Progress 07/01/03 to 06/30/07
Outputs
This research was initiated to develop a basic understanding of the factors that influence weed seed bank decline. Two cycles of field, greenhouse and lab experiments were completed to determine the relationships between dormancy (and/or other seed characteristics) and the ability of wild oat seeds to persist in soil. The germination of wild oat seed in water and gibberellic acid was used to rank the six pure lines for the degree of primary dormancy. This ranking was confirmed from field experiments conducted over two years. The order was M73 > AN86 > AN51 > AN84 > SH99 > SH430 from highly dormant to non-dormant lines. Environmental conditions during seed development, and seed after-ripening treatments, each affected the dormancy levels and the fate of wild oat seed banks. Drought conditions during seed development and after-ripening treatments reduced seed dormancy. Consequently, seed bank mortality was 3-16% higher under dryland conditions as compared to the
irrigated treatments, and from 5-21% higher for after-ripened seed compared to non-after ripened seed. Total seed bank loss was 93% in 2004 and 88% in 2005. Seed bank loss was relatively consistent over the two years. However, the cause of seed bank decline was different mainly due to the higher spring rainfall in 2005. In 2004 a greater portion of seed bank decline was attributed to seed mortality (59%) than seedling emergence (26%), while in 2005 seedling emergence caused a greater reduction (58%) in seed bank numbers than did seed mortality (29%). As a result of higher seedling emergence, seed infection on the remaining seeds was lower in 2005 (3.1 to 7.5) than in 2004 (3.9 to 9.8). In general, low dormancy lines exhibited higher infection levels. In both years, most of the seed bank decline (>79%) occurred within six months of seed banks establishment. This rapid decline in seed bank was more pronounced for dehulled seed and for low dormancy lines compared to seed with intact
hulls and for high dormancy lines. Wild oat lines responded differently to sterilized and non-sterilized soil treatments. Seedling emergence was higher for seed banks established using non-sterilized soil compared to seed banks established with sterilized soil for the high dormancy line (M73). However, for the low dormancy line (SH430) seedling emergence was higher from seed banks establish using sterilized soil.
Impacts
The long-term goal of this research is to improve weed management by developing a basic understanding of factors that influence weed seed bank decline and identifying causes of weed seed mortality. We will determine if wild oat dormancy mechanisms or other maternal plant or seed characteristics are associated with the ability of nongerminated wild oat seeds to resist attack by soil microorganisms, thus allowing seeds to remain viable over extended periods of time.
Publications
- Qasim A. Khan and James A. Mickelson (2006). Quantifying factors associated with wild oat seed bank decline. Weed Sci. Soc. Am. Abstr. no. 245. [CD-ROM Computer File]. Weed Sci. Soc. Am., Lawrence, KS. (Feb. 2006).
- Qasim A. Khan and James A. Mickelson (2006). Role of microorganisms on seed mortality in wild oat. Weed Sci. Soc. Am. Abstr. no. 113. [CD-ROM Computer File]. Weed Sci. Soc. Am., Lawrence, KS. (Feb. 2006).
- Qasim A. Khan and James A. Mickelson (2006). Effects of hull on the germination, viability and mortality of wild oat seed. Proceedings of Western Soc. of Weed Sci. 2006. Vol. 59, P. 31.
|
Progress 01/01/06 to 12/31/06
Outputs
Field, greenhouse and lab experiments were completed and data analysis was done in 2006. A combined analysis from both years was performed to determined the relationships between dormancy (and/or other seed characteristics) and the ability of wild oat seeds to persist in soil. The germination of wild oat seed in water and gibberellic acid was used to rank the six pure lines for degree of primary dormancy in the lab. This ranking was confirmed from two years of field experiments. The order was M73 > AN86 > AN51 > AN84 > SH99 > SH430 from highly dormant to non-dormant lines. Environmental condition during seed development and seed after-ripening treatments affected dormancy levels and the fate of wild oat seed banks. Both drought conditions during seed development and after-ripening treatments reduced seed dormancy. Consequently, seed bank mortality was increased from 3-16% and from 5-21%, compared to irrigated and non after-ripened seed, respectively. Total seed bank
loss was 93% in 2004 and 88% in 2005. Seed bank loss was consistent over the two years; however, the cause of seed bank decline was different mainly due to the higher spring rainfall in 2005. In 2004 a greater portion of seed bank decline was attributed to seed mortality (59%) than seedling emergence (26%). While in 2005 seedling emergence caused greater reduction (58%) in seed bank than seed mortality (29%). As a result of higher seedling emergence, microbial infection on the remaining seeds was lower in 2005 (3.1 to 7.5) than in 2004 (3.9 to 9.8). In general, low dormancy lines exhibited higher infection from microorganisms. In both years, most of the seed bank decline (>79%) occurred within six months of seed bank establishment. This rapid decline in seed bank was more pronounced for dehulled seed and for low dormancy lines compared to seed with intact hulls and for high dormancy lines. Wild oat lines responded differently to sterilized and non-sterilized soil treatments. Seedling
emergence was higher for seed banks established using non-sterilized soil compared to seed banks established with sterilized soil for the high dormancy line M73. However, for low dormancy line, SH430, seedling emergence was higher from seed banks establish using sterilized soil. Based on these results we concluded that seed dormancy mechanisms may also confer resistance to attack by microorganisms and thus allow dormant wild oat seed to remain viable and persist in soil.
