No description available.

Thiobencarb (TB), widely used for the control of broadleaf weeds, grasses, and sedges in rice fields, is considered safe for rice plants when used at recommended rates. TB's reductive dechlorination product, dechlorinated thiobencarb (DTB), is highly toxic to rice. TB is naturally transformed into DTB in field soils in certain areas in Japan and the United States. The resultant syndrome is called delayed phytotoxicity syndrome (DPS). This research was conducted to characterize DPS in Louisiana, to compare the toxicity of TB and DTB to rice, to determine uptake and retention rates of TB and DTB by rice, to confirm that soil microorganisms convert TB to DTB, to determine factors affecting the dechlorination of TB, and to develop methods for isolating dechlorinating microorganisms. An in vitro bioassay developed in this study showed that seedling heights were reduced as concentrations of TB and DTB in soil increased. The effective dosage for 50% reduction in height, using Lafitte rice, was 6.6 μg/ml for TB and 0.3 μg/ml for DTB. By developing and using a gas chromatography/mass spectrometry (GC/MS) method, it was shown that DTB was not taken up preferentially by rice plants. Rice plants absorbed and accumulated more TB than DTB when exposed at equal concentrations. The toxic effects of TB and DTB to rice seedlings was additive. When rice cultivars were evaluated for sensitivity to DTB, M201 was more tolerant than Bengal, Cocodrie, and Lafitte. The conditions affecting the transformation of TB into DTB in soil were studied using a special apparatus developed to measure the redox potential of soil columns at different depths. Reductive dechlorination of TB peaked after 14 days incubation, at a position in the soil column corresponding to an Eh of -230 mV. TB was converted to DTB in vitro in a conducive soil, but not after the soil was autoclaved. Bacterial and fungal isolates from conducive soil inoculated into sterile soil suspensions, or the soil column, all failed to dechlorinate TB. Repeated attempts to isolate the organisms responsible for dechlorination of TB in Louisiana rice field soils failed.

Field studies conducted over two growing seasons evaluated the effect of 2,4-D applied at 1.6 kg ai/ha to LCP 85-384 sugarcane (Saccharum interspecific hybrid) 7, 5, 3, and 1 wk before planting (WBP). Sugarcane was planted in mid-September using both whole stalk and billet (45 cm) seed pieces. When 2,4-D was applied 5 wk or closer to planting, sugarcane shoot emergence and population averaged across planting methods was reduced 5, 7, and 28 wk after planting (WAP) when compared to the nontreated control. Sugarcane height in one of two years was reduced when 2,4-D was applied 5 wk or closer to harvest of sugarcane for seed and sugarcane and sugar yield were reduced around 11% when compared with the nontreated control. For LCP 85-384 a 7 wk period should be allowed between 2,4-D application and harvest for seed when planted using whole stalks or billets. In field studies complete control of red morningglory (Ipomoea coccinea L.) 30 and 60 cm in height was obtained 14 or 21 days after treatment (DAT) over two years with 2,4-D at 0.53 kg/ha, 2,4-D at 0.4 kg/ha or more plus dicamba, atrazine at 2.23 kg ai/ha, flumioxazin at 0.10 kg ai/ha, sulfentrazone at 0.35 kg ai/ha, and V10064 at 1.75 kg ai/ha. Red morningglory 1.8 m tall was controlled 100% 28 DAT the first year with 2,4-D at 1.06 kg/ha and 78% the second year. In the second year when herbicides were applied three weeks earlier than the previous year and when weed growth was more vigorous, the 2,4-D plus the 2,4-D and dicamba premix at 0.79 + 0.1 / 0.04 kg/ha provided control greater than that of 2,4-D alone at 1.06 kg/ha, but was the only treatment that included dicamba to control red morningglory equal to that of 2,4-D at 1.59 kg/ha (87%). Directed applications to the lower 45 cm of 1.8 m red morningglory plants with atrazine at 4.47 kg/ha, sulfentrazone at 0.35 kg/ha, and V10064 at 1.75 kg/ha the first year controlled weeds at least 96%, but control was 23 to 30 percentage points less the second year.

