An endophytic Beauveria bassiana strain increases spike production in bread and durum wheat plants and effectively controls cotton leafworm (Spodoptera littoralis) larvae

Abstract

Entomopathogenic fungi have traditionally been assumed to help regulate insect populations. However, some hypocrealean ascomycetes, such as Beauveria bassiana, play other, poorly understood ecological roles that might be useful in developing novel strategies for both increased crop production and crop protection. The primary aims of this work were (a) to assess endophytic colonization of bread wheat and durum wheat plants by the applied fungus B. bassiana strain EABb 04/01-Tip; (b) to examine the impact of various B. bassiana inoculation methods on growth, yield, phytohormone levels and nutrient uptake in the plants, and (c) to quantify mortality of cotton leafworm (Spodoptera littoralis) larvae fed with leaves from inoculated plants. Three experiments involving different inoculation methods (viz., ‘soil treatment’, ‘seed dressing’ and ‘leaf spraying’), and a fourth experiment to assess mortality in S. littoralis larvae fed with leaves from endophytically-colonized plants, and were conducted according to a completely randomized design. Beauveria bassiana successfully established within, and colonized, bread wheat and durum wheat plants. The fungus was, for the first time, re-isolated from grains produced by plants inoculated using the ‘seed dressing’ and ‘soil treatment’ methods. The fungus boosted spike production in bread wheat inoculated using the ‘seed dressing’ and ‘soil treatment’ methods, and also in durum wheat but only using the ‘soil treatment’ method. ‘Seed dressing’ increased grain yield by about 40%, and also root length, in bread wheat compared with control plants. Mortality in S. littoralis larvae fed with leaves from inoculated plants ranged from 30% using the ‘seed dressing’ method to 57% using the ‘leaf spraying’ method compared with 0% when fed the control leaves. However, no fungal outgrowth was detected in larval cadavers. The sustainability of crop production and crop protection strategies based on B. bassiana therefore depends on the effectiveness of the inoculation method and on the particular host plant.