Albert Fischer | University of California, Davis (original) (raw)
Papers by Albert Fischer
SIDALC - Servicio de Informacion y Documentacion Agropecuaria de las Americas.
PLoS ONE, 2013
Echinochloaoryzicola(syn.E. phyllopogon) is an exotic weed of California rice paddies that has ev... more Echinochloaoryzicola(syn.E. phyllopogon) is an exotic weed of California rice paddies that has evolved resistance to multiple herbicides. Elimination of seedlingsthroughcertain weed control methods can limit the spread of this weed, but is contingent on accurate predictions of germination and emergence timing, which are influenced by seed dormancy levels.In summer annuals, dormancy can often be relieved through stratification, a period of prolonged exposure to cold and moist conditions.We used population-based threshold models to quantify the effects of stratification on seed germination of four E. Oryzicola populations at a range of water potential (Y) and oxygen levels. We also determined how stratification temperatures, moisture levels and durations contributed to dormancy release. Stratification released dormancy by decreasing base Y and hydrotimerequired for germination and by eliminating any germination sensitivity to oxygen. Stratification also increased average germination rates (GR), which were used as a proxy for relative dormancy levels. Alternating temperatures nearly doubled GR in all populations, indicating that seeds could be partially dormant despite achieving high final germination percentages. Stratification at Y = 0 MPa increased GR compared to stratification at lower water potentials, demonstrating that Y contributed to regulating dormancy release. Maximum GR occurred after 2-4 weeks of stratification at 0 MPa; GR were often more rapid for herbicide-resistant than for herbicide-susceptible seeds, implying greater dormancy in the latter. Manipulation of field conditions to promote dormancy alleviation of E. oryzicola seeds might improve the rate and uniformity of germination for seed bank depletion through seedling weed control. Our results suggest field soil saturation in winter would contribute towards E. oryzicola dormancy release and decrease the time to seedling emergence.
Agronomy Journal, 2001
... Albert J. Fischer,* Hector V. Ramırez, Kevin D. Gibson, and Beatriz Da Silveira Pinheiro ... ... more ... Albert J. Fischer,* Hector V. Ramırez, Kevin D. Gibson, and Beatriz Da Silveira Pinheiro ... 95616; HV Ramirez, Instituto Rio Grandense do Arroz, 94930 Ca-... of California, Davis, CA 95616; B. Da Silveira Pinheiro, EMBRAPA Arroz e Feijao, 75375-000 Santo Antonio de Goiás, GO, ...
ABSTRACT Weed resistance to herbicides was first discovered nearly 30 years ago. To date, 396 dif... more ABSTRACT Weed resistance to herbicides was first discovered nearly 30 years ago. To date, 396 different weed biotypes showing resistance to diverse herbicide chemical classes have so far been reported. Herbicide- resistance in Cyperus difformis L., a major weed of rice, is widespread worldwide but has thus far only been reported for acetolactase synthase-inhibiting herbicides. Faced with the ensuing reduced control options, rice growers in California have come to rely on the contact herbicide propanil (3,4- dichloropropionanilide) for control of ALS-resistant C. difformis populations. Nonetheless, growers have recently experienced poor control with any of the available propanil formulations, suggesting resistance to this photosystem II-inhibiting herbicide may have evolved in C. difformis populations. The objectives of this study were to (a) confirm resistance to propanil in C. difformis lines by means of whole-plant dose- response experiments and establish resistance levels, and to (b) examine whether or not mutations at the photosystem II thylakoid-membrane-bound D1 protein could be playing a role in the propanil-resistant plant’s ability to survive a rather lethal dose of propanil. A C. difformis line derived from populations collected in rice fields of California’s Sacramento Valley was confirmed resistant to propanil; its resistance level (R/S ratio) equaled 16.8. This is the first case of such resistance outside the Poaceae family and the first time C. difformis exhibits resistance to an herbicide mechanism of action other than ALS inhibition. Carbaryl - a known propanil synergist due to its role as substrate for the propanil- degrading enzyme aryl acylamidase - did not increase propanil toxicity in R plants but did synergize propanil against S plants, resulting in an R/S ratio of 38.9 when carbaryl was present. Such results indicate enhanced degradation of the herbicide molecule is not playing a role in C. difformis resistance to propanil. By means of whole-plant dose-response experiments, R plants were shown to resist greater levels of the PSII- inhibitors bromoxynil, diuron and metribuzin relative to S plants, but are as susceptible to atrazine as the latter. Following such results, we selectively amplified the herbicide-binding region of the chloroplast psbA gene of propanil-R and -S plants using PCR. Sequence analysis of the R plants exhibited a substitution from valine to isoleucine at position 219 of the D1 protein encoded by the psbA gene, thus suggesting a partial loss of affinity between propanil and its binding site could be playing a role in C. difformis resistance to propanil. Such mutation (Val219Ile) has been reported for metribuzin, diuron-resistant Poa annua populations. To our knowledge this is the first report of a higher plant exhibiting resistance to propanil due to a psbA mutation, for all previous cases were attributed to enhanced propanil degradation by aryl acylamidases. The loss of propanil to control this important weed of rice underscores the fragility of herbicide-based weed control in monoculture rice. Integrated weed management approaches to decrease herbicide selection pressure are needed to mitigate the evolution of multiple-herbicide resistance in C. difformis of California rice.
