Modified Half‐Sib and Phenotypic Recurrent Selection for Resistance to Powdery Mildew in Winter Wheat

Abstract

Specific resistance to powdery mildew of wheat (Triticum aestivum L.), incited by Erysiphe graminis f. sp. tritici, has been associated with several major genes that are relatively easy to select in segregating populations. Nonspecific resistance is more difficult to select because of genetic and nongenetic factors that lower heritability. The objectives of this study were to: (i) determine the effectiveness of recurrent selection for accumulating genes for nonspecific resistance to powdery mildew in two winter wheat populations, and (ii) examine the effect of changes in the level of resistance on other components of resistance. Two winter wheat populations (designated Early and Elite) carrying a dominant male sterile gene were subjected to two cycles of recurrent selection for powdery mildew resistance using phenotypic recurrent selection and modified half‐sib family selection. Ten‐day‐old seedlings were inoculated in the greenhouse with a spore suspension consisting of equal amounts of four isolates possessing combined virulence that overcame all known powdery mildew resistance genes except Pm3b and Pm8. Beginning 7 d after inoculation, area under the disease progress carve (AUDPC) was determined four times at 4‐d intervals and used select individuals for the next cycle. The mean AUDPC on the primary leaves of S1 families and the realized gains after two cycles of selection indicated that the Elite population averaged 46% gain over the two selection methods compared to 35% gain for the Early population. Over two cycles, half sib selection gains of 40 and 53% were realized in the Early and Elite population, respectively, while phenotypic recurrent selection reduced AUDPC 30% in the Early population and 40% in the Elite population. For both populations, selection for low AUDPC resulted in significantly decreased final disease severity ratings, colony number, and cumulative sporulation capacity. Duration of the incubation period was significantly increased only with two cycles of half‐sib selection for AUDPC. A high correlation between AUDPC and the final disease severity rating indicated that the breeder could select for nonspecific resistance using a final disease severity rating provided the test materials are all inoculated simultaneously.

Recurrent Selection for Partial Resistance to Crown Rust in Oat

“…Lower absolute responses (−3%) were found by Reinhold et al (1993) and Walker and Schmitthenner (1984) after eight cycles of recurrent selection for adult plant resistance to leaf rust in barley and three cycles of recurrent selection for tolerance to Phytophthora rot in soybean, respectively. Higher absolute gains per cycle have been reported for resistance to scab (−18%; Jiang et al, 1994) and powdery mildew (−18%; Abdalla et al, 1989) in wheat and leaf rust and powdery mildew in barley (−32 and −19%, respectively; Parlevliet and Van Ommeren, 1988). The four rapid recurrent selection cycles for partial resistance to oat crown rust of Phase II produced an average reduction in AUDPC of −8.87 cycle −1 (Fig.…”

“…Marchal) (Parlevliet and Van Ommeren, 1988), in wheat ( Triticum aestivum L.) to powdery mildew (caused by Erysiphe graminis f. sp. tritici ) (Abdalla et al, 1989), and scab (caused by Gibberella zeae Petch.) (Jiang et al, 1994), and in oat to barley yellow dwarf virus (Baltenberger et al, 1988).…”

Effects of recurrent selection for resistance to scab (Gibberella zeae) in wheat

“…In wheat, it has been applied for increasing grain protein content (McNeal et al ., 1978 ;Loffler et al ., 1983), kernel weight (Busch & Kofoid, 1982), early heading Tablet . Average,variance(V),coefficientofvariation(CV)andrangeofvariation(RV)ofpercentageofscab-infectedspikelets and seeds per spike in successive generations of recurrent selection, and selection responses (R) for Fusarium (Avey et al ., 1982), and improving resistance to powdery mildew (Abdalla et al ., 1989) . The discovery of the dominant male-sterile gene Tal (Ms2) promoted the application and development of recurrent selection in wheat breeding program in China (Deng & Gao, 1982) .…”

“…Hence, progress in breeding for scab resistance was rather late in coming compared to breeding for other objectives (Wu, 1990) . An advantage of population improvement through recurrent selection is that large amounts of genetic variability can be utilized and many traits can be simultaneously improved in the population (Abdalla et al ., 1989 ;Loffler et al ., 1983 ;Wang et al ., 1991) . The experimental results show that, except for plant height, most of the agronomic characteristics observed remain the same or tend to be slightly improved during the development of the scab resistant gene pool through phenotypic recurrent selection for head blight resistance .…”

Ms3 dominant genetic male sterility for wheat improvement with molecular breeding

“…The Ms3 DMS trait has been used in several US wheat breeding programs. The utility of Ms3‐ facilitated recurrent selection for disease resistance was demonstrated by Abdalla, Coffman, Sorrells, and Bergstrom (1989), who evaluated two cycles of selection for nonspecific resistance to powdery mildew [ Blumeria graminis (DC) Speer f. sp. tritici emend.…”