Impacts
The long-term goal of this research is to improve weed management by developing a basic understanding of factors that influence weed seed bank decline and identifying causes of weed seed mortality. We will determine if wild oat dormancy mechanisms or other maternal plant or seed characteristics are associated with the ability of nongerminated wild oat seeds to resist attack by soil microorganisms, thus allowing seeds to remain viable over extended periods of time.
Publications
- No publications reported this period
|
Progress 01/01/05 to 12/31/05
Outputs
The second cycle of field and greenhouse experiments were conducted during 2005. Emerged seedlings were counted and removed during the 2005 growing season from all the seed banks that had been established during 2004. Seed banks were excavated on March 3, May 19, September 3, and November 1, 2005 from the field experiments and on June 8, 2005 from the greenhouse experiment. The seed was stored at 3 C until intact seeds and empty hulls were extracted by washing the samples through a 1.2 mm rotating sieve with water. Seeds were tested for germination, viability, and were visually examined for evidence of microbial infection using a scale of 1(no infection) to 10 (decayed) based on the proportion of the seed that was discolored or decayed. Seedling emergence rates, seed mortality rate, and total seed bank decline were calculated. Preliminary analysis was performed to determine relationships between dormancy (or other seed characteristics) and the ability of wild oat
seeds to persist in the soil. The results obtained from this years experiment confirm the results obtained during the previous cycle. The six wild oat lines showed significant differences for all plant and seed characteristics studied. The total seed bank decline ranged from 79 to 100%. About 82% of measured seed bank decline occurred during the first six months after burial. The contribution of seedling emergence towards seed bank decline was 58%, whereas seed mortality accounted for 42% of the total decline. A strong association was observed between microbial infection and seed dormancy levels. High dormancy lines exhibited lower seed infection (2.6 to 3.0) compared to low dormancy lines (3.5 to 5.8). Hull removal increased seed mortality by 21%, seed bank decline by 6%, and decreased seed viability by 12%. Water stress during seed development and seed after-ripening treatments accelerated seed mortality. Soil sterilization treatments resulted in 15% higher seedling emergence and
32% lower seed mortality compared to the non-sterilized treatments. Histological traits on the palea and lemma are currently being determined. Wild oat seedling emergence and seed mortality data will be correlated to the physiological, morphological, and histological data to determine relationships between dormancy (or other seed characteristics) and the ability of wild oat seeds to persist in the soil.
Impacts
The long-term goal of this research is to improve weed management by developing a basic understanding of factors that influence weed seed bank decline and identifying causes of weed seed mortality. We will determine if wild oat dormancy mechanisms or other maternal plant or seed characteristics are associated with the ability of nongerminated wild oat seeds to resist attack by soil microorganisms, thus allowing seeds to remain viable over extended periods of time.
