Location: Tropical Crops and Germplasm Research2010 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 fifth year of commercial production (2009), cultivars Gula Batu, R-162 and Binjai produced significantly more fruit and had higher yield at Isabela, PR (Oxisol soil) averaging 199,495 fruits/ha and 5,919 kg/ha, respectively. In Corozal, PR (Ultisol soil), cultivars Gula Batu and R-162 were the highest producers averaging 442,856 fruits/ha and yielding 14,764 kg/ha. At both locations, significantly lower fruit soluble solids (Brix) values (19.8) were obtained from fruits of cultivars R-156-Y and Gula Batu. There were no significant differences in Brix among six more cultivars used in the study which averaged 21.2. After five years, 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 commercial production (2009), cultivars Tazumal and Magana were the highest yielders at Isabela with average yield of 23,381 kg/ha. At Corozal, higher yields were also obtained by cultivars Tazumal and Magana averaging 26,452 kg/ha. Cultivar Mayapan showed the highest average Brix value (31.6) at both locations. After five years, 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 fourth year of commercial production (2009) cultivar Geffner significantly outperformed all other cultivars for yield (14,054 kg/ha). Cultivar Bradley and Geffner had the highest average Brix value (22.1). 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 fifth and third year of production (2009), respectively, cultivar Kaimana had the highest yield at La Balear (8,338 kg/ha) and Mauritius at UPR-Limani (7,966 kg/ha). Bosworth-3 had the highest Brix (sweetness) value (19.6). We have evidence that hedges of tall grass severely impede immigration by winged aphids, transmitters of papaya ringspot virus. The results from these experiments help to fill the knowledge gaps on cropping management systems for tropical/subtropical fruit crops.
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 by ARS Researchers in Mayaguez, PR during a 2-year field study. High levels of soil acidity did not affect growth and dry matter production of rambutan seedlings demonstrating 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. Follow up studies in nutrient culture confirmed tolerance to Al up to a concentration of 4.2 mM Al. The physiological mechanism of this tolerance, mainly exudation of organic acids, is being investigated. This study provides useful information to growers and Extension personnel about the adaptability of rambutan to acid soils.
2. Identification and field assay of the pheromone of Phyllophaga vandinei and P. portoricensis. Phyllophaga species are important pests of fruit trees and turf. ARS researchers in Mayaguez, PR and collaborators, identified the pheromone of the two principal Phyllophaga pest species in Puerto Rico and reported its efficacy in attracting males for monitoring purposes. The pheromone may be used to monitor Phyllophaga vandinei and P. portoricensis populations, eliminating the need for expensive and inefficient cone emergence traps. Studies are needed to determine the feasibility of mating disruption using these pheromones.
3. 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 was described and illustrated by ARS researchers in Beltsville, MD, Mayaguez, PR, and Hilo, HI. Its relationship to other disease-causing fungi was also determined. This research provides plant pathologists to accurately identify the cause of this disease of specialty crops. Knowledge of this fungus is 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 impacts 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.
Rossman, A.Y., Farr, D.F., Schoch, C., Nishijima, K.A., Keith, L.M., Goenaga Portela, R.J. 2010. Phylogeny and redescription of Dolabra nepheliae on rambutan and litchi. Mycoscience. 51:300-309.