Location: Tropical Crops and Germplasm Research
2014 Annual Report
Objectives
1. Devise optimum production practices for tropical and subtropical fruit crops that help expand local and export markets.
1.A. Evaluate, across various agroenvironments, the performance of cultivars of cacao, breadfruit, dragon fruit, mandarin orange, and papaya for yield, fruit quality traits and abiotic stress tolerance.
1.B. Determine nutrient requirements of rambutan and dragon fruit so as to optimize nutrient applications.
1.C. Evaluate trap-and-kill technology as a tool to suppress fruit fly populations in and around orchards.
1.D. Determine host status of dragon fruit to the fruit flies Anastrepha suspensa and A. obliqua.
2. Evaluate the performance of selected cultivars of tropical/subtropical fruit crops for tolerance to economically-limiting diseases, including, but not limited to black Sigatoka, and the Puerto Rican strain of Papaya ringspot virus (PRSV).
2.A. Evaluate plantain and banana cultivars for productivity under pressure of black Sigatoka disease.
2.B. Evaluate avocado rootstocks for productivity and tolerance to Phytophthora root rot.
2.C. Evaluate the performance of suitable papaya varieties and assess their response to PRSV for optimized productivity in Puerto Rico and surrounding ecosystems.
2.D. Identify potential intercrop candidates for papaya that reduce the propensity for the aphid vector to transmit PRSV in orchards.
3: Evaluate and develop new means for reducing or eliminating the threat and impact of key insect pests and the ability of insect vectors to transmit specific diseases.
3.A. Determine effect of altitude gradients on Asian citrus psyllid (ACP) populations and citrus greening incidence.
3.B. Survey ACP populations in Puerto Rico to identify parasitoids and predators for potential use in biocontrol.
4. Develop means of increasing the effectiveness of pollinators that maximize crop productivity.
4.A. Determine differences in biotic and abiotic factors associated with colony collapse disorder of Apis mellifera in Puerto Rico and mainland U.S.
4.B. Assess the efficacy of nitidulid pheromones or other pollinator attractants in increasing pollination, fruit set, and yield in atemoya.
Approach
Field evaluations for yield and fruit quality traits of selected tropical fruit crop scion and/or rootstock germplasm will be conducted in various agro-environments. Nutrient requirements and utilization efficiency studies will be conducted to optimize nutrient applications. Rootstocks will be field-evaluated for tolerance to acid soil conditions or root diseases. Sustainable management strategies, including biological control and orchard layout, will be developed for plant pathogens of tropical and subtropical fruit crops and their arthropod vectors. Strategies to increase pollinator visits to Annonaceae, thus increasing fruit set and fruit quality, will be developed. Pollinator health will be examined, including identifying important factors contributing to the decline in honey bee population.
Progress Report
Progress was made on all four objectives and their subobjectives. The following research was conducted: 1) In collaboration with scientists in Fort Pierce, Florida, certified, disease-free budwood pieces of seven mandarin cultivars were received, grafted onto rootstocks and are being increased for grafting onto three rootstocks for field evaluation for yield, fruit quality traits, and citrus greening incidence at three locations. These accessions have never been evaluated in a replicated experiment; 2) In collaboration with scientists in Miami, Florida, budwood of seven disease-resistant cacao accessions were received and grafted onto Amelonado rootstock for increase of propagating material. Once increased, accessions were grafted onto Amelonado rootstock again for transplanting to the field later in the year. Accessions will be evaluated for yield, pod index, and organoleptic quality traits. These accessions have never been evaluated in a replicated experiment; 3) Breadfruit budwood pieces of seven varieties were received from collaborating scientists in USDA-ARS in Hilo, Hawaii and grafted on breadnut rootstock. Grafting was successful with some accessions, but not with others. Different techniques are being implemented to successfully graft difficult-to-graft cultivars; 4) Seedlings of eight papaya lines developed by collaborators at the University of the Virgin Islands Experiment Station are being grown in the greenhouse and will be transplanted to the field for evaluation for yield, fruit quality traits, and Papaya ringspot virus (PRSV) tolerance. These accessions have never been evaluated in a replicated experiment; 5) An experiment to evaluate 12 dragon fruit (pitahaya) cultivars and lines continued in the field with the objective of determining yield of cultivars, fruit quality traits, and if fruit is host to Anastrepha spp. fruit flies; 6) In collaboration with scientists in Beltsville, Maryland, an experiment (year 1) to screen cacao germplasm for acid soil tolerance was harvested and biomass production for each accession determined; 7) An experiment (year 2) to evaluate for yield and fruit quality traits cultivar FHIA-17 (Sigatoka-tolerant banana cultivar) and FHIA-21 (Sigatoka-tolerant plantain cultivar) was completed and data is being analyzed; 8) An experiment (Year 1) to determine nutrient uptake of four rambutan cultivars grown at two locations in Puerto Rico was completed; 9) In collaboration with scientists at the University of Puerto Rico, Phytophthora root rot tolerant (PRR) rootstocks of four cultivars were purchased from a California nursery and grafted with Semil-34 budwood for field evaluation for