Brian M. Irish

Effect of coconut palm proximities and Musa spp. germplasm resistance to colonization by Raoiella indica (Acari: Tenuipalpidae)

Although coconut (Cocos nucifera L.) is the predominant host for Raoiella indica Hirst (Acari: Tenuipalpidae), false spider mite infestations do occur on bananas and plantains (Musa spp. Colla). Since its introduction, the banana and plantain industries have been negatively impacted to different degrees by R. indica infestation throughout the Caribbean. Genetic resistance in the host and the proximity of natural sources of mite infestation has been suggested as two of the main factors affecting R. indica densities in Musa spp. plantations. Greenhouse experiments were established to try to determine what effect coconut palm proximities and planting densities had on R. indica populations infesting Musa spp. plants. Trials were carried out using potted Musa spp. and coconut palms plants at two different ratios. In addition, fourteen Musa spp. hybrid accessions were evaluated for their susceptibility/resistance to colonization by R. indica populations. Differences were observed for mite population buildup for both the density and germplasm accession evaluations. These results have potential implications on how this important pest can be managed on essential agricultural commodities such as bananas and plantains.

Development of Microsatellite Loci in Artocarpus altilis (Moraceae) and Cross-Amplification in Congeneric Species

Premise of the study: Microsatellite loci were isolated and characterized from enriched genomic libraries of Artocarpus altilis (breadfruit) and tested in four Artocarpus species and one hybrid. The microsatellite markers provide new tools for further studies in Artocarpus. Methods and Results: A total of 25 microsatellite loci were evaluated across four Artocarpus species and one hybrid. Twenty-one microsatellite loci were evaluated on A. altilis (241), A. camansi (34), A. mariannensis (15), and A. altilis × mariannensis (64) samples. Nine of those loci plus four additional loci were evaluated on A. heterophyllus (jackfruit, 426) samples. All loci are polymorphic for at least one species. The average number of alleles ranges from two to nine within taxa. Conclusions: These microsatellite primers will facilitate further studies on the genetic structure and evolutionary and domestication history of Artocarpus species. They will aid in cultivar identification and establishing germplasm conservation strategies for breadfruit and jackfruit.

Genomics of Tropical Fruit Tree Crops

The genetic improvement of tropical fruit trees is limited when compared to progress achieved in temperate fruit trees and annual crops. Tropical fruit tree breeding programs require significant resources to develop new cultivars that are adapted to modern shipping and storage requirements. The use of molecular markers in tropical fruit tree breeding is greatly assisting in solving a number of difficult challenges for breeders such as the development of complex family structures for recombination mapping and for recurrent selection. A review of the literature on molecular markers development and new techniques for increasing single-nucleotide polymorphic markers is discussed. The development of marker-assisted breeding for these tropical tree crops is also discussed.

Genetic diversity of naturalized cacao ( Theobroma cacao L.) in Puerto Rico

Identification of genetically diverse cacao with disease resistance, high productivity, and desirable organoleptic traits is vitally important to the agricultural crop’s long-term sustainability. Environmental changes, pests, and diseases as well as nation’s sovereign property rights have led to a decrease in accessibility and exchange of germplasm of interest. Having been introduced during colonial times, naturalized cacao in Puerto Rico could serve as an unexplored source of genetic diversity in improvement programs. An island-wide survey was carried out to identify naturalized trees and to determine their genetic associations to reference cacao accessions. Samples were genotyped with Expressed Sequence Tag-derived single nucleotide polymorphism (SNP) markers. Principal coordinate, cluster, and population structure analysis using the genotype data for both local and reference samples assigned individuals into five distinct genetic backgrounds: Criollo, Trinitario, Amelonado, Upper Amazon Forastero (UAF), and Nacional. Puerto Rican cacao fit into four (Criollo, Trinitario, Amelonado and UAF) of the five genetic backgrounds, being mainly composed of individuals of Criollo ancestry. Based on historical evidence, cacao of Criollo background was probably brought to Puerto Rico from Venezuela and/or Central America during colonial times. Trinitario, Amelonado, and UAF genetic backgrounds are most likely products of more modern introductions. Genotyping cacao in Puerto Rico provides information on the history and possible origin of the naturalized trees on the island. In addition, the assessment has allowed the targeting of material for incorporation and long-term conservation filling gaps in the existing collection and providing new germplasm to be evaluated for agronomic performance.

