Genetic diversity of avocado from the southern highlands of Tanzania as revealed by microsatellite markers.

BACKGROUND: Avocado is an important cash crop in Tanzania, however its genetic diversity is not thoroughly investigated. This study was undertaken to explore the genetic diversity of avocado in the southern highlands using microsatellite markers. A total of 226 local avocado trees originating from seeds were sampled in eight districts of the Mbeya, Njombe and Songwe regions. Each district was considered as a population. The diversity at 10 microsatellite loci was investigated. RESULTS: A total of 167 alleles were detected across the 10 loci with an average of 16.7 ± 1.3 alleles per locus. The average expected and observed heterozygosity were 0.84 ± 0.02 and 0.65 ± 0.04, respectively. All but two loci showed a significant deviation from the Hardy-Weinberg principle. Analysis of molecular variance showed that about 6% of the variation was partitioned among the eight geographic populations. Population FST pairwise comparisons revealed lack of genetic differentiation for the seven of 28 population pairs tested. The principal components analysis (PCA) and hierarchical cluster analysis showed a mixing of avocado trees from different districts. The model-based STRUCTURE subdivided the trees samples into four major genetic clusters. CONCLUSION: High diversity detected in the analysed avocado germplasm implies that this germplasm is a potentially valuable source of variable alleles that might be harnessed for genetic improvement of this crop in Tanzania. The mixing of avocado trees from different districts observed in the PCA and dendrogram points to strong gene flow among the avocado populations, which led to population admixture revealed in the STRUCTURE analysis. However, there is still significant differentiation among the tree populations from different districts that can be utilized in the avocado breeding program.

Comparison of Morphological and Genetic Characteristics of Avocados Grown in Tanzania.

Tanzania has been growing avocado for decades. A wide variability of the avocado germplasm has been found, and the crop is largely contributing to the earnings of the farmers, traders, and the government, but its genetic diversity is scantly investigated. With the purpose of comparing morphological and genetic characteristics of this germplasm and uncovering the correlation between them and the geographical location, 226 adult seedling avocado trees were sampled in southwestern Tanzania. Their morphological characters were recorded, and their genetic diversity was evaluated based on 10 microsatellite loci. Discriminant analysis of principal components showed that the germplasm studied consisted of four genetic clusters that had an overall average gene diversity of 0.59 and 15.9% molecular variation among them. Most of the phenotypes were common in at least two clusters. The genetic clusters were also portrayed by multivariate analysis and hierarchical clustering for the molecular data but not for the morphology data. Using the Mantel test, a weak significant correlation was found between the genetic, morphological, and geographical distances, which indicates that the genetic variation present in the material is weakly reflected by the observed phenotypic variation and that both measures of variation varied slightly with the geographical sampling locations.

Transcriptomic analysis of differentially expressed genes and related pathways in Harmonia axyridis after sulfoxaflor exposure.

Harmonia axyridis (Pallas) is a major biological control agent that is indirectly threatened by sulfoxaflor insecticide applications targeting pests in agro-ecosystems. However, the genome-wide response of H. axyridis to sulfoxaflor remains largely unknown. Here, we used high-throughput RNA-seq technology to characterize the variation in the transcriptomic profile of second-instar H. axyridis larvae after exposure to sulfoxaflor. Two libraries were generated, with 50,702,976 and 47,005,096 clean reads for the sulfoxaflor treatment and control, respectively; these were grouped into 112,497 transcripts and 52,229 unigenes, of which 33,820 and 25,175 unigenes were respectively matched to proteins in the NCBI (Nr) and Swiss-Prot databases. From these unigenes, 794 significant differentially expressed genes (DEGs) consisting of 446 up- and 348 down-regulated genes, namely P450s, GSTs, USTs, ESTs, and others, were identified between the sulfoxaflor-treated and control groups. Furthermore, these DEGs were involved in several KEGG pathways including drug metabolism and metabolism of xenobiotic pathways. For transcriptome validation, 10 specifically expressed genes were selected and verified by quantitative real-time PCR analysis. Together, these results demonstrated that sulfoxaflor induces notable variation in the transcriptome profile and pathways of H. axyridis, which establishes a basis for further molecular investigations.

Toxicity and sublethal effects of chlorantraniliprole on the development and fecundity of a non-specific predator, the multicolored Asian lady beetle, Harmonia axyridis (Pallas).

In order to further develop integrated pest management (IPM) approaches for controlling insect pests, it is important to estimate the effects of pesticides. In this study, the toxicity and sublethal effects of the insecticide chlorantraniliprole on a non-specific predator, the multicolored Asian lady beetle Harmonia axyridis, were evaluated and life table parameter data were analyzed statistically using the age-stage, two-sex life table procedure. The results of this study show that the development time of second and fourth instar larvae as well as pupa was significantly prolonged in populations treated with LC10 (2.42 mg (a.i.) L-1) and LC30 (12.06 mg (a.i.) L-1), while adult longevity and fecundity were both significantly reduced and the preoviposition period (POP) was significantly prolonged following treatment compared to the control. In addition, the net reproductive rate (R0), as well as the intrinsic (r) and finite rate of increase (λ) were significantly decreased in groups treated with the insecticide. These results reveal that because sublethal concentrations of chlorantraniliprole impair the population growth of H. axyridis, more attention should be paid to the use of this chemical as a component of IPM strategies.

No impact of transgenic cry1C rice on the rove beetle Paederus fuscipes, a generalist predator of brown planthopper Nilaparvata lugens.

T1C-19 is newly developed transgenic rice active against lepidopteran pests, and expresses a synthesized cry1C gene driven by the maize ubiquitin promoter. The brown planthopper, Nilaparvata lugens, is a major non-target pest of rice, and the rove beetle (Paederus fuscipes) is a generalist predator of N. lugens nymphs. As P. fuscipes may be exposed to the Cry1C protein through preying on N. lugens, it is essential to assess the potential effects of transgenic cry1C rice on this predator. In this study, two experiments (a direct feeding experiment and a tritrophic experiment) were conducted to evaluate the ecological risk of cry1C rice to P. fuscipes. No significant negative effects were observed in the development, survival, female ratio and body weight of P. fuscipes in both treatments of direct exposure to elevated doses of Cry1C protein and prey-mediated exposure to realistic doses of the protein. This indicated that cry1C rice had no detrimental effects on P. fuscipes. This work represents the first study of an assessment continuum for the effects of transgenic cry1C rice on P. fuscipes. Use of the rove beetle as an indicator species to assess potential effects of genetically modified crops on non-target arthropods is feasible.