Pathogenic variation in, sources of, and breeding for resistance to Phaeoisariopsis griseola causing angular leaf spot in common bean

If we are to breed common bean (Phaseolus vulgaris L.) for durable resistance to diseases, we must understand pathogenic variation and find sources of resistance. Our first objective was to determine the patterns of pathogenic variation found among isolates of Phaeoisariopsis griseola (PG), the fungus that causes angular leaf spot (ALS) in common bean. We characterized 433 PG isolates from 11 Latin American and 10 African countries, using differential cultivars, isozymes, and/or random amplified polymorphic DNA (RAPD) markers. We also systematically screened, for ALS resistance, common bean accessions from the world collection held at CIAT, and assessed the progress so far made in breeding for resistance to ALS. Despite their great diversity within and between countries on both continents, the PG isolates were classified into two major groups: Andean, and Middle American. Although each group had internal differences for virulence, and biochemical and molecular characteristics, the ‘Andean’ PG isolates were more virulent on common beans of Andean origin, than on those of Middle American origin, thus, suggesting a host-pathogen co-evolution. The ‘Middle American’ PG isolates, although more virulent on common beans from Middle America, also attacked Andean beans, thus, exhibiting a much broader virulence spectrum. To find sources of resistance, we tested 22,832 common bean accessions against naturally occurring PG isolates in the field at CIAT's Experiment Station, Quilichao, Colombia, between 1985 and 1992. The resulting 123 intermediate (scores of 4 to 6) and resistant (scores of 1 to 3) accessions were then tested in the greenhouse against selected 14 PG isolates of diverse origins. Nineteen accessions were intermediate or resistant to at least 13 of 14 PG isolates. Similarly, of 13,219 bred lines tested in the field between 1978 and 1996, 89 were intermediate or resistant. Of these, 33 bred lines proved intermediate or resistant to at least eight of nine PG isolates to which they were challenged in the greenhouse. We suggest that, to breed for durable resistance to ALS, common bean populations should be developed from crosses between Andean and Middle American gene pools. The populations should then be systematically evaluated and selected against the broadest range of the most virulent PG isolates of diverse evolutionary origins. This revised version was published online in August 2006 with corrections to the Cover Date.     

Analysis of genes controlling photoperiod sensitivity in common bean using DNA markers

The genetic basis of the photoperiod response in common bean (Phaseolus vulgaris L.) was investigated using DNA markers and recombinant inbred populations. Two loci affecting photoperiod response were resolved, the previously defined primary locus (Ppd), at which the dominant allele confers sensitivity to photoperiod, and a second locus (herein defined as Hr), which influences the degree to which a plant responds to photoperiod. The DNA marker P5₁₆₀₀ cosegregated with the recessive allele, ppd, displaying a recombination frequency with the photoperiod locus of about 3%. A second marker, B303₆₀₀, was linked to the recessive allele at Hr and mapped approximately 13 cM from this locus. The markers demonstrated that in crosses involving Redkloud and several photoperiod sensitive lines, insensitivity to photoperiod is primarily controlled by ppd and that Hr does not significantly affect flowering time in ppd/ppd plants under the environmental conditions used. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of salt stress on interaction between lentil (Lens culinaris) genotypes and Rhizobium spp. strains: symbiotic N2 fixation in normal and sodic soils

 Following screening, selection, characterization and examination of their symbiotic N₂ fixation, only two Rhizobium strains (ND-16 and TAL-1860) and four lentil genotypes (DLG-103, LC-50, LC-53 and Sehore 74-3) were found to be suited to sodic soils. Interactions between salt-tolerant lentil genotypes and Rhizobium strains were found to be significant, and resulted in greater nodulation, N₂ fixation (nitrogenase activity), total nitrogen, plant height, root length and grain yield in sodic soils under field conditions compared to uninoculated controls. Significantly more nodulation, nitrogenase activity, glutamine synthetase (GS) and NADH-dependent glutamate synthase (NADH-GOGAT) activities were found in normal soil as compared to the soil supplemented with 4% and 8% NaCl. Salt stress inhibited nitrogenase, GS and NADH-GOGAT activities. However, nitrogenase activity in nodules was more sensitive to salt stress than GS and NADH-GOGAT activities (NH₄ ⁺ assimilation). The relevance of these findings for salt-tolerant symbionts is discussed. Received: 14 November 1997     

Properties and Composition of Concentrates and Syrup Obtained by Microfiltration of Saccharified Corn Starch Hydrolysate

