Gardening commentator Peter Seabrook said: "Strategically, it looks like a very sensible deal for Syngenta. Goldsmith was the biggest seed company in the world in the immediate past."
He added: "An awful lot of varieties have been put into one hand, which could be very controlling. I fear there will be a reduction in the number of varieties on offer. When Syngenta bought Fischer it merged its Pelargonium varieties and, inevitably, there was a reduction in the choice of cultivars."
Pentland Plants managing director David Spray agreed: "We have been an active promoter of Goldsmith plug varieties in the UK for many years and are naturally concerned that these varieties may no longer be available to us to produce plugs for our customers in this country, (because) S&G is also a very active seller of plugs in the UK.
"When Syngenta bought Fischer we were unable to continue to sell its varieties and are concerned that this takeover may well stifle competition in the UK."
International agribusiness firm Syngenta, which includes the $272m (£173m) brand Syngenta Flowers, is set to finalise the purchase of Goldsmith early next year.
Goldsmith has been owned and operated by the Goldsmith family since 1962. Reported sales in 2007/08 were $50m (£31.8m) and the firm employs 1,500 staff.
Syngenta is not ruling out job losses at Goldsmith Seeds, but Goldsmith family members will remain involved with the company.
Goldsmith Seeds president Joel Goldsmith told HW: "I will remain at the company and continue to run it for Syngenta. I will also be involved on the Syngenta Flowers management team.
"Because Syngenta and Goldsmith do some similar work, we will need to integrate the operations, but we are not anticipating any major job losses. Goldsmith Seeds Europe will continue to do breeding work under the new structure."
He added that his brothers, Richard and Jim Goldsmith, will also stay at the business.
Syngenta marketing and communications manager Jodie Champion said integration teams will be employed to bring the two companies together. She said: "Changes to personnel cannot be excluded.
"The Syngenta Flowers management team will make this decision in the future based on the work of the integration teams ... we do not anticipate any personnel changes due to this acquisition."
In 2007, Syngenta acquired:
- Vegetative flowers company Fischer for $67m (£42.7m)
- Vegetable seeds company Zeraim Gedera for $95m (£60.5m)
- A 49 per cent minority stake in Chinese corn seeds company Sanbei