SIDALC - Servicio de Informacion y Documentacion Agropecuaria de las Americas.
PLoS ONE, 2013
Echinochloaoryzicola(syn.E. phyllopogon) is an exotic weed of California rice paddies that has ev... more Echinochloaoryzicola(syn.E. phyllopogon) is an exotic weed of California rice paddies that has evolved resistance to multiple herbicides. Elimination of seedlingsthroughcertain weed control methods can limit the spread of this weed, but is contingent on accurate predictions of germination and emergence timing, which are influenced by seed dormancy levels.In summer annuals, dormancy can often be relieved through stratification, a period of prolonged exposure to cold and moist conditions.We used population-based threshold models to quantify the effects of stratification on seed germination of four E. Oryzicola populations at a range of water potential (Y) and oxygen levels. We also determined how stratification temperatures, moisture levels and durations contributed to dormancy release. Stratification released dormancy by decreasing base Y and hydrotimerequired for germination and by eliminating any germination sensitivity to oxygen. Stratification also increased average germination rates (GR), which were used as a proxy for relative dormancy levels. Alternating temperatures nearly doubled GR in all populations, indicating that seeds could be partially dormant despite achieving high final germination percentages. Stratification at Y = 0 MPa increased GR compared to stratification at lower water potentials, demonstrating that Y contributed to regulating dormancy release. Maximum GR occurred after 2-4 weeks of stratification at 0 MPa; GR were often more rapid for herbicide-resistant than for herbicide-susceptible seeds, implying greater dormancy in the latter. Manipulation of field conditions to promote dormancy alleviation of E. oryzicola seeds might improve the rate and uniformity of germination for seed bank depletion through seedling weed control. Our results suggest field soil saturation in winter would contribute towards E. oryzicola dormancy release and decrease the time to seedling emergence.
Agronomy Journal, 2001
... Albert J. Fischer,* Hector V. Ramırez, Kevin D. Gibson, and Beatriz Da Silveira Pinheiro ... ... more ... Albert J. Fischer,* Hector V. Ramırez, Kevin D. Gibson, and Beatriz Da Silveira Pinheiro ... 95616; HV Ramirez, Instituto Rio Grandense do Arroz, 94930 Ca-... of California, Davis, CA 95616; B. Da Silveira Pinheiro, EMBRAPA Arroz e Feijao, 75375-000 Santo Antonio de Goiás, GO, ...
ABSTRACT Weed resistance to herbicides was first discovered nearly 30 years ago. To date, 396 dif... more ABSTRACT Weed resistance to herbicides was first discovered nearly 30 years ago. To date, 396 different weed biotypes showing resistance to diverse herbicide chemical classes have so far been reported. Herbicide- resistance in Cyperus difformis L., a major weed of rice, is widespread worldwide but has thus far only been reported for acetolactase synthase-inhibiting herbicides. Faced with the ensuing reduced control options, rice growers in California have come to rely on the contact herbicide propanil (3,4- dichloropropionanilide) for control of ALS-resistant C. difformis populations. Nonetheless, growers have recently experienced poor control with any of the available propanil formulations, suggesting resistance to this photosystem II-inhibiting herbicide may have evolved in C. difformis populations. The objectives of this study were to (a) confirm resistance to propanil in C. difformis lines by means of whole-plant dose- response experiments and establish resistance levels, and to (b) examine whether or not mutations at the photosystem II thylakoid-membrane-bound D1 protein could be playing a role in the propanil-resistant plant’s ability to survive a rather lethal dose of propanil. A C. difformis line derived from populations collected in rice fields of California’s Sacramento Valley was confirmed resistant to propanil; its resistance level (R/S ratio) equaled 16.8. This is the first case of such resistance outside the Poaceae family and the first time C. difformis exhibits resistance to an herbicide mechanism of action other than ALS inhibition. Carbaryl - a known propanil synergist due to its role as substrate for the propanil- degrading enzyme aryl acylamidase - did not increase propanil toxicity in R plants but did synergize propanil against S plants, resulting in an R/S ratio of 38.9 when carbaryl was present. Such results indicate enhanced degradation of the herbicide molecule is not playing a role in C. difformis resistance to propanil. By means of whole-plant dose-response experiments, R plants were shown to resist greater levels of the PSII- inhibitors bromoxynil, diuron and metribuzin relative to S plants, but are as susceptible to atrazine as the latter. Following such results, we selectively amplified the herbicide-binding region of the chloroplast psbA gene of propanil-R and -S plants using PCR. Sequence analysis of the R plants exhibited a substitution from valine to isoleucine at position 219 of the D1 protein encoded by the psbA gene, thus suggesting a partial loss of affinity between propanil and its binding site could be playing a role in C. difformis resistance to propanil. Such mutation (Val219Ile) has been reported for metribuzin, diuron-resistant Poa annua populations. To our knowledge this is the first report of a higher plant exhibiting resistance to propanil due to a psbA mutation, for all previous cases were attributed to enhanced propanil degradation by aryl acylamidases. The loss of propanil to control this important weed of rice underscores the fragility of herbicide-based weed control in monoculture rice. Integrated weed management approaches to decrease herbicide selection pressure are needed to mitigate the evolution of multiple-herbicide resistance in C. difformis of California rice.