Effects of no tillage and genetic resistance on sunflower wilt by Verticillium dahliae

From 2001 to 2006 crop seasons three field experiments were run to compare the effect of no tillage (NT) vs. conventional tillage (CT) on Verticillium wilt of sunflower. One experiment had sunflower monocropping (SM) and the others the sequence wheat–sunflower (WS) with 6 years of fescue pasture or seven WS cycles as previous crops. All experimental fields have history of the disease. One cultivar with low resistance was used in SM and two genotype-resistance levels (high and low; characterized by six and eight cultivars each, respectively) in the WS sequences. Leaf mottle severity in all environments, Verticillium dahliae colony forming units (CFU)/g of soil in 2005 or 2006 trials, density of microsclerotia in the stem pith at 0.5 m above the soil line in WS, and grain yield and oil content in WS with fescue as previous crop were recorded. Every year, disease severity was higher in CT than in NT in all trials. In SM, disease severity increased during the 3 years in CT from 58% to 88%, while in NT disease severity remained around the initial level (49%). The V. dahliae-CFU/g of soil after 3 years in SM or three cycles of WS was approximately three times higher in CT than in NT. In WS, density of microsclerotia in stem pith were higher in CT than in NT. In WS with fescue pasture as previous crop, grain yield and oil content tend to increase with NT in relation to CT. The combination of NT and high-resistant genotypes reduced the disease and the production of microsclerotia in stem pith to very low values. NT + high resistance should be viewed as a preventative, not a curative disease management option because the microsclerotia persist in soil for a long time. Therefore, NT + high resistance programs should be initiated early, before inoculum builds up to high levels in the soil. Thus, the combination of NT and high-resistant cultivars promises to be an interesting tool to manage V. dahliae and Verticillium wilt in sunflower and would have potential in other crops like alfalfa, cotton or strawberry.     

Embryo transfer,a useful technique to be applied in small community farms?

The objective of this study was to determine if the technique of embryo transfer in cattle can be commercially feasible in a region situated in the humid tropics of Mexico. Twenty-six Bos taurus and twenty-six Bos indicus cows were estrous synchronized and superovulated to obtain a total of 80 embryos of both sub-species. Embryos were classified using stereoscopic microscopy based on established criteria. Nine dual-purpose farms situated in the tropics of Mexico were chosen to provide ten recipient cows each to transfer one embryo per cow. The females were transferred using a fixed-time protocol after verifying the presence of a corpus luteum on the seventh day after the end of hormonal treatment. Pregnancy diagnosis was carried out 28 days after embryo transfer by ultrasonography. Estimation of the cost was determined by calculating the expenses for preparation of the donor and embryo recovery, which were US 633 and US633 and US 589 for B. taurus and B. indicus, respectively. The cost of each embryo was determined considering the number of transferable embryos recovered, which was 3.8 on mean. The cost of each conception was calculated taking into account the percentage of pregnant animals (27% on mean), and the cost for preparing donor and recipient cows, for transferring embryo. The overall cost per gestation was US 1,447. Considering a 50:50 ratio of male to female born, the cost for a replacement heifer calf was US1,447. Considering a 50:50 ratio of male to female born, the cost for a replacement heifer calf was US 2,894, which surpassed by far the commercial cost of a crossbred ready-to-bred heifer normally used as replacement (approximately US $900).     

Monitoring changes in back fat thickness and its effect on the restoration of ovarian activity and fertility in Bos indicus cows

With the objective of testing the hypothesis if animals with a stable layer of body fat (FAT) during the peripartum have a better chance of becoming pregnant after calving, fifty‐nine multiparous Brahman cows in their last trimester of pregnancy were used. Animals averaged four parturitions and were stocked at a rate of 1.25 animal units per hectare and divided into two groups depending on the time postpartum (dpp) that the intravaginal releasing device CIDR was inserted; Group 1 (<30 dpp; n = 30) received the implant at 25.2 ± 4.21 and withdrawn 9 days later. Group 2 (≥30 dpp; n = 29) received the CIDR at 38.41 ± 5.8. Animals were AI at detected oestrus until 170 dpp and calculated as pregnant at first service or requiring more than one service (1s and >1s), not pregnant but cycling (not pregnant) and those not cycling at all (anestrus). The FAT measurements were taken twice each month from the last trimester of gestation until 96 dpp. The onset of ovarian activity was monitored through blood levels of progesterone (P4) at days 14 and 9 prior to CIDR insertion and days 10, 13, 30 and 33 after CIDR withdrawal. Animals pregnant did not have any major changes in their fat thickness. In contrast, cows pregnant in the group ≥30 dpp had changes in their FAT homoeostasis, and pregnant animals in the 1s and >1s groups did not show differences in dorsal back fat in the last trimester of pregnancy and early postpartum. In contrast, animals not pregnant and in anestrus FAT values decreased considerably after parturition. Overall, fertility was 49%, but 18% of all the animals remained anestrus losing FAT. Thus, animals with adequate metabolic conditions will have a better chance of pregnancy regardless of the time postpartum when the reproductive programme starts.     

Forest cover and landscape heterogeneity shape ant–plant co-occurrence networks in human-dominated tropical rainforests

Landscape Ecology - The effects of habitat loss and fragmentation on biodiversity involve a series of mechanisms and processes that cannot be studied in isolation, mainly because human-modified...     

Effect of blood metabolites, body condition and pasture management on milk yield and postpartum intervals in dual-purpose cattle farms in the tropics of the state of Veracruz, Mexico

Research was conducted on typical smallholder farms with dual-purpose cattle (DPC) (Bos indicus x B. taurus) in the coastal north-central area of Veracruz, Mexico. The study was divided into two phases. The aim of the first phase was to investigate the effect of blood metabolities, body condition and pasture management on milk yield and postpartum intervals, in order to investigate if the former are suitable indicators of the reproductive and nutritional status of DPC. One hundred and sixty-five calvings of crossbred cows were recorded from January 1992 to November 1994 on 12 small farms. Milk samples were collected twice a week for progesterone analysis. Blood samples and BCS were taken once a month. However, in Phase II emphasis was placed on the effect of pasture management upon reproductive and productive performance of DPC. Records of four farms were obtained from June 1995 to November 1996. Stocking rates were 0.40, 0.87, 0.35 and 1.5 cows/ha for farms A, B, C and D, respectively. Farms A and C used a slow rotation while B and D used a rapid rotation. In Phase I, the changes in BCS during the last month of pregnancy and first month postpartum did not correlate (p > 0.05) with milk yield or reproductive performance. Blood the metabolite profiles were not consistently related to productive or reproductive variables. The effect of farm and season was significant (p < 0.05) on most of the response variables and low productivity on overstocked farms lead to the conclusion that the low reproductive performance of DPC was linked to poor pasture management. During Phase II, farms A (FA) and D (FD) produce more milk than the others. Days to first service, days open, and calving interval were similar for farms B (FB) and C (FC), highest for Farm A, and lowest for Farm D. The forage availability mean was above the critical range of 6-8 kg of dry matter per 100 kg of liveweight (kg DM/100 kg LW) in all farms (range from 6.1 +/- 5.0 to 21.1 +/- 11.2 kg DM/100 kg LW). Farm D had the highest stocking rate (1.5 cows/ha), a rapid rotation (10 paddocks), a good forage availability (7.1 +/- 3.9 kg DM/100 kg LW) with a good quality for a tropical pasture (11.6 +/- 2.4% crude protein), and an economic energy supplementation. These results suggest this type of management could be more widely employed to improve the productivity of DPC on smallholder farms in the Mexican tropics.