Relationship between bacterial streak and black chaff symptoms in winter wheat

Disease symptoms caused by Xanthomonas campestris pv. translucens (J.J.R.) Dye occur on leaves (bacterial streak), spikes (black chaff), and peduncles of wheat (Triticum aestivum L. em. Thell.). Bacterial streak-black chaff has become prevalent in semi-tropical regions and cultivar resistance is the best control method. The objective of this work was to determine the relationship between bacterial streak and black chaff symptoms on wheat. In field tests during 1991 to 1994, black chaff severity and bacterial streak severity were not correlated among 15 soft red winter wheat cultivars and advanced lines or 387 wheat cultivars and germplasm accessions. Greenhouse tests during 1993 to 1994 showed that 'Florida 304' was susceptible to bacterial streak, but resistant to black chaff. In contrast, 'Coker 9877' was susceptible to black chaff, but moderately resistant to bacterial streak. The cultivar Terral 101 was resistant to both black chaff and bacterial streak, whereas LA85426 was susceptible to both diseases. Wheat genotypes may be resistant to black chaff but susceptible to bacterial streak or vice-versa. This may have caused the lack of correlation between black chaff and bacterial streak in the field. The results indicate that breeders cannot select indirectly for resistance to bacterial streak by selecting for resistance to black chaff. Since yield loss is related to bacterial streak but not to black chaff, wheat should be evaluated for resistance to bacterial streak and not black chaff.