Abstract
Slash and burn practices affect tropical forests. Our results showed strong introgression between Inga ingoides and Inga edulis in the species contact area. Interspecific hybridization could be sought to improve yield and tolerance to flooding and further increase the economic potential of the poorly drained Amazonian soils and minimize deforestation. Inga species are important components of tropical American forests, as well as a local food source. Little is known about the genetic structure of these species; in particular the amount of introgression among species remains unknown. We assessed the degree of genetic divergence and introgression among populations of I. ingoides (Rich.) Willd. and I. edulis Mart. (Fabaceae) from three Peruvian Amazon tributary rivers. Using microsatellite markers we determined the genetic structure of populations using an analysis of molecular variance and a Bayesian analysis of population structure in areas affected by seasonal river fluctuations and in ‘terra firme’ forests. Overall genetic differentiation was weak. The degree of genetic variation was similar in the two species. A putatively strong introgression was detected between the two species and an intense gene flow was identified among populations. This indicates that an intense gene flow had happened in the past, leading also to a small differentiation among populations within species. Selection of natural hybrids or artificial hybridization between I. edulis and I. ingoides could be applied to improve legume size and yield in the later species, while maintaining tolerance to flooding. Improved I. ingoides could be used in multipurpose agroforestry on open areas along the rivers, instead of using the usual slash and burn practice to create inland open areas.
Highlights
The Amazon drainage basin containing mainly lowland rainforest habitats is a major component of the Neotropical region, with more than 8 million km2 and about 25 million people (Junk and Piedade 2011)
All populations displayed high values of expected heterozygosity. These estimates were slightly lower than estimates in natural populations of tropical trees I. vera (He = 0.87; allelic richness (AR) = 7.7) (Cruz-Neto et al 2014), Symphonia globulifera L. (He = 0.89) (Dick and Heuertz 2008) and Swietenia macrophylla King (He = 0.78) (Lemes et al 2003), but were very similar to the expected heterozygosity estimated for I. edulis by Hollingsworth et al (2005) in the same region (Peruvian Amazon) (He = 66 %)
High levels of genetic diversity are maintained by high levels of gene flow facilitated by efficient pollen movement and the widespread occurrence of efficient self-incompatibility mechanisms (Dick et al 2008)
Summary
The Amazon drainage basin containing mainly lowland rainforest habitats is a major component of the Neotropical region, with more than 8 million km and about 25 million people (Junk and Piedade 2011). The species-rich floodplain forests along the large Amazonian rivers are able to survive floods up to 10 m deep for as long as up to 8 months per year (Junk and Piedade 2011, and references therein). Due to the continuing massive pressure exerted by farmers, cattle ranchers, and logging companies on the forests, new management concepts are urgently required to avoid the destruction of this unique forest type (Junk and Piedade 2011). 661,000 km2) suffered disturbance and deforestation at the average rate of 647 km per year from 1999 to 2005: 75 % within legally sanctioned areas, 64 % concentrated around the Ucayali logging centre Pucallpa, and 1–2 % occurred within natural protected areas (Oliveira et al 2007) The Peruvian Amazon tropical area (ca. 661,000 km2) suffered disturbance and deforestation at the average rate of 647 km per year from 1999 to 2005: 75 % within legally sanctioned areas, 64 % concentrated around the Ucayali logging centre Pucallpa, and 1–2 % occurred within natural protected areas (Oliveira et al 2007)
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