Experimental Infections of Bluegill with the Trematode Ribeiroia ondatrae (Digenea: Cathaemasiidae): Histopathology and Hematological Response

Infections by the digenetic trematode, Ribeiroia ondatrae, cause severe limb malformations in many North American amphibians. Ribeiroia ondatrae also infects fishes as second intermediate hosts, but less is known about the pathology and immune responses initiated in infected fish, even though reports of infected fish date back to early 1900s. To this end, we experimentally exposed juvenile Bluegills Lepomis macrochirus to three doses of R. ondatrae cercariae and monitored the pathology, parasite infection success, and humoral responses over 648 h. All exposed fish became infected with metacercariae, and the average infection load increased with exposure dose. Histologically, infection was associated with acute hemorrhages in the lateral line and local dermis at 36 h, followed by progressive granulomatous inflammation that led to the destruction of encysted metacercariae. Correspondingly, over the course of 648 h we observed an 85% decline in average infection load among hosts, reflecting the host's clearance of the parasite. Infection was not associated with changes in fish growth or survival, but did correlate with leukocytosis and neutrophilia in circulating host blood. Understanding the physiological responses of R. ondatrae in Bluegill will help to clarify the ecological effects of this parasite and provide a foundation for subsequent comparisons into its effects on behavior, individual health, and population dynamics of Bluegill.

Received March 4, 2015; accepted August 9, 2015     

Effects of Coconut Husk and Sphagnum Moss-Based Media on Growth and Yield of Romaine and Buttercrunch Lettuce (Lactuca Sativa) in a Non-Circulating Hydroponics System

A comparison was made to investigate the effects of two potting methods: coconut husk/ sphagnum moss and a plastic forestry tube with a peat-based medium (Sunshine® mix #1, Sungro Horticulture, Agawam, MA, USA), on the growth and yield of Romaine ‘Ridgeline’ and Buttercrunch ‘UH Manoa’ lettuce (Lactuca sativa) using a non-circulating hydroponics system. Two-week old lettuce seedlings were transplanted into 5 cm holes, 20 × 30 cm apart on polystyrene bead boards fitted on top of a 0.6 m wide, 1.2 m long and 25 cm deep hydroponics tanks. A standard hydroponics nutrient solution was prepared using Chem Gro® (Hydro-Gardens, Colorado Springs, CO) (8-15-36 + micronutrients), calcium nitrate [Ca(NO₃)₂] and magnesium sulfate (MgSO₄). Each tank contained either one lettuce variety, replicated 12 times in completely randomized design. Growth and yields significantly increased in both lettuce varieties grown in coconut husk/sphagnum moss plugs which were attributed by their relatively greater water holding capacities and a more favorable media that allowed better root growth.     

Determination by near-infrared spectroscopy of perseitol used as a marker for the botanical origin of avocado (Persea americana Mill.) honey

This paper reports the application of near-infrared (NIR) reflectance spectroscopy to determine the concentration in honey of perseitol, a sugar that is specific to avocado honey. Reference values for perseitol were obtained by high-performance liquid chromatography analysis in 109 honey samples. Although the average concentration of perseitol in honey samples was only 0.48%, accurate prediction equations were successfully developed. The regression model of modified partial least squares was superior to that of principal component regressions. Calibrations based on the first or second derivative of Log(1/R) were equally good (R(2) > 0.95). Using half of the samples for calibration and the second half for validation, the correlation between actual and predicted values of the second half was satisfactory (R(2) = 0.87), the slope did not differ from 1, bias was low (0.005%), and the standard error of prediction was relatively low (0.13%). It was concluded that NIRS analysis may be used to detect to what extent honeybees have harvested avocado nectar but not to authenticate avocado honey as unifloral.     

Effects of tolazoline and yohimbine on xylazine-induced central nervous system depression, bradycardia, and tachypnea in sheep

We compared the ability of tolazoline and yohimbine to antagonize xylazine-induced central nervous system depression, bradycardia, and tachypnea in 9 ewes and 5 rams. Once a week for 3 weeks, each sheep received one IV treatment of 0.4 mg xylazine/kg, 0.4 mg xylazine/kg followed in 10 minutes by 2 mg tolazoline/kg, or 0.4 mg xylazine/kg followed in 10 minutes by 0.2 mg yohimbine/kg. The order of the 3 treatments in each sheep was randomized. Xylazine alone caused recumbency for 41.0 +/- 3.7 minutes (mean +/- SEM). Tolazoline and yohimbine shortened the xylazine-induced recumbency to 12.1 +/- 0.9 minutes and 18.1 +/- 1.5 minutes, respectively. Sheep given xylazine alone had head droop for 34.0 +/- 5.4 minutes after rising. Head drooping of sheep given tolazoline or yohimbine was reduced to 10.1 +/- 1.7 minutes and 14.2 +/- 1.7 minutes, respectively. Both tolazoline and yohimbine reversed the bradycardia and tachypnea that followed xylazine administration. No statistical differences in the rate and magnitude of the reversal were observed between the 2 drugs.     

