Tropical Agriculture Research Station Research Articles

First Report of Diaporthe tulliensis Causing Necrotic Spots and Leaf Blight on Rambutan in Puerto Rico.

Rambutan (Nepehelium lappaceum) is a tropical exotic fruit belonging to the Sapindaceae family. Several pathogens have been identified in rambutan causing different diseases on fruits, inflorescences, and branches (Serrato-Diaz et al., 2015, 2017, 2020) but few on leaves. From 2015 to 2021, a disease survey was conducted in one greenhouse in Mayaguez, Puerto Rico and experimental rambutan field orchards of the USDA-ARS Tropical Agriculture Research Station located at Isabela, Corozal, Santa Isabel, and Adjuntas, Puerto Rico (Latitude: 18°12'28"N, 18°34'10'' N, 18°00'47''N, 18°16'35''N and Longitude: 67°08'17"W, 66°31'74'' W, 66°38'98''W, 66°72'32''W, respectively). Varieties Benjai, Gula Batu, Jitlee, R-134, R-156Y, R-162, R-167 and Rongren were sampled. Necrotic spots and leaf blight were commonly observed with a disease incidence of 80%. Diseased leaves showed necrosis starting from the apex and spreading through the lamina. Ten diseased leaves were collected from each location and sections of symptomatic tissue (5mm2) were disinfected and plated on potato dextrose agar (PDA) and oatmeal agar (OA). Two representative isolates of Diaporthe tulliensis, A3 and A4, were obtained, purified, and identified morphologically and by PCR amplifications of three nuclear genes of the Internal Transcribed Spacer ITS1-5.8S-ITS2 region of the ribosomal DNA primers ITS5/ITS4, portions of the β tubulin (BT) primers Bt2a/Bt2b and the translation elongation factor 1-α (TEF1-α) primers EF1728F/EF1986R. On PDA and OA colonies of isolates A3 and A4 were initially white and flat with sparse mycelia that turned yellowish-white to grey with age. Pycnidia were black with cream to pale yellow conidial droplets that exuded from ostioles. Hyaline, unicellular alpha conidia were oval to cylindrical, rounded at apex and obconically truncate at base. Alpha conidia (n = 50) for isolates of D. tulliensis were 4.9 to 5.9 μm long by 2.2 - 2.5 μm wide. DNA sequences of the ITS region and partial sequences of TEF1-α and BT genes were compared by BLASTN with Diaporthe sequences deposited in GenBank. ITS, BT and EF1-α sequences of isolates A3 and A4 (OP219651 and OP161553 for ITS region; OP222137 and OP168832 for TEF1-α; OP222136 and OP168831 for BT, respectively) were grouped to the holotype BRIP 62248a (Bootstrap BS=100) of Diaporthe tulliensis R.G. Shivas, Vawdrey & Y.P. Tan. Pathogenicity tests were conducted on six of six-months-old rambutan seedlings of R-167 variety. Three unwounded healthy non-detached leaves were inoculated per isolate with one 5mm mycelial disk from pure cultures grown on PDA. Rambutan seedlings were kept in a humid chamber using plastic bags for 8 days under greenhouse conditions. Two of six seedlings were used as controls and inoculated with PDA disks only. Eight and 14 days after inoculation (DAI), D. tulliensis isolates caused necrotic spots and leaf blight, on leaves. Diseased leaves turned from light to dark brown starting from the apex and spreading through the lamina with necrotic lesions ranging in size from 5 - 10 mm. Untreated controls showed no symptoms, and no fungi were re-isolated from tissue. D. tulliensis was re-isolated from diseased leaves, fulfilling Koch's postulates. D. tulliensis has been reported in Taiwan causing Diaporthe leaf spot in Boston Ivy (Huang, C. et al., 2021) and Bodhi trees (Li, K.Y. et al., 2022), as well as Jasmin stem canker (Ching Hsu, C. et al., 2022). It has been reported as causing leaf blight of coffee (Gong, J. L., et al., 2019), kiwifruit stem canker in China (Bai et al., 2017), and most recently causing cacao pod rot in Puerto Rico (Serrato-Diaz, L.M. et al., 2022). To our knowledge, this is the first report of Diaporthe tulliensis causing necrotic spots and leaf light on rambutan in Puerto Rico and often associated with a potassium deficiency in many parts of the world. It will be important to establish an adequate and effective control management of this disease in rambutan producing countries worldwide. References and doi hyperlinks: 1. Huang, C. et al. Plant Dis. 105:2718, 2021 https://doi.org/10.1094/PDIS-12-20-2652-PDN 2. Li, K.Y. et al. Plant Dis. 0:ja, 2022 https://doi.org/10.1094/PDIS-01-22-0211-PDN 3. Ching Hsu, C. et al. Plant Dis. 0:ja, 2022 https://doi.org/10.1094/PDIS-09-21-1908-PDN 4. Gong, J. L., et al. Plant Dis. 104:570, 2019 https://doi.org/10.1094/PDIS-09-19-1833-PDN 5. Bai et al. Plant Dis. 101:508, 2017 https://doi.org/10.1094/PDIS-10-16-1445-PDN 6. Serrato-Diaz L.M., et al. 2015. Plant Dis. 99: 1187. https://doi.org/10.1094/PDIS-09-14-0923-PDN 7. Serrato-Diaz L.M. et al. 2017. Plant Dis. 101: 1043. https://doi.org/10.1094/PDIS-11-16-1557-PDN 8. Serrato-Diaz, L.M., et al. 2020. Plant Dis. 104: 105-115. https://doi.org/10.1094/PDIS-02-19-0295-RE 9. Serrato-Diaz, L.M. et al. 2022 Plant Dis. 106: 2530. https://doi.org/10.1094/PDIS-12-21-2634-PDN.

