Mortality of Eucalyptus pilularis progenies and provenances after frost

We aimed to quantify frost tolerance and damage on Eucalyptus pilularis provenances and progenies in Curitibanos, Santa Catarina State, Brazil. Mortality and severity of damage were assessed before frost at 7 months old and at 14 and 19 months old after frost events. Frost resulted in plant mortalityof 55.7%, with no difference among progenies and provenances. The tolerance of 5.3% may have occurred due to specific local conditions (escape). We concluded that the species does not have tolerance to frost in subtropical environment, with daily thermal range from - 5 °C to 28 °C.

Competitive ability of canola (Brassica napus var. oleifera) hybrids with black oat (Avena strigosa) in a subtropical environment

The objective of this study was to assess the competitive ability of canola (Brassicanapus var. oleifera) hybrids in competition with black oat (Avena strigosa) in a subtropical environment. The experiments were conducted in a greenhouse where canola hybrids ‘Hyola 61,’ ‘Hyola 76,’ ‘Hyola 433,’ and ‘Hyola 571’ were tested individually for their competitive performance with black oat. The plant proportion between black oat and the canola hybrid was changed (100%:0%; 75%:25%; 50%:50%; 25%:75%; and 0%:100%) while keeping the total population of plants constant (20 plants plot‑1). Photosynthesis rate (μmol m-2 s-1), internal CO2 concentration (μmol mol-1), and transpiration rate (mol H2O m-2 s-1) were assessed using an infrared gas analyzer 55 days after emergence. Leaf area (m2 m-2) and dry matter (g m-2) were also assessed on the same day. The data set was analyzed by the replacement series method for competition studies. There was evidence of intense competition between canola and black oat, independent of plant proportion. The competitive ability of canola was distinct among hybrids; Hyola 571 performed better than the others in the competition against black oat. Choosing the most competitive hybrid, such as Hyola 571, helps maintain high canola grain yield levels in areas infested with black oat. Highlights: There is difference in competition among canola hybrids against black oat; Hyola 571 performed better in the competition; Preference should be given for most competitive canola genotypes against weeds, and weed control should be carried out early in the critical period of interference; Aggressiveness is the most preponderant parameter in determining canola genotypes with superior ability in competition against weeds.

Hybrids of Paspalum plicatulum × P. guenoarum: Selection for forage yield and cold tolerance in a subtropical environment

Selection of improved genotypes is important for pasture-based feeding systems in subtropical regions. Our goal was to identify hybrids of Paspalum with enhanced forage yield and cold tolerance across 2 sites [Bagé and Eldorado do Sul (ES)], in Rio Grande do Sul, Brazil. We evaluated 19 P. plicatulum × P. guenoarum hybrids, P. plicatulum genotype 4PT, P. guenoarum cultivars Azulão and Baio and, as Control, Megathyrsus maximus cv. Aruana. At both sites, the experimental design was a completely randomized block with 4 replications. Total dry mass (total-DM), leaf-DM and cold tolerance (ColdT) were recorded. At Bagé, hybrid 102069 produced higher total-DM and leaf-DM than the progenitors and cv. Aruana, while at ES, hybrids 102069 and 10308 produced higher total-DM than 4PT, Azulão and Aruana; hybrid 102069 had higher leaf-DM. At Bagé, 16 hybrids displayed ColdT similar to their progenitors and higher than Aruana, while at ES, 12 hybrids showed ColdT similar to Azulão and Baio and higher than 4PT and Aruana. This study demonstrated that hybrids of Paspalum with superior forage yield to their progenitors and Aruana, and hybrids with higher ColdT than 4PT and Aruana are in existence. The hybridization technique shows potential for producing alternative genotypes with higher forage yield and ColdT for sowing in subtropical regions.

EVALUATION OF THE REPRODUCTIVE PROBLEMS OF FRIESIANS, BUNAJI AND CROSSED COWS IN A SUBTROPICAL ENVIRONMENT

Herd health fertility records of 248 cows comprising 103 Friesians, 84 Bunaji and 61 Crossbreeds in Vom from 1992-1999 were utilized to study the incidence of reproductive problems. The overall incidence of various reproductive problems was 54.4% and this was more frequent (P<0.001) in crossbred cows (72.6%) than in Friesians, (59.9%) and in Bunaji (32.7%). Second Calvers (67.1%) were more susceptible (P<0.01) to reproductive problems than heifers (56.0%) and mature cows (45.3%). The incidence of still birth (8.10%) and relative infertility (8.2%), were influenced by genotype (P<0.05); similarly genotypic differences (P<0.001) were observed in the incidence of retained placenta (7.4%). Abortion (5.6%), dystocia (12.2%) and repeat breeding (12.5%) were uniformly distributed among genotypes. Parity of dams had marked influence (P<0.001) on dystocia, still birth and retained placenta. Significant differences (P<0.0l) were also observed on the incidence of relative infertility, but the rate of dystocia (P<0.01), abortion and repeat breeding (P<0.001) varied with the years. The results emphasize the need for greater management intervention to reduce the incidence of reproductive problems in sub tropical cattle herds.