Attraction of Pollinators to Atemoya ( Annona squamosa × Annona cherimola ) in Puerto Rico Using Commercial Lures and Food Attractants

ABSTRACT Atemoya is a hybrid between Annona squamosa L. and Annona cherimola Miller (Annonaceae) and has potential to be an important fruit crop in tropical and subtropical areas. A major impediment to fruit production is low fruit set due to inadequate pollinator visits, typically, by beetles in the family Nitidulidae. We used Universal moth traps to monitor the attractiveness of two commercially available Nitidulidae lures in combination with various food attractants, including raw bread dough, apple juice, and malta beverage, a soft drink by-product of the brewing process. The most commonly trapped beetles were, in order of decreasing frequency, Carpophilus dimidiatus (F.), Brachypeplus mutilatus Erichson, Urophorus humeralis (F.) (Coleoptera: Nitidulidae), and Europs fervidus Blatchley (Coleoptera: Monotomidae). All traps, except the unbaited control traps, caught beetles. In a previous study, we found that combining two commercial lures had a synergistic effect on the attraction of these beetle species. In this study, the addition of food attractants increased the number of beetles trapped compared with traps baited with only the commercial lures. Also, food attractants appear to be key in attracting U. humeralis; only one U. humeralis individual of the 206 caught during the experiment was trapped without a food attractant. The variation between the number of beetles caught in traps containing the same treatments was high and may explain the erratic results reported in other studies of pollination in Annona spp. The results are discussed with respect to the use of nitidulid lures and food attractants to increase fruit set in atemoya and other Annonaceae.

Development of a Large Set of Microsatellite Markers in Zapote Mamey (Pouteria sapota (Jacq.) H.E. Moore & Stearn) and Their Potential Use in the Study of the Species.

Pouteria sapota is known for its edible fruits that contain unique carotenoids, as well as for its fungitoxic, anti-inflammatory and anti-oxidant activity. However, its genetics is mostly unknown, including aspects about its genetic diversity and domestication process. We did high-throughput sequencing of microsatellite-enriched libraries of P. sapota, generated 5223 contig DNA sequences, 1.8 Mbp, developed 368 microsatellites markers and tested them on 29 individuals from 10 populations (seven wild, three cultivated) from Mexico, its putative domestication center. Gene ontology BLAST analysis of the DNA sequences containing microsatellites showed potential association to physiological functions. Genetic diversity was slightly higher in cultivated than in the wild gene pool (HE = 0.41 and HE = 0.35, respectively), although modified Garza–Williamson Index and Bottleneck software showed evidence for a reduction in genetic diversity for the cultivated one. Neighbor Joining, 3D Principal Coordinates Analysis and assignment tests grouped most individuals according to their geographic origin but no clear separation was observed between wild or cultivated gene pools due to, perhaps, the existence of several admixed populations. The developed microsatellites have a great potential in genetic population and domestication studies of P. sapota but additional sampling will be necessary to better understand how the domestication process has impacted the genetic diversity of this fruit crop.

Characterization of Fusarium spp. isolates recovered from bananas (Musa spp.) affected by Fusarium wilt in Puerto Rico

Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (FOC), is one of the most destructive diseases of bananas (Musa spp.) worldwide. Although the first report of this disease in Puerto Rico was in 1919, little has been published since that time. We report the first systematic description of FOC on the island. A total of 28 single-spore isolates of Fusarium spp. were recovered from symptomatic bananas from several municipalities. Species identity of the isolates was initially based on morphology and later confirmed with partial sequences of the translation elongation factor 1α (TEF-1α) gene. Isolates were examined for vegetative compatibility, race identity using PCR primers reported for different races, and virulence on tissue-culture-derived plantlets of differential cultivars for races 1, 2 and 4. Most isolates of F. oxysporum belonged to VCG 0124 of FOC, and amplified with primers designed for race 1. Several isolates amplified with primers developed for race 4, but no isolate amplified with primers specific for tropical race 4 (TR4). Most isolates produced symptoms on race 1 or race 2 susceptible cultivars. Although some isolates caused minor symptoms on ‘Gran Nain’, disease severities on this race 4 differential were considerably lower than those in susceptible race 1 or race 2 interactions. Based on these results, race 1 and race 2, but not TR4, are present in Puerto Rico. We discuss the disease and FOC’s population structure in Puerto Rico, as well as the reliability of different PCR primers that have been developed to identify races of this pathogen.