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United States Department of Agriculture

Agricultural Research Service


Location: Tropical Crops and Germplasm Research

2009 Annual Report

1a. Objectives (from AD-416)
Evaluate tropical/sub-tropical fruit production systems and germplasm for broad agro-environmental adaptation, high yield and productivity, and ability to produce fruits of superior quality. Develop efficient and sustainable monitoring and/or control methods for key pests that limit tropical/subtropical fruit production and quality.

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. Control strategies for plant pathogens of tropical and subtropical fruit crops will be developed using systemic acquired resistance agents. Strategies to increase pollinators in Annonaceae will be developed. Field evaluation of biological agents for biocontrol of important insect pests of tropical and subtropical fruit crops will be conducted.

3. Progress Report
Little information is available on yield performance of rambutan. Experiments to evaluate eight rambutan cultivars for yield and fruit quality traits at two locations in Puerto Rico were established in 1999. In their sixth year of production (2008), cultivars Binjai and R-162 were the highest yielders at Isabela (Oxisol soil) with yields of 6,693 and 5,357 kg/ha, respectively. In Corozal (Ultisol soil), cultivars Gulu Batu and Rongren were the highest producers with yields of 22,588 and 21,880 kg/ha, respectively. Cultivar R-162 had the highest average Brix (sweetness) value (22.0). After six harvests, fruit production has still not plateaued. Little, if any information is available on yield performance and fruit quality traits of mamey sapote. Experiments to evaluate six mamey sapote clones at two locations in Puerto Rico were established in 2000. In their fifth year of production (2008), cultivars Magana and Pantin were the highest yielders at Isabela with average yield of 21,034 kg/ha. At Corozal, higher yields were obtained by cultivars Tazumal and Pantin averaging 28,841 kg/ha. Cultivar Pace showed the highest average Brix (sweetness) value (31.7) at both locations. After five harvests, fruit production has still not plateaued. Little information is available on yield performance and fruit quality traits of atemoya. An experiment to evaluate six atemoya clones was established in Isabela, Puerto Rico in 2001. In their second year of production (2008) cultivar Geffner significantly outperformed all other cultivars for yield. Cultivar Bradley and 75-9 had the highest average Brix (sweetness) value. Little, if any information is available on yield performance and fruit quality traits of lychee grown in the tropics. An experiment to evaluate six lychee cultivars in Puerto Rico was established in 2000 (UPR-Limani) and 2003 (Castaner). In their third and first year of production (2008), respectively, cultivar Kaimana had the highest yield at La Balear (9,365 kg/ha) and Groff at UPR-Limani (2,844 kg/ha). Bosworth-3 had the highest Brix (sweetness) value (20.7). Preliminary results indicate that a commercially available pheromone for nitidulids significantly increases fruit set in atemoya trees containing this pheromone. Studies are underway to determine the density of pheromone lures needed for maximum pollination. Phyllophaga vandinei is a key pest of tropical/subtropical fruit trees. Experiments to control this pest demonstrated that physical barriers, including hedgerows or barrier crops, have significant negative impact on the ability of this insect to colonize orchards. These studies also demonstrated that the key monitoring tool used for this pest, the cone emergence cage, has some drawbacks, including variability of effectiveness based on placement; traps placed to the west side of a tree always catch more beetles than traps placed anywhere else. The results from these experiments help to fill the knowledge gaps on cropping management systems for tropical/subtropical fruit crops.

4. Accomplishments
1. Rambutan resistance to acid soils. 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 (Al) and/or manganese (Mn). These elements could drastically reduce crop yield 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 soil acidity factors on dry matter production and leaf nutrient composition of four rambutan cultivars was assessed during a 2-year field study. High levels of soil acidity did not affect growth and dry matter production of rambutan seedlings. The results of this study demonstrate that rambutan is highly tolerant to acid soils and that tolerance may involve a physiological process to keep Al and Mn from entering the roots. This study provides useful information to growers and Extension personnel about the adaptability of rambutan to acid soils.

2. Iridovirus infection in Phyllophaga vandinei: a system for delivering biological control to soil borne pests. Phyllophaga vandinei is an important pest of fruit trees, the adults defoliating trees and even killing young seedlings. We completed research demonstrating that P. vandinei is susceptible to an iridovirus. Although the iridovirus causes low levels of mortality (typically less than 30%), it has a significant impact on behavior: infected individuals do not reproduce or feed. Furthermore, infected individuals serve as delivery systems for the virus, infecting the soil so that healthy individuals also contract the virus. This work has potential to be extended into an even more effective biocontrol program.

3. Release of high-yielding cacao clones. World average cacao yield is low. To increase yield it is highly recommended that cacao be propagated through the use of controlled-pollinated seed obtained from crosses of two or more productive parental clones. The use of hybrid seed is considered the simplest and cheapest method of cacao propagation and may offer the opportunity to assemble into a single tree useful traits from distant parents. In most cases, however, the data available to support the high yielding assumption attributed to controlled-pollinated seed is based only on the production obtained from a few segregating trees and without validation from long-term experiments. During a four-year evaluation/period at three locations we obtained individual tree yield data from about 1,320 trees originated from five single crosses. Scionwood of 40 high-yielding trees representing all crosses and locations, and scionwood of five parental trees used in the development of the crosses was grafted onto a common rootstock. The 40 selections were compared for yield with the five parents in replicated plots during a four full-year evaluation period. The results indicated that of the 1,320 initial trees observed in all populations and locations only nine trees were superior yielders with a mean production of 2,170 kg/ha/year of dry beans. A description of organoleptic characteristics demonstrated wide diversity in flavor characteristics among the nine high yielding clones. Results from this study suggest that the use of hybrid seed should be avoided in cacao propagation and substituted with grafting of superior clones onto a compatible rootstock. Genetic material of this release was deposited in the National Plant Germplasm System where it is now available for research purposes, including development and commercialization of new cultivars.

4. Description of the fungus Dolabra nepheliae on rambutan and lychee. Fungi are a large and diverse group of organisms that cause serious diseases of crop and forest plants. Accurate knowledge of fungi is critical for controlling the diseases they cause. Rambutan and lychee are tropical plants that produce delicious edible fruits. A little known fungus causes a canker disease of rambutan and lychee in Hawaii and Puerto Rico known as corky bark disease. In this research the fungus causing this disease is described and illustrated. Its relationship to other disease-causing fungi was also determined. This research will help plant pathologists to accurately identify the cause of this disease of specialty crops. Knowledge of this fungus will be useful to plant regulatory officials working to control the spread of this disease.

5. Significant Activities that Support Special Target Populations
The research conducted in this project directly impact small and socially disadvantaged/limited resource producers in rural areas by providing growers in these regions alternative high-cash crops and best management practices for production of these crops.

Review Publications
Flores, D., Hall, D.G., Jenkins, D.A., Setamou, M. 2009. Abundance of Asian citrus psyllid on yellow sticky traps in Florida, Puerto Rico, and Texas citrus groves. Southwestern Entomologist. 34(1):1-11.

Goenaga, R., Irizarry, H., Irish, B. 2009. TARS Series of Cacao Germplasm Selections. HortScience 44(3):826-827.

Jenkins, D.A., Diaz, E., Jenkins, D.M., Goenaga, R.J. 2008. Solar sterilization of abscised fruit: a cultural practice to reduce infestations of Anastrepha spp. around orchards. Journal of Agriculture of the University of Puerto Rico. 92(3-4):197-206.

Last Modified: 06/23/2017
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