Heritability of Resistance to Bacterial Streak in Winter Wheat B. L. Tillman* andS. A. Harrison ABSTRACT Bacterial streak caused by Xanthomonas campestris pv. translucens reduces yield of wheat [Triticum aestivum (L.) em Thell] worldwide. Attempts to control the disease with bactericides have been unsuccess- ful. Resistant cultivars offer the best protection against yield loss, but little is known about the inheritance of resistance. The objectives of this study were to estimate the heritability of resistance to bacterial streak in soft red winter wheat andto derive an effective strategy for selecting resistant genotypes. About 60 F2:3 and F2:4 lines from each of three populations (Popl, Pop2, and Pop3) were tested for resistance to bacterial streak in three Louisiana environments with two to three replications per environment from 1991 to 1994. Variation due to genotype x environment (G × E) interaction occurred in each of the populations and was one-fourth to one-half the magnitude of error variance. Heritability of resistance to bacterial streak was relatively low and rangedfrom 0.12 to 0.70 (average 0.31) with parent-offspring regression and from 0.18 to 0.40 with variance components (average 0.36). Heritability increased by 0.22, 0.29, and 0.29 for Popl, Pop2, and Pop3, respectively, with means of two replications and two environ- ments. Non-normaldistributions in two of the three populations may have inflated estimates of heritability. Across populations, four lines were resistant in all three environments and 12 lines were resistant in two of three environments. Because of GxE interaction, testing should be conducted with at least two replications in two environments under high disease pressure. Such a testing program should be effective in selecting wheatlines resistant to bacterial streak. B ACTERIAL STREAK/BLACK CHAFF is caused by Xantho- monas campestris pv. translucens (J.J.& R.) Dye (Xct) (Cunfer, 1988; Wiese, 1987). Bacterial streak re- fers to streaked or blotched symptoms on the leaves (Cunfer, 1987; Duveiller, 1994; Wiese, 1987). Black chaff describes partial to complete darkening of the glumes (Bamberg, 1936; Smith et al., 1919). Darkening of glumes, similar to that caused by Xct, also can be induced by high temperature, high light intensity and high humidity in certain stem rust (Puccinia graminis Pers.:Pers. f. sp. tritici Eriks & E. Henn.) resistant wheat cultivars (Broadfoot and Robertson, 1933; Johnson and Harborg, 1944). The reaction may be a pleiotropic effect of stem rust resistance genes resulting from envi- ronmental extremes (Duveiller et al., 1993). For this reason, some researchers do not consider black chaff symptoms to be reliable indicators of susceptibility to Xct (Duveiller et al., 1991). Among several hundred wheat lines tested in Louisiana, there was no correlation between the severity of black chaff and bacterial streak (Tillman, 1994). Greenhouse results showed that wheat genotypes can be resistant to black chaff but susceptible to bacterial streak and vice-versa. B.L. Tillman, Texas A&M Univ. Agric. Res. and Ext. Center, Rt. 7, Box 999, Beaumont, TX 77713-8530 and S.A. Harrison, Dep. of Agron- omy, 104 M.B. Sturgis Hall, Louisiana State Univ., Baton Rouge, LA 70803. Contribution of the Louisiana State Univ. Agric. Center, Louisiana Agric. Exp. Stn. J. no. 95-09-9071. Received27 Feb. 1995. *Correspond- ing author. Published in Crop Sci. 36:412-418 (1996). Yield loss, caused by bacterial streak ranging from 3 to 40%has been reported in Idaho, Minnesota, Mexico, and Louisiana (Duveiller and Maraite, 1993; Forster and Schaad, 1988; Shane et al., 1987; Tillman, 1994). The disease reduces grain weight per spike, the number of grains per spike, and test weight. Thus far, yield loss has not been associated with black chaff. Several chemical and cultural methods are recom- mended for controlling bacterial streak. The disease was evidently controlled for many years with mercuric chlo- ride seed treatments (Forster and Schaad, 1988; Sands et al., 1986); however, this chemical is no longer in use. In Idaho, acidified cupric acetate controlled Xct on wheat seed (Forster and Schaad, 1988). However, this compound also adversely affected seed germination and plant stand. Foliar sprays of bactericidal chemicals have not proven beneficial. In yield loss studies, the use of foliar sprays to maintain disease-free control plots has not been successful (Shane et al., 1987). Currently chemical, for either seed or foliar application, is recom- mended for bacterial streak control in wheat. The use of pathogen-free seed also is a possible control method. A semi-selective agar medium has been devel- oped which allows the detection of Xct on wheat seed. This technique could be used to produce pathogen-free seed in a foundation seed-health program (Schaad and Forster, 1985). Early investigators suggested plowing under crop residues and destroying perennial weeds that may harbor Xct, as well as using clean seed as possible control measures (Boosalis, 1952; Smith, 1917). In Ar- kansas, the pathogen does not oversummer in crop debris or on weeds so this may not be an effective control measure in that area (Milus and Mirlohi, 1994a). Europe, where bacterial streak apparently does not occur, the European and Mediterranean Plant Protection Orga- nization has recommended Xct as a potential quarantine organism (Paul and Smith, 1989). Given the current lack of practical chemical control, resistant cultivars will likely play an important role in the control of bacterial streak of wheat (Cunfer, 1988; Cunfer and Scolari, 1982; Duveiller et al., 1991; Duveiller et al., 1993). Resistance to bacterial streak in the triticale (X. tritico- secale Wittmack) genotypes ’Siskiyou’, ’M2A-Beagle’, and OK77842 was found to be controlled by a single dominant gene (Johnson et al., 1987). Two triticale germplasm lines from Georgia have been released which possess the dominant gene in the homozygous condition (Johnson et al., 1989). Transfer of the gene from tri- ticale to wheat maybe possible. For example, resistance to speckled leaf blotch [Septoria tritici Rob ex Desm (perfect stage: Mycospharella graminicola (Funckel) Schroeter)] in triticale has been successfully transferred into hexaploid wheat (May, 1983). In Mexico, analysis of a five-parent diallel in wheat Abbreviations: Xct, Xanthomonas campestris pv. translucens; G×E, genotype × environment. 412 Published March, 1996