Bibliography: leaves 132-140.

Bibliography: leaves 132-140. / ix, 140 leaves. [6] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1995?

Bibliography: leaves 111-120. This study investigated various aspects of genetic resistance in fava beans to Ascochta blight (A. fabae) with the objective to facilitate an efficient breeding strategy for long-term control. Pathogenic variability of A. fabae was found to be high, as was genetic variation between resistant fava bean accessions. A number of alternative resistance genes to that of Ascot cultivar were identified.

No description available.

After a wild-type isolate of Epicoccum purpurascens was exposed to shortwave ultraviolet light, several new strains were recovered which were improved in sporulation, fungicide tolerance, and performance in suppression of white mold caused by Sclerotinia sclerotiorum. The efficacy of E. purpurascens in controlling white mold of snap bean (Phaseolus vulgaris) was assessed in greenhouse and field trials. White mold was significantly reduced in both greenhouse and field trials when 2-4 sprays of E. purpurascens conidial suspensions (in 1% malt extract) were sprayed onto the plant surface during the flowering period. Germination of E. purpurascens conidia on senescent petals was greater than on younger flowers. Addition of malt extract to conidial suspensions improved germination on flowers and increased colonization of emerging flowers. Application of E. purpurascens did not accelerate senescence of bean leaves or affect pod yield of bean in greenhouse trials. Mycoparasitism of S. sclerotiorum by E. purpurascens was found only rarely in in vitro tests and was not observed on flower disks. Production of inhibitory compounds by E. purpurascens was the most important mechanism in suppression of white mold but competition for nutrients also appeared to play a role in biocontrol. The influence of nutrients on conidial germination, growth, sporulation and production of antifungal compounds by E. purpurascens were also investigated.

No description available.

Double infection by cowpea strains of southern bean mosaic virus (CP-SBMV) and of tobacco mosaic virus (CP-TMV) caused additive growth reductions in California blackeye cowpea. Plant height, weight and numbers of seed and pods were significantly reduced by double infection and by CP-TMV single infection compared to healthy and CP-SBMV-sing 1 y infected plants. Singly and doubly inoculated California blackeye cowpea plants developed CP-SBMV symptoms on the primary leaves, but CP-SBMV symptoms in doubly infected trifoliates were masked by CP-TMV symptoms. CP-TMV symptoms did not mask CP-SBMV symptoms in systemically infected trifoliate leaves of another cowpea variety, V45-Bots. CP-TMV infection conditioned systemic infection of V45~Bots by CP-SBMV, as indicated by infectivity,serology and analytical sucrose density gradient centrifugation. CP-TMV also induced susceptibility of Pinto to infection by CP-SBMV, as ascertained by infectivity, immunodiffusion and electron microscopy. Analytical sucrose density gradient centrifugation measurements demonstrated that in doubly inoculated primary leaves of California blackeye cowpea CP-SBMV and CP-TMV were synthesized less than in the same leaves singly inoculated. CP-SBMV synthesis in trifoliate leaves, following simultaneous inoculations of primary leaves, was enhanced 5 times that in singly infected trifoliate leaves, whereas CP-TMV synthesis was not greatly affected. When CP-TMV preceded CP-SBMV in the primary leaves by 2k and 72 hr CP-SBMV synthesis was enhanced more in trifoliate leaves that were undifferentiated at the time of inoculation than in those of plants simultaneously inoculated. When CP-TMV preceded CP-SBMV into preformed 3rd trifoliate leaves by 22 hr, the ratio of CP-SBMV concentration in doubly infected tissue to that in singly infected tissue was 2.7 versus 1.9 when both viruses arrived simultaneously at these leaves. When either virus preceded the other by 72 hr into preformed 3rd trifoliate leaves the synthesis of the challenging virus was greatly retarded. CP-SBMV synthesis was also enhanced by CP-TMV infection under differential temperature synchronous system of infection. Although virions of both viruses were detected in the same cell no genomic masking was detected by infectivity neutralization test. It is theorized that CP-TMV infection predisposes the host cells to infection by CP-SBMV and thus the enhanced synthesis of CP-SBMV. The effect of CP-TMV infection on CP-SBMV synthesis in cowpea seems to be a physiological one. CP-SBMV, but not CP-TMV, was transmitted through planted seed and decontaminated embryos of California blackeye cowpea. Buffer extracts made from decontaminated embryos also were infectious for CP-SBMV. Seed coats contained both viruses. Double infection of California blackeye cowpea decreased seed transmission of CP-SBMV from 13-5 to 7.6%. Buffer extracts of healthy seed were inhibitory to infectivity of both viruses. Germination of seed reduced infectivity of CP-SBMV in the seed coats, but not of CP-TMV. It is also concluded that seed transmission of CP-SBMV is a result of embryo infection rather than contamination with virus in the seed coats. / Land and Food Systems, Faculty of / Graduate