Seed Yam Production Using High-Quality Minitubers Derived from Plants Established with Vine Cuttings

Yam (Dioscorea spp.) is a valuable food security crop in West Africa, where 92% of the world production occurs. The availability of quality seed tubers for increased productivity is a major challenge. In this study, minitubers weighing 1, 3, and 5 g produced from virus-free single-node vine cuttings of two improved yam varieties (Asiedu and Kpamyo) growing in an aeroponics system were assessed for suitability in seed production at a population of 100,000 plants ha−1. A 3 × 2 factorial experiment with randomized complete block design and three replications was set up during the cropping seasons of 2017 to 2019 at the International Institute of Tropical Agriculture Research Station in Kubwa, Abuja, Nigeria. Results showed field establishments of 87%–97.8%. Yields differed with minituber size, variety, and cropping season; the highest was 31.2 t ha−1 in 2019 and the lowest, 10 t ha−1 in 2018 from 5 and 1 g Kpamyo minitubers, respectively. The estimated number of tubers produced per hectare by 1, 3, and 5 g minitubers was 101,296, 112,592, and 130,555, with mean weights per stand of 159.2, 187.3, and 249.4 g, respectively. We recommend using less than 6 g minitubers for seed yam production due to their high multiplication rates.

Host Response to Black Leaf Streak and Agronomic Performance of Banana Genotypes in Puerto Rico

