We screened a total of 1365 pea (Pisum sativum) lines for response to inoculation with Agrobacterium tumefaciens, strain B6, and characterized resistance in one cultivar, Sweet Snap. Sweet Snap seedlings were highly resistant to tumorigenesis under most conditions. Resistance was overcome at inoculum concentrations of greater than 109 bacteria per milliliter. At such high concentrations, very small tumors developed on Sweet Snap in response to four wide-host-range Agrobacterium strains, but tumors on other cultivars were two-to sevenfold larger than those that formed on Sweet Snap. The hypervirulent strain A281 induced larger tumors on Sweet Snap than did other Agrobacterium strains, but tumors on other genotypes were more than 100% larger than those on Sweet Snap. Physiological experiments suggested that tumorigenesis in Sweet Snap is not blocked in early stages of infection, and genetic analysis indicated that inheritance of resistance to crown gall is a quantitative trait. In addition to the observed resistance in Sweet Snap, three 'supersusceptible' genotypes, which developed very large tumors, also were identified.
Six matricaria esters (MEs) and two matricaria lactones (MLs), isolated from members of the tribe Astereae (Asteraceae), were tested against Mycobacterium tuberculosis and M. avium, using a radiorespirometric bioassay. (2Z,8Z)-ME and (2E-8Z)-ME gave minimum inhibitory concentrations (MICs) of 50 micrograms ml-1 against M. tuberculosis and respective MICs of 25 and 50 micrograms ml-1 against M. avium. The (4Z,8Z)-ML, (2Z)-8-dehydro-ME and (2Z,8Z)-10-angeloyloxy-(2Z,8Z)-ME showed respective MICs of 12.5, 25, 25 micrograms ml-1 against M. tuberculosis and MICs of 50, 25, 25 micrograms ml-1 against M. avium, respectively. The MICs of (2Z,8Z)-10-tigloyloxy-ME and (2E,8Z)-10-angeloyloxy-ME and (4E,8Z)-ML ranged from 50 to > 100 micrograms ml-1 against both pathogenic mycobacteria.
We developed a quantitative assay to measure tumorigenesis on roots and root crowns, the natural sites of Agrobacterium tumefaciens infection. Efficiency of tumor formation and tumor weight on seedlings of Pisum sativum 'Little Marvel' were directly proportional to the logarithm of inoculum concentration. Depth of wounding prior to inoculation also significantly influenced tumor weight but not efficiency. Mean weight of tumors that developed in response to inoculation with strain B6 varied significantly among 34 different commercial cultivars. Tumors on the most susceptible cultivar, Target, were more than tenfold heavier than those formed on the least susceptible cultivar, Sweet Snap. Efficiency of tumorigenesis on 'Sweet Snap' was also relatively low: only 64% of inoculated seedlings developed tumors compared with 89 to 100% efficiencies for all other cultivars. evaluate resistance and susceptibility in Pisum sativum L., a well characterized diploid species that is a known host of A. tumefaciens (16). To initiate studies of crown gall resistance in pea, we established a reproducible quantitative assay for tumorigenesis on roots of intact plants and used it to survey genotypic variation among 34 commercial cultivars of pea. MATERIALS AND METHODS Bacterial Strains and CultureSingle colony cultures of bacterial strains were maintained at -70C in 50:50 (v/v) glycerol:yeast extract-mannitol (YEM) medium. Strain B6 was a gift from J. A. Lippincott (Northwestern University). For assays, cultures were grown overnight on YEM solidified with 0.7% agar and were suspended in water. Inoculum concentrations were estimated turbidimetrically and confirmed by dilution plating.Agrobacterium tumefaciens is a soil-borne bacterial pathogen that causes crown gall on most dicots and some gymnosperms and monocots (5). Although most parts ofmany plants are susceptible to experimental inoculation, A. tumefaciens normally infects through wounds in roots and at the rootshoot interface, the crown (18). Crown gall is among the major disease problems in fruit tree and ornamental nurseries and vineyards (25,26 Plant Inoculation and AssayPisum sativum L. seeds were surface-sterilized by consecutive 5-min immersions in 95% ethanol and 50% commercial bleach and then washed 4x in at least 50 mL of sterile water. Seeds were germinated on water agar overlaid with filter paper for 2 to 3 d or until the radicles were approximately 1 to 3 cm in length. Each seedling was wounded either by stabbing the root with a marked scalpel blade to a depth of 1 mm or by pushing the blade through the root to a depth of approximately 3 mm. Three wounds were made on each plant at approximately 5-mm intervals from the crown to the root tip. Seedlings were immersed into 5 mL of inoculum for 5 min and were then placed into moistened growth pouches (Northrup King, Minneapolis, MN), with 4 or 5 seedlings per pouch. Pouches were moistened daily with approximately 5 mL of water and were incubated at 250C day/230C night for 2 weeks.
Key indicatorsSingle-crystal X-ray study T = 120 K Mean '(C±C) = 0.002 A Ê R factor = 0.050 wR factor = 0.137 Data-to-parameter ratio = 22.3 For details of how these key indicators were automatically derived from the article, see
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