Yoncada (medicago sativa l.) Kuraklık Stresi ve Tolerantlık Mekanizması

İskender TİRYAKİ
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Kuraklık dünya genelinde tarımsal üretimi tehdit eden en önemli abiyotik stres faktörlerinin başında gelmektedir. Ilıman iklim kuşağının en önemli bitkilerinden birisi olan yoncanın (Medicago sativa L.) sürdürülebilir tarıma sağladığı olumlu katkılar ve hayvan beslenmesindeki önemi, bu bitkinin dünya ve ülkemizdeki kıymetini giderek artırmaktadır. Gelişimini tamamlamış 3-4 yıllık yonca bitkisi kurağa kısmen tolerant olmasına karşın özellikle çimlenme ve erken fide evreleri ile biçim sonrası dönemlerde meydana gelebilecek kuraklık stresinden büyük oranda etkilenmektedir. Diğer taraftan yoncada kuraklık stresi uygulayarak doğrudan seleksiyon ya da klasik melezleme yolu ile mevcut genotipler arasında tolerant bitkilerin elde edilmesi, kurağa tolerantlığın düşük bir kalıtım değerine sahip olması ve zaman alıcı uygulamalar olması nedeniyle oldukça güçtür. İntrodüksiyon ve yabancı çeşitlerin bu amaçla kullanılması ise beraberinde adaptasyon ve royalty ödemeleri gibi farklı sorunları beraberinde getirmektedir. Biyoteknolojik yaklaşımlar kullanarak kurağa tolerant transgenik çeşitlerin geliştirilmesi kısmen mümkün olmakla birlikte bu bitkilerin kabulüne yönelik dünya genelindeki tartışmalar halen devam etmekte ve ülkemizde bu bitkilerin yetiştirilmesine izin verilmemektedir. Bu nedenle kurağa tolerant yeni bitki genotiplerinin geliştirilmesindeki başarılar, bitkilerin stres ilişkili morfolojik, fizyolojik ve moleküler mekanizmalarının anlaşılmasına ve bunların birlikte değerlendirildiği yeni ıslah yaklaşımlarına bağlıdır. Bu çalışmanın amacı güncel literatür varlığında bitkilerde ve özellikle de yoncada kuraklık stresi ve kurağa tolerantlık mekanizmasının anlaşılmasına katkı sağlamaktır.

Anahtar Kelimeler: Yonca, kuraklık, su stresi, tolerant


Drought Stress and Tolerance Mechanisms in Alfalfa (Medicago sativa L.)


ABSTRACT: Drought is one of the major abiotic stresses threatening agricultural productivity all around the world. Alfalfa (Medicago sativa L.) is the most important forage crop in temperate regions whose importance may further increase because of its positive contribution to sustainable agriculture and its productivity on animal feeding. Although 3-4 years old alfalfa is relatively drought tolerant, it is very vulnerable to drought stress at germination and early seedling growth stages as well as at regrowth stage right after grazing. On the other hand, development of drought tolerant alfalfa varieties by selection or classical crossing is very difficult to due to low heritability of drought tolerance traits and longtime requirement. Introduction of foreign drought tolerant varieties comes along with adaptation and royalty payment problems. Although it is possible to develop relatively drought tolerant transgenic varieties by applying biotechnological approaches, the acceptance of such crops are still controversial and planting of those crops is not yet allowed in our country. Therefore, success for development of drought tolerant new plant genotypes will depend on understanding of stress related morphological, physiological and molecular mechanisms, and collective use of such new breeding approaches. The aim of this study is to help the understanding of drought stress and tolerant mechanisms of plants, specifically alfalfa, under the light of current literature.

Keywords: Alfalfa, drought, water stress, tolerance

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