Bananas are one of the most important fruits, serving as a cash crop and staple food in many regions of the world. In Puerto Rico, bananas are an important agricultural industry, supplying all the fruit needed for local demand. Diseases significantly limit production, and the evaluation and adoption of improved genetic resistance in bananas might provide an avenue for long-term sustainable production. To this end, nine enhanced genotypes from international selection and breeding programs were introduced and evaluated for their response to black leaf streak (BLS) (Pseudocercospora fijiensis Morelet) and for their agronomic performance. Bananas were evaluated as part of a collaborative effort between the U.S. Department of Agriculture Agricultural Research Service (USDA-ARS) Tropical Agriculture Research Station (TARS) and Bioversity International’s International Musa Testing Program (IMTP). Improved genotypes were compared with disease-resistant and disease-susceptible reference genotypes across two cropping cycles. Field plants were grown following commercial production practices with no BLS management. Significant differences in disease reactions were observed during both cropping cycles for test and reference genotypes. Under high disease pressure, ‘FHIA-21’, ‘FHLORBAN 916’, and ‘FHLORBAN 920’ test genotypes showed higher numbers of functional leaves and lower disease severity at harvest in both cycles. Short cycling times were also observed for the two FHLORBAN genotypes. Larger bunches with a high number of fruits were produced by the ‘IBP 12’, ‘IBP 5-B’, and ‘IBP 5-61’ selections. Several of the GCTCV test genotypes were extremely susceptible to BLS, did not perform as expected, and appeared to be off-types. Several of the test genotypes performed well, although currently none possessed all needed traits for a commercial banana substitute. Regardless, several test genotypes have agronomic potential because they have been selected for disease resistance to other important pathogens (e.g., fusarium wilt) and therefore have become part of the permanent TARS collection. Future efforts will continue to focus on the IMTP collaboration and introduction of promising banana genotypes for evaluations.

Comparison of Polyphenol Concentration and Composition between Genetically Diverse Cacao (Theobroma cacao L.) Accessions Selected for High Yield

There is abundant evidence that consumption of cacao and dark chocolate promotes human health and that the main cacao components contributing positive health effects are polyphenols. The polyphenols in cacao bean constitute 12–18% dry weight of the whole bean and are predominantly catechins (37% w/w), procyanidins (58% w/w) and anthocyanins (4% w/w). Variation in cacao polyphenol composition and concentration can result from differences in genetic backgroud, agro‐environment and cultural practices. It is therefore important to consider several factors when selecting cacao seed (beans) for research investigating the mechanisms underlying its health benefits. In this study, dried unfermented seeds of five different cacao clones (TARS‐9, TARS‐14, TARS‐27, TARS‐30, TARS‐31) were obtained from USDA‐ARS Tropical Agriculture Research Station (TARS) located in Mayaguez, Puerto Rico. These clones were developed through controlled‐pollinated hybridization for improved agronomic performance, specifically high yield. Prior sensory evaluation of 65% chocolate made from these clones revealed that each conferred distinct profiles in bitterness. We thus hypothesized that differences in polyphenol profiles would exist between these clones. To test this hypothesis, total polyphenols, total flavan‐3ols, polyphenol extraction yield, and qualitative flavanol profile were compared between the five cacao clones. TARS‐27 had the lowest total polyphenol concentration (36 ± 1.2 mg gallic acid equivalents/g cacao bean) (mean ± STDEV), whereas TARS‐14 showed highest concentration (66 ± 4.7 mg gallic acid equivalents/g cacao bean). For total flavan‐3‐ols, a similar trend was observed; TARS‐27 showed the lowest concentration (42.3 ± 1.1 mg procyanidin B2 equivalents/g cacao bean) with TARS‐9 having the highest concentration (76.7 ± 4 mg procyanidin B2 equivalents/g cacao bean). Polyphenol extraction yield (cacao extract weight/cocoa bean weight) differed among clones ranging from 0.1–0.16. Qualitative flavanol profiles obtained using normal‐phase high‐performance liquid chromatography (HPLC) indicated that mean degree of polymerization (mDP) of polyphenols is likely similar between these clones. Further research is required to quantitatively determine mDP, and to identify and quantify individual polyphenols. In conclusion, these insights into the variability of polyphenol composition among genetically diverse cacao will help to inform targeted selection of cacao clones for future studies investigating the impact of cacao consumption on human health.Support or Funding InformationFunding was provided, in part, by the Virginia Agricultural Experiment Station and the Hatch Program of the National Institute of Food and Agriculture (NIFA), U.S. Department of Agriculture

Selección recurrente recíproca en maíz: tolerancia al ataque del gusano de la mazorca y el cogollero (Lepidoptera: Noctuidae).

