Bayer's pesticides arm CropScience is to buy California-based firm AgraQuest for $425 million plus milestone payments to boost its vegetable and fruit protection business.

The purchase of AgraQuest, which breeds fungi-killing bacteria to fight plant disease, will help Bayer CropScience diversify its product range to offer biological pesticides that have a lower risk of resistance development, Bayer said in a statement late on Tuesday.

Resistance is a major problem linked to crop chemicals that occurs when new mutations of weeds, fungi and insects evolve that withstand prevailing pesticides.

Bayer's chief executive Marijn Dekkers arrived last year with a reputation for being able to handle transformational takeovers, but the AgraQuest deal is the latest in a line of small and medium-sized acquisitions.

Dekkers has said that he will try to boost the group's healthcare and crop protection and genetically modified seeds bu siness via takeovers.

The U.S. target company's current product portfolio includes brands such as Serenade, Rhapsody, Sonata and Ballad fungicides and Requiem insecticides.

The head of Bayer CropScience, Sandra Peterson, said the addition of AgraQuest would help the unit serve the growing fruits and vegetables market, which already accounts for more than 25% of the unit's revenues.

"We plan to achieve €3 billion ($3.78 billion) of sales in this segment by 2020 and with the acquisition of AgraQuest we are underlining our growth ambitions," she said in a statement.

Bayer CropScience is the world's second-largest maker of conventional farming pesticides after Syngenta and also makes genetically modified seeds.