Identification of pathogens and control of spot blotch disease of barley (Hordeum vulgare) by combining plant resistance and biological control

Abstract

Spot blotch is one of the most important diseases of barley (Hordeum vulgare) in Libya and worldwide. The overall aim of this study was to investigate the potential of biological control in combination with disease resistance to control spot blotch without the potential hazards of chemical application. Fungi were isolated from barley plants with spot blotch symptoms from different areas in Libya. As well as the commonly known spot blotch pathogen Bipolaris sorokiniana (teleomorph Cochliobolus sativus), Bipolaris spicifera (teleomorph Cochliobolus spicifer), Curvularia inaequalis, and Alternaria alternata were identified by their morphology and ribosomal DNA sequences. Bipolaris sorokiniana was the most serious pathogen under the test conditions; the others infected barley but caused less severe symptoms. Spot blotch resistance of barley seedlings was tested under greenhouse conditions with four Libyan cultivars (ACSAD, Nibola, Rehan, and Wadi Utbah) and two UK cultivars (Gaelic and Pastoral). Nibola was the most resistant. The ability of the organisms in three commercial biocontrol products, Trichoderma harzianum T-22 (Trianum), Streptomyces lydicus WYEC 108 (Actinovate) and Bacillus subtilis QST 713 (Serenade), to control spot blotch individually and in combination was investigated. On agar plates, all three inhibited growth of the pathogens completely on the second day of culture, except that for B. spicifera with S. lydicus there was an inhibition zone and the pathogen grew in the opposite direction. Disease severity was lowest when T. harzianum T-22 was applied individually to the most resistant cultivar, Nibola. Foliar application, soil treatment and seed coating all reduced disease severity. With foliar application, T. harzianum T-22 was more effective when applied at the same time as the pathogen than when applied one week before or four days after. In a field experiment with T. harzianum T-22, foliar application combined with seed treatment suppressed spot blotch more effectively than either method individually.