The progressive selection of yield, agronomic characteristics and quantification of damages caused by Spodoptera frugiperda (J.E. Smith) and Helicoverpa zea (Boddie), were evaluated after four selection cycles on maize populations (Zea mays L., varieties Ohio S9, Ohio S10, Mayorbela and Diente de caballo, under chemical control and natural infestation conditions. The experiments were carried out at an experimental site in a tropical agriculture research station (TARS), a USDA station located in Isabela, Puerto Rico. The experimental design consisted of random entire blocks with five repetitions, and treatments were asigned according to a factorial arrangement with parcels divided at a density of 44.444 plants/ha. Significant differences were found among populations and selection cycles for yield, plant and cob height, and percentage of insect-related losses*. The highest yield was obtained from the Ohio S 10 population with 4.824 kg/ha, and 169 kg/ha - a profit of 1.2% per selection cycle. The latest selection cycles showed a greater yield and better agronomic characteristics than the initial selection cycle of each population under improvement. Losses in yield caused by S. frugiperda and H. zea oscillated between 3-21 % and 17-28%, respectively. Ohio S9 showed the greatest los s in yield caused by these insects.

Musa spp. Germplasm Management: Microsatellite Fingerprinting of USDA–ARS National Plant Germplasm System Collection

ABSTRACTThe USDA–ARS Tropical Agriculture Research Station (TARS) is responsible for conserving germplasm of a number of important agricultural crop species. Its banana (Musa spp.) collection is comprised of diploid, triploid, and tetraploid accessions of cultivated, ornamental, wild, and synthetic hybrid accessions. To estimate genetic diversity, identify gaps, determine integrity, and generate clonal reference multilocus DNA profiles for a total of 175 accessions in the collection, a set of 22 microsatellite markers developed in the framework of the Generation Challenge Program (www.generationcp.org/, accessed 30 June 2014) by Centre de Coopération Internationale en Recherche Agronomique pour le Développement and recommended by the Global Musa Genomics Consortium were screened with an additional 15 reference DNA samples. Twenty‐one of the 22 microsatellite markers amplified well and generated a total of 302 alleles with an average number of 14.4 alleles per locus. In general, profiles were reproducible and consistent for the 21 loci when clonal field and tissue culture plants were compared with reference samples. The average number of alleles and gene diversity estimates demonstrated substantial genetic diversity in the collection. Principal coordinate and cluster analyses grouped accessions in the collection according to their ploidy level and genomic compositions. Markers that were used in the study distinguished accessions to the subgroup level and identified mislabeled accessions, notably in the tissue culture collection where phenotypic differences are difficult to observe. The accessions and fingerprint profiles for the TARS collection are available through the USDA National Plant Germplasm System, Germplasm Resource Information Network (GRIN‐Global) database www.ars‐grin.gov/ (accessed 30 June 2014).

First Report of Gliocephalotrichum bulbilium and G. simplex Causing Fruit Rot of Rambutan in Puerto Rico.

