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ARS Home » Southeast Area » Mayaguez, Puerto Rico » Tropical Crops and Germplasm Research » Research » Research Project #426143

Research Project: Management Strategies to Improve Subtropical/Tropical Fruit Crop Production

Location: Tropical Crops and Germplasm Research

2019 Annual Report

1a. Objectives (from AD-416):
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.

1b. Approach (from AD-416):
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.

3. Progress Report:
This is the final report for the project 6090-21000-055-00D which terminated in December 2018. All planned field experiments were completed prior to the start of FY 2019; no experiments were initiated in the timeframe corresponding to this project. Substantial results were realized over the 5 years of the project. Pertaining citrus research, the Asian citrus psyllid transmits huanglongbing, or citrus greening. There have been anecdotes that Asian citrus psyllid becomes less abundant as elevation increases. ARS researchers in Mayaguez, Puerto Rico, tested that hypothesis by monitoring Asian citrus psyllid 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 Asian citrus psyllid abundance declines with elevation. No Asian citrus psyllid was detected above 600 meters. Trials conducted by ARS scientists in Mayaguez, Puerto Rico, indicate that curry leaf, Bergera koenigii, is very attractive to the Asian citrus psyllid. This plant does not host the putative causal organism of citrus greening disease and so does not pose a threat as a source of infection. Trials by ARS scientists in Mayaguez, Puerto Rico, in orchards indicate that potted curry leaf trees can draw psyllids from adjacent trees, increasing the ability to detect psyllids in and around orchards. This could be very useful in determining when to apply pesticides in citrus orchards. Pertaining to cacao, 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. 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. Pertaining to tropical fruit crops, six atemoya (Annona squamosa x A. cherimola) hybrids (Bradley, Geffner, Priestly, Lisa, 47-18, and 75-9) grown on an Oxisol soil were evaluated by ARS researchers at Mayaguez, Puerto Rico, for yield performance and fruit quality traits for 4 years. There were no significant differences in marketable fruit production between ‘Geffner’ and ‘Lisa’ which averaged 8,542 fruit/ha. Significantly higher yield of marketable fruit was obtained by ‘Geffner’ and ’Lisa’, averaging 1,507 kg/ha. Individual weight of marketable fruit was significantly higher in ’75-9’ and ‘Priestly’ which averaged 264.8 g. Significantly higher soluble solids concentration values were obtained from fruit of ’75-9’, ‘Bradley’ and ‘Geffner’ which averaged 23.8%. This study provides for the first time valuable information to growers and Extension specialists on yield and fruit quality traits of atemoya hybrids. Six lychee cultivars (Bosworth-3, Brewster, Groff, Mauritius, Kaimana, Salathiel) were evaluated for 8 years in Puerto Rico on Mollisol (UPR-Adjuntas site) and Inceptisol (Balear site) soils, respectively by ARS scientists in Mayaguez, Puerto Rico. At both locations, cultivar Groff had a significantly higher production (257,296 fruit/ha) of total fruit than other cultivars, whereas Salathiel had the lowest. However, total fruit production of ‘Groff’ was not significantly different from ‘Kaimana’ and ‘Bosworth-3’at La Balear farm, Puerto Rico. At UPR-Adjuntas, cultivars 'Groff' and 'Bosworth-3' had significantly higher number of marketable fruit than the rest of the cultivars averaging 171,760 fruit/ha. At La Balear, ‘Kaimana’ had a higher number of marketable fruits, but it was not significantly different from ‘Groff’, ‘Bosworth-3’, and ‘Mauritius’, averaging 291,360 fruit/ha. At both sites, individual fruit weight of marketable fruit was higher in ‘Kaimana’ than the rest of the cultivars. However, at La Balear farm, there were no significant differences between ‘Kaimana’ and ‘Mauritius’. At current farm gate prices and fruit yield reported in this study, cultivars 'Groff', 'Bosworth-3', and 'Kaimana' can generate a good income for growers and allow them to diversify crops as part of their farm operations. A field study was conducted by ARS scientists in Mayaguez, Puerto Rico, 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. 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. In rambutan (Nephelium lappaceum) production, fruit rot is the main pre- and post-harvest disease of concern. In a fruit disease field survey conducted by ARS researchers at Mayaguez, Puerto Rico, fruit rot was observed in eight orchards in Puerto Rico. 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 agar media. Untreated controls were inoculated with sterile water only. Fruits were kept in a humid chamber for 8 days. Eight days after inoculation with Cof and Coq, all fruit turned brown, and acervuli were produced on spinterns (hairlike appendages). 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. 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. Replicated field trials to evaluate performance of rambutan cultivars have been very limited and there is a scarcity of information on best management practices and optimal growing conditions for rambutan. ARS scientists in Mayaguez, Puerto Rico determined the yield potential of three rambutan cultivars (Jitlee, R-134, R-162) when the age of grafted trees was ~20 years. The data were compared with that obtained from an early production period when the age of the trees was ~10 years. This information helps rambutan growers make expansion and/or investment plans. Number of fruit and yield in 2017 were significantly higher in 2017 than in 2016. In 2017, average fruit number and yield of cultivars were 582,774 fruit/ha and 19,528 kg/ha, respectively, whereas in 2016 were 394,269 fruit/ha and 13,164 kg/ha, respectively. There were no significant differences among cultivars for number of fruits produced, averaging 488,521 fruit/ha. This production is higher than the 5-year average obtained from the 2005–09 harvest period when grafted trees were about 9 years old. The results of this study demonstrate that grafted rambutan trees can remain prolific in mature orchards. The genetic resources evaluated by this project are critical for diversifying these horticultural production systems. During FY 19, a total of 12 distributions of the nine cacao selections released in 2009 were made to farmers in Puerto Rico. These received 110 budwood pieces, 20 fruit and 80 seeds of cacao from these clones. This not only is an indication that the USDA cacao collection recovered completely after being hit by Hurricane Maria but thanks to this distribution effort the cacao industry in Puerto Rico is being assisted in its recovery and expansion by USDA by providing growers with high-yielding clones exclusively developed by ARS scientists in Mayaguez, Puerto Rico. These same clones were requested by collaborating scientists and budwood was 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. This project which seeks to evaluate cultivars, lines and clones for productivity and abiotic/biotic stress tolerance for improved subtropical and tropical fruit production and quality, was merged with project 6090-21000-057-00D from which similar objectives will be addressed. Evaluation data will be disseminated through publications, field days with growers and Extension personnel, and via GRIN-Global and other data sources.

