Cucurbit Genetics Cooperative Report 4:41-42 (article 22) 1981

Virus Studies with Cucurbita foetidissima

M. E. Rosemeyer and W. P. Bemis

University of Arizona, Tucson, AZ 85721

Two isometric viruses have been isolated from field-grown buffalo gourd (bg), Cucurbita foetidissima. Host range studies, electron microscopy, and serology have been used to identify these viruses as squash mosaic virus (SqMV) and a cucumber mosaic-like (CMV-like) virus. These viruses have then been reinoculated to buffalo gourd as well as reisolated and characterized.

Host Range. After SqMV was transferred from buffalo gourd to Cucurbita pepo var. 'sugar Pumpkin', the viruses range was determined by inoculating cultivated species. Squash mosaic virus-buffalo gourd did not infect Chenopodium amaranticolor or Nicotiana tabacum var. 'Xanthi', which is identical to known SqMV but unlike other isometric cucurbit viruses.

The CMV-like virus has host range identical to known CMV (ATCC PV-242, PV-59): local lesions (no systemic reaction on C. amaranticolor, systemic mosaic on N. tabacum var. 'Xanthi', local lesions (no systemic necrosis) on cowpea, Vigna sinensis, thereby eliminating tobacco ringspot virus (TRSV), tomato ringspot virus (TmRSV), and SqMV. Its isometric shape eliminates the possibility of watermelon mosaic virus (WMV).

Electron-Microscopy and Serology (Transmission Electron Microscopic Serology). The SqMV-bg aggregates when combined with SqMV antisera and viewed in the electron microscope. These findings correspond to that of Ochterlony agar gel diffusion tests.

The CMV-like virus disintegrated when stained with phosphotungstic acid but is stable in uranyl acetate, as does known CMV. The Derrick technique (1) has been employed to avoid the aggregations present in the control when the previous technique was used. Three different strains of ATCC CMV antisera (PVAS 30, 242, 260) have provided no conclusive results, though two known strains of CMV (ATCC PV-59, PV-242) react moderately to very well with the antisera. Tomato ringspot virus, TRSV, alfalfa mosaic virus (AMV) and SqMV antisera were also tried unsuccessfully, Agar gel tests have proved inconsistent.

Therefore, there are several possible identities of the CMV-like virus: it is a known strain of CMV, which we do not have antiserum to as yet, it is a unique strain of CMV, it is not CMV but another virus, known or unknown.

Reinoculation to Buffalo Gourd and Subsequent Reisolation. When SqMV-bg was reinoculated to seedlings of buffalo gourd in the greenhouse, a mild systemic mosaic appeared. However, about 1-2 weeks later, the new leaves appear normal. Squash mosaic virus was recovered from these buffalo gourd plant. Known SMV II (Cantaloupe; Mesa, AZ) produced identical symptoms.

Similar symptom patterns appeared when the CMV-like virus was reinoculated to buffalo gourd except that the mosaic was very severe, leaves recurved. However, new leaves appeared normal in three weeks. The virus was recovered from the inoculated buffalo gourd. However, buffalo gourd is resistant to known CMV (ATCC PV-59, PV-242). Provvidenti also reported buffalo gourd as resistant to CMV in New York (2).

Watermelon mosaic virus (cantaloupe; Yuma, AZ) and TRSV (ATCC PV-157) have been inoculated to seedling buffalo gourds in the greenhouse. The plants were mechanically inoculated three times over a 10-day period, allowed to express symptoms for one month, viewed in the electron microscope, and then inoculated to appropriate host plants. Buffalo gourd has proved resistant to both WMV and to RSV, which has concurred with observations of Provvidenti (2).

Literature Cited

1. Derrick, K. S. and R. H. Brlansky. 1976. Phytopathology 66:815-820.
2. Provvidenti, R., R. W. Robinson and H. M. Munger. 1978. Research in feral species to six viruses infecting Cucurbita. Plant Disease Reporter 62:326-329.