Post-harvest disease losses of rambutan (Nephelium lappaceum L.) have been reported worldwide and several pathogens have been associated with fruit rot (3,4). In 2011, fruit rot of rambutan was observed on 11-year-old trees at the USDA-ARS Tropical Agriculture Research Station in Mayaguez, Puerto Rico. Infected fruit sections (1 mm2) were surface-sterilized, rinsed with sterile deionized-distilled water, and transferred to acidified potato dextrose agar (APDA). Gliocephalotrichum bulbilium J.J. Ellis & Hesseltine (Gb) and G. simplex (J.A. Meyer) B. Wiley & E. Simmons (Gs) were identified using a taxonomic key (1). In corn meal agar (CMA), five isolates of Gb were light yellow-to-light brown. Conidiophores had sterile stipe extensions ranging from 120 to 150 μm long and were produced contiguous to the erect conidiogenous penicilli. Conidia were unicellular, smooth, oblong to elliptical, and 5.5 to 7.5 μm long by 2.0 to 2.5 μm wide. Bulbilloid aggregates were observed and averaged 70 μm long. In CMA, five isolates of Gs were light brown-to-chestnut brown. Conidiophores had sterile stipe extensions 130 to 180 μm long that were produced approximately 15 to 30 μm away from the conidiogenous penicilli. Conidia were unicellular, smooth, cylindrical to elliptical, and with slightly curved ends ranging from 6.5 to 8.5 μm long by 2.0 to 2.5 μm wide. Chlamydospores were unicellular, brown, smooth and thick-walled, averaging 35 μm long. Pathogenicity tests were conducted on five detached fruits per isolate. Five isolates of each Gliocephalotrichum spp. were inoculated on fruits using 5-mm mycelial disks of 8-day-old pure cultures grown in APDA. Untreated controls were inoculated with APDA disks only. Inoculated fruit was kept in a humid chamber for 8 days at 25°C under 12 hours of fluorescent light. Test was repeated once. Five days after inoculation (DAI), white mycelial growth for Gb and golden mycelial growth for Gs were observed on rambutan fruits. Eight DAI, fruit rot, and aril (flesh) rot symptoms were observed on fruits inoculated with isolates of Gb and Gs. Infected fruit changed in color from red to brown, and, on average, mycelia of Gb and Gs covered 50 and 60% of the fruit, respectively. Conidiophores were observed on spintems (hair-like appendages). Control fruit did not rot. Both species were reisolated from diseased plant tissue, thus fulfilling Koch's postulates. For molecular identification of these species of Gliocephalotrichum, the ITS1-5.8S-ITS2 region of the rDNA and a fragment of the β-tubulin gene were amplified by PCR and aligned with other Gb and Gs sequences in NCBI GenBank for comparison. The sequences submitted to GenBank included Gs Accession Nos. JQ688045 and JQ688046 and Gb Accession Nos. JQ688044 and JQ68847 for the ITS sequences. For the β-tubulin gene, Gs Accession Nos. JQ688049 and JQ688050 and Gb Accession Nos. JQ688048 and JQ688051. Both DNA regions had 99.9 to 100% sequence identity to other isolates of Gb and Gs reported in GenBank (1). Gliocephalotrichum spp. have been associated with rambutan fruit rot in Hawaii, Sri Lanka and Thailand (2,4). To our knowledge, this is the first report of G. bulbilium and G. simplex causing fruit rot of rambutan in Puerto Rico.

Anthracnose Resistance in Sorghum Germplasm from the Segou Region of Mali

Sorghum (Sorghum bicolor [L.] Moench) germplasm from Mali is an important source of anthracnose resistance, and 59 accessions from the Segou region were inoculated with Colletotrichum sublineolum and evaluated for anthracnose resistance to determine the prevalence of resistant accessions from this region. Disease evaluations were conducted at the Tropical Agriculture Research Station in Isabela, Puerto Rico, during the 2005 and 2009 growing seasons. Twenty-one accessions were rated as resistant across replications and growing seasons and showed reddening of inoculated leaves without acervuli development. These accessions represent new sources of anthracnose resistance for sorghum improvement. Fewer accessions were rated as resistant from the drier, northern Niono district as compared to the San and Segou districts that receive greater annual rainfall, suggesting an ecogeographic association. Additionally, susceptible accessions from the Niono district frequently showed higher mean disease severities than susceptible accessions from the San and Segou districts. Accessions classified as race guinea were more frequently rated as resistant compared to race durra accessions. Mean disease severities were also significantly lower for race guinea accessions. The majority of accessions in the collection were race guinea with most durra accessions collected from the Niono district. However, the frequency of resistant guinea accessions was similar across districts. These results indicate ecogeographic origin and race classification could be used to select accessions for anthracnose screening and to identify regions where resistance is more prevalent for the acquisition of additional anthracnose-resistant germplasm.

