Introduction to the lab report on controlling barley powdery mildew - Essay Example

Cultural methods of control: Cultural methods of control of powdery mildew aim to ensure the eradication of inoculums from volunteer cereals and crop debris by disposing them and ensuring the removal of suitable conditions for disease development. Thus volunteer cereals which carry the inoculums through winter are uprooted and removed, and the cleistothecia inhabiting the crop residue too is eradicated by disposing off the crop residue. Other cultural practices used for control of powdery mildew in barley are application of larger quantities of nitrogen fertilizers, crop rotation and late sowing of the crop (Brooks, 1970).

Chemical Control: Chemical agents used for control of powdery mildew in barley include azole fungicides and morpholine based fungicides. Systemic treatment of seed with azole fungicide was able to control the disease development on the saplings for a few weeks. Later if the disease appeared the same was applied on the leaves. However, with years of usage the E. graminis has developed tolerance for this fungicide, thereby limiting their use and efficiency (Brown, 2002). Morpholine based fungicides are now used for chemical control of powdery mildew. . The first pathway involves resistance imparted by recessive alleles at Mlo locus.

It further requires two more host genes namely, Ror1 and Ror2 (Buschages et al., 1997). The resistance resulting as a consequence of this pathway is able to protect barley plant from all powdery mildew strains tested as yet. The other pathway involves collaborative action of multiple race specific resistance genes collectively known as R gene e.g. Mla, Mlg, Mlk etc (Jorgensen, 1994). Resistance imparted by the Mlo locus: Durable resistance The term durable resistance is indicative of the fact that resistance acquired by the plant is and will remain effective against all known and yet to appear varieties of the pathogen.

This is the significance of the Mlo allele and the disease resistance imparted by it. Moreover the Mlo mutant allele renders the barley plant resistant exclusively to powdery mildew pathogen and has no effect on the activity of any other disease causing organism. Wild type Mlo allele encodes a cell membrane receptor protein (Mlo protein) and is the dominant allele. It is the recessive and non functional allele which is responsible for powdery mildew resistance (Buschages et al., 1997). It has been reported that Mlo protein is imperative for the successful colonization of the pathogen in absence of which the fungal spores are unable to penetrate the epidermal cell layer of the host (Buschages et al., 1997). This is unlike the mechanism of resistance development by most resistant imparting genes, i.e. hypersensitivity (Shirasu and Schulze-Lefert, 2000).

The first mutant at Mlo locus was introduced in 1942 the mutation caused by application of X-rays, and ever since improvements have been continuously done with