Publications
- No publications reported this period
|
Progress 01/01/04 to 12/31/04
Outputs
Emerged seedling were counted and removed during the growing season from all the seed banks that were established in the field and greenhouse in 2003. The seed banks were removed on March 8, May 12, September 2, and October 26, 2004 from the field experiments and on March 3, 2004 from the greenhouse experiment and stored at 3 C until intact seeds and empty hulls were extracted by washing the soil through a 1.2 mm rotating sieve with water. Seeds extracted from the seed banks were tested for germination and viability. Seed were examined for evidence of infection by microorganisms and visually rated 1(no infection) to 10 (decayed) based on the proportion of the seed that was discolored or decayed. Seedling emergence rates, seed mortality rate, and total seed banks decline were calculated. Preliminary data analysis was performed on all the data collected to determine relationships between dormancy (or other seed characteristics) and the ability of wild oat seeds to
persist in the soil. The six lines showed significant differences for all the plant and seed characteristics studied. The total decline in seed bank ranged from 55 to 81% for high dormancy lines (AN86, AN51, M73) and ranged from 93 to 100% for low dormancy lines (AN84, SH99, SH430). Most of the measured decline in seed bank occurred during the first six months of the seed bank establishment. Seed infection increased as the age of the seed bank increased. A strong association was observed between the infection by microorganisms and the dormancy levels of the seed. High dormancy lines exhibited lower seed infection (a rating of 3.3 to 4.0) compared to low dormancy lines (a rating of 5.1 to 9.0). Seed bank mortality was 5, 7, and 18 % higher for dryland treatments compared to irrigated treatments after 4, 6 and 10 months of seed banks establishment respectively. The removal of hulls increased seed bank emergence by 13%, mortality by 11% and seed infection by 24%. Soil sterilization
treatments resulted in significantly lower seed mortality rates compared to treatments containing non-sterilized soil for SH430, a low dormancy line while seed mortality in M73, a high dormancy line showed no effect to these treatments. A repeat of the study was started in May 2004. Six wild oat inbred lines were grown in the field under irrigated and dryland conditions. Seed was harvested, stored, and subjected to two after ripening treatments as in 2003. Plant and seed physiological and morphological characteristics were measured during and after the growing season. Morphological and histological traits on the palea and lemma are currently being determined. Wild oat seed banks were established in the field and in the greenhouse in October and November 2004 using seed produced from the 6 inbred lines, 2 irrigation treatments, and 2 after ripening treatments. Wild oat seedling emergence and seed mortality data will be collected on these seed banks in 2005 and correlated to the
physiological, morphological, and histological data already collected to determine relationships between dormancy (or other seed characteristics) and the ability of wild oat seeds to persist in the soil.
Impacts
The long-term goal of this research is to improve weed management by developing a basic understanding of factors that influence weed seed bank decline and identifying causes of weed seed mortality. We will use wild oat as a model weed species to determine if dormancy mechanisms or other maternal plant or seed characteristics are associated with the ability of nongerminated wild oat seeds to resist attack by soil microorganisms, thus allowing seeds to remain viable over extended periods of time.
Publications
- No publications reported this period
|
Progress 01/01/03 to 12/31/03
Outputs
Field experiments were initiated in 2003 at Huntley, MT. Six wild oat inbred lines (M73, SH99, AN84, AN86, AN51, and SH430) were grown in the field under irrigated and dryland conditions at Huntley, MT. Seed was collected from each plot once per week, cleaned, and stored at -20C until seed harvest was complete. Seed from each plot was divided and subjected to two after-ripening treatments (-20 C and 26 C) following harvest. This resulted in 24 wild oat seed treatments that provide a range in dormancy levels and other seed characteristics. Plant physiological and morphological characteristics measured during or after the growing season included: vegetative development time (days from 50% emergence to 50% anthesis), seed development time (days from 50% anthesis to 50% seed drop), reproductive tillers per plant, glumes per panicle, and seeds per glume. Physiological and morphological characteristics measured on wild oat seeds included: dry weight, viability, germination
of hulled and dehulled seeds in petri dishes and in pots with soil, primary dormancy level (concentration of GA required to induce germination), and duration of primary dormancy (days of after-ripening required to induce germination). Morphological and histological traits on the palea and lemma that have been or are currently being determined include: dry weight, thickness, cell density, number of cell layers, and difference in potential water infiltration. Wild oat seed banks were established in the field and in the greenhouse in October and November, 2003 using seed produced from the 6 inbred lines, 2 irrigation treatments, and 2 after-ripening treatments. Wild oat seedling emergence and seed mortality data will be collected on these seed banks in 2004 and correlated to the physiological, morphological, and histological data already collected to determine relationships between dormancy (or other seed characteristics) and the ability of wild oat seeds to persist in the soil.
Impacts
The long-term goal of this research is to improve weed management by developing a basic understanding of factors that influence weed seed bank decline and identifying causes of weed seed mortality. We will use wild oat as a model weed species to determine if dormancy mechanisms or other maternal plant or seed characteristics are associated with the ability of nongerminated wild oat seeds to resist attack by soil microorganisms, thus allowing seeds to remain viable over extended periods of time.
Publications
- No publications reported this period
|
|