Evaluation of an agricultural experiment station as a case study site for the establishment of a multi-use urban forest

In an attempt to contribute towards a more sustainable development for the island of Puerto Rico, this project focuses on the documentation and evaluation of the Tropical Agriculture Research Station (TARS) near the urban center of the city of Mayagüez, Puerto Rico as a case study site to establish a multi-use and research-oriented urban forest. This location has been used since the beginning of the 20th century as a plant introduction and evaluation site, and as an in situ germplasm collection for numerous plant species. The evaluation methods consisted of identifying unique resources within the study area and stressors which could affect the latter. Unique resources were also identified on a Preliminary Resource Inventory Map (PRIM) using GPS technology. Obtained results and observations indicate that the study area represents a major potential asset for the positive economic, social, and educational development of the Mayagüez urban area due to its unique, historic, and complex ecosystems with significant environmental and cultural resources. Of the identified stressors, urban expansion was considered as the most threatening. Hypothetical recommendations providing a base for future development and management efforts in the study area were formulated with the objective of protecting and sustainably using its resources, while promoting environmental and socioeconomic benefits in the region.

Anthracnose field evaluation of sorghum germplasm from Botswana

Sorghum anthracnose is a disease of worldwide importance and host-plant resistance is the most practical method of disease management. In this study, 154 sorghum accessions from the Botswana collection maintained by the United States National Plant Germplasm System were inoculated with Colletotrichum sublineolum and evaluated for disease resistance at the Tropical Agriculture Research Station in Isabela, Puerto Rico during 2007 and 2008. A resistant response was observed for 69 accessions in 2007 and for 48 accessions in 2008 with no acervuli development observed on inoculated leaves. The low frequency of resistant germplasm is expected from a region of low annual rainfall. However, disease severity was low for the susceptible accessions with a mean severity of 11% for the 85 susceptible accessions observed in 2007 and 17% for the 106 susceptible accessions identified in 2008. The highest frequency of resistant accessions was observed for the Ngamiland district with 58% of the accessions rated as resistant, whereas the frequency of resistant accessions ranged from 22% to 36% for the other districts. The lowest mean disease severity was also observed for the susceptible accessions from the Ngamiland district with the highest mean disease severity observed for susceptible accessions from the Kgatleng district. The resistant accessions identified in this study would be useful for the development of disease resistant varieties and the results indicated an ecogeographic association with disease resistance.

Anthracnose disease response in the Burundi sorghum germplasm collection

The United States National Plant Germplasm System maintains 151 sorghum accessions from Burundi of which 148 accessions were evaluated for resistance to Colletotrichum sublineolum at the Tropical Agriculture Research Station in Isabela, Puerto Rico in replicated evaluations during the 2007 and 2008 growing seasons. For the 2007 experiment, 120 accessions showed a resistant response with 89 of these accessions rated as resistant in 2008. The resistant accessions showed reddening of inoculated leaves with no acervuli development, whereas accessions rated as susceptible showed acervuli development on inoculated leaves. Mean infection severity based on the percentage of infected leaf area for the susceptible accessions was 2% in 2007 and 2.5% for the 2008 experiment. Only four accessions showed an infection severity more than 10% and eight accessions showed a susceptible response across replications and growing seasons. Results of this study indicate that sorghum germplasm from Burundi is an important source of anthracnose resistance for sorghum improvement and that germplasm from regions of high annual rainfall is frequently associated with anthracnose resistance.

Anthracnose Resistance in Sorghum Breeding Lines Developed from Ethiopian Germplasm

Ninety-nine dwarf and photoperiod-insensitive breeding lines developed from Ethiopian sorghum germplasm were inoculated with Colletotrichum sublineolum and evaluated for anthracnose resistance at the Tropical Agriculture Research Station in Isabela, Puerto Rico, during the 2008 and 2009 growing seasons. A resistant response was observed for 57 lines in 2008 and for 47 lines in 2009 with 44 lines showing a resistant response across growing seasons. These lines showed reddening of inoculated leaves and no acervuli. Variation in resistance across growing seasons and replications within a growing season was observed for 19 lines rated as susceptible and these lines also showed low disease severity. Mean disease severity for the susceptible accessions was similar across growing seasons with a mean of 26% for 42 lines in 2008 and 23% for 52 lines in 2009. The resistant lines showed phenotypic diversity in response to anthracnose, suggesting potential genetic variation for resistance. Accepted for publication 31 October 2010. Published 23 November 2010.

