<p>Purple and yellow nutsedge are herbaceous perennial weeds that are among the world?s worst pests. Nutsedge species are problematic due to their perennial nature, longevity of tubers, and prolific tuber production. Due to the relatively difficulty in reducing purple and yellow nutsedge populations, herbicide-management programs in cropping systems that target nutsedge species need to be developed. Field studies were conducted to evaluate potential reduction in purple and yellow nutsedge populations using sulfentrazone and glyphosate management programs and site-specific management in a tobacco and soybean rotation, as well as using sulfentrazone, glyphosate, and halosulfuron management programs in a soybean and corn rotation. All weed management systems reduced purple nutsedge densities similarly in the tobacco and soybean rotation. Sulfentrazone plus clomazone preplant incorporated (PPI) in tobacco or preemergence (PRE) in glyphosate-resistant (GR) soybean reduced yellow nutsedge densities 82 and 99%, respectively. Postemergence (POST) treatments of glyphosate in GR soybean did not increase yellow nutsedge reductions when sulfentrazone was applied in tobacco or GR soybean. Glyphosate applied on a site-specific basis POST with a light-activated hooded sprayer (LAS) reduced yellow nutsedge populations as effectively as glyphosate POST broadcast treatments in GR soybean. Weed management systems that included sulfentrazone PRE fb the LAS in GR soybean reduced POST herbicide use by at least 86%, compared to broadcast applications. Sulfentrazone plus clomazone PRE alone in GR soybean followed by (fb) nicosulfuron POST in GR corn reduced purple and yellow nutsedge populations by 48 and 85% relative to the nontreated control, respectively. Clomazone PRE in GR soybean fb sequential treatments of glyphosate POST in GR soybean and in GR corn, reduced purple and yellow nutsedge populations equivalent to soybean PRE herbicide programs and other GR corn POST management programs. Halosulfuron POST treatments reduced yellow nutsedge populations (> 90%) equivalent to glyphosate POST treatments in corn regardless of soybean PRE herbicide program. Greenhouse studies were conducted to evaluate cotton POST herbicides fb MSMA late postemergence (LPOST) for foliar and tuber reduction of yellow and purple nutsedge when applied to nutsedge foliage at two different application timings. CGA-3626222 treatments reduced purple and yellow nutsedge shoot and root/tuber dry weights equivalent to glyphosate POST fb MSMA LPOST. MSMA at 1120 and 2240 g ai/ha and glufosinate POST fb MSMA LPOST reduced purple and yellow nutsedge shoot dry weights, although reduction was greater at smaller nutsedge application heights. Less reduction was obtained with pyrithiobac POST fb MSMA LPOST. The addition of MSMA in mixture to other POST herbicides was of benefit for nutsedge growth reductions with pyrithiobac, but was seldom beneficial with other herbicides. These data initiated studies to evaluate the physiological behavior of CGA-362622 in purple and yellow nutsedge for possible reasons of control. Lab studies were conducted to evaluate absorption, translocation, and metabolism of 14C-CGA-362622 when foliar applied to purple and yellow nutsedge. Less than 53% of the herbicide was absorbed after 96 h. Both nutsedge species translocated appreciable herbicide (30%) out of the treated leaves. Translocation was both acropetal and basipetal, with at least 25% transported basipetally. Neither nutsedge species translocated over 4% of applied radioactivity to the tubers and roots. Most of the metabolites formed by the nutsedge species were more polar than 14C-CGA-362622 and averaged 69 and 61% of the radioactivity in purple and yellow nutsedge. The half-life of CGA-362622 was estimated at 4 h in both purple and yellow nutsedge.<P>

