• Authors:
    • Gamba, F.
    • Cruz, G.
    • Scattolini, A.
    • Prieto, V.
  • Source: Agrociencia (Montevideo)
  • Volume: 16
  • Issue: 1
  • Year: 2012
  • Summary: Citrus canker, caused by Xanthomonas citri pv citri, affects all Citrus production regions worldwide with tropical or subtropical climate. This work studies the relationship between rain, temperature, susceptibility of lemon leaves, and the appearance of symptoms of canker The evolution of citrus canker symptoms during five months of vegetative growth in a lemon Lisbon type orchard with disease background were analyzed. The data used were generated in the assessment of three growth flushes in plots with six (Treatment I) and ten (Treatment II) copper oxide sprays respectively. Daily rainfall and temperature were registered every 20 minutes. The parameters of the logistic curve of disease progress were calculated. Shoot age at disease outbreak and maximum disease value were determined. Rain was assumed to initiate an infection event from which a model of hour-degree accumulation was applied to predict the date for new symptoms appearance. Under the conditions of local infection, only the rains over 10 mm produced symptoms at the predicted date according to the model used. It was demonstrated that tissue susceptibility became a secondary factor once the environmental conditions became favourable to dissemination and symptoms expression. The method used demonstrated to be an useful tool to predict the risk of new symptoms appearance and to plan monitoring of the disease.
  • Authors:
    • Wang, N. Y.
    • Mondal, S. N.
    • Sutton, B.
    • Jeyaprakash, A.
    • Palm, M. E.
    • Peres, N. A.
    • Dewdney, M. M.
    • Schubert, T. S.
    • Rascoe, J.
    • Picton, D. D.
  • Source: Plant Disease
  • Volume: 96
  • Issue: 8
  • Year: 2012
  • Summary: In March 2010, citrus black spot symptoms were observed on sweet orange trees in a grove near Immokalee, Florida, USA. Symptoms observed on fruit included hard spot, cracked spot and early virulent spot. Hard spot lesions were up to 5 mm, depressed with a chocolate margin and a necrotic, tan centre, often with black pycnidia (140-200 m) present. Cracked spot lesions were large (15 mm), dark brown, with diffuse margins and raised cracks. In some cases, hard spots formed in the centre of lesions. Early virulent spot lesions were small (up to 7 mm long), bright red, irregular, indented and often with many pycnidia. In addition, small (2-3 mm), elliptical, reddish brown leaf lesions with depressed tan centres were observed on some trees with symptomatic fruit. Chlorotic halos appeared as they aged. Most leaves had single lesions, occasionally up to 4 per leaf. The causal organism was identified as Guignardia citricarpa based on cultural, morphological and genetic (ITS) analyses. This is thought to be the first report of black spot in North America.
  • Authors:
    • Samar, S. M.
    • Shahabian, M.
    • Talaie, A.
    • Emdad, M. R.
  • Source: Archives of Agronomy and Soil Science
  • Volume: 58
  • Issue: 3
  • Year: 2012
  • Summary: This work examines the effects of two deficit irrigation strategies, conventional deficit irrigation (DI) and partial root-zone drying (PRD), on mature navel orange trees. The study carried out during two consecutive years (2008 and 2009) in a semi-arid climate on a silty-clay-loam soil in the north of Iran. Both DI and PRD trees were irrigated at two levels, 75 and 50% (DI75, PRD75, DI50 and PRD50) of the full irrigation (FI). In DI, irrigation water was applied to both sides of the tree rows, similar to FI. In PRD, irrigation water was applied alternately to only one side, at each irrigation event. Results showed that DI treatments reduced fruit yield by ~30% compared with FI, but PRD treatments caused no reduction in fruit yield. No negative impact was detected in fruit quality after applying DI and PRD treatments. Shoot growth decreased in all DI and PRD treatments in both years. In DI, stomatal resistance was higher (50%) than in FI, but it was not significantly affected in PRD. The irrigation water use efficiency of PRD trees increased to nearly twice that of FI. According to these two years' results, we recommend PRD as an acceptable deficit irrigation strategy in the region.
  • Authors:
    • Foratto, L. C.
    • Salomão, L. C.
    • Quaggio, J. A.
    • Boas, R. L. V.