First Report of Phytophthora palmivora, Causal Agent of Black Pod, on Cacao in Puerto Rico.

Black pod or Phytophthora pod rot is the most economically important and widespread disease of cacao, Theobroma cacao L. Total losses due to Phytophthora exceed $400 million worldwide (1), and several species are known to attack cacao with P. palmivora (E.J. Butler) E. J. Butler as the most common. All plant parts are infected, but pod infections are particularly damaging. Symptoms resembling those of black pod disease were observed at the National Plant Germplasm Collection System of cacao at the USDA-ARS Tropical Agriculture Research Station (TARS) in Mayaguez, Puerto Rico for a number of years. During May of 2005, to determine the etiology of the disease, small, surface disinfested sections of pod lesions were placed on water agar and incubated for 4 days. The formation of papillate, deciduous, ellipsoidal to ovoid sporangia produced on sympodial sporangiophores on fruits, fit the description of P. palmivora and the identification was confirmed on cultures on water agar (2). Chlamydospores were readily observed in diseased pods and observed in pure cultures on V8 agar (2). Eight, single hyphal tips were transferred to potato dextrose agar (PDA) (Sigma-Aldrich, St. Louis, MO) and maintained as stock cultures. For pathogenicity tests, healthy mature pods were surface disinfested and placed in a humidity chamber lined with moist paper towels. Eight isolates were tested on four fruits per isolate and the pathogenicity test was repeated once. Inoculum was prepared by growing each isolate on PDA for 5 days with irradiation at 24°C, adding approximately 3.0 ml of water to each plate, dislodging the sporangia with a glass rod, mixing the suspension, estimating spore numbers with a hemacytometer, and adjusting to 104 sporangia per ml. A small, sterile scalpel was used to make an approximately 20.0 mm cut on the fruit epidermis, and approximately 0.2 ml of inoculum was placed on the wound. Pods were evaluated daily for 2 weeks. For molecular analysis, each of the eight cultures were grown in 50% potato dextrose broth to produce mycelia for DNA extraction using the FastDNA kit (Q-Biogen1, Irvine, CA). The internal transcribed spacer (ITS) region of the ribosomal RNA gene cluster was amplified, purified, and sequenced for all eight isolates. The ITS sequences of GenBank Accession Nos. DQ987915 to DQ987922 were identical and exhibited strong similarity (>99% identity) to that of three previously described isolates of P. palmivora from cacao (GenBank Accession Nos. AF 228097, AF467093, and AF467089). P. palmivora has been reported on citrus, coconut, black pepper, and Arracacia xanthorrhiza in Puerto Rico (2,3) and inoculum may have originated from these host or imported on cacao planted into the cacao collection before 2000. USDA-ARS-TARS is the official site for the cacao germplasm collection, thus, a detailed integrated pest management plan that includes the evaluation for resistance, sanitation measures, and use of fungicides to reduce disease levels has been implemented. Decreasing incidence and severity of this disease is a top priority. To our knowledge, this is the first report of P. palmivora on cacao in Puerto Rico.

Mycosphaerella fijiensis, Causal Agent of Black Sigatoka of Musa spp. Found in Puerto Rico and Identified by Polymerase Chain Reaction.

