Barley Breeding and Pest Control
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Barley represents one of the major crops grown worldwide. It is the fourth largest grown crop in the world. Barley is a short season ,early maturing grain with high yield potential which is utilized in the production of both human and animal feed. The production of 2005 was estimated to be 138 million metric tons (UN Food and Agriculture Organization, FAO). Because of its true diploidy Barley has been used as a genetic model system, along with the similarity of its genome to that of other small grain cereals. It enables genetic engineering approaches towards crop improvement. (Hensel et al. , 2008).
Barley has remained a successful cereal crop because of its short growing time and ability to survive in poor conditions. Although it is grown throughout most of the UK it is often the dominant arable crop in the north and west of Britain where growing conditions are most difficult and less favourable for wheat.
Barley is striking because of the long spikes that emerge from the end of each grain. These are known as awns. Barley is also easily identifiable on breezy days in the early summer when "waves" blow through the crop. Although barley is versatile and tolerant it is not as productive as wheat. As a result it is often grown as the second cereal in a rotation where potential yields are lower; for example a field might first grow wheat, then barley, then a break crop like sugar beet or peas before returning to wheat. Barley can also be grown continually in the same field, a process known as continuous cropping. This was relatively common in the 1970s and 1980s but is rarely if ever practiced now. Around half of all the barley produced ends up as stock feed. This is either incorporated into compound rations or rolled on farm and fed to cattle as a supplement to their forage. Barley (Hordeum vulgare L. ) is the only cultivated species. Among the wild barleys there are annuals and perennials, self pollinators and cross pollinators, and self incompatibility species that are found in nature (Poehlman, 1987).
Difficulties in the production of Barley
There are various diseases that affect the barley production, like various bacterial, fungal and viral diseases. Nematodes and parasites can also hamper the barley production.
Fusarium is a genus of filamentous fungi widely distributed in soil and is mostly in association with plants. Some species produce mycotoxins in cereal crops that can affect human and animal health if they enter the food chain. The main toxins produced by these Fusarium species are fumonisins and trichothecenes. Fusarium graminearum commonly infects barley if there is rain late in the season. It is of economic impact to the malting and brewing industries as well as feed barley. Fusarium contamination in barley can result in head blight and in extreme contaminations the barley can appear pink. It can also cause root rot and seedling blight.
Lush, green fields become blighted seemingly overnight. The factors that favour infection and development of disease in the crop are frequent rainfalls, high humidity, or heavy dews that coincide with the flowering and early kernel-fill period of the crop. Damage from head scab is multifold. It reduces yields, discoloration, shriveled "tombstone" kernels, contamination with mycotoxins, and reduction in seed quality. The disease also reduces weight and lowers market grade. It causes difficulties in marketing, exporting, processing, and feeding scabby grain. The fungus persists and multiplies on infected crop residues of small grains. The chaff, light weight kernels, and other infected head debris of barley, are returned to the soil surface during harvest. This serves as an important site of overwintering of the fungus. Continued moist weather during the crop growing season favors development of the fungus, and spores are windblown or water-splashed onto heads of cereal crops. Barley is susceptible to head infection from the flowering (pollination) period up through the soft dough stage of kernel development. Spores of the this fungus land on the exposed anthers of the flower and then grow into the kernels, glumes, or other head parts. (McMullen et. al. , 1997).
Creating a new variety:
Chevron is six rowed non malting barley originating from Switzerland, and it is most widely used. This can be used as a source for the Fusarium Head Blight (FHB) as it has resistance genes for kernel discolorations. So the wild variety can be crossed with Chevron and the F1 generation can be generated.
H. vulgare X Chevron
Depending on the way the genes behave the combination produced from each cross are not to be revealed until the next generation (F2). The most likely plant is then selected to meet the breeding objective. Seeds from the best plant can again be sown in rows or plots and best plants can again be selected.
This process is repeated until the best plants are not selected. This technique takes a long time but the results are bred true.
Generally, awned genotypes with a short peduncle and a compact spike have faster disease spread than genotypes that are awnless, have a long peduncle, and a lax spike. In addition, short statured genotypes with a long grain filling.
On the other hands hybrid breeding technique can also be used, but it's just that while hybrid lines breed true year after year, the performance gains of F1 hybrids are not maintained in subsequent generations. QTL analysis can be done at every level to find out the gene where is it situated in the loci. This will give us a genetic information of the hybrids. If the QTL analysis is done the phenotype can be identified using biometrics or metabolomics.
There are various ways in which breeding can be done. Somatic hybridization, embryo rescue, double haploid breeding, genomics, MAS ,genetic modification Proteomics.
Mesterhazy (1995) had described five types of physiological resistance ,expanding on the the two types of barley available. These included (I) resistance to initial infection, (II) resistance to spread within the spike, (III) kernel size and number retention,(IV) yield tolerance, and (V) decomposition or non inherently accumulation of mycotoxins. It is believed that type 1 is very difficult to because the amount of innoculum initially applied is very difficult to quantify.
Molecular markers can also be used at every stage of crossing till the final generation is obtained, as in the pure lines are obtain. The use of molecular markers will help us in indentifying the gene integeration. As it is QTL
Analysis done will show us the location of the gene on which loci.
Different molecular markers have been used till date, so markers like RFLP, AFLP, SSR and many more can be used.
Pest and disease tolerance in Barley
Barley is infected with many pests and other diseases as mentioned above. The easy and the quickest option is the use of certified seeds obtained after F1 generation. There are various sprays like fungicidal sprays available which can also be used but they decrease the vigor and cause root rot.
So in order to avoid these pest resistance genes can also be added in barley. That means you induce the gene already there in the pest which infects,into the barley genes,with selectable ,markers. These markers will help in future to score the gene of interest and its location. Places where these markers are not accepted ,marker free plants can be generated.
This multi-faceted and cooperative approach should enable breeders to develop highly resistant barley cultivars thereby, significantly reducing if not eliminating the devastating effects of FHB both nationally and worldwide. (Rudd et al. ,2001)
There are as such no problems with drought or any problem with barley, but the major one is that if it rains late the whole of the production cycle of barley is disturbed. Due to less, late or no rains only there is development of these kind of fungal diseases due to the little moisture that is left on the leaf surface. Hence if we can increase the transpiration rate or the WUE (water usage efficency) by changing the leaf area exposed to the sun ,the retention capacity will increase.
"Only by working on a theory on breeding will the investigator be able to achieve real control over the organism- the ultimate aim of modern biology" --N. I. Vavilov
So as rightly said above, plant breeding is a very efficient way to conserve the wild species as well to grow crops that are resistant to the harsh conditions and pathogens and diseases caused by them. Through plant breeding technology we try to build up a perfect plant that has all the necessary resistant genes against all the possible problems faced by a plant to grow. As seen in barley also various other methods can also be inculcated along with these and newer varieties can be introduced which have better yield.
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