    • Souza, T. R. de
  • Source: Pesquisa Agropecuária Brasileira
  • Volume: 47
  • Issue: 6
  • Year: 2012
  • Summary: The objective of this work was to evaluate nutrient dynamics in soil solution after fertigated application of nitrogen, phosphorus, and potassium to orange trees. The experiment was carried out from September 2007 to October 2009, in 'Valencia' and 'Hamlin' orange orchards grafted onto citrumelo 'Swingle' rootstock. Five doses of N, P 2O 5 and K 2O (0, 25, 50, 100 and 200% of the recommended dose) were evaluated. Soil solution was extracted from 30 and 60 cm soil depths using extractors with porous cups. Eleven evaluations were done during the experimental period, with extractions beginning 12 hours after fertigation. Increasing nutrient doses decreased pH (pH-3.5, at the highest dose), and increased electrical conductivity (CE-1.5 dS m -1, at the highest dose) and the amounts of NH 4, NO 3, P, K, Mn, and Zn in the soil solution, in both sampled depths. In the months with heavier rainfall, there was nutrient potential losses by leaching, since higher concentrations of NO 3, K, and B were observed at the 60 cm soil depth. Soil solution analysis, obtained by extractors with porous ceramic cups, can be considered an auxiliary tool for monitoring and assessing nutrient availability to plants.
  • Authors:
    • Albrigo, L. G.
    • Syvertsen, J. P.
    • Melgar, J. C.
  • Source: Acta Horticulturae
  • Issue: 928
  • Year: 2012
  • Summary: The loss of leaves, branches and flowers along with bark scuffing and root exposure that can occur during mechanical harvesting (MH) has not reduced long term yields of healthy trees. Nonetheless, such visible injuries have limited the widespread adoption of mechanical harvesting in Florida's citrus industry. There was little measurable physiological stress from MH in healthy, well-managed trees as leaf water relations, CO 2 assimilation and final yield were not affected. The abscission compound CMNP, can effectively reduce fruit detachment force and result in fewer visible injuries. Late season MH of 'Valencia' sweet orange remains a major problem when young fruitlets for next crop become large enough to be harvested prematurely. We determined if winter drought stress from January to March could delay flowering and fruitlet development so they would be too small to be susceptible mechanical harvesting. Drought stress during winter delayed flowering 2-3 weeks, reduced flowering and vegetative growth but did not reduce new fruit set relative to irrigated trees. Fruit growth after the delayed bloom caught up with the irrigated treatments so final yield and fruit quality were not affected. During mechanical harvesting, previously drought stressed trees had a higher fruit removal efficiency and less loss of the smaller young fruit than continuously irrigated trees for up to three months. Thus, winter time drought stress can be an effective practice to delay flowering and to avoid young fruit loss during late season mechanical harvesting of 'Valencia' oranges. Fruitlet oleocellosis in late season mechanical harvested trees did not increase fruitlet drop nor alter internal fruit quality.
  • Authors:
    • Ghosh, P. D.
    • Tarafdar, A.
    • Biswas, K. K.
  • Source: Indian Phytopathology
  • Volume: 65
  • Issue: 2
  • Year: 2012
  • Summary: In planta accumulation of Citrus tristeza virus (CTV) in different plant tissues of infected citrus host was determined using enzyme linked immuno-sorbent assay (ELISA) and reverse transcriptase polymerase chain reaction (RT-PCR). CTV was not found to be evenly distributed in all the plant parts. The tender bark of 6 months to 1 year old, petiole and mid rib of young leaves, and apical bud showed high amount of CTV. The result was confirmed by RT-PCR assay showing amplicons of coat protein (CP) gene (672 nt) of CTV genome. Infected acid (Kagzi) lime ( C. aurantifolia) and sweet orange (Mosambi) ( C. sinensis) trees harbored accumulated higher amount of virus than Darjeeling mandarin ( C. reticulata). However, the severity of symptom caused by CTV in acid lime could not be correlated to virus titer. CTV was found to move faster in acid lime and sweet orange than mandarin tree. It was observed that virus persisted up to 180 days in crude sap prepared with 0.05 M phosphate buffer, pH 7.0 stored at 4°C, but only up to 2-4 days in same crude sap kept at 25-32°C.
  • Authors:
    • Wise, J. C.
    • van Timmeren, S.
    • Isaacs, R.
  • Source: Pest Management Science
  • Volume: 68
  • Issue: 4
  • Year: 2012
  • Summary: BACKGROUND: Soil application of systemic neonicotinoid insecticides can provide opportunities for long-term control of insect pests in vineyards, with minimal risk of pesticide drift or worker exposure. This study compared the effectiveness of neonicotinoid insecticides applied via irrigation injection on key early-season and mid-season insect pests of vineyards in the eastern United States. RESULTS: On vines trained to grow on drip irrigation, early-season application of imidacloprid, clothianidin, thiamethoxam and dinotefuran provided high levels of control against the potato leafhopper, Empoasca fabae. Protection of vines against Japanese beetle, Popillia japonica, and grape berry moth, Paralobesia viteana, was also observed after mid-season applications. Efficacy was poor in commercial vineyards when treatments were applied to the soil before irrigation or rain, indicating that vines must be grown with an irrigation system for efficient uptake of the insecticide. CONCLUSIONS: In drip-irrigated vineyards, soil-applied neonicotinoids can be used to provide long residual control of either early-season or mid- to late-season foliage pests of vineyards. This approach can reduce the dependence on foliar-applied insecticides, with associated benefits for non-target exposure to workers and natural enemies.
