In afternoon trade, the S&P/ASX 200 Index (ASX: XJO) is bouncing back from yesterday's selloff. At the time of writing, the benchmark index is up 0.4% to 8,414.4 points.

Four ASX shares that are rising more than most today are listed below. Here's why they are jumping:

Appen Ltd (ASX: APX)

The Appen share price is up 9% to $2.79. This appears to have been driven by a broker note out of Ord Minnett this morning. According to the note, the broker has upgraded the artificial intelligence data services company's shares to a buy rating with an improved price target of $3.30. This follows the release of a quarterly update which the broker felt was unfairly punished by the market. Ord Minnett was pleased with the solid update and is positive on the company's growth prospects.

Nufarm Ltd (ASX: NUF)

The Nufarm share price is up 4% to $3.70. Investors have been buying this agricultural chemicals company's shares following the release of a trading update this morning. Nufarm revealed that it has "made a pleasing start to FY25." It notes that "[d}emand for crop protection products has been strong and, although active ingredient prices have not moved materially, we are seeing the benefits of stability in cost of goods on crop protection margins." In addition, the company revealed that it expects to achieve $100 million in omega-3 revenue in FY 2025, subject to market pricing. It has also identified $50 million of annualised cost savings. The full impact of these savings is expected to be realised in FY 2026.

Pro Medicus Limited (ASX: PME)

The Pro Medicus share price is up 4.5% to $282.06. This morning, this health imaging technology company announced yet another major contract win. Pro Medicus has signed a $53 million, seven-year deal with BayCare. It is the leading health care system in the Tampa Bay and central Florida regions of the United States. The contract will see its cloud-based Visage 7 Enterprise Imaging Platform, including Visage 7 Viewer and Visage 7 Workflow modules, implemented throughout BayCare. This will provide the health care system with a unified diagnostic imaging platform.

WA1 Resources Ltd (ASX: WA1)

The WA1 Resources share price is up 13% to $14.71. This follows the announcement of results from continued metallurgical testwork that is being undertaken on niobium concentrate from the Luni deposit at the 100% owned West Arunta Project in Western Australia. Management revealed that it achieved excellent results from the first conversion testwork completed on refined concentrate from Luni. It highlights that this demonstrates the final stage in a conventional process flowsheet and completes proof-of-concept testwork to produce ferroniobium.