Field studies were conducted over two years in drill- and water-seeded rice to evaluate weed control and crop response with imazethapyr programs. Barnyardgrass [Echinochloa crus-galli (L.) Beauv.] was evaluated with imazethapyr applied alone at various rates and timings. Imazethapyr controlled barnyardgrass 95 to 97% with a soil application at 87 or 70 g/ha fb 53 or 70 g/ha EPOST or LPOST. A single EPOST application of imazethapyr at 140 g/ha controlled barnyardgrass and rice yield was equal to or above those treatments receiving two applications of imazethapyr. Research was also conducted at Crowley, LA and Rayne, LA to evaluate the addition of a herbicide with broadleaf activity into imazethapyr programs applied alone early postemergence (EPOST) and in combination with imazethapyr postemergence (POST). Weeds evaluated included barnyardgrass, red rice (Oryza sativa L.), alligatorweed [Alternanthera philoxeroides (Mart.) Griseb.], and hemp sesbania [Sesbania exaltata (Raf.) Rydb. ex A.W. Hill]. Treatments consisting of imazethapyr applied at 87 g/ha alone to the soil fb a POST imazethapyr application at 53 g/ha controlled barnyardgrass above 90% late season in all studies, expect in water-seeded rice when an imazethapyr application was made at the three- to four-leaf rice stage. Red rice control with a total imazethapyr program was equivalent to, or higher, than other treatments in both drill- and water-seeded studies. Single imazethapyr applications resulted in reduced control of red rice indicating two applications of imazethapyr are required to obtain adequate control. Alligatorweed control increased with soil applications of imazethapyr. However, alligatorweed control with imazethapyr as the only herbicide in a weed control program was inconsistent and suggested only suppression. Treatments receiving a broadleaf herbicide application increased hemp sesbania control as compared with the total imazethapyr program; however, treatments with bensulfuron and triclopyr were inconsistent at controlling hemp sesbania. In drill-seeded studies, hemp sesbania was less of a problem and red rice had a greater impact on rice yield. Rice yields with total imazethapyr programs were equal to, or higher than, other treatments. However, in water-seeded studies, hemp sesbania growth was favored and yields from rice treated with broadleaf herbicides were higher than total imazethapyr programs.

This research was conducted to enhance utilization of the Liberty herbicide resistance transgene in rice. Non-lethal methods to determine the sensitivity of transgenic rice plants to hygromycin B and Liberty were developed, tested and used in this research. Four homozygous transformed plants were selected to make reciprocal crosses with their non-transformed parent cultivars Taipei 309 and Nipponbare. Their resistances to Liberty and hygromycin B were controlled by the closely linked single dominant genes bar and hpt. Some non-resistant phenotypes in the F2 populations were due to gene silencing. The bar gene in some of these plants were allelic and some were non-allelic. When seven independently transformed homozygous transgenic plants with bar and hygromycin genes from Taipei 309 and Nipponbare were crossed reciprocally, progeny evaluations showed five allelic locations among the seven transgenic plants. Twenty additional homozygous transgenic plants from independent transformation events were crossed reciprocally with the previous seven transgenic plants. Evaluation of F1, F2, and F3 populations showed that some of the genes were allelic, but most of them were non-allelic with two or more pairs of genes being expressed. The functional foreign gene (bar) appeared to be restrictively inserted into the rice genome in some cases and was not randomly inserted and expressed. Three to five repeated backcrosses were made using transgenic plants as the donor and current cultivars as the recurrent parents. The results from selected progeny rows, and two-years of yield tests with selected lines, indicated that the target bar gene could be transferred to lines similar to commercial cultivars from homozygous transformants in 4-5 years of backcrossing, giving lines similar to the recurrent parents based on phenotype and yield potential. Liberty herbicide has antibiotic characteristics and suppressed growth of several rice fungal pathogens and Burkholderia glumae in in vitro tests. Liberty had a short residual activity against Rhizoctonia solani in field tests, but single applications of Liberty after disease development had started in the field significantly reduced sheath blight ratings and yield loss. Control of sheath blight by Liberty was equal to or better than that given by the registered fungicide Quadris.

Sugarcane (inter-specific hybrids of Saccharum) is grown largely under long-term monoculture production in Louisiana. This can lead to a complex problem termed "yield decline" that results in poor root health and reduced productive capacity of sugarcane. This problem has been documented to be a limiting factor for sugarcane production in diverse regions, including Louisiana, Hawaii, Jamaica, and Australia. Previous work showed that biological factors affect root health and contribute to yield decline. The objectives of this study were to increase our understanding of microbial communities in sugarcane soils, to determine if there are differences in microbial communities associated with sugarcane roots in soil with and without a sugarcane cropping history, and to provide information on possible changes in the microbial communities resulting from monoculture that may contribute to yield decline. <p> To achieve these objectives, two approaches were used for comparing culturable organisms in soil microbial communities from soil with and without a sugarcane cropping history, and methods were adapted to reliably obtain DNA from soil microbial communities for molecular comparisons. In one approach, colonies grown on different types of culture media were quantified and characterized. In the other approach, sole carbon source utilization profiles (SCSUP) of soil communities grown in Biolog(tm) GN2 microplates were compared. Comparisons of the numbers and types of microorganisms that grew on various culture media demonstrated that differences exist between microbial communities associated with sugarcane roots in Louisiana soils with and without a recent sugarcane cropping history. The differences in community functional diversity detected by SCSUP supported the differences found in types of microorganisms isolated on selective media. The SCSUP results showed that differences in community functional diversity exist between sites in soils with a long-term sugarcane cropping history in common. <p> Methods for DNA extraction and polymerase chain reaction (PCR) amplification were optimized for sugarcane soil microbial community samples from Louisiana. This will allow molecular characterization of sugarcane rhizosphere microbial communities in the future.

