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Matos L.A.,University of Florida | Matos L.A.,Instituto Dominicano Of Investigaciones Agropecuarias Y Forestales | Hilf M.E.,U.S. Department of Agriculture | Chen J.,U.S. Department of Agriculture | Folimonova S.Y.,University of Florida
PLoS ONE | Year: 2013

Citrus greening (Huanglongbing, HLB) is one of the most destructive diseases of citrus worldwide. In South Asia HLB has been known for more than a century, while in Americas the disease was found relatively recently. HLB is associated with three species of 'Candidatus Liberibacter' among which 'Ca. Liberibacter asiaticus' (CLas) has most wide distribution. Recently, a number of studies identified different regions in the CLas genome with variable number of tandem repeats (VNTRs) that could be used for examination of CLas diversity. One of the objectives of the work presented here was to further validate the VNTR analysis-based approach by assessing the stability of these repeats upon multiplication of the pathogen in a host over an extended period of time and upon its passaging from a host to a host using CLas populations from Florida. Our results showed that the numbers of tandem repeats in the four loci tested display very distinguishable "signature profiles" for the two Florida-type CLas haplotype groups. Remarkably, the profiles do not change upon passage of the pathogen in citrus and psyllid hosts as well as after its presence within a host over a period of five years, suggesting that VNTR analysis-based approach represents a valid methodology for examination of the pathogen populations in various geographical regions. Interestingly, an extended analysis of CLas populations in different locations throughout Florida and in several countries in the Caribbean and Central America regions and in Mexico where the pathogen has been introduced recently demonstrated the dispersion of the same haplotypes of CLas. On the other hand, these CLas populations appeared to differ significantly from those obtained from locations where the disease has been present for a much longer time.

Nunez Ramos P.A.,Instituto Dominicano Of Investigaciones Agropecuarias Y Forestales | Sandoval Sandoval Y.,Especialista Ambiental independiente | Demanet R.,University of the Frontier
Ciencia del Suelo | Year: 2012

In pasture systems, management practices can affect pasture productivity differently due to their impact on soil microorganisms and nutrient cycling. The objective of this study was to evaluate the relationship between soil microbial biomass (MB) nitrogen (MBN), carbon (MBC) and urease activity (UA) in a permanent pasture in southern Chile. Two grazing systems were evaluated between spring 2005 and winter 2006: heavy grazing (HG), light grazing (LG) and a control treatment (C). Treatments were arranged in a randomized block design with three replications. Concerning the average values of the variables measured at the beginning and at the end of grazing, there was an increase in the content of BC of 21.8 and 8.6% for HG and LG, while the control was only 1.9%. BN contents were also increased by 16 and 19% for HG and LG, respectively, compared with the control (4%). The urease activity increased by 13 and 27% for HG and LG, respectively, compared with the control (5%). Grazing produced a higher flow of organic residues in the soil, stimulating microbial biomass and therefore increasing the UA and the BC and BN content. Thus, soil biological fertility and nutrient availability s increase under grazing systems.

Marte W.E.,Kyushu University | Marte W.E.,Instituto Dominicano Of Investigaciones Agropecuarias Y Forestales | Nanseki T.,Kyushu University | Takeuchi S.,Kyushu University
Journal of the Faculty of Agriculture, Kyushu University | Year: 2012

Rice is the main staple food crop in the Dominican Republic (DR). Although 45% of the rice farmers hold less than 4 ha, rice plays a significant role in food security and provision of employments. However, the process of trade liberalisation given by the Dominican Republic, Central America and the United States of America free trade agreement (DR-CAFTA) questions the viability of Dominican rice farming. Besides, the US rice farmers have larger farms, better access to technology and credit and higher yield compared to those in the DR. This calls for sound management strategies and policies to overcome some of the forthcoming effects of the DR-CAFTA on the Dominican rice farming. Thus, this study identifies and evaluates the Dominican rice farmers' agronomic and economic strategies on this FTA. The analysis used cross-sectional survey data collected from 93 rice farmers in Monte Cristi province. The results indicate that to reduce rice-production costs, self-financing, and expanding farmland size were the main agronomic strategies. While land levelling, buying certified seeds, and increasing yield were the main economic strategies. The evaluation of these strategies revealed that fertilizer, machinery service costs and paid interest on operating capital were key components to reduce rice-production costs. Further, results indicate increasing returns to scale for rice farmers. To undertake such strategies, the transformation of farmers' association to a cooperative is a promising strategy from farmers' side.