<p>Transgenic, glyphosate-resistant (GR) cotton has been available to U.S. growers since 1997. Despitewide-spread acceptance, there have been performance complaints by growers citing lower boll retention in GRvarieties than in conventional varieties. Field and greenhouse studies confirmed grower observations,demonstrating a glyphosate-associated decrease in boll retention compared to non-treated GR or conventionalplants. Late (beyond the 5 leaf stage) foliar applications were the most injurious, presumably because plantswere entering early reproductive stages. Boll ?cavitation,? (dessicated bolls attached to plants) also observed bygrowers following glyphosate treatment, resulted from abnormal abscission zone formation and was related tovariety.<p>14C-glyphosate absorption per square centimeter was greater when applied to stem tissue than leaf tissue, but overallabsorption is likely greater when applied foliarly, due to a greater total surface area. Because glyphosatetypically moves from source tissue to sink tissue, up to 3.7% of applied 14C-glyphosate was translocated toreproductive tissues.<p>Seedling development in both GR and conventional cotton was inhibited by root-absorbed glyphosate.Root tissues were more sensitive to glyphosate than cotyledons or hypocotyls, as was demonstrated byinhibition of lateral root formation and shikimic acid accumulation. CP4-EPSPS content was significantly lowerin GR seedling roots than cotyledons, accounting for glyphosate sensitivity.<p>Further studies compared the accumulation of shikimic acid in response to glyphosate in reproductiveand vegetative tissues in GR and conventional cotton. Shikimic acid accumulation per mM of glyphosate, wasgreater in reproductive than vegetative leaf tissue in both GR and conventional cotton, suggesting thatreproductive tissue is innately more sensitive to glyphosate than vegetative tissue. The quantity of theglyphosate-resistant CP4-EPSPS enzyme was significantly less in stamens than in vegetative leaf tissues.Several morphological differences were apparent in flowers of glyphosate-treated GR cotton.<p>Glyphosate applications inhibited stamen elongation, resulting in anthers not extending to the tip of the stigma,thereby limiting pollen deposition to the lower, less receptive portion of the stigma. Total pollen deposition on the stigma was less in glyphosate-treated GR cotton than non-treated GR or conventional cotton. Microscopicanalysis of pollen revealed that glyphosate arrested maturation in at least 3 pollen developmental stages. Atanthesis, pollen grains from glyphosate-treated GR plants were collapsed, highly vacuolated, and had 60% lowerviability (ability to germinate) than pollen from non-treated GR or conventional plants. Retained bolls fromglyphosate-treated plants had fewer seeds than those from non-treated GR or conventional plants. Hand crossesbetween glyphosate-treated plants demonstrated that the number of seeds per boll was decreased when the maleparent, but not the female parent, was glyphosate treated. Hand pollinations using pollen from treated plants,although overcoming the increased anther-stigma distance, did not restore the normal number of seeds per boll.Treatment of GA onto glyphosate-treated GR plants did not remediate glyphosate effects on pollen viability andfloral morphology. Therefore, presumably, several of the bolls that were shed due to glyphosate-treatments,contained an insufficient number of fertilized ovules and are thus shed.<p>This research proposes that boll shed due to glyphosate in GR cotton is due to insufficient levels ofCP4-EPSPS in stamens, which are highly sensitive to glyphosate. As glyphosate accumulates in reproductivestructures, stamen elongation and pollen development are inhibited, resulting in poor fertilization of ovules.Because fewer ovules are fertilized, bolls are either shed or contain fewer seeds if retained. Growers shouldlimit glyphosate contact with GR cotton, especially during the reproductive stages in order to minimize thepotential for glyphosate-induced boll shed.<P>

Research in Europe and the United States showed that interplot competition in variety trials can result in distortion of yield and misleading conclusions from yield comparisons. Field trials were conducted at Swift Current and Saskatoon in 1993 and 1994 to find out if interplot competition occurs in the wheat growing region of Saskatchewan. Four spring wheat (<i>Triticum aestivum</i> L.) cultivars, Biggar, Oslo, Genesis and Glenlea, were grown in four-row plots in a diallel competition treatment design, with the competition treatments applied randomly to each of eight replications in a randomized complete block design. Generally, yield was distorted from pure stand yield when adjacent plots differed for height ($-$0.34% cm$\sp{-1}).$ Plots with Biggar or Oslo flanked by a tall cultivar, Genesis or Glenlea, yielded less than when flanked by themselves, and the reverse occurred when the tall cultivars were flanked by the short cultivars. Interplot competition also affected spike density in the same fashion, did not significantly affect height, and was inconclusive with regards to kernel weight. Simulation indicated that a correlation between height and yield would not affect the covariance adjustment with average height difference. Sixty-five historical data sets were tested to see if an adjustment for interplot competition with average height difference as a covariate would be effective. The negative relationship between yield and the height covariate was significant for 25 of the data sets. At Saskatoon in 1995, row directions were compared and interplot competition was significant in the north/south rows and not significant in the east/west rows. An experiment at Regina and Swift Current in 1995 indicated that less interplot competition occurred when plots were separated by spring planted winter wheat than when plots were 23 cm apart. It was concluded that when plots differ for height, yield distortion can occur in the Saskatchewan wheat growing region.

