Evolution of Surface Hydrology in the Sahelo-Sudanian Strip: An Updated Review

In the West African Sahel, two paradoxical hydrological behaviors have occurred during the last five decades. The first paradox was observed during the 1968–1990s ‘Great Drought’ period, during which runoff significantly increased. The second paradox appeared during the subsequent period of rainfall recovery (i.e., since the 1990s), during which the runoff coefficient continued to increase despite the general re-greening of the Sahel. This paper reviews and synthesizes the literature on the drivers of these paradoxical behaviors, focusing on recent works in the West African Sahelo/Sudanian strip, and upscaling the hydrological processes through an analysis of recent data from two representative areas of this region. This paper helps better determine the respective roles played by Land Use/Land Cover Changes (LULCC), the evolution of rainfall intensity and the occurrence of extreme rainfall events in these hydrological paradoxes. Both the literature review and recent data converge in indicating that the first Sahelian hydrological paradox was mostly driven by LULCC, while the second paradox has been caused by both LULCC and climate evolution, mainly the recent increase in rainfall intensity

Comparison between a coffee single copy chromosomal region and Arabidopsis duplicated counterparts evidenced high level synteny between the coffee genome and the ancestral Arabidopsis genome

The Arabidopsis thaliana genome sequence provides a catalogue of reference genes that can be used for comparative analysis of other species thereby facilitating map-based cloning in economically important crops. We made use of a coffee bacterial artificial chromosome (BAC) contig linked to the S(H)3 leaf rust resistance gene to assess microsynteny between coffee (Coffea arabica L.) and Arabidopsis. Microsynteny was revealed and the matching counterparts to C. arabica contigs were seen to be scattered throughout four different syntenic segments of Arabidopsis on chromosomes (Ath) I, III, IV and V. Coffee BAC filter hybridizations were performed using coffee putative conserved orthologous sequences to Arabidopsis predicted genes located on the different Arabidopsis syntenic regions. The coffee BAC contig related to the S(H)3 region was successfully consolidated and later on validated by fingerprinting. Furthermore, the anchoring markers appeared in same order on the coffee BAC contigs and in all Arabidopsis segments with the exception of a single inversion on AtIII and AtIV Arabidopsis segments. However, the S(H)3 coffee region appears to be closer to the ancestral genome segment (before the divergence of Arabidopsis and coffee) than any of the duplicated counterparts in the present-day Arabidopsis genome. The genome duplication events at the origin of its Arabidopsis counterparts occurred most probably after the separation (i.e. 94 million years ago) of Euasterid (Coffee) and Eurosid (Arabidopsis)

Introgressive hybridization between the allotetraploid Coffea arabica and one of its diploid ancestors, Coffea canephora, in an exceptional sympatric zone in New Caledonia

The importance of introgressive hybridization in plant evolution has long been recognized. Nevertheless, information on gene flow between allopolyploids and their diploid relatives is very limited, even though gene flow could play a major role in polyploid establishment and evolution. Here, we investigated the processes governing hybrid formation and introgression between the allotetraploid Coffea arabica and one of its ancestral diploid progenitors, C. canephora, in a sympatric zone of New Caledonia. The occurrence of a large assortment of hybridization events between the 2 coffee species is clearly established. First-generation hybrids (FI) and post-F-1 hybrids were characterized. The involvement of unreduced gametes of C. canephora is suggested, because tetraploid F-1 hybrid plants were detected. Moreover, although bidirectional mating was observed, only unidirectional gene flow from C canephora to C. arabica was noted in post-F-1 hybrids. Most of the collected post-F1 hybrid plants exhibited a high level of introgression, and the frequency of introgression observed among the different analyzed loci was homogeneous, suggesting no significant counterselection against introgressions from C canephora. Overall, the New Caledonian central mountains appear to be a highly favourable environment for introgressive hybridization and a genetic diversity center for C. arabica

A new source of resistance against coffee leaf rust from New-Caledonian natural interspecific hybrids between Coffea arabica and Coffea canephora

The development of cultivars resistant to coffee leaf rust caused by the fungal pathogen Hemileia vastatrix is a priority in coffee breeding. However, only very few descendants of interspecific hybrids between Coffea arabica and diploid relative species have been used as resistance source. Identification of new sources of resistance appeared therefore particularly worthwhile. Hybrid plants derived from interspecific hybridization between C. arabica and Coffea canephora and found in neo-natural coffee tree populations of New Caledonia were therefore investigated. Amplified Fragment Length Polymorphism and micro-satellites amplification were used to evaluate the genetic diversity of 14 hybrid plants, and rust resistance was evaluated by inoculation with a panel of rust races representing a large variability in virulence. An important genetic diversity was characterized in hybrid plants originating from introgressions into C. arabica from various C. canephora progenitors. On the 14 plants tested for leaf rust resistance, eight appeared resistant to all races investigated. Such plant material should represent a highly valuable resource for C. arabica breeding against coffee leaf rust