Breeding Progress

Development and identification of high yielding genotypes with wide adaptation and resistance to biotic and abiotic stresses remain the top priorities of the wheat breeding programs. There are different approaches of determining the breeding progress or the rate of genetic gain for grain yield and other traits. Some studies use yield of historical genotypes grown in the same environment while others have used mean yield to examine progress over time in highly productive environments. Trethowan et al. (2002) have used regression analysis using the mean of the five highest yielding entries expressed as per cent of the trial mean across years to determine the rate of breeding progress in elite spring wheat yield trial (ESWYT) and semi-arid wheat yield trial (SAWYT). Tadesse et al. (2010) have used success rate analysis of best lines for the high rain-fall wheat yield trials (HRWYT) of CIMMYT to demonstrate yield gains over years or trials. Genetic gain studies for the CIMMYT/ ICARDA wheat breeding program have shown continuous progress in yield and other traits (Sayre et al. 1997; Trethowan et al. 2002; Sharma et al. 2012; Tadesse et al. 2010). Recently, Tadesse et al. (2013) have determined the breeding progress for IWWIP and reported that the grain yield of the best line (BL) increased at a rate of 110 kg/ha/year (R2 = 0.66; P = 0.001), while the trial mean (TM) increased at a rate of 91.9 kg/ha/year (R2 = 0.53; P = 0.007) indicating a continuous yield improvement at IWWIP.

In addition to grain yield, significant progress has been made by the IWIN in developing resistant wheat germplasm to diseases and pests ensuring that developing and deploying genetically resistant varieties adapted to target growing environments is the best economical and environmentally friendly strategy for controlling rust diseases of wheat particularly for resource poor farmers. However, because of the co-evolution of the host and pathogen, the deployment of individual resistance genes leads to the emergence of new virulent pathogen mutants, and hence the 'boom and bust cycle' of cultivars performance continues. Recently, a new stem rust race Ug99 (TTKS) has been first detected in Uganda in 1999 and then spread to Kenya, Ethiopia, Yemen, Sudan and Iran, and became a global threat to the wheat industry of the world for the very fact that it over comes many of the known and most common stem rust resistance genes such as Sr31, Sr24 and Sr36 (Singh et al. 2006; Jin et al. 2007; Haile et al. 2012). Similarly, the breakdown of yellow rust resistance genes Yr9 in cultivars derived from “Veery” in the 1980s and Yr27 in 2000s in major mega cultivars derived from “Attila” cross such as PBW343 (India), Inquilab-91 (Pakistan), Kubsa (Ethiopia) and others such as Achtar in Morocco, Hidab in Algeria and many other cultivars in the CWANA region (Solh et al. 2012) has caused significant wheat production loss. Through a coordinated international effort, many wheat varieties resistant to Ug99 and yellow rust have been released and replaced the susceptible cultivars.

In most developing countries, apart from grain yield and disease resistance, grain quality was not a strong criterion of variety selection. However, things have changed through time and some developing NARS are critically looking for better quality varieties suiting for preparation of different end products. Varieties such as Bezostaya, Achtar, Veery, HD1220, and Pavon-76 are known for their excellent grain quality. These varieties are still dominantly grown in some countries not only because of their wide adaptation, high yield potential and stability but also because of their high protein content and quality. With this understanding the wheat breeding programs at CIMMYT and ICARDA undertake evaluation of germplasm for quality traits following standard grain quality procedures. Most of the currently available elite genotypes for both irrigated and rain fed environments are excellent in quality with protein levels of 12–16 %. Most of these genotypes have the 5 + 10 (Glu-D1), 7 + 8 (Glu-B1) and 2* (Glu-A1) alleles. These alleles, especially the 5 + 10 Glu-D1 allele, have been reported to be highly correlated with protein quality and are being used intensively as a selection criterion in wheat breeding for improving end-use quality.

 
< Prev   CONTENTS   Next >