Effects of Beauveria bassiana (Bals.-Criv.) Vuill. on the growth of Vigna unguiculata (Linnaeus) Walpers under laboratory and field conditions, and the resistance of the plant to insect attack

Abstract

Beauveria bassiana (Bals.-Criv.) Vuill. is an established biocontrol agent in laboratory, but studies have shown negative effects of temperature and Ultraviolet radiation on its potential in vitro. Nevertheless, there is a lack of studies about its endophytic colonization in vivo, especially in field conditions in cowpea [Vigna unguiculata (L.) Walp.]. In this sense, this study aimed to evaluate the effects of B. bassiana applied to cowpea seed on the growth of the plants under laboratory and field conditions, and on their resistance to insect attack. Cowpea seeds were treated with suspension of 5 x 10⁸ conidia/mL of B. bassiana. The plants were cultivated in two independent conditions (laboratory and field). The resistance to attack of the pest in field conditions was assessed by monitoring weekly the plants three times a week during 12 weeks, from the initial vegetative to the reproductive stage. According to the results, in laboratory conditions, there were significant differences among the inoculated and control plants for the variables of height of the plants (31.17 cm for treatment and 23.00 cm for control plants) and dry mass of the root (2.38 g for treatment and 0.97 g for control plants). In field conditions, the observed pest insects were miner fly [Liriomyza sp.] (Diptera: Agromyzidae), Cerotoma arcuata Olivier, 1791 (Coleoptera: Chrysomelidae), aphid (Aphis craccivora Koch, 1854) (Hemiptera: Aphididae) and the polyphagous hemipteran [Crinocerus sanctus (Fabricius, 1775)] (Hemiptera: Coreidae). The treated plants were less affected than control plants by these pests, especially at the beginning of the vegetative phase.