Black Sigatoka, also known as black leaf streak, is caused by Mycosphaerella fijiensis Morelet (anamorph Pseudocercospora fijiensis (Morelet) Deighton). It is the most significant disease of bananas and plantains (Musa spp.) because most of the economically important cultivars of exported and staple commodities are highly susceptible. The Caribbean is one of the few regions of the world where black Sigatoka is not widespread. Black Sigatoka has been reported in the Bahamas, Cuba, Hispaniola, and Jamaica (2). Yellow Sigatoka, caused by M. musicola Leach (anamorph P. musae (Zimm.) Deighton), has been recognized in Puerto Rico since 1938-1939 (3). In August 2004, symptoms resembling black Sigatoka were first observed in Añasco, Puerto Rico by extension personnel from the University of Puerto Rico. Since black and yellow Sigatoka produce similar disease symptoms, a survey was conducted in the western banana- and plantain-production region of Puerto Rico to confirm the presence of black Sigatoka. Leaf samples were collected from production fields near the towns of Las Marias, Maricao, and Añasco. Single-ascospore isolates were recovered using the discharge technique from moistened pseudothecia in necrotic lesions that were inverted over water agar, and ascospores were transferred to potato dextrose agar. The isolates were subcultured in potato dextrose broth for mycelium production. DNA was isolated from mycelium with the FastDNA kit (Q-Biogen, Irvine, CA) for 19 isolates. Internal transcribed spacer as well as the 5.8s rDNA regions were polymerase chain reaction amplified with primers specific to M. fijiensis or M. musicola (1). Amplification products (˜1,100 bp) were observed for 18 of the 19 isolates, 6 of which were M. fijiensis and the remaining 12 were M. musicola, while the positive controls for both species were also amplified with the respective primer pairs. M. fijiensis was recovered from production fields close to all three towns. The source of M. fijiensis in Puerto Rico is unclear, but it may have originated from introduced leaf material and/or wind dispersed ascospores from neighboring countries. The presence of black Sigatoka in Puerto Rico will most likely increase production costs where fungicide applications will be needed to maintain yields. The USDA-ARS, Tropical Agriculture Research Station is the official Musa spp. germplasm repository for the National Plant Germplasm System. As such, efforts are underway to introduce and evaluate black Sigatoka disease-resistant clones that can satisfy local and export market criteria.

RAPID IN VITRO PROPAGATION OF MANGOSTEEN THROUGH SHOOT DIVISION

RAPID IN VITRO PROPAGATION OF MANGOSTEEN THROUGH SHOOT DIVISION

Comparación agronómica de cuatro híbridos de Panicums y dos cultivares a tres intervalos de corte en Puerto Rico

Tres problemas importantes asociados con el cruzamiento de la yerba guinea (Panicum maximum Jacq,) son: la caída prematura de la semilla; pobre germinación; y su reproducción por apomixis. En la Estación de Investigaciones en Agricultura Tropical (TARS) se desarrollaron tres híbridos resultado del cruce entre plantas sexuales femeninas y selecciones apomícticas de la yerba guinea. Además, se logró un cruce interespecífico entre malojllio (Brachiaria purpurascens Raddl) y la yerba klein (Panicum coloratum L.). Los cuatro híbridos, las yerbas guinea común yTobiata, una introducción de Brazil, se evaluaron durante un año a intervalos de corte (Cl) de 4, 6, y 8 semanas. El contenido de materia seca (DMC), rendimiento de materia seca (DMY), rendimiento de proteína cruda (PCY), y altura de la planta (PHt) promedio aumentaron (P < 0.01) del Cl de 4 al de 8 semanas. Por otro lado, la concentración de proteína cruda (CPC) disminuyó (P < 0.01). La digestibiiidad aparente in vitro (IVDMD) disminuyó (P < 0.01) sólo del Cl de 4 al de 6 semanas. El DMC, CPC y PHt correlacionaron positivamente con el DMY mientras que CPC e IVDMD lo hicieron negativamente con respecto a DMY. Al Cl de 8 semanas, Tobiata y BPIH104 fueron ios mejores productores con rendimientos anuales equivalentes a 43 y 41 t/ha, respectivamente. Estos y los demás híbridos de Panicum, deben ser evaluados bajo pastoreo en Puerto Rico.