An upgrade by Goldman Sachs analysts helped Monsanto shares pull out of the nosedive which has cost them some 40% of their value this year, while rival Syngenta notched up smaller gains after a Credit Suisse recommendation.

Monsanto shares, which ended the last session at their lowest since 2006, rebounded 4% to $50.74 in morning trade in New York after Goldman Sachs raised them to "buy" and placed them on its conviction buy list.

The investment bank noted the seeds and sprays group's lower exposure than many other companies to the threats to Chinese and European economic growth that are rocking many sectors.

Monsanto has talked down growth expectations in a series of announcements over the past year, curbing in the main hopes for its herbicides division thanks to soaring competition to its Roundup brand from generic competitors.

However, Goldman analyst Robert Koort said that "given the massive underperformance of [Monsanto] shares in past several quarters, we believe most of the bearish news is likely priced into the stock".

Idiosyncratic benefits 

Monsanto's woes have helped drag shares in many rivals lower too – an influence not deserved in the case of stock in Swiss-based Syngenta, Credit Suisse said.

Syngenta has "minimal exposure" to glyphosphate, and furthermore was "not buffeted by volatile soft commodity and energy prices", the investment bank said.

Indeed, the group's shares showed "no statistically significant correlation" with soft commodity prices, unlike those in Yara, the Norwegian fertilizer company.

"We believe the reason for this is the more specialty nature of Syngenta's business model," Credit Suisse said.

"This helps to insulate Syngenta's earnings from the impact of fluctuations in commodity prices."

Historic rating 

Syngenta shares were trading at a 20% discount to their historic rating, on a forward price-earnings basis, presenting "an attractive entry point" for investors.

Credit Suisse raised its rating on the stock to "outperform" from "neutral", with a price target of SFr320.

The shares, which have lost some 11% this year, closed up 0.2% at SFr259.00.