4. Accomplishments
1. Yield and fruit quality traits of two plantain cultivars grown at two locations in Puerto Rico under Black Leaf Streak Disease Pressure. Plantains are an important cash crop and a staple for inhabitants in many parts of the world, including various ethnic groups in the U.S. Black leaf streak disease (BLSD), caused by Pseudocercospora fijiensis, is responsible for significant losses to this crop due to the high susceptibility of the most economically important cultivars. Without cultural and chemical control, yields can be reduced by 20 to 80%, depending on severity. ARS scientists in Mayaguez, Puerto Rico, evaluated ‘FHIA-21’, a BLSD-resistant cultivar, against ‘Maricongo’, a standard commercial cultivar with no BLSD tolerance, at two locations in Puerto Rico on an Ultisol (Corozal site) and Oxisol (Isabela site) soils. Total number of fruit and bunch yield were significantly higher at Isabela with BLSD severity being significantly lower at this location. Average fruit production for ‘FHIA-21’ was significantly higher than ‘Maricongo’ at both locations with fruit yield of 122,522 and 99,948 fruit/ha at Isabela and Corozal, respectively. Overall, fruit in ‘FHIA-21’ were significantly longer and of greater diameter than those of ‘Maricongo’. At Isabela, bunch mean fruit weight was significantly higher in ‘FHIA-21’ but both cultivars exceeded the local marketable fruit weight criterion of 270 g. At both locations the number of functional leaves present at flowering and at harvest was significantly higher in ‘FHIA-21’ than in ‘Maricongo’, indicating more availability of photosynthetic area in ‘FHIA-21’ during the fruit-filling period. ‘FHIA-21’ showed to have good resistance against BLSD and should be a viable alternative to current commercial cultivars.

Review Publications
Baligar, V.C., Almeida, A.A., Ahner, D., Pires, J.L., Arevalo-Gardini, Goenaga, R.J., He, Z., Elson, M.K. 2018. Impact of drought on morphological, physiological and nutrient use efficiency of elite cacao genotypes from Bahia-Brazil, Tarapoto-Peru and Puerto Rico-USA. Symposium Proceedings. 87:1-11.
Goenaga, R.J. 2019. Long term productivity of three rambutan cultivars grown in an ultisol soil in Puerto Rico. HortTechnology. 28:863-866.