Flow properties, clarity and composition of concentrates (retentates) and clarified syrup (permeates) obtained by membrane microfiltration of saccharified corn starch hydrolysate were determined. Clarified syrup (permeate) had low color and no suspended solids at all volume concentration ratios (VCRs) up to 100 X. The color and suspended solids in the concentrate increased linearly with increase in volume concentration ratio. Viscosity of the concentrates increased at higher VCR, but the viscosity of permeates remained essentially unchanged. The densities of all retentates and permeates were not significantly different from each other. Dextrose content of retentates and permeates at all VCRs did not change significantly during the microfiltration, averaging 28·90±1·01% w/w. Total solids, nitrogen, fat and ash content of the retentates increased with increase in VCR. In contrast, total solids, nitrogen, fat and ash of the permeates remained the same for all VCRs, averaging 29·44, 0·011, 0·07 and 0·042% respectively.     

High prevalence of antimicrobial resistance in Escherichia coli,Salmonella spp. and Staphylococcus aureus isolated from fish samples in India

Antibiotic resistance, driven by inappropriate use of antimicrobial agents for fish farming, is an expanding global health threat. Demand of animal protein for human consumption is entraining at remarkable pace which in turn, upturning the non‐judicial use of life‐saving drugs in these modern animal production practices at an incautious rate. Hence, study was devised to observe the antimicrobial resistance (AMR) pattern of human prominence bacteria, against drugs of critically and highly importance of both human and veterinary medicine, circulating over the fish farming in India. One hundred sixty fish faecal samples were obtained from distinct geographical locales of Rajasthan, India. Overall, 202 isolates comprising of Escherichia coli (81, 51%), Salmonella spp. (72, 45%) and Staphylococcus aureus (49, 31%) were isolated to screen for resistance. Antimicrobial resistance has been analysed using broth microdilution method. In case of E. coli and Salmonella spp., highest resistance (>95%) was observed against streptomycin while for S. aureus, it was observed against trimethoprim, along with high resistance to other antibiotics. Majority of the isolates were found to be resistant to more than three antibiotics implying multi‐drug resistance (>89%) relative to the critical and highly important antibiotics. The high AMR is a reflection of misuse of these agents in the fish farming, which is a concern of serious health issues. Our findings persuade the prudent use of antimicrobial agents in fish farming and other aquaculture settings that may assist in drafting of the new policies for the judicial use of these life‐saving drugs in these sectors.     

Genetics and molecular mapping of gynoecious (F) locus in cucumber (Cucumis sativus L.)

Gynoecious is an important economic trait of cucumber for determinant of earliness and yield, yet genetic mechanism is not well understood for this trait. The experiment was conducted using F₂ mapping population by crossing of PPC-2, a gynoecious and parthenocarpic line with Pusa Uday (monoecious and non-parthenocarpic cultivar). Out of 179 SSR markers screened, 39 markers differentiated the gynoecious and monoecious parents. However, only 17 markers were segregating with F₂ mapping population, those were used for genotyping and linkage map analysis and these markers were placed along with F locus on chromosome 6 covering a total distance of 100.4cM. The SSR markers, SSR13251 and UW020605 were found to be closely linked to gynoecious (F) locus at 1.0 and 4.5 cM, respectively. The segregation of F₂ population of PPC-2 × Pusa Uday and GPC-1 × Punjab Naveen and test crosses for sex type herein suggested that single dominant gene controlled the gynoecious sex expression in cucumber particularly in gynoecious genotypes PPC-2 and GPC-1. Therefore, the monogenic dominant nature of gynoecious sex identified in the present experiment and SSR markers closely linked to the F locus will be useful in marker-assisted backcross breeding for transfering gynoecious trait into horticulturally desirable varieties.     

Genetic analysis of gene‐specific resistance to mungbean yellow mosaic virus in mungbean (Vigna radiata)

Six intervarietal crosses involving two resistant and three susceptible genotypes of mungbean were attempted with the objectives to determine the mode of inheritance of gene‐specific Mungbean Yellow Mosaic Virus (MYMV) resistance. An infector row technique along with artificial inoculation was used for evaluating parents, F₁, F₂ and F₃ plants for MYMV resistance. Disease scoring for MYMV indicated that F₁s were highly susceptible as were the susceptible parents while resistant parent exhibited resistant reaction. The F₂ progeny segregated in the ratio of 9 S:3 MS:3 MR:1 R suggesting that the resistance was governed by digenic recessive genes (r_m1 and r_m2). When one gene (r_m1) was present in the homozygous recessive condition in different plants, it conferred moderately susceptible (MS) reaction, whereas when other gene (r_m2) was in homozygous condition, moderately resistant (MR) reaction was obvious. When both genes (r_m1 and r_m2) were present together in the homozygous recessive condition, resistant reaction (R) was observed. The F₂ segregation explained on the basis of phenotypic expression was further confirmed by F₃ segregation.     

