Puccinia purpurea (rust (of grasses, sorghum))

P. purpurea needs to be controlled to protect grain and fodder sorghums grown in the cool humid tropical regions of the world. Rust severity may be assessed on a scale from 1 to 5: a severity of 3 or more has been found to be economically important and should be considered as the point to start control measures (Anahosur et al., 1981). Rust control is achieved primarily by cultivating resistant varieties and also by cultivating the slow-rusting sorghum varieties in different countries, including: Southern Africa (Malawi, Swaziland, Zambia and Zimbabwe), East and West Africa, South and Central America and Caribbean basin, Mexico, North America, and Asia (e.g. India, Philippines and Thailand).

Cultural practices which help the crop to escape the disease (e.g. early sowing) are used in India (Anahosur et al., 1982) and elsewhere (Frederiksen, 1980). Earlier planted sorghum crops essentially escaped the disease, whereas those planted later were devastated (Frederiksen, 1980; Anahosur et al., 1982). Infected residues from both crop and weed hosts should be destroyed, for example, by collecting and burning 'rusted' leaves (Tarr, 1962). Healthy seed should be used for planting: seeds may be treated to prevent seedborne infection from urediniospores present on the surface of seeds. However, the role of seedborne urediniospores in disease transmission is questionable.

In regions where rust is an economically important disease, growing less-susceptible or resistant cultivars provides practical control of P. purpurea. Genotypes with generalized or polygenic resistance are widely cultivated. In North America, rust is a naturally stabilized disease (Frederiksen and Rosenow, 1972). The generalized resistance has proven very stable. Slow-rusting lines such as TAM-428 have performed well in North America. In India, screening procedures using urediniospores and evaluation of disease severity with a scale from 1 to 5 have been standardized. Several germplasm lines, varieties, hybrids and R lines have been tested over the years: several are resistant to the disease (Sharma, 1980; Anahosur, 1992; Miller and Prihoda, 1996; Miller et al., 1996; Sotomayor Rios et al., 1996; Palakshappa and Padaganur, 2002; Peterson et al., 2007). Testing several germplasm lines has revealed that the frequency of resistance was greater in 'tan type' sorghums than 'purple types' (Anahosur et al., 1981). Some of the most prominent resistant sources include IS-12610C, 2816C, 12539C, 12564C, 12666C, 3758, 3547, 3443 and 1257. Naik et al. (1981) and Naik and Anahosur (1988) reported that the biochemical basis of disease resistance in sorghum (e.g. TAM 428 and SPV 193) may be attributed to a high quantity of phenols and amino acids and a low level of sugars. Berquist (1971) showed that resistance to rust was inherited as a dominant trait. In India, Patil-Kulkarni et al. (1972) and Rana et al. (1976) argued that susceptibility was the dominant character among the parents they had used. Anahosur (1992) studied various crosses that indicated that resistance is dominant and may be governed by one or two genes. Rana et al. (1982) reported that resistances to leaf rust, downy mildew (Peronosclerospora sorghi) and charcoal rot (Macrophomina phaseolina) are inherited independently. It is possible to combine these traits through selection by choosing rust-resistant plants from segregating F3 progenies which have less than 1% downy mildew susceptibility and 10% charcoal rot susceptibility: a line with multiple resistance is thus selected. Shivanna et al. (1994) reported that inheritance of resistance to zonate leaf spot (Gloeocercospora sorghi), rust and downy mildew was governed by dominant genes and inherited independently. By accepting lines where 90% of plants are resistant to zonate leaf spot and downy mildew, the limit for rust can be fixed (at 80% of plants resistant) to select lines with a high degree of multiple disease resistance. The inherited pattern of disease resistance depended on the combinations of parents studied. Berquist (1974) described two races of P. purpurea. Sorghum variety IS-2814-TSC separated the population into two races whereas Rio (SC-599) was resistant to both the races.

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources: