The competitiveness of dual-strain inoculum of Bradyrhizobium strains S24 and GR4 was demonstrated for nodulation of green gram (Vigna radiata). Strain S24 formed pink nodules, GR4 produced visually distinguishable dark-brown nodules. When a mixture of these Bradyrhizobium strains was applied as inoculum, nodules of both pink and dark-brown types were formed on the same root. The strain GR4, which was less competitive than strain S24, was mutagenized with N-methyl-N'-nitro-N-nitrosoguanidine to obtain pigment-diverse mutants and six selected mutants were screened for symbiotic parameters. One mutant produced pink nodules and appreciably increased plant dry mass. The competitive ability of this mutant lacking brown pigment was compared with that of strain S24 by using antibiotic resistance markers; it showed increased nodulation competitiveness than its parent strain GR4. The dark-brown nodule-phenotype could be useful in evaluating nodulation competitiveness of "cowpea miscellany" bradyrhizobia in soil where dark-brown nodule-forming strains are not indigenous.

• MeSH
• Bradyrhizobium classification   genetics   growth & development   MeSH
• Fabaceae growth & development   microbiology   MeSH
• Nitrogen Fixation * MeSH
• Plant Roots microbiology   MeSH
• Melanins metabolism   MeSH
• Methylnitronitrosoguanidine MeSH
• Symbiosis MeSH
• Publication type
• Journal Article MeSH
• Comparative Study MeSH
• Names of Substances
• Melanins MeSH
• Methylnitronitrosoguanidine MeSH

Seeds of Karwinskia humboldtiana obtained from a 1997 collection in the locality of Villa de Gracía Nuevo (León, Mexico) were contaminated with spores of filamentous fungi, bacteria and yeasts. The concentration of microorganisms in unscarified seeds ranged from 3.0 x 10(3) to 7.5 x 10(3) CFU/g. Predominant were bacterial isolates of the genera Aeromonas sp., Bacillus, and Pseudomonas; from filamentous fungi were identified Alternaria, Aspergillus niger, Cladosporium sp., Fusarium sp., Mucor sp., Penicillium commune, Trichothecium sp.; from yeasts Rhodotorula sp. and Saccharomyces cerevisiae. Seed scarification significantly reduced the microbial contamination. Of the original fungal isolates, only two were identified on scarified seeds, viz. Cladosporium sp. and Saccharomyces cerevisiae; although a relatively high incidence of a unidentifiable of Penicillium sp. was found, the bacterial spectrum was not altered. Treatment of scarified seeds with Vitavax 200 WP and Pomarsol Forte 80 WP (3 mg/g seeds) augmented germination by 10-19% compared to treated unscarified seeds, and by 16-31% compared to untreated unscarified seeds.

• MeSH
• Bacteria isolation & purification   MeSH
• Carboxin pharmacology   MeSH
• Fungi isolation & purification   MeSH
• Germination drug effects   MeSH
• Rhamnus microbiology   MeSH
• Colony Count, Microbial MeSH
• Fungicides, Industrial pharmacology   MeSH
• Seeds drug effects   microbiology   MeSH
• Thiram pharmacology   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Carboxin MeSH
• Fungicides, Industrial MeSH
• Thiram MeSH