Development of resistant cultivars is the main control measure against sugarcane brown rust caused by Puccinia melanocephala. Durability is uncertain, since the pathogen possesses adaptive ability to overcome host plant resistance. A differential gene expression study utilizing suppressive subtraction hybridization was conducted to improve understanding of brown rust resistance mechanisms in sugarcane. The expression patterns of 11 unigenes representing biosynthetic pathways, defense-related genes, and signaling genes were analyzed in L 99-233, a cultivar exhibiting quantitative resistance, L 01-299, a resistant cultivar with the major resistance gene Bru1, and two susceptible cultivars, Ho 95-988 and L 09-125, at 24 h, 48 h, 72 h, and 1 week after inoculation with P. melanocephala using (semi)quantitative RT-PCR. All genes analyzed for their expression showed message accumulation upon infection in susceptible and resistant cultivars, but the maintenance of high amounts of mRNAs of the genes for a prolonged time period appeared to be the most important factor contributing to brown rust resistance. Differences in the time-course of gene expression were detected between L 01-299 and L 99-233 suggesting variable mechanisms for resistance between the cultivars. Molecular markers were used to screen the World Collection of Sugarcane and Related Grasses (WCSRG) for Bru1 to determine its distribution and frequency in Saccharum species and related genera. A total of 1,282 clones were screened. Bru1 was distributed across the Saccharum complex, but the frequency varied among species. Bru1was more prevalent in S. robustum clones (59.1%), whereas it occurred in low frequency and exhibited the highest level of variability in clones of S. spontaneum (18.8%). Bru1 frequency was highest in the two secondary cultivated species, S. barberi (79.3%) and S. sinense (71.8%). The frequency of Bru1 detection was 26.4% and 21.0% for S. officinarum and interspecific hybrid clones, respectively. The characterization of the WCSRG for Bru1 distribution and prevalence will complement efforts to characterize diversity in the Saccharum complex for the expected expanded use of marker-assisted selection in the future. Selection for quantitative resistance in combination with Bru1 could allow breeding programs to develop sugarcane cultivars with effective and durable resistance against brown rust.

Common bean (Phaseolus vulgaris) is the most important legume for direct human consumption. Common bean originated and was domesticated in the Americas but now is grown worldwide. As in the case of other crops, common bean can be infected with acute and persistent plant viruses. A modified dsRNA extraction method was developed and used in this study. The method was fast, economic, versatile, and required relatively small amounts of desiccated plant tissue. The method was successfully used to extract dsRNAs from plants infected with RNA plant viruses and to investigate the occurrence of two endornaviruses, Phaseolus vulgaris endornavirus 1 (PvEV1) and Phaseolus vulgaris endornavirus 2 (PvEV2), in breeding lines, cultivars, landraces, and wild genotypes of common bean from the two centers of common bean domestication: Mesoamerica and the Andes. The two endornaviruses were detected in many common bean genotypes of Mesoamerican origin but rarely in genotypes of Andean origin. A comparative study of morphological and physiological characteristics between two common bean lines of the cultivar Black Turtle Soup (BTS); one infected with PvEV1 and PvEV2 (BTS+) and the other endornavirus-free (BTS-) was conducted. Morphological differences between the two lines were not observed. However, the study revealed that common bean endornaviruses may promote seed germination, pod length, and carotenoid content. Nevertheless, endornaviruses were associated with lower chlorophyll content. When interactions studies were conducted between PvEV1 and PvEV2 and three acute viruses, synergistic effects were obtained. Quantitative RT-PCR results supported a synergism between PvEV1 and Sunn-hemp mosaic virus. More research should be conducted to determine the type of symbiotic interaction that exists between common bean and endornaviruses.

No description available.

Brown rust, caused by Puccinia melanocephala, is an important disease of sugarcane. Breeding for host plant resistance is the primary control measure. Screening for resistance has relied on rating the severity of symptoms caused by natural infection; however, erratic results make this method problematic. A method accomplishing both infection and disease expression under controlled conditions could avoid the problems associated with resistance evaluations under natural infection. Inoculation of seedlings was evaluated to determine whether it could provide accurate resistance ratings in cross appraisal, and inoculation under controlled conditions was evaluated for the potential to accurately determine resistance reactions in clones with known and unknown reactions in comparison to field reactions. Seedlings from crosses between parents with different levels of resistance were inoculated with urediniospores at concentrations ranging from 1 x 103 to 1 x 106 spores per ml. Disease severity was visually assessed at 1 and 2 weeks after inoculation, and resistance ratings were assigned on a modified 1 to 9 scale. Inoculum concentration strongly affected severity and the frequency of resistant progeny in crosses. Brown rust resistance is a heritable trait; however, parental reaction was not a consistent determinant of progeny distribution across resistance rating categories. These results suggest that seedling inoculation may not be suitable for the evaluation of brown rust resistance. Clones were inoculated with 1 x106 spores per ml, and severity was determined as percentage of leaf area occupied by rust lesions by image analysis. Resistance reactions could not be reliably determined for susceptible clones in single inoculations. Controlled conditions inoculation and natural infection results were not correlated. Multiple inoculations under controlled conditions accurately identified resistant and susceptible clones with severe infection resulting from any single inoculation indicating susceptibility. Therefore, controlled conditions inoculation has the potential to be useful in limited studies to characterize parents in a recurrent selection program and for basic studies of resistance to brown rust.