Location: Tropical Crops and Germplasm Research
2018 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 many of the four objectives and their subobjectives. The following research was conducted: 1) In collaboration with ARS scientists in Fort Pierce, Florida, certified disease-free budwood pieces of seven mandarin cultivars were received, grafted onto a common rootstock, increased, grafted again onto three rootstocks and established in August 2015 in a replicated trial at two locations for field evaluation for yield, fruit quality traits, and citrus greening incidence. These accessions have never been evaluated in a replicated experiment. As of FY 18, determination of citrus greening incidence using enzyme-linked immunosorbent assay (ELISA) tests so far are confirming that the disease is not a problem at elevations above 600 meters. Fruit harvest at the high elevation site will begin in July 2018. Trees in the lower elevation site were severely defoliated and/or had branches broken by Hurricane Maria winds and are recovering; 2) Seven disease-resistant cacao accessions grafted onto EET-400 rootstock were established in a replicated experiment for evaluation of yield, pod index, and organoleptic quality traits. These accessions have never been evaluated in a replicated experiment. Two years after planting, some genotypes showed precocity producing pods; yield data were collected. On the third year after planting, trees suffered severe defoliation; 3) Seven breadfruit accessions grafted onto breadnut rootstock were established in a replicated experiment at two locations in August 2015 for evaluation of yield, disease and insect response, canopy volume, and organoleptic quality traits. These accessions have never been evaluated in a replicated experiment. Yield data collection was initiated; 4) Eight papaya lines developed by collaborators at the University of the Virgin Islands Experiment Station and ARS scientists were established in a replicated experiment at three locations for field evaluation of yield, fruit quality traits, and papaya ringspot virus (PRSV) tolerance. These accessions have never been evaluated in a replicated experiment. Year 2 has been planted. One line (Line 41) shows great potential. This line is also being evaluated in commercial orchards in Florida and Puerto Rico. These experiments were completely destroyed by Hurricanes Irma in Florida and Maria in St. Croix and Puerto Rico. Consequently, year 2 will be planted again during the fall of 2018; 5) A 3-yr experiment to evaluate 12 dragon fruit (pitahaya) cultivars and lines with the objective of determining yield of cultivars and fruit quality traits was completed and data is being analyzed; 6) In collaboration with scientists in Beltsville, Maryland, a 3-yr experiment to screen cacao germplasm for acid soil tolerance was completed and data is being analyzed; 7) In collaboration with scientists at the University of Puerto Rico, Semil-34 avocado grafted onto five avocado rootstocks were established in a replicated experiment for field evaluation for productivity and tolerance to local strains of Phytophthora root rot (PRR). Unfortunately, rootstock trees propagated using the Frolich-Platt grafting technique from the California nursery where they were purchased did not root appropriately and a re-order had to be made. New material had to be established again and trees were transplanted to the field in November 2015. Preliminary data have shown severe susceptibility even in the most tolerant clones. This experiment was completely destroyed by landslides caused by Hurricane Maria rains at this site; and 8) An experiment (Year 2) to determine nutrient uptake of four dragon fruit was terminated and data will be analyzed soon.
During FY 18, distributions of the nine cacao selections released in 2009 were made to farmers in Puerto Rico. These received 300 budwood pieces, 35 fruit and 25 plants of cacao from these clones. Thanks to this effort a completely new cacao industry is being established in Puerto Rico with clones exclusively developed by ARS scientists in Mayaguez, Puerto Rico. The distribution effort has been significant particularly after Hurricane Maria. These same clones were requested by scientists at the "Centro Agronómico Tropical de Investigación y Enseñanza" (CATIE; Tropical Agricultural Research and Higher Education Center) and budwood sent for grafting and field evaluation in Costa Rica.
The results from these experiments help to fill the knowledge gaps on cropping management systems for tropical/subtropical fruit crops.