Cinnamamide,an avian repellent,reduces woodpigeon damage to oilseed rape

Woodpigeons Columba palumbus cause significant damage to oilseed rape Brassica napus. (Cruciferae) in Britain, especially between January and March. The potential of cinnamamide, a non-lethal chemical repellent, to protect growing oilseed rape from woodpigeon damage was assessed in 20×20 m plots laid out in a 9-ha field frequented by >500 woodpigeons. Despite a low initial loading of cinnamamide and low persistence of the compound after spraying, the inner leaves of treated plants received less damage than the inner leaves of untreated plants (P<0·05). This was reflected later in the trial in a decline in damage to the outer leaves of treated plants (P<0·05). No signs of phytotoxicity were seen on treated leaves during the trial. Cinnamamide did not completely protect the rape, and some plants in treated plots received considerable damage. This was probably due to the compound's poor persistence on the leaf and because it was applied late in the growing season (late February) when birds had already made inroads into the crop. © 1998 SCI.     

Carbofuran-induced biochemical changes in Clarias batrachus

The effect of carbofuran, an organo-carbamate pesticide, upon the level of protein as well as the activity of lactate dehydrogenase (EC 1.1.1.28, LDH) was studied by exposing the teleost fish, Clarias batrachus, to different subacute con-centrations (0·01 and 0·02 mg litre^-1) for 96 h and 15 days. The results showed a drastic decrease in the protein content in different body organs of the fish. The pesticide also caused a significant decrease in the level of activity of LDH in different body tissues of the fish, the effect being more pronounced in the gills, muscle, brain and liver than in kidney and heart. The decrease in protein content and the activity of LDH in fish tissues was more marked at the higher concentration of the pesticide for the longer duration of treatment. The results suggested that carbofuran has an effect at very low concentration (compared to its LC₅₀ value) possibly at the level of protein metabolism, and also inhibits the activity of LDH, the terminal glycolytic enzyme. © 1998 SCI     

Effect of ABT on the activity and rate of degradation of isoproturon in susceptible and resistant biotypes of Phalaris minor and in wheat

The effect of the monooxygenase inhibitor, 1-aminobenzotriazole (ABT) on isoproturon phytotoxicity and metabolism was studied in resistant (R) and susceptible (S) biotypes of Phalaris minor and in wheat (Triticum aestivum). Addition of ABT (2·5, 5 and 10 mg litre^-1) to isoproturon (0·25, 0·5, 1, 2 and 4 mg litre^-1) in the nutrient solution significantly enhanced the phytotoxicity of isoproturon against the R biotype. Isoproturon at 0·25 mg litre^-1 reduced the dry weight (DW) of the S biotype by 77%, whereas the R biotype required 4·0 mg litre^-1 for similar reduction. Addition of 10 mg litre^-1 of ABT to the 0·25 mg litre^-1 isoproturon caused 71 and 82% reduction in DW of R and S biotypes, respectively. Wheat was more sensitive to the mixture of isoproturon and ABT than the R biotype of P. minor. Reduced concentrations of ABT in the mixture from 10 to 2·5 mg litre^-1 increased the DW of the R biotype more than that of the S biotype. The R biotype metabolised [¹⁴C]isoproturon at a faster rate than the S biotype. ABT (5 mg litre^-1) inhibited the degradation of [¹⁴C]isoproturon in both biotypes of P. minor and in wheat. In the presence of ABT, about half of the applied [¹⁴C]isoproturon remained as parent herbicide in all the three species after two days. The metabolites were similar in the R and S biotypes and wheat as determined by co-chromatography with reference standards and mass spectroscopy (MS). ABT inhibited the appearance of the hydroxy and monomethyl metabolites and their conjugates in all the test plants. These results suggest that the activity of the enzymes responsible for the degradation of isoproturon is greater in the R than in the S biotype of P. minor, resulting in its rapid detoxification. Incorporation of the monooxygenase inhibitor ABT into the nutrient solution greatly inhibited the degradation of [¹⁴C]isoproturon in the R biotype and increased its phytotoxicity. Both hydroxylation and N-dealkylation reactions were found to be sensitive to ABT; inhibition of hydroxylation was greater than that of demethylation. Since ABT could not completely suppress isoproturon degradation, it is possible that more than one monooxygenase is involved. © 1998 SCI