No description available.

The inheritance of resistance to ascochyta blight in lentil (Lens culinaris Medik.) caused by Ascochyta fabae Speg. f. sp. lentis Gossen et al (Syn. A. lentis Vassil.) was studied using as parents the Canadian cultivars Eston (susceptible) and Laird (moderately resistant) and two resistant lines from ICARDA, ILL-5588 and ILL-5684. The F2, F2-derived Fa families and F2-derived F4 families of each cross were evaluated for ascochyta resistance under field conditions in an ascochyta nursery during 1987, 1988 and 1989, respectively. The parents and segregating populations were rated for ascochyta reaction on the basis of foliage symptoms, using a 1 to 9 disease rating scale, with plants rated 1 to 5 considered resistant and plants rated 7 to 9 considered susceptible. In addition percent seed-borne ascochyta infection was evaluated, using the seed plating technique. The cuItivar Eston was susceptible. Laird lentil was resistant to foliar infection by ascochyta, but its resistance breaks down in the late podding stage and under the wet conditions of the ascochyta nursery percent seed-borne ascochyta infection was even higher than in the susceptible cultivar Eston. The lines ILL-5588 and ILL-5684 were highly resistant with resistance persisting after maturity and the seed coats do not become infected and discolor materially even with prolonged exposure to wet weather at harvest. A chi-square test for goodness-of-fit of the F2 and F2- derived F3 families indicated that resistance to foliar infection by ascochyta in Laird lentil was conditioned by a single recessive gene, ral1• Results also indicated that the resistance to foliage and seed infection by ascochyta of ILL- 5588 and ILL-5684 was due to two - dominant genes,' Ral2 and Ral3. ILL-5588, but not ILL-5684, also carried the ral1 gene for resistance to foliar infection by ascochyta and is the better source of resistance to ascochyta. The high correlation between percent seed-borne ascochyta infection in Fz-derived F3 families and in F2-derived F4 families plus the medium to high heritability estimates (0.52 to 0.8l) indicate that it will be easy to select for ascochyta resistance in these crosses. An effective method of selecting for ascochyta resistance in lentil was developed. An ascochyta nursery is developed by spreading infected lentil straw between the lentil rows prior to flowering. This nursery is then sprinkled intermittently once or twice each day until about two weeks after maturity. The crop is permitted to dry naturally and selections made for ascochyta resistant F2 plants or replicated progeny rows in later generations. Ascochyta resistance is based on a low level of discolored seed (0 to 5%), reconfirmed by plating the seed to determine percent seed-borne ascochyta infection in replicated progeny rows. Only a few selections have a high level of clean bright seed and require seed planting. This technique is quick, easy, effective and efficient. Resulting selections are resistant to both foliar infection and seed infection by ascochyta.

Thesis (Ph. D.)--Oklahoma State University, 2005. / Vita. Includes bibliographical references (p.80-82).

Thesis (Ph. D.)--Oklahoma State University, 2005. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--Oklahoma State University, 2005. / Vita. Includes bibliographical references (p.99-100).

Thesis (Ph. D.)--Oklahoma State University, 2005. / Vita. Includes bibliographical references (p.39-44).

Thesis (Ph. D.)--Oklahoma State University, 2005. / Vita. Includes bibliographical references (p.123-127).