Variation in sugar levels and invertase activity in mature fruit representing a broad spectrum of Cucumis melo genotypes

Sugar accumulation is a very important physiological process that determines dessert-melon fruit quality. Considerable variation in the sugar content and composition in the mature flesh of Cucumis melo L. fruits was observed among 56 genotypes which represent the wide range of morphological and horticultural types found in this species. Sucrose accumulation was observed not only among 'dessert melons' of the inodorus and cantalupensis types, but also in representatives of other subgroups of C. melo, including some of the accessions from agrestis and conomon groups. Among the genotypes that accumulate sucrose, the levels of this sugar, and not of the hexoses, were correlated with the total sugar concentration. Hexose levels were correlated with total sugar levels only among low-sugar genotypes that did not accumulate sucrose. Activities of the sucrose hydrolyzing enzymes acid invertase (EC 3.2.1.26) and alkaline invertase (EC 3.2.1.27) were measured in the mature fruit flesh and the results of this survey support the hypothesis that low acid invertase activity is a prerequisite for sucrose accumulation. The sucrose accumulating, high sugar genotypes had less-acidic flesh pH values (pH> 6) than the low-sugar genotypes. The latter were characterized by a broader range of pH values, including acidic (pH< 5.5) fruit flesh.     

Water savings, nutrient leaching, and fruit yield in a young avocado orchard as affected by irrigation and nutrient management

This project was designed to determine the effect of fertilizer rate and irrigation scheduling on water use, nutrient leaching, and fruit yield of young avocado trees (Persea americana Mill. cv. Simmonds). Seven nutrient and irrigation management practices were evaluated: (1) irrigation based on crop evapotranspiration (ET) with 50% fertilizer at a standard rate (FSR); (2) ET irrigation with FSR (typical for avocado production in the area); (3) ET irrigation with 200% FSR; (4) irrigation based on exceedance of 15-kPa (SW) soil water suction with 50% FSR; (5) SW with FSR; (6) SW with 200% FSR; and (7) irrigation at a set schedule (based on timing and frequency typically used in local avocado production) with FSR. The SW with FSR treatment saved 87% of the water volume applied and reduced total phosphorus leached by 74% compared to the set schedule irrigation with FSR. The SW with FSR treatment had higher avocado fruit production, tree water-use efficiency, and fertilizer-use efficiency than the other six treatments. Thus, the use of soil water monitoring for irrigation management can substantially increase sustainability of young avocado orchards in southern Florida.     

Reponses of mamey sapote (Pouteria sapota) trees to continuous and cyclical flooding in calcareous soil

Physiological and growth responses of ‘Pantin’ and ‘Magana’ mamey sapote (Pouteria sapota) trees to continuous and cyclical flooding were studied in a series of experiments. Trees were grown in containers in a very gravelly loam soil and were subjected to continuous flooding of the root zone for 30–66 days (Experiments 1 and 2) or alternating flooding–unflooding cycles for 50 days (Experiments 3–5). For all experiments, the control treatment consisted of nonflooded trees. Net CO₂ assimilation (A) and stomatal conductance (g_s) decreased within 3 days of continuous flooding and internal CO₂ concentration was significantly higher in leaves of flooded than nonflooded plants. In the cyclic flooding experiments, trees were flooded in 3- to 6-day cycles and then unflooded for the same time periods. Stomatal conductance and A decreased within 3 days of flooding, leaf epinasty occurred between days 5 and 10, leaf senescence and abscission occurred between days 15 and 30, and branch dieback and tree death occurred between days 30 and 60. Three cycles of 3-day flooding and 3-day recovery of trees had little effect on leaf gas exchange of ‘Magaña’ trees. Similarly, ‘Pantin’ trees survived 3 cycles of 6 days of flooding interspersed with 3–6 days of recovery despite consistent decreases in g_s and A during flooding. Stomatal conductance and A of both mamey sapote cultivars decreased within a few days of flooding and this species appears to have intermediate flooding tolerance compared with other tropical fruit crops based on tree survival.     

Effect of acetochlor treatment on Fusarium wilt and sugar content in melon seedlings

Pretreatment of soil with the herbicide acetochlor at 0.1–1g g^–1 significantly decreased incidence of wilt due toFusarium oxysporum f. sp.melonis in melon seedlings. Glucose, fructose and sucrose increased in leaves of inoculated and uninoculated melon plants following acetochlor treatment. The increase in sugar levels in stems and roots was less pronounced. Light intensity affected sugar content and disease incidence. The percentage of diseased plants was significantly higher in untreated plants grown under 165E m^–2 sec^–1 compared to plants grown under 300E m^–2 sec^–1. Lowering light intensity resulted in reduction of levels of total sugars on the third and sixth day after inoculation. Acetochlor had little or no effect on growth rate or sporulation of the pathogen in culture. The colonization rate of diseased plant stems by the pathogen was similar in herbicide-treated and untreated plants, thus excluding the possibility that disease reduction by the herbicide is related to direct fungitoxicity.Contribution from the Agricultural Research Organization. No. 1560-E, 1995 series.