is tolerant to PLRV. Greenhouse grown BelRus and PLRV susceptible potato cvs. Green Mountain and Katahdin were tested for PLRV with enzyme linked immunosorbant assay (ELISA) and subsequently infested with PLRV infected green peach aphids (Myzus persicae). ELISA was used to test leaves from the top, middle and bottom portion of the plants at 7 day intervals beginning 7 days after aphid infestation. PLRV was detected in all tested locations of the Green Mountain and Katahdin plants 21 days after inoculation. In BelRus, throughout the 11 week test, PLRV was detected predominantly in the top portion of the plants and at low titres. These results suggest that tolerance to PLRV infection in the cv. BelRus may be due to suppression of virus replication.
Bacterial soft rot of bell pepper (Capsicum annuum L.), caused by Erwinia spp., is a destructive postharvest market disease of this crop. Control is presently limited to chemical treatments. Methods of inoculating pepper fruit were evaluated to develop a reliable technique for soft rot resistance screening. Erwinia carotovora subsp. atroseptica (Eca) was isolated from partially decayed field grown pepper fruit at Beltsville, MD. Fruit were inoculated with suspensions of Eca via: (a) abrasion with Carborundum, (b) hypodermic puncture, or (c) non-wounded tissue. Inoculated fruit were held under high humidity at 21-23C for two to three days prior to scoring. Degree of soft rot decay was determined via fruit weight loss from two replicates of the experiment over the course of the growing season. Significant differences were not evident among varieties or experiment dates for weight loss due to tissue decay. Hypodermic puncture inoculation was superior to other methods for inducing fruit rot.
The use of mulches in vegetable production is undergoing a radical change away from high-input, nonrenewable resources, such as plastic, to the use of high-residue organic mulches from cover crops. The purpose of this study was to compare the marketable yield of various fresh-market tomato genotypes when grown under plastic and hairy vetch mulches. In 1996 and 1997, 12 fresh-market tomato genotypes were evaluated for yield on the North Farm of the Beltsville Agricultural Research Center (BARC), MD in a randomized split-plot design. Tomatoes were grown in conventional tillage plastic mulch (PM) and no-till hairy vetch mulch (HVM). Early blight, caused by Alternaria solani Sor., developed naturally in the plots both years and was recorded over time. All 12 genotypes were susceptible to early blight. Area under the disease progress curve (AUDPC) was calculated for each plot. AUDPC was similar both years. However, the year × mulch and year × mulch × genotype interactions were significant for AUDPC. Adjusting yields for AUDPC had a minimal effect on the data. Overall, yields were similar in PM and HVM both before and after adjusting for AUDPC. However, the mulch × genotype interaction was significant. The yield of eight of the genotypes was significantly higher in the HVM than in the PM system both years, ranging from 12% to 57% higher in 1996 and 10% to 48% higher in 1997. There was no yield difference for one genotype in HVM as compared to PM. The yield in the remaining three genotypes was either higher under HVM than PM or there was no difference. As yields from the HVM system are greater than or equal to yields in the PM system, soil compaction is reduced and nitrogen inputs are lower. The no-till HVM system is at least as good, and often better, than the conventional tillage PM system.