ABSTRACT
Both spot blotch (SB) and common root rot (CRR) are responsible for significant yield reductions during severe disease outbreaks. In Asian and especially in Indian growing regions, Bipolaris sorokiniana is considered the foliar and root pathogen of greatest concern. SB symptoms appear on leaf tissue as small dark brown necrotic lesions. Ovular in shape and 1-3 mm in length with tapered ends, lesions appear in the early stages of infection and coalesce into broad chlorotic regions (Poloni et al., 2009; Singh et al., 1998; Duveiller, 2004). This reduction in photosynthetically active tissue limits plant growth and grain production, leading to overall reductions in yield quality, as measured by thousand kernel weight (TKW) and quantity (Joshi et al., 2007a). Disease severity in the field is largely assessed by measuring the intensity and development of tissue damage over a defined time period, to generate an area under the disease progress curve (AUDPC) or AUDPC/day. This quantification allows comparisons between annual disease outbreaks and a standardised method of assessing susceptibility among wheat cultivars (Sharma et al., 2007; Jeger, 2004; Duveiller and Sharma, 2012). CRR symptoms are characterised by the browning and necrosis of root tissue. Tissue damage resulting from infection is suggested to compromise nutrient and water uptake, resulting in stunted vegetative and reproductive growth (Duveiller and Sharma, 2009). Wheat infected with B. sorokiniana may also show blackening of the grain. High incidences are associated with high precipitation during reproductive growth (Viedma and Kohli, 1998).
