Breeding for resistance to Helminthosporium blights in Nepal: Strategies and genetic gains

• Main Authors: Bhatta, M.R, Pokhrel, D.R, Devkota, R.N, Dubin, H.J, Mudwari, A, Bimb, H.P, Thapa, B.R, Sah, B.P, Bhandari, D
• Format: Conference Proceeding
• Language: English
• Published: Mexico, DF (Mexico) CIMMYT/UCL/BADC 1998
• Subjects: AMELIORATION DES PLANTES; BLIGHTS; BREEDING METHODS; DEPERISSEMENT; DISEASE RESISTANCE; ENFERMEDADES DE LAS PLANTAS; FITOMEJORAMIENTO; GENETIC RESOURCES; HELMINTHOSPORIUM; MALADIE DES PLANTES; METHODE D'AMELIORATION GENETIQUE; METODOS DE MEJORAMIENTO GENETICO; NEPAL; PLANT BREEDING; PLANT DISEASES; PYRENOPHORA; RECURSOS GENETICOS; RESISTANCE AUX MALADIES; RESISTENCIA A LA ENFERMEDAD; RESSOURCE GENETIQUE; TIZON; TRITICUM
• ISBN: 9706480013; 9789706480019

Helminthosporium leaf blight (HLB) of wheat, caused by Bipolarissorokiniana and Pyrenophora tritici-repentis, is a disease of economic importance in the terai of Nepal. Most commercial varieties show inadequate HLB resistance. Yield loss assessments conducted by the National Wheat Research Program, Bhairahawa, have shown losses of 23.8-27 percent in highly susceptible varieties. On-farm studies indicated yield losses of up to 16 percent. Considering the sizable losses, top priority is being given to breeding for HLB resistance. This paper summarizes the breeding strategy adopted by the National Wheat Research Program to develop and identify HLB resistant wheats and to assess the genetic gains achieved. Breeding begins with the identification of resistant donor lines from different sources. To date, the best materials identified have come from China, CIMMYT alien gene lines from Thinopyrum curvifolium, Brazil, and Zambia. Crossing strategies of the hybridization program are designed to involve one parent from our adapted varieties to incorporate earliness, acceptable grains, and other desirable traits into the progeny. Plants in the segregating populations are selected based on resistance governed by quantitative traits such as small lesions on uppermost leaves, low disease severity, 'stay green' at high temperatures during grain filling, freedom from black point, and grain plumpness. A limited backcross program has been initiated, assuming inheritance to be qualitative in some cases; however, progress has remained slow. The best progeny have resulted from three-way and single crosses. Besides hybridization, selection and identification of resistant genotypes from different international collaborative nurseries is continuing. The major outcome of this work is the identification of resistant lines that are now at different stages of multilocation testing.