Phenotyping of Urochloa humidicola grass hybrids for agronomic and environmental performance in the Piedmont region of the Orinoquian savannas of Colombia

In the low fertility acid soils of the Orinoquian savannas of Colombia, Urochloa humidicola cv. Tully or Humidicola is one of the most widely planted tropical forage grasses for improving livestock productivity. Low nutritional quality of this grass limits sustainable livestock production in this region. In this study, we conducted a phenotypic evaluation under field and greenhouse conditions of one of the first hybrid populations of U. humidicola generated from the forage breeding program of CIAT. Our objective was to identify a set of new hybrids of U. humidicola that combine improved productivity and nutritional quality plus the biological nitrification inhibition (BNI) trait/ability to reduce nitrogen (N) losses via leaching and nitrous oxide (N₂O) emissions. To this end, we tested 118 hybrids (planted in pots) in the greenhouse for over 6 months and measured potential nitrification rates (NR) using soil microcosm incubation. NR values observed ranged from 0.27 to 5.75 mg N-NO₃⁻ kg soil⁻¹ day⁻¹. Later, 12 hybrids with different levels of NR were selected and field-tested in the Orinoquia region over a 4 years period (2013–2017) for dry matter production, nutrition quality (crude protein, in vitro digestibility and fibres content) and NR in each year. In the rainy season of 2018, two hybrids with superior agronomic performance and contrasting field level NR (Uh08/1149 and 0450) were subjected to analysis of soil-borne N₂O emissions after fertilization during 13 days. The NR values recorded were not directly correlated with the forage quality parameters evaluated, however, the two grasses with the lowest NR values were among those with the highest biomass production, crude protein content, and N uptake. The grass hybrid Uh08/1149 and the germplasm accession CIAT 16888 were found as materials with superior forage value, with production of 14.1 and 14.6 tons dry matter ha⁻¹ year⁻¹ (up to 8% higher than the cv. Tully), crude protein of 11.5 and 9.1% per cut (up to 20% higher than the cv. Tully), and N uptake of 31.6 and 25.7 kg N ha⁻¹ cut⁻¹ (up to 30% higher than the cv. Tully). Additionally, these two grasses are likely to exhibit high-BNI ability, with potential to improve N use efficiency in managed pastures.     

The BamHI site in the Internal Transcribed Spacer Region of Mungbean ribosomal RNA gene is partially methylated

The 18s-5.8s-25s ribosomal gene (18s-25s rDNA) in higher plants is present in multiple copies, on different chromosomes, as tandemly repeated units. Among the multiple BamHI sites that occur in the repeat unit, only the site in the middle of the 25s rRNA coding region is methylated in most cereals and pulses. BamHI restriction enzyme analyses of the mungbean 18s-25s rDNA showed the presence of two populations. Nearly 50% of the 18s-25s rDNA population had BamHI site situated in the internal transcribed spacer region (ITS-BamHI) resistant to cleavage by BamHI. The amplified ITS fragment was completely digestible by BamHI showing that partial cleavage by BamHI is not due to variation in the recognition sequence but most probably due to methylation. The complete cleavage of the ITS-BamHI site by BstYI that recognizes BamHI site but is insensitive to methylation confirms that the ITS-BamHI site is methylated. Methylation is probably due to the presence of a guanosine residue adjacent to the 3′ cytosine in the recognition sequence. This revised version was published online in July 2006 with corrections to the Cover Date.     

Biochemical alteration induced by monocrotophos in the blood plasma of fish, Channa punctatus (Bloch)

Monocrotophos (MCP), commonly known as azodrin, is one of the organophosphate (OP) pesticides extensively used in agricultural practices throughout the world. Channa punctatus were exposed to sublethal concentrations (0.96 and 1.86 mg/L) of monocrotophos for 15 and 60 days to assess the alterations in the level of some biochemical parameters in blood plasma. Significant alterations in all the biochemical parameters were found to be dose dependent. Hypoglycemia and hypocholesteremia were observed in plasma of fish at both exposure periods (15 and 60 days). Increased activities of glutamate-oxalacetate transaminase (GOT), glutamate-pyruvate transaminase (GPT), acid and alkaline phosphatase of blood plasma indicated hepatic tissue damage. Decrease in lactate dehydrogenase (LDH) content in plasma further indicated lower metabolic rate after 60 days of exposure. Significant decline in triglycerides content was observed in fish exposed to both sublethal concentrations of monocrotophos. We suggest that analysis of biochemical parameters in the fish blood may be useful in environmental biomonitoring.     

Relationships Between Verticillium dahliae Inoculum Density and Wilt Incidence, Severity, and Growth of Cauliflower

ABSTRACT Microplot and field experiments were conducted to evaluate the effects of inoculum density on Verticillium wilt and cauliflower growth. Soil containing Verticillium dahliae microsclerotia was mixed with various proportions of fumigated soil to establish different inoculum densities (fumigated soil was used as the noninfested control). Seven inoculum density treatments replicated four times were established, and the treatments were arranged in a randomized complete block design. Soil was collected from each microplot immediately after soil infestation for V. dahliae assay by plating onto sodium polypectate agar (NP-10) selective medium using the Anderson sampler technique. Five-week-old cauliflower was transplanted into two beds within each 1.2- by 1.2-m microplot. At the same time, several extra plants were also transplanted at the edge of each bed for destructive sampling to examine the disease onset (vascular discoloration) after planting. Cauliflower plants were monitored for Verticillium wilt development. Stomatal resistance in two visually healthy upper and two lower, diseased leaves in each microplot was measured three times at weekly intervals after initial wilt symptoms occurred. At maturity, all plants were uprooted, washed free of soil, and wilt incidence and severity, plant height, number of leaves, and dry weights of leaves and roots were determined. The higher the inoculum density, the earlier was disease onset. A density of 4 microsclerotia per g of dry soil caused 16% wilt incidence, but about 10 microsclerotia per g of soil caused 50% wilt incidence. Both wilt incidence and severity increased with increasing inoculum density up to about 20 microsclerotia per g of soil, and additional inoculum did not result in significantly higher disease incidence and severity. A negative exponential model described the disease relationships to inoculum levels under both microplot and field conditions. Stomatal resistance of diseased leaves was significantly higher at higher inoculum densities; in healthy leaves, however, no treatment differences occurred. The height, number of leaves, and dry weights of leaves and roots of plants in the fumigated control were significantly higher than in infested treatments, but the effects of inoculum density treatments were variable between years. Timing of cauliflower infection, crop physiological processes related to hydraulic conductance, and wilt intensity (incidence and severity) were thus affected by the inoculum density. Verticillium wilt management methods used in cauliflower should reduce inoculum density to less than four micro-sclerotia per g of soil to produce crops with the fewest number of infected plants.