Inheritance of Resistance to Stagonospora nodorum Leaf Blotch in Kansas Winter Wheat Cultivars

Stagonospora nodorum blotch, caused by Stagonospora nodorum (Berk.) Castellani & E.G. Germano (= Septoria nodorum (Berk.) Berk. in Berk. & Broome, teleomorph: Phaeosphaeria nodorum (E. Müller) Hedjaroude) can cause serious yield and quality losses of wheat (Triticum aestivum L.) in many countries worldwide (3,14,20). Yield losses caused by this disease have been reported as high as 40% in severe epidemics (8,18,31). Under severe epidemics, the kernels of susceptible wheat cultivars are shriveled and are not fit for milling (11). The fungus causes both leaf and glume blotch of wheat. Although glume blotch was stated to be the main cause of yield reduction (16,18), foliar infection can be as detrimental to yield as head infection (11). For example, Walther and Bohmer (34) reported that Stagonospora nodorum blotch severity on leaves had the highest correlations with yield loss, whereas head infection was poorly correlated with yield. Although there are several control methods, including crop rotation and foliar fungicides, the preferred method of control is the use of resistant cultivars (4,36). However, breeding for resistance to S. nodorum is difficult because resistance can be correlated with undesirable agronomic traits such as tall plant height and late maturity (32). Resistance to the leaf and head phases may be under separate genetic control (2,15,35). Fried and Meister (13) also reported evidence for independent segregation of genes controlling resistance to leaf and glume blotch. Resistant genes for reaction on the flag leaf were found on chromosomes 3A, 4A, and 3B, while those for the head phase were located on the same chromosomes and on 7A (15). The testing of wheat seedlings in the greenhouse has been reported to be an effective strategy for identifying reactions to S. nodorum because the susceptibility of seedlings was correlated with that of the adult plants in the field (10,20,28). This type of testing permits use of quantitative inoculation techniques and eliminates the influence of undesirable agronomic traits such as tall plant height and late maturity on selection (37). Many sources of resistance to Stagonospora nodorum blotch have been identified in species related to wheat: Triticum timopheevii (23,33), T. monococcum (22), Aegilops tauschii (22,27), A. speltoides (5), and A. longissima (6). In addition, resistance also has been identified in several wheat cultivars and their genetic control studied. However, most studies were conducted for resistance to glume blotch and indicated that the resistance was polygenically controlled (7,13,17,25,26,37). A few studies were undertaken to study resistance to leaf blotch. In recent studies, Wilkinson et al. (37) and Wicki et al. (35) reported that the resistance to the leaf phase is inherited polygenically in winter wheat cultivars commonly grown in the United States and Europe, respectively. However, Frecha (12) reported a single dominant gene for seedling resistance to Stagonospora nodorum blotch in the wheat cv. Atlas 66. This gene was located on chromosome 1B (19). Wong and Hughes (38) also reported monogenic control for resistance to the leaf phase of Stagonospora nodorum blotch in three winter wheat cultivars (81IWWMN 2095, Coker 76-35, and Red Chief). In addition, Scharen and Eyal (30) provided evidence that resistance in highly resistant cultivars might be governed by major resistance genes. Although simple inheritance of resistance to leaf blotch has been reported, use of the resistance has lagged because of lack of supporting reports for additional single-gene resistances. The reason for failure to identify other resistances controlled by single genes is because many studies were conducted in the field where other foliar diseases may confound disease ratings. In recent years, several winter wheat cultivars adapted to Kansas have been released with improved resistance to the leaf phase of Stagonospora nodorum blotch (1). These were developed by recurrent-selection for green leaf duration in numerous field nurseries during the breeding period. These cultivars have been grown extensively in Kansas with one cultivar (Jagger) occupying 43% of the seeded acreage in 2002. Because of their ABSTRACT Kim, Y. K., Brown-Guedira, G. L., Cox, T. S., and Bockus, W. W. 2004. Inheritance of resistance to Stagonospora nodorum leaf blotch in Kansas winter wheat cultivars. Plant Dis. 88:530-536.