Please read the abstract in the section 00front of this document / Thesis (PhD (Microbiology))--University of Pretoria, 2005. / Microbiology and Plant Pathology / unrestricted

Made available in DSpace on 2017-07-10T17:36:59Z (GMT). No. of bitstreams: 1 Lindomar Assi.pdf: 402640 bytes, checksum: 85ec0b36b17f5430a459dd263ecd9fce (MD5) Previous issue date: 2005-10-03 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The concern with the environment and the human health has stimulated the search for methods that reduce the use of fungicides in the control of phytopathogens. Considering many positive results already reached by using induced resistance, and the great demand for new elicitors of resistance to pathogens, this work had the objective to evaluate the fungitoxic effect in vitro of the aqueous extract (EA) of Pycnoporus sanguineus basidiocarp, against Colletotrichum lindemuthianum and evaluate under greenhouse conditions, the control of anthracnose in beans, as well as the induction of resistance by the determination of peroxidases activity. For the assays in vitro were used EAs, in the concentrations of 1, 5, 10, 15 and 20 %, autoiclavated or not. And evaluating the micelial growth and spores germination of C. lindemuthianum. For the in vivo assays, EAs not autoclavated at 5, 10 and 20% were sprayed in 7th´s leaves of beans plants three days before the inoculation of the pathogen (5x104 conidia/mL) that was occurred in 7th´s and 8th´s leaves. Water and fungicide (azoxystrobin 0,6 g. p. c./L) were used as control tratments. For peroxidase, 7th´s and 8th´s leaves were sampled at the moment of treatments and after three, six, nine and twelve days. The results showed direct antimicrobial activity of the EAs of P. sanguineus, with inhibition of up to 96% of the germination in vitro of the spores of C. lindemuthianum, independent of the autoclavation of the extracts. The EAs stimulated in up to 34 % the micelial growth. In the plants, eA 20% controlled the anthracnose with reduction of 70% severity in 7th´s leaf (treated and inoculated), while for the fungicide the reduction was of 73%. For 8 th´s leaf (only inoculated), the EAs at 5, 10 and 20% reduced the severity in 58, 64 and 68%, respectively, while for the fungicide the reduction was of 74%. This reduction in severity can be associated with the activity of peroxidase, which was presented high, in both 7th´s and 8th´s leaves in the moment of the inoculation, it means, three days after the treatment. These results indicate the P. sanguineus extracts potential for control of anthracnose in beans plants, that can occurr by direct antimicrobial activity and/or local and systemic induction. / A preocupação com o ambiente e a saúde humana tem incentivado a busca por métodos que reduzam o uso de fungicidas no controle de fitopatógenos. Considerando-se os vários resultados positivos já alcançados pela utilização da resistência induzida, bem como a grande demanda de novos eliciadores de resistência a fitopatógenos, este trabalho teve como objetivos avaliar o efeito fungitóxico in vitro do extrato aquoso (EA) de basidiocarpos de Pycnoporus sanguineus, sobre Colletotrichum lindemuthianum; e avaliar em de casa de vegetação, o controle da antracnose em feijoeiro por esses extratos, bem como a indução de resistência pela determinação da atividade de peroxidase. Para os ensaios in vitro foram utilizados EAs, nas concentrações de 1, 5, 10, 15 e 20 %, autoclavados ou esterilizados por filtração, avaliando-se o crescimento micelial e a germinação de esporos de C. lindemuthianum. Para os ensaios in vivo, EAs não autoclavados a 5, 10 e 20% foram aplicados nas 7ªs folhas de plantas de feijoeiro três dias antes da inoculação do patógeno (5x104 conídios /mL) que ocorreu nas 7ªs e 8ªs folhas. Água e fungicida azoxystrobin (0,6 g. p. c. / L) foram utilizados como testemunhas. Para a dosagem de peroxidase foram amostradas as 7ªs e 8ªs folhas no momento dos tratamentos e após três, seis, nove e doze dias. Os resultados indicaram atividade antimicrobiana direta dos EAs de P. sanguineus, com inibição de até 96% da germinação in vitro dos conídios de C. lindemuthianum, independente da autoclavagem ou não dos extratos. Os EAs estimularam em até 34 % o crescimento micelial. Nas plantas, apenas o EA a 20% controlou a antracnose, com redução de 70% na severidade na 7ª folha (tratada e inoculada), enquanto que para o fungicida a redução foi de 73%. Para a 8ª folha (apenas inoculada), os EAs a 5, 10 e 20% reduziram a severidade em 58, 64 e 68%, respectivamente, enquanto que para o fungicida a redução foi de 74%. Essa redução na severidade pode estar associada com a atividade de peroxidase, a qual se apresentava alta, tanto na 7ª quanto na 8ª folha, no momento da inoculação, ou seja, três dias após o tratamento. Estes resultados indicam o potencial de controle da antracnose em feijoeiro pelo extrato de P. sanguineus, que pode ocorrer por atividade antimicrobiana direta e/ou indução de resistência local e sistêmica.

