Evaluation of Bread Wheat Germplasm for Resistance to Bacterial Streak
- B. L. Tillman ,
- S. A. Harrison,
- C. A. Clark,
- E. A. Milus and
- J. S. Russin
Texas A&M Univ. Agric. Res. and Ext. Center, Rt. 7, Box 999, Beaumont, TX 77713-8530 Dep. of Agronomy, 104 M.B. Sturgis Hall Dep. of Plant Pathology and Crop Physiology, 302 Life Sciences Bldg., Baton Rouge, LA 70803, Louisiana State University, LSU Agricultural Center Dep. of Plant Pathology, 217 Plant Science Bldg., Univ. of Arkansas, Fayetteville, AR 72701 Abstract
Bacterial streak caused by Xanthomonas campestris pv. translucens (J.J.&R.) Dye (Xct) reduces grain yield of wheat (Triticum aestivum L. em. Thell) by as much as 40%. Resistant cultivars offer the best control in the absence of effective bactericides. However, few resistant genotypes have been identified for use in breeding programs. Five thousand bread wheat accessions from the USDA National Small Grains Collection were inoculated with Xct and evaluated for resistance to bacterial streak in the field during 1992. On the basis of agronomic characteristics and bacterial streak severity, a total of 428 accessions was selected for continued testing. These accessions were inoculated with Xct and evaluated in replicated hill plots in the field during 1993 and 1994. Accessions were also evaluated for water-soaking (WS) reaction to Xct in growth chambers using a seedling syringe inoculation method. Average bacterial streak severity (BSS) during 1993 and 1994 was negatively correlated with heading day (HD) (r = −0.55;P< 0.001). To reduce the maturity effect, accessions with HD >106 were dropped and the remaining accessions were grouped into the HD classes: ≤84, 85 to 89, 90 to 94, 95 to 99, and ≥100. Selection was practiced within a HD class based on the following criteria: (i) BSS ≤ 10% in each year, (ii) if HD ≤ 94, then maximum average BSS ≤10%, (iii) if HD 95–99, then maximum average BSS ≤ 9%, and (iv) if HD ≥ 100, then maximum average BSS ≤ 7%. Twenty-six resistant accessions are recommended for the southern USA. Two controls, Terral 101 and GA 22 triticale (X. triticosecale Wittmack), also met these criteria with 6% average BSS. BSS and WS were not positively correlated, suggesting that the WS reaction to Xct from the syringe inoculation test may have limited usefulness. Field screening was effective in identifying resistance, but reaction of genotypes was confounded by relative maturity and genotype × environment (G×E) interactions.
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