Tropical Plant Biology

Estep, Matt; Mourik, Thomas; Muth, Peter; Guindo, Diarah; Parzies, Heiko; Koita, Ousmane; Weltzien, Eva; Bennetzen, Jeffrey

2011 Tropical Plant Biology

doi: 10.1007/s12042-011-9073-6

Eleven populations of witchweed, Striga hermonthica, were collected in four regions of Mali and investigated with 12 microsatellite markers. Extensive genetic diversity was observed, with most plants heterozygous for most markers. Allelic diversity was broadly distributed across populations with little genetic differentiation and large amounts of gene flow. Nearby fields of pearl millet and sorghum were found to have indistinguishable witchweed populations. Some population structure was apparent, but did not correlate with the local environment or host genotype, suggesting that seed transportation or other human-driven variables act to differentiate central Malian S. hermonthica populations from southern Malian populations.

Costa Silva, Silvokleio; Marques, André; Santos Soares Filho, Walter; Mirkov, T.; Pedrosa-Harand, Andrea; Guerra, Marcelo

2011 Tropical Plant Biology

doi: 10.1007/s12042-011-9072-7

A cytogenetic map was established for the trifoliate orange, Poncirus trifoliata. Chromosome size, centromere position and CMA+ heterochromatin content were determined for each chromosome pair, together with the position of BAC clones previously described as chromosome-specific markers. Although P. trifoliata is a true biological species, heteromorphisms for the size of the heterochromatic bands in two chromosome pairs were observed. A minimum set of four BACs was proposed for chromosome identification in P. trifoliata, as well as a chromosome nomenclature that can be applied to all citrus species. The Ctv locus was assigned to chromosome 9 and the remaining linkage groups can now be integrated to this physical map. This standard nomenclature for trifoliate orange will be valuable for genome-sequencing projects in all citrus species.

Zhang, Dapeng; Gardini, Enrique; Motilal, Lambert; Baligar, Virupax; Bailey, Bryan; Zuñiga-Cernades, Luiz; Arevalo-Arevalo, Carlos; Meinhardt, Lyndel

2011 Tropical Plant Biology

doi: 10.1007/s12042-010-9064-z

Knowledge of genetic diversity in farmers’ selections is essential for planning on-farm conservation and rehabilitation. Using 15 microsatellite loci, we analyzed parentage and population structure in 220 farmer selections of cacao from the Huallaga valley in Peruvian Amazon. A high level of allele richness and heterozygosity were detected in these selections. Coordination analysis showed that these farmer selections are mainly comprised of hybrids derived from Trinitario and Upper Amazon Forastero germplasm. Bayesian clustering analysis assigned 54 selections as Trinitario and 166 as Upper Amazon Forastero hybrids. Parentage analysis identified 15 international clones as probable parents for 96 farmer selections, which corresponded to a fraction of the known hybrid families disseminated in this region in the late 1980s. Combined analysis of demographic and molecular data revealed a significant spatial autocorrelation (r = 0.235; P = 0.006) at short geographical distances (<5.0 km). This patch-like distribution of spatial heterogeneity suggests a significant “neighborhood effects” in seeds distribution or variety adoption, where closely related hybrid progenies were adopted in the neighboring farms or villages. The outcomes of this study indicate that in spite of the introgressions of exotic germplasm in the past, Upper Amazon Forastero is still the dominant component in the Huallaga valley of Peru. The high level of on-farm diversity can offer needed variability for participatory selection of superior clones in this low input, small-scale production system, where adaptability to specific environment is more preferred than in a high input, large scale production system.

Adeyemo, Oluwabusayo; Kolmos, Elsebeth; Tohme, Joe; Chavariaga, Paul; Fregene, Martin; Davis, Seth

