Cucurbit Genetics Cooperative Report 23:112-113 (article 37) 2000
Virus Infections Levels of Oil Seed Pumpkins in New Zealand
Future Resources, 633a Queen Street, Levin, New Zealand; firstname.lastname@example.org
Crop & Food Research, PB 4704 Christchurch, New Zealand
Abstract: Small commercial plantings of the oil seed pumpkin, 'Weis 371' and an unknown Hungarian variety, were made in Hawke's Bay, new Zealand during November and December of 1998. The first experiments with 'Weis 371' had started in 1991. The Hungarian seeds were tested in a glasshouse and showed 2-4% WMV2 and 0.6-1.4% ZYMV infection. Visual inspection of 'Weis 371' revealed a 20% infection early in the season which in February 1999 increased to 25%.. No virus symptoms were visible on the fruit but the foliage infection of oil seed pumpkins was often higher than in the neighbouring fields of pumpkin and squash.
Introduction: Seed of the variety Weis 371 was first introduced into New Zealand in 1991 and various plantings for research purposes have been carried out since that time. In 1998 small commercial plantings of 'Weis 371' and another variety, (of Hungarian origin) were carried out in Hawke's Bay.
Seed of the later variety was tested for virus presence in a glasshouse before planting out, but no 'Weis 371' seed has been tested. During trials since 1991 no visual virus infections were detected on the plants as has been the case with squash variety trials.
Results of virus checks: The seed of Hungarian oil seed pumpkins had a 2-4% WMV2 and 0.6-1.4% ZYMV in a glasshouse test. The crop had a 12% level of visual infection (on foliage) in January 1999. (estimate from 100 plants).
'Weis 371' had 20% visual infection in 1999. Close to the two experimental blocks were small areas of zucchini and watermelon, which showed no sign of virus infection. In February, 1999 these two blocks had an infection of 32% in the Hungarian line and 25% infection in 'Weis 371'. Only WMV2 was confirmed in February. No virus symptoms were noted on the fruit in the wy of distortion or blistering as is often seen on squash crops or other pumpkins. By February there was some virus infection in the zucchini crop.
Other squash crops were monitored in the district over the season. Apart from two crops, one early squash and a late crop which had 20% and 30% visual infection respectively, most other crops had a very low infection. the 1998/1999 season was a very mild one with respect to virus infections since most crops were sown after the main aphid activity which was cut short by high temperatures in November.
Over the years the virus had been not detected visually but it may occur during very early plant growth in squash, tomatoes, peppers and broad beans, especially when the virus is seed borne. It is possible that the plant is providing some kind of mechanism to mask or minimise virus infection as is the case with some other crops.
The high levels of virus infection of the seeds, caused by WMV2, (2-4%) and ZYMV, (0.6-1.4%) may have been the reason for the higher than normal visual field symptoms of around 20% to 25% in the plants during the growing season. This is considered too high for our normal squash and pumpkin crops. As further plantings may be planned for next season it is important that the seed stock be free from virus infection and imported seed should be certified virus free.
Some observations are:
- Virus infection is not always visible during early plant growth
- The high level of virus in oil seeds could be due to seed borne viruses
- Other virus sources are present in the surrounding weeds
- Damage to squash crops will result eventually if this high level is not reduced
- There is an urgent need for virus free foundation seed or resistant plants
- Fletcher, J.D. 1996. Zucchini yellow mosaic virus in buttercup squash - a new record in New Zealand, Australian Plant Path 25:142.
- Fletcher, J.D., H.M. Nott, A.R. Wallace, B.T. Rogers and T.J.B. Herman 1998. Potyviruses in New Zealand Buttercup squash. (Cucurbita maxima). 9th Conference International working group on vegetable viruses, Turin, Italy.
- Fletcher, JD (1995); Mosaic viruses of squash. Crop & Food Research broadsheet 66.