Cytology, ploidy and molecular taxonomy of prosopis juliflora DC and prosopis pallida HBK

Abstract

Prosopis juliflora (Sw.) DC. and P. pallida (H.&.B. ex Willd.) H.B.K. occur naturally
in the Americas and they are morphologically similar species. They are multipurpose trees and their ability to grow in poor soil conditions has encouraged their introduction throughout the arid regions of the tropics and semi tropics. The taxonomy of the genus Prosopis Linnaeus emend. Burkart is unclear and a revision of the genus is suggested by several studies. Due to their similarity, the differentiation of P. juliflora and P. pallida is difficult. Although there has been some success in differentiating the species using ploidy, leaf morphology and molecular markers, further approaches are required. This study looked for suitable cytological characters and molecular markers that would differentiate the two tropical species. The cytological character analysis allowed for the development of a dichotomous key for their identification based on leaf stomatal
characters. Stomatal length and epidermal cell density are the two characters on which the keys were developed. Correct identification of the species will allow for genetic improvement programmes and conservation efforts in the native regions. Multivariate statistical analysis showed that P. juliflora and P. pallida were separable into two groups. This could help in the classification of unknown herbarium specimens or previously misidentified samples. The phylogenetic relationship of the two species is also disputed and previous RAPD studies show close genetic similarity between the two species, suggesting a reconsideration of the series within section Algarobia. There are also disputes regarding the geographical distribution of both species and naming of new species. In this study, similarity index analysis and cluster analysis on the RAPD data revealed P. juliflora to be more closely related to North American Prosopis spp. than to
P. pallida. This result does not agree with other published studies which identifies them as closely related species, but agrees with the classification of Burkart. In the present study, the transferability of microsatellite markers developed from P. chilensis (Molina) Stuntz emend. Burkart and P. flexuosa DC. to other Prosopis species was studied. The microsatellite markers gave successful amplification profiles in some of the 13 Prosopis species analysed. Chloroplast DNA intron region was also utilised in this study to detect potentially informative sequences which could differentiate the two species. The trnLtrnF intergenic spacer region in the cpDNA was utilised. This approach was able to confirm the sequence difference in the spacer region between the two species and future work involving additional DNA regions in the chloroplast gene would provide more insight into the phylogenetic relationship of all the species. This could also clear the
taxonomical confusion surrounding the genus as a whole. This study has improved knowledge on the relationship between the morphologically similar tropical P. juliflora and P. pallida. The differentiation of the two species using cytology and molecular markers has provided an improved understanding of these resourceful species.

Date of Award	2012
Original language	English
Awarding Institution	Coventry University
Supervisor	Ashok Patel (Supervisor), Phil Harris (Supervisor) & Steve Smith (Supervisor)