Friday, September 5, 2008

Selection Index for Improving HLB Resistance and other traits

Foliar blight, also known as HLB, is a serious disease of wheat in the warmer areas of South Asia
where spring wheat is grown during the winter season (November to April). Yield losses due to foliar blight are variable but significant. In farmers’ fields, losses of up to 20% have been reported. In the Nepal lowlands where most wheat is produced, HLB develops as a complex of spot blotch, caused by C. sativus (Ito & Kurib.) Drechsler ex Dastur[anamorph Bipolaris sorokiniana (Sacc.) Shoemaker], and tan spot, caused by P. tritici-repentis (Died.) Drechs.
[anamorph Drechslera tritici-repentis (Died.) Shoemaker]. Although significant progress has been made in recent years by wheat breeding programs targeting materials suitable for the Gangetic Plains, most cultivars grown in the Indian Subcontinent still possess relatively
low levels of foliar blight resistance.

Wheat breeders in the region are currently devoting a great deal of effort to finding genotypes that are early maturing and HLB resistant, two important traits that promising high-yielding modern varieties must have to be suitable for eastern South Asia. In the past decade, breeders in South Asia have used several exotic sources showing good levels of HLB resisdisease
tance. However, this has been reported that the best foliar blight-resistant wheats in South Asia were late and tall, two less desirable agronomic characters.The use of late-maturing HLB-resistant wheats in crossing programs with early maturing, HLB-susceptible commercial cultivars generated segregating populations where it was difficult to identify early maturing HLB-resistant lines with regular selection schemes.

Simultaneous selection for early maturity, HLB resistance, and heavier kernels in wheat has proven difficult in the warm, humid region of South Asia because of a complex negative relationship among the three traits. Thus index has been devised to select for these three traits together making selection index.

IS = Area Under Disease Progress Curve (AUDPC) rank in ascending order + DHD (days to heading) rank in ascending order + TKW (thousand kernel weight) rank in descending order

How to use it?

For more details:

Sharma RC, Duveiller E (2003) Selection index for improving Helminthosporium leaf blight resistance, maturity, and kernel weight in spring wheat. Crop Science 43:2031–2036.

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