Identificação, diagnóstico e estratégias de manejo de patógenos fúngicos causadores de manchas foliares em Lolium multiflorum no sul do Brasil

Abstract

The phytosanitary diagnosis of fungi that cause leaf spots in Lolium multiflorum has become very relevant in recent years because it indirectly affects cattle feeding, which is one of the main economic activities in southern Brazil. This pasture contributes highly to the food needs in this sector in winter periods due to the availability and nutritional quality. Fungal diseases that cause leaf spots have been identified as the main problem affecting production in this forage. Currently, the identity and importance of these pathogens are unknown and there are no recommended measures for their management. Therefore, this study aimed to identify the main fungi associated with these diseases and to evaluate management strategies to reduce disease intensity by inducing resistance and reducing the inoculum source. To this end, the taxonomic identity of pathogens was revealed from a polyphasic approach and their pathogenicity was tested through Koch's Postulates. Subsequently, strategies based on the incorporation of silicon in the soil (Si), seed inoculation with Trichoderma atroviride (T), or both (TSi) against Pyricularia oryzae (in a greenhouse) were tested. Finally, these strategies, along to the management of the cutoff frequency (C), were tested in the field against naturally occurring diseases. Seven species of fungi associated with leaf spots were identified, of which P. oryzae and Bipolaris sorokiniana were new reports in Brazil, Pyrenophora nobleae, Colletotrichum plurivorum, and Exserohilum rostratum were determined as new associations in the host, while Curvularia sp. nov. and Cercospora sp. nov. they are presented as two new contributions to science. Concerning management, it was found that the application of T. atroviride in the seeds and the application of silicon in the soil resulted in protection against P. oryzae. Also, the gray leaf spot (P. oryzae), brown leaf spot (B. sorokiniana) and parrot eye leaf spot (Cercospora sp. nov.) were detected as the main diseases associated with L. multiflorum. The T, Si, TSi, and C strategies reduced the severity of brown leaf spot and gray leaf spot in 30 and 65%, respectively. These results form a basis for the diagnosis of pathogens that cause leaf spots in L. multiflorum, as well as providing viable strategies for management, thus reducing damage sustainably.