Accomplishments
1. Yield, fruit quality traits and leaf nutrient concentration of sapodilla cv ‘Prolific’ grafted onto 16 rootstocks in Puerto Rico. The globalization of the economy, increased ethnic diversity and a greater demand for healthy and more diverse food products have opened a window of opportunity for the commercial production and marketing of tropical fruit. Sapodilla, a member of the Sapotaceae family, is a delicious tropical fruit which has received little research attention. A field study was conducted to determine the yield potential, fruit quality traits, leaf nutrient composition and scion/rootstock compatibility of cultivar ‘Prolific’ grafted onto 16 sapodilla rootstocks and evaluated during 7 years of production at the USDA-ARS Research Farm in Isabela, Puerto Rico. Rootstocks ‘Timothe’, ‘Vasallo-1’, ‘Larsen’, and ‘Aruz’ had the highest 7-year mean for number and yield of fruit averaging 4,479 fruit/ha and 1,245 kg/ha, respectively. The number of fruit per hectare and corresponding yield obtained in this study were very low probably the result of wind exposure and/or the presence of the fungus Pestalotia spp. causing floral necrosis. Scion/rootstock incompatibility was not the cause of the low yield performance of grafted trees. Average individual weight of fruit was 282 g and ranged from 264 g to 303 g. Averaged over rootstocks, leaf tissue nutrient concentration did not vary greatly over time. Moreover, tissue nutrient concentration was similar before and after fertilization events. This study provides for the first time information from a replicated experiment on fruit quality traits, leaf nutrient composition and scion/rootstock compatibility of cultivar ‘Prolific’ grafted onto various sapodilla rootstocks that should be useful to Extension Agents and growers.
2. First report of Colletotrichum (C.) fructicola and Colletotrichum queenslandicum causing fruit rot of rambutan (Nephelium lappaceum L.). In rambutan production, fruit rot is the main pre- and post-harvest disease of concern. In a fruit disease field survey, fruit rot was observed in eight orchards in Puerto Rico. Infected fruit were collected and tissue sections were surface disinfested with 70% ethanol followed by 0.5% sodium hypochlorite, rinsed with sterile water (SW) and transferred to acidified potato dextrose agar (APDA). Two isolates of Colletotrichum fructicola (Cof) and two isolates of C. queenslandicum (Coq) were identified morphologically using taxonomic keys and molecularly. Pathogenicity tests were conducted on five healthy superficially sterilized fruits per isolate. Both scalpel-wounded and unwounded fruit tissues were inoculated with 2 x 105 conidial suspensions from 8-day-old pure cultures grown in APDA. Untreated controls were inoculated with sterile water only. Fruits were kept in a humid chamber for 8 days at 25°C under 12 h of fluorescent light. The test was repeated once. Eight days after inoculation with Cof and Coq, all fruit turned brown, and acervuli were produced on spinterns (hairlike appendages). Rot of spinterns and exocarp (skin), water-soaked lesions on the fruit surface and aril (flesh) rot were observed. Untreated controls had no symptoms of fruit rot and no fungi were isolated from tissue. Both Cof and Coq were reisolated from their respective diseased tissue, fulfilling Koch's postulates. Colletotrichum gloeosporioides has been reported causing fruit rot of rambutan in Thailand and Sri Lanka. To our knowledge, this is the first report of C. fructicola and C. queenslandicum causing fruit rot of rambutan. Knowledge of the identity of this plant pathogen is the first step to assess its impact on production of trees and to develop control measures, if necessary.
3. Dry matter production and nutrient content of mamey sapote grown on an acid ultisol. The most productive soils of the world are already under cultivation, and those available for agricultural expansion are often strongly acid, possessing toxic levels of soil aluminum and/or manganese. These elements could drastically reduce crop yields when present in the soil at high concentrations. Incorporation of lime to the soil is a common practice to ameliorate acidity but it is not very effective below the plough layer and often lime is not available to farmers with limited resources. The effect of oil acidity factors on dry matter production and leaf nutrient composition of four mamey sapote clones was assessed during a 2-year field study. The results of this study demonstrate that dry matter production and stem diameter in young trees growth of mamey sapote were not significantly affected when grown at soil Al concentrations ranging from 3.5 to as high as 7.8 cmol/kg. The concentration of leaf and stem Al was not significantly affected but the Al concentration in roots declined sharply with increases in soil Al, suggesting the activation of an Al-exclusion mechanism.
Review Publications
Goenaga, R.J., Irizarry, H., Jenkins, D.A., Boykin, D.L., Marrero Soto, A.R. 2018. Yield, fruit quality traits and leaf nutrient concentration of sapodilla cv ‘Prolific’ grafted onto 16 rootstocks in Puerto Rico. HortTechnology. 27(4)563-571.
Goenaga, R.J. 2018. Dry matter production and nutrient content of mamey sapote grown on an acid ultisol. Experimental Agriculture. pgs. 1-9. https://doi.org/10.1017/S0014479718000054.