productivity and tolerance to local PRR strains. Unfortunately, rootstock trees from the nursery, propagated using the Frolich-Platt grafting technique there did not root appropriately and a re-order had to be made; 10) An experiment to monitor Asian citrus psyllid (ACP) abundance at different elevations was completed and the results are being submitted to a peer-reviewed journal; 11) In collaboration with scientists at the University of Puerto Rico, a survey of PRSV diversity on the island was initiated; 12) An experiment to determine the impact of lures and food attractants on atemoya yield and fruit size was initiated; 13) A survey was started to identify the main species composing aphid immigrations; 14) In collaboration with scientists at the University of Puerto Rico, an experiment was initiated to determine the impact various legumes (Canavalia sp., Cajanus cajan and Crotalaria juncea) have on growth, production and PRSV incidence in papaya orchards; 15) In collaboration with scientists at the University of Puerto Rico, an experiment was initiated to look at the effects intercropping has on the infestation of banana corms by the weevil, Cosmopolotes sordidus; 16) An experiment was conducted to look at the effects of plant nutrition on ACP populations; 17) In collaboration with scientists at the University of Florida, an experiment was initiated to determine the efficacy of the entomopathogenic fungus Isaria fumosorosea on the Asian citrus psyllid; 18) In collaboration with scientists at the University of Florida, an experiment was initiated to improve methods of trapping ACPs; 19) In collaboration with scientists at the University of Florida, an experiment was initiated to determine the efficacy of different stimuli on ACP movement; 20) In collaboration with scientist at Southwest Forestry University, China, a shipment of 20 seeds each of bayberry (Myrica rubra) accession San Li, Dong Kui, and Tse Min were provided for increase at the National Plant Germplasm System; 21) In collaboration with scientists at the Guangxi Subtropical Crops Research Institute, China, accessions of longan seedlings collected from a wild population near Vietnam are growing vigorously in the field. Upon flowering this year, the fruits will be evaluated in October for quality traits.
The results from these experiments help to fill the knowledge gaps on cropping management systems for tropical/subtropical fruit crops.
This project replaces project 6635-21000-050-00D which expired in December 2013.
Accomplishments
1. Asian citrus psyllid (ACP) abundance declines with elevation. The ACP transmits huanglongbing, or citrus greening, the most devastating disease of citrus worldwide. There have been anecdotes that ACP becomes less abundant as elevation increases. ARS researchers in Mayaguez, Puerto Rico tested that hypothesis by monitoring ACP populations in citrus orchards at 17 different elevation sites (between 10 and 880 meters above sea level) in Puerto Rico. Results provided strong evidence that ACP abundance declines with elevation. No ACP was detected above 600 meters. Identifying the factors affecting the geographical and ecological distribution of psyllid populations could help develop management strategies for the insect and the disease it spreads.
2. Yield performance and bean quality traits of cacao propagated by somatic embryogenesis and grafting. Cacao (Theobroma cacao) has great potential as a component of a small tropical farming system. The U.S. chocolate industry alone generated $19.5 billion in sales of chocolate products in 2012. However, it is estimated that diseases in cacao production caused losses of potential crop amounting to 43% in America, 20% in Africa, 13% in Oceania and 9% in Asia. In order to satisfy future global demand for cacao products and reduce crop losses, research is needed to develop and/or identify superior cacao genotypes possessing disease tolerance and high yielding traits. In addition, methods of propagation that are more efficient in producing true-to-type genotypes are needed. ARS researchers at Mayaguez, Puerto Rico evaluated 12 cacao clones propagated by grafting and orthotropic rooted cuttings of somatic embryo-derived plants on an Ultisol soil at Corozal, Puerto Rico for six years of production under intensive management. Propagation treatments had a significant effect on dry bean yield. Dry bean yield of varieties propagated by grafting was 7% higher (2,166.7 kg.ha-1.yr-1) than those propagated by orthotropic rooted cuttings of somatic embryo-derived plants (2,009.2 kg.ha.yr-1). This yield difference could not be attributed to grafted plants being more vigorous or by differences in root architecture. In general, flavor characteristics were not significantly affected by propagation treatments. Although there were significant differences between plant propagation treatments for some of the variables measured in this study, these were not of a magnitude that would preclude the use of somatic embryogenesis as a viable propagation system for cacao. The use of somatic embryogenesis for cacao propagation could contribute to efforts to improve yield per area, germplasm conservation and rapid distribution of high yielding clones.
Review Publications
Serrato-Diaz, L.M., Rivera-Vargas, L.I., Goenaga, R.J., French-Monar, R.D. 2014. First report of Lasiodiplodia theobromae causing inflorescence blight and fruit rot of longan (Dimocarpus longan L.) in Puerto Rico. Plant Disease. 98(2):279.
Jenkins, D.A., Mizell, R., Vanbloem, S., Whitmore, S., Wiscovitch, L., Zaleski, K., Goenaga, R.J. 2014. An analysis of arthropod interceptions by APHIS-PPQ and Customs and Border Patrol in Puerto Rico. American Entomologist. 60:44-55.
