Ecological setup, ploidy diversity, and reproductive biology of Paspalum modestum, a promising wetland forage grass from South America

Abstract

With ever-rising demand for food, forage breeding for intensification of cattle production is also taking a leap. In South America, cattle production systems are displaced to marginal areas poorly exploited with cultivated pastures yet with high potential for growing stocking rates. This places the need for using native genetic resources to breed locally adapted plant genotypes that benefits from better forage quality, yield, and lesser threat to the local biodiversity. Paspalum modestum Mez is a grass species that produces quality forage and grows in marginal areas like estuaries and floodplains, suitable for introduction in breeding programs. In this study we characterize the species' reproductive biology and ecological preferences needed beforehand any improvement. P. modestum plants found in nature are commonly diploids, rarely triploids, and tetraploids. Chromosome associations during meiosis in polyploids indicate they are autopolyploids. While diploids are sexual self-sterile, analyses of embryology, gamete fertility and experimental crossings show tetraploids are self-compatible facultative apomicts, highly fertile and have a high proportion of sexuality compared to other apomictic species. Ecological niche analysis and species distribution modelling show mean annual temperature and precipitation as main ecological drivers and a wide geographical area of climatic suitability where P. modestum can grow and be exploited as a forage grass. Our study points to P. modestum as a native plant resource appropriate for breeding waterlogging tolerant ecotypes and genotypes of high biomass production adapted to low flow areas in the Subtropics of Brazil, Paraguay, Uruguay and Argentina.

Single Independent Autopolyploidization Events From Distinct Diploid Gene Pools and Residual Sexuality Support Range Expansion of Locally Adapted Tetraploid Genotypes in a South American Grass

“… Zozomová-Lihová et al, 2015 ), they are much less frequent among sexual–apomictic polyploid complexes mainly because egg cells in apomictic ovules do not receive pollen, and yet, apomicts’ pollen can exert sizeable reproductive interference on sexuals ( Hersh et al, 2016 ). Studies in natural populations from different Paspalum species depict a lack of interploidy hybrids, even when they are easily produced under experimental conditions (e.g., Hojsgaard et al, 2008 , 2013 ; Karunarathne et al, 2020a ). The lack of triploids, the occurrence of higher number of effective genotypes, and the levels of admixture among tetraploids from mixed-ploidy populations compared to those in pure populations of P. intermedium suggest either that tetraploids are regularly formed de novo in these contact zones or that the levels of sexuality in tetraploids are higher and recombinant genotypes are produced at higher frequencies than in pure populations (population Hojs481/2W, for instance, contains five different tetraploid genotypes; Table 1 ).…”