Beaver J.S.,University of Puerto Rico at Mayaguez | Rosas J.C.,Escuela Agricola Panamericana | Porch T.G.,Tropical Agriculture Research Station | Pastor-Corrales M.A.,U.S. Department of Agriculture | And 2 more authors.
Journal of Plant Registrations | Year: 2015

PR0806-80 (Reg. No. GP-296, PI 672994) and PR0806-81 (Reg. No. GP-297, PI 672995) are multiple disease-resistant dry bean (Phaseolus vulgaris L.) germplasm lines adapted to the humid tropics, developed and released cooperatively by the University of Puerto Rico Agricultural Experiment Station, the USDA–ARS, the Escuela Agrícola Panamericana (Zamorano), the Instituto Dominicano de Investigaciones Agropecuarias y Forestales, and the Ministry of Agriculture, Natural Resources and Rural Development of the Republic of Haiti. The breeding objective was to develop white dry bean lines that combine resistance to Bean common mosaic virus (BCMV), Bean common mosaic necrotic virus (BCMNV), Bean golden yellow mosaic virus (BGYMV), and rust, caused by Uromyces appendiculatus (Pers.) Unger. PR0806-80 and PR0806-81 were developed by pedigree selection to the F6 generation on the basis of superior agronomic traits, disease resistance, and commercial seed type. Advanced generation lines were screened for rust resistance in Honduras and were resistant to BGYMV, BCMNV, and rust in trials planted in Puerto Rico, the Dominican Republic, and Haiti. Results from greenhouse inoculations suggest that the lines combine the Ur-4, Ur-5, and Ur-11 alleles of rust resistance genes. Greenhouse inoculations were used to detect the presence of the bc-3 gene for resistance to BCMV and BCMNV, and marker-assisted selection was used to identify the presence of the bgm-1 allele and the SW12 quantitative trait locus for BGYMV resistance. The presence of SA14 and SI19 sequence characterized amplified region (SCAR) markers provided further evidence that these lines have the rust resistance genes Ur-4 and Ur-5. The lines were evaluated in field trials in the Dominican Republic, Haiti, and Puerto Rico. Mean seed yields of PR0806-80 (2048 kg ha-1) and PR0806-81 (2091 kg ha-1) were comparable to the check cultivar ‘Verano’ (2251 kg ha-1). These multiple disease-resistant white lines should be useful as parents to enhance the virus and rust resistance of white, small red, and black beans. © Crop Science Society of America. All rights reserved.

Torres S.V.,University of Puerto Rico at Mayaguez | Vargas M.M.,University of Puerto Rico at Mayaguez | Godoy-Lutz G.,Instituto Dominicano Of Investigaciones Agropecuarias Y Forestales | Porch T.G.,Tropical Agriculture Research Station | Beaver J.S.,University of Puerto Rico at San Juan
Plant Disease | Year: 2016

In common bean (Phaseolus vulgaris L.), Rhizoctonia solani Kühn is an important pathogen causing web blight (WB) in the tropics, and it is also a soilborne pathogen causing root rot (RR) worldwide. This pathogen is a species complex classified into 14 anastomosis groups (AG). AG 1-IA, AG 1-IB, AG 1-IE, AG 1-IF, AG 2-2, and AG 4 have been reported to cause WB of the aboveground structures of the plant, while AG 4 and AG 2-2 have been associated with RR. There is limited information, however, concerning the ability of particular isolates of specific AG to cause both diseases in common bean. Nine R. solani isolates, including three AG 1 and three AG 4 WB isolates and three AG 4 RR isolates collected from both leaves and roots, respectively, of common bean in Puerto Rico, were used to evaluate the response of 12 common bean genotypes to WB inoculated using a detached-leaf method and to RR inoculated using a solution suspension of R. solani mycelia in the greenhouse. All R. solani isolates were able to induce both RR and WB symptoms. RR readings were generally more severe than the WB readings. The RR isolate RR1 (AG 4) produced the most severe RR scores. A few bean lines had mean RR scores ≤4.4 for specific R. solani isolates on a scale of 1 to 9, with 1 representing resistant and 9 highly susceptible. However, all of the bean lines had mean RR scores ≥5.0 when inoculated with the isolates RR1, RR2, and RR3, which were determined to be AG 4 in this study. Significant line–isolate interactions were observed for the WB and RR inoculations for the three planting dates, suggesting a differential response of the common bean lines to the pathogen. This genotypic interaction may require bean breeders and pathologists to monitor the virulence patterns of R. solani in specific growing environments, while the compatibility of specific R. solani isolates to both aerial and root tissue needs to be considered for disease control strategies. © 2016 The American Phytopathological Society.

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