2011 Tropical Plant Biology

doi: 10.1007/s12042-011-9065-6

The angiosperm circadian clock has been well established from molecular-genetic studies in a temperate plant model. Conservation of clock function is less explored in plants from the tropics. Cassava (Manihot esculenta) is a staple crop grown in the tropics that has been of limited research interest, and more generally, research on photoperiod and clock genes has been sparse. EARLY FLOWERING 4 (AtELF4) of the temperate plant Arabidopsis thaliana (Arabidopsis) has been reported to be required for photoperiod perception and circadian function. Here, we describe our start to identify circadian and photoperiod genes in cassava with an account on the characterization of its ELF4 gene (MeELF4). After isolating MeELF4, a phylogenetic study was conducted and it was found to cluster within the ELF4 subclade of the ELF4/EFL super-family. Similar to studies in temperate plants, MeELF4 was shown to be an evening-expressed gene in cassava. This collectively suggested to us that MeELF4 could be a functional ortholog of AtELF4. To test this, complementation studies of MeELF4 were performed in the Arabidopsis elf4 mutant. Hypocotyl-length measurements and flowering-time analysis were performed. MeELF4-complementation transgenics in the elf4 background were restored to the wild-type growth habit, suggesting a total rescue of photoperiodic perception. To expand on the molecular role of MeELF4 in the resulting transgenic-complementation lines, the CCA1 and CCR2 promoter-luciferase markers where respectively introduced and bioluminescence-imaging experiments revealed a restoration of circadian-regulated gene expression. The collective results showed that the cassava gene MeELF4 is a functional clock ortholog of AtELF4.

Emche, Stephen; Zhang, Dapeng; Islam, Melissa; Bailey, Bryan; Meinhardt, Lyndel

2011 Tropical Plant Biology

doi: 10.1007/s12042-011-9070-9

Four taxa of the plant genus Erythroxylum; Erythroxylum coca var. coca (Ecc), Erythroxylum coca var. ipadu (Eci), Erythroxylum novogranatense var. novogranatense (Enn) and Erythroxylum novogranatense var. truxillense (Ent) are cultivated primarily for the illicit extraction and processing of cocaine. Despite their economic and medical importance, the evolutionary history of these species remains unknown in a modern phylogenetic framework. The aims of this study were to: (a) investigate the relationship among the cultivated and a select number of non-cultivated taxa, and (b) test Plowman’s (Journal of Psychodelic Drugs 11:103–117, 1979b) linear progression hypothesis of the cultivated Erythroxylum taxa versus Johnson’s et al. (Annals of Botany 95:601–608, 2005) hypothesis that Ec and En are sister species. AFLP phylogeny was used to compare the relationships among 36 Erythroxylum species (133 accessions) spanning the geographic distribution of the genus. A Maximum Parsimony tree revealed both geographic and taxonomic partitioning into clades representing species from Africa, Asia-Pacific and the New World (Tropical Americas). Ec and En formed distinct clades, indicating they are sister species and a cluster of non-cultivated species were the most closely related to the cultivated species. Multivariate ordination analysis was used to evaluate the relationship between cultivated and non-cultivated Erythroxylum taxa from the Tropical Americas. Our results support the hypothesis that the cultivated species are more closely related to each other than to any other species of Erythroxylum, but refute the hypothesis that Ent (and Enn) descended from Ecc. Instead our data suggest an independent, non-linear evolutionary relationship between Ec and En. Finally, the AFLP analyses identified significantly different genetic groups within Erythroxylum suggesting that the current intrageneric classification of this genus be revised.

B. Cavalcante, Maria; Escoute, Jacques; Madeira, Jean; Romero, Rocio; Nicole, Michel; Oliveira, Luis; Hamelin, Chantal; Lartaud, Marc; Verdeil, Jean

2011 Tropical Plant Biology

doi: 10.1007/s12042-011-9071-8

Globally, the banana plant (Musa spp) is the fourth most important crop after rice, wheat and corn (based on production in tons). It is cultivated in more than 100 tropical and subtropical countries, mainly by small producers and is a fundamental food source for millions of people. Black leaf streak disease (BLSD), caused by Mycosphaerella fijiensis Morelet (sexual phase) or Paracercospora fijiensis (Morelet) Deighton (asexual phase), is the main disease affecting the world’s banana culture. This disease has a wide geographical distribution accounting for losses exceeding 50% of global banana production. We conducted a comparative histocytological study on the kinetics of the infection process using three banana genotypes with phenotypes that differ in resistance to BLSD: Grand Naine (Susceptible), Pisang Madu (Partially Resistant) and Calcutta 4 (Resistant). Experiments were conducted under controlled conditions with the objective of characterizing the cellular interaction processes between M. fijiensis and Musa acuminata. Conidia germination occurred 24 hours after inoculation. Germination rates were high (97%) and there were no significant differences between the three genotypes (P > 0.147). The Peroxidase enzyme and H2O2 were associated with a hypersensitivity-like reaction in the resistant genotype Calcutta 4, indicating a possible role of the enzyme or its product as defense mechanisms against M. fijiensis in banana plants.