As sessile organisms, plants evolved a plethora of defenses against their attackers. Given the role of plants as a primary food source for many organisms, plant defense has important implications for community ecology. Surprisingly, despite the potential to alter entire food webs and communities, the factors determining plant investment in defense are not well-understood, and are even less understood considering the numerous symbiotic interactions in the same plant. Legume-rhizobia symbioses engineer ecosystems by fixing nitrogen from the atmosphere in trade for plant photosynthates, yet connecting symbiotic resource exchange to food web interactions has yet to be established. Here I test how rhizobia influence plant defense and tritrophic interactions in lima bean (Fabaceae - Phaseolus lunatus L.): a model plant in chemical ecology research characterized by a broad range of different defenses. Examining suites of traits among lima bean genotypes, highly cyanogenic cultivars and wild type plants (high cyanotypes) produce more hook-shaped trichomes, as a putative combined approach of chemical and mechanical defenses, forming defense syndromes to protect against multiple feeding guilds (Chapter 2). Testing costs that may have contributed to forming tradeoffs among strategies, high cyanotypes show reduced fitness under plant-plant competition relative to low cyanotypes, but when challenged with herbivory, high cyanotypes fitness reductions are no longer evident (Chapter 3). Young leaves, not reproductive organs, are the most cyanogenic lima bean organ, and removal quantitatively decreases fitness, supporting assumptions that the most valuable tissues will be most highly defended (Chapter 4). Testing the degree to which nitrogen-fixing rhizobia contribute to cyanogenesis, high cyanotypes form more nodules than low cyanotypes. Quantitative relationships between nodule number and plant traits highlight the role symbiotic investment plays a role in plant defense and nutritive phenotype, while simultaneously, genotypically-determined levels of defense shape plant investment in symbiosis (Chapter 5). Interestingly, traits that trade off by cyanotype (i.e. high cyanogenesis but low indirect defense) reflect the patterns in plants with nitrogen-fixing rhizobia. Rhizobia-inoculated lima beans show reduced indirect defenses, recruiting fewer parasitoid wasps (Chapter 6) and predatory ants (Chapter 7). Examining plant-ant attraction in greater detail, ants prefer headspace regions above EFN droplets, corresponding with species-specific differences in suites of volatiles, indicating EFN, like floral nectar, can be scented to manipulate insect behavior (Chapter 8). Overall, understanding when investing in traits to recruit predators is more effective than investing in defensive chemistry, and how particular ecological contexts, such as symbioses can influence the outcome of defense allocation strategies remains a fascinating area of research. Determining the mechanisms underlying why rhizobia and other belowground microbial symbionts influence their host plants' above ground interactions, whether plants traits affected by symbiotic microbes are simply a function of the costs and benefits from resource exchange, or whether symbionts can influence the success of primarily direct versus indirectly defended plants is an important question for understanding complex trophic systems and connecting to agricultural implications for more effective biological pest control.