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The Vibrio cholerae O1 chromosomal integron is discussed. The cloning of the ends of large cassette arrays has been investigated and a method developed. Data of the study help in identification of par of a new class 5 integron from V. mimicus. Until the discovery of the vibrio cholerae repeat (VCR), the gene capture and expression systems called integrons were associated in general with antibiotic resistance gene cassettes with fewer than five genes, usually, in an array.

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: [less than or equal to]84, 85 to 89, 90 to 94, 95 to 99, and [greater than or equal to]100. Selection was practiced within a HD class based on the following criteria: (i) BSS [less than or equal to] 10% in each year, (ii) if HD [less than or equal to] 94, then maximum average BSS [less than or equal to] 10%, (iii) if HD 95-99, then maximum average BSS [less than or equal to] 9%, and (iv) if HD [greater than or equal to] 100, then maximum average BSS [less than or equal to] 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 x environment (G x E) interactions.

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.