School of Botany - Theses

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End date: 2015 × Start date: 2010 × Subject: disease management × Subject: diversity ×

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    The epidemiology and control of spot form of net blotch of barley in Victoria, Australia
    McLean, Mark S. ( 2011)
    Spot form of net blotch (SFNB) caused by the fungus Pyrenophora teres f. maculata is a relatively new foliar disease of barley in Victoria. It was first detected during the 1990s and has since become common throughout, due to widespread adoption of stubble retention practices and the cultivation of susceptible varieties. Due to the relatively recent establishment of SFNB, current importance and management strategies have not been investigated. This thesis describes the prevalence of SFNB in Victoria, the associated production loss, effectiveness of chemical fungicides and host plant resistances for future management of this disease. Additionally the genetic and pathogenic diversity of the pathogen population and its ability to develop new virulent pathotypes is reported. The importance of SFNB was investigated during surveys of foliar diseases in barley crops throughout Victoria during 2007, 2008 and 2009. Pyrenophora teres f. maculata was present in more than 90% of crops with severity of up-to 56% on the top three leaves. Severity was typically less than 1% and as a result approximately 25-51% of barley crops grown in Victoria would have experienced grain yield loss, of which the majority was less than 6%. Spot form of net blotch caused significant reductions to grain quality in the Wimmera region of Victoria, with measurements of screenings and retention significantly reduced at two and four out of five trial sites, respectively. This indicates that while SFNB infection was common in barley crops of Victoria, significant production loss was restricted to a low percentage of crops where disease pressure was high. To manage SFNB, a single application of chemical foliar fungicide (propiconazole) was applied at different growth stages of crop development where disease pressure was high. A single application of foliar fungicide at stem elongation (Z31) or flag leaf emergence (Z39) consistently provided the best suppression of SFNB infection, however, these applications did not always maximise grain quality. A range of different fungicides applied to the seed were ineffective in controlling SFNB in the field. Cultivation of barley varieties with host resistance is the best strategy for managing SFNB in Victoria. However, this is reliant on the identification of suitable resistance sources for inclusion into breeding programs. The resistance response of ninety-three barley lines with diverse genetic background was tested toward Australian and North American isolates of P. teres f. maculata as seedlings and as adults. In general, seedling and adult plant resistance was not related with two and fifteen resistant lines identified, respectively. These lines require further investigation to determine the resistance genes involved and to identify suitable molecular markers for their identification in breeding programs. The effectiveness of seedling, adult and complete host resistances in four barley lines was tested. The var. Barque, which possessed complete resistance to SFNB, provided the best control. Varieties with resistance effective at the seedling and adult stages provided control of SFNB in most cases but were generally less effective than Barque, indicating that multiple partial resistances may be required to provide adequate resistance. The population of P. teres f. maculata is genetically and pathogenically diverse and potentially able to overcome host resistances. Analysis of P. teres f. maculata isolates from Victorian barley crops using sequence tagged microsatellite (STMs) primers and mating type primers revealed high genetic diversity and the presence of two-mating types necessary for sexual reproduction. This indicates that the Victorian population of P. teres f. maculata frequently undergoes its sexual cycle and is therefore able to develop new virulent pathotypes. This study has identified several areas of research that can be undertaken in order to better manage this important disease in the future. Further research to determine which of the barley lines identified in this study are suitable for inclusion into barley breeding programs and to monitor the virulences in the P. teres f. maculata population is required. A differential set of barley lines has been proposed for discriminating the effectiveness of resistance sources to P. teres f. maculata.