Date of Award

1974

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

The epidemiology of several viruses known to infect bell peppers was studied in two pepper producing areas of Louisiana. The St. James area has a history of severe losses due to virus diseases which fre­ quently infect 100% of the pepper plants. TI!.is is in sharp contrast to the Hanmond area in which virus-infected peppers are seldom found. Viruses were identified by mechanical transmission to indicator hosts and by serology. In the St. James area, tomato spotted wilt virus (TSWV) was found to spread primarily in April and infect up to 5% of the plants in a given field. Peppers infected with cucumber mosaic virus (CMV), potato virus Y (PVY), and tobacco etch virus (TEV) were not detected until the 1st of May, but these three aphid transmitted viruses spread rapidly and quite often entire fields were infected by the middle of June. TSWV was the only virus found infecting bell peppers in the Hammond area, and then only in an occasional plant. Eighteen indigenous plant species found in the vicinity of bell pepper fields in the St. James area were shown by mechanical trans­ mission to be infected with one or more of the four viruses (TEV, PVY, CMV, and TSWV). Three of the 18 weed hosts; Medicago arabica (L.) Huds., Melilotis officinalis (L.) Lam., and Rudbekia amplexicaulis Vahl.; shown to be infected with CMV and PVY; CMV, PVY, and TEV; and CMV, PVY, TJW, and TSWV; respectively, were abundant near pepper fields at the time infection occurred in the peppers. Solanum nigrum L. was shown to be infected with CMV, PVY, and TEV; although this species is not widespread, several dense stands were found in disturbed sites around the area. Furthermore,.[. nigrum has been reported to be an annual, but it was shown to act as a perennial in St. James by resprouting from semi-woody stems and root-stocks. A survey of field borders in the St. James area and in the "virus-free" Hanmond area was made to compare the population densities of the 18 identified weed hosts. Only nine of the 18 weed species were detected by the survey in the Hamnond area; none of the four species mentioned above were found. Attempts to transmit viruses from the known weed host species that do occur in Hanmond resulted in a single transmission of TSWV. Populations of alate aphids in pepper fields were determined by trapping them on yellow sticky traps. Ten predominant aphid species were identified and found to be the same in both the St. James and H8111DOnd areas, although counts were usually higher in St. James. Peak aphid flights occurred during the 1st and 4th weeks of May in St. James. The first peak coincided with initial infection of aphid-borne viruses in the fields; Aphis craccivora Koch was the predominant species in this peak. In addition,!• craccivora was found colonizing§_. nigrum and M. arabica which strongly suggests its involvement in initial virus spread. Myzus persicae (Sulzer) was the predominant species in the second peak flight which coincided with the period of rapid virus spread in the field. Species of alate aphids visiting pepper plants were determined by trapping them on plants that had some of their leaves coated with Stickum. The same predominant species were identified from "sticky plants" and yellow sticky traps which adds validity to the use of yellow sticky traps for studies of this kind.

Pages

45

Share

COinS