  • Authors:
    • Nogues, I.
    • Michelozzi, M.
    • Lauteri, M.
    • Mantia, T. la
    • Velikova, V.
    • Loreto, F.
  • Source: Functional Plant Biology
  • Volume: 39
  • Issue: 3
  • Year: 2012
  • Summary: We investigated the consequences of recurrent winter flooding with saline water on a lemon ( Citrus * limon (L.) Burm.f.) orchard, focussing on photosynthesis limitations and emission of secondary metabolites (isoprenoids) from leaves and fruits. Measurements were carried out immediately after flooding (December), at the end of winter (April) and after a dry summer in which plants were irrigated with optimal quality water (September). Photosynthesis was negatively affected by flooding. The effect was still visible at the end of winter, whereas the photosynthetic rate was fully recovered after summer, indicating an unexpected resilience capacity of flooded plants. Photosynthesis inhibition by flooding was not due to diffusive limitations to CO 2 entry into the leaf, as indicated by measurements of stomatal conductance and intercellular CO 2 concentration. Biochemical and photochemical limitations seemed to play a more important role in limiting the photosynthesis of flooded plants. In young leaves, characterised by high rates of mitochondrial respiration, respiratory rates were enhanced by flooding. Flooding transiently caused large and rapid emission of several volatile isoprenoids. Emission of limonene, the most abundant compound, was stimulated in the leaves, and in young and mature fruits. Flooding changed the blend of emitted isoprenoids, but only few changes were observed in the stored isoprenoids pool.
  • Authors:
    • Tolentino, J. B.
    • Coelho, R. D.
    • Vellame, L. M.
  • Source: Revista Brasileira de Fruticultura
  • Volume: 34
  • Issue: 1
  • Year: 2012
  • Summary: The total citrus area irrigated in Brazil has increased over the decades. The main cause of this increasing is due to the use of rootstocks tolerant to Citrus Sudden Death however they are less tolerant to drought than Rangpur lime. This research aims to study the influence of rootstock and soil type on transpiration of young plants of Valencia orange. The experiment was conducted in a greenhouse at the Department of Biosystems Engineering, ESALQ/USR Orange seedlings were planted in boxes of 500 L. It was determined simultaneously sweating of 20 plants through thermal dissipation probes (sap flow). It was monitored solar radiation, relative humidity and air temperature sensors were installed to 2 m tall at the center of the greenhouse. The reference evapotranspiration (ETo PM) was calculated by the standard method suggested by FAO. According to these results it is concluded that plant transpiration of Valencia oranges are influenced not only by the type of rootstock but also by leaf area growth and phenological stage, and its relationship with ETo pM is not linear in the whole range of evaporative demand of the atmosphere.
  • Authors:
    • García-Jiménez, J.
    • Botella-Rocamora, P.
    • Vicent, A.
    • Bascón, J.
    • de la Roca, E.
    • López-Quílez, A.
  • Source: European Journal of Plant Pathology
  • Volume: 133
  • Issue: 3
  • Year: 2012
  • Summary: Phytophthora branch canker, caused by Phytophthora citrophthora, has been an increasing problem in clementine ( Citrus reticulata) production in Spain during last years. The disease was particularly severe in the new citrus-growing areas of the southwestern coastal areas in Huelva Province. Recent studies revealed that disease emergence was not related to either genetic drift or host specificity changes in P. citrophthora population. Therefore, the possible association of agronomic factors with the disease was investigated. A total of 110 orchards were selected arbitrarily from the main citrus-growing areas in Huelva Province. The presence of branch cankers together with agronomic factors including soils, cultivars, rootstocks, irrigation, pruning, techniques to improve fruit production, fungicide treatments, presence of brown rot of fruit and frost damage were recorded. Logistic regression analysis was used to detect correlations between the agronomic factors studied and disease prevalence. Phytophthora branch canker was significantly associated with mature clementine orchards. Sweet orange and hybrid cultivars as well as young clementine orchards were less affected by the disease. Although disease was less frequent in Salorthid soils, alternative high resolution procedures are required to draw conclusions about the effect of soil properties on disease prevalence. As in other Phytophthora-induced diseases, soil flooding during the rainy season was correlated positively with the prevalence of branch cankers. Improving fruit production by branch scoring showed a strong positive correlation with Phytophthora branch canker. This is the first time that girdling has been associated with Phytophthora disease epidemics on a fruit tree crop, but further research is needed to determine the cause of this relationship. Cultural practices including pruning, regulated deficit irrigation, additional phosphonate sprays, and abiotic and disease factors such as frost damage and presence of brown rot of fruit were not significantly correlated with disease prevalence.