A perfect storm: ploidy and preadaptation facilitate Saccharum spontaneum escape and invasion in the Republic of Panama

Abstract

Polyploidy may contribute to invasive ability as it can lead to high survival and fitness during establishment and enhance the processes of adaptation to novel environments by increasing genetic diversity in invading propagules. Many grasses are polyploid and many are aggressive invaders, making them persistent problems in disturbed environments worldwide. Today, vast areas of central Panama are dominated by Saccharum spontaneum, a perennial grass that originates from Asia. While widely regarded as invasive, it is not known when or how it arrived in Panama. We explore hypotheses regarding the timing and origins of this invasion through literature review and comparisons of genetic diversity in Panama with accessions from available sugarcane germplasm collections, highlighting historical accessions that were likely brought to Panama in 1939 as part of a USDA sugarcane germplasm collection. Samples were haplotyped at two chloroplast loci and genotyped using eight microsatellite markers. All sequenced individuals from Panama belong to a single chloroplast lineage which is common worldwide and was common in the Historic germplasm collection. Although genotypic diversity was extremely high in all samples due to high ploidy, samples from Panama had reduced diversity and clustered with several accessions in the Historic collection which had the same haplotype and high ploidy levels. Our results suggest that accidental escape from the historical sugarcane germplasm collection is the likely origin of the S. spontaneum invasion in Panama. Intraspecific hybridization among several historical accessions and pre-adaptation to local conditions may have facilitated its rapid spread and persistence. We discuss the implications of our findings for biosecurity of germplasm collections.

The Influence of Nitrogen and Phosphorus Addition on Growth of the Invasive C4 Grass Saccharum spontaneum

“…In summary, we found that nutrient addition increased the growth of Saccharum spontaneum, but these effects varied seasonally and differed between biomass and density responses. Given the substantial impacts of S. spontaneum within the Panama Canal Watershed [24] and in many other parts of the world where it is a weedy invader [45], there is a great need to understand the management activities that help suppress, or unintentionally promote, its growth. This study highlights a potential risk of fertilizer applications during restoration, agriculture, agroforestry, or other activities in which S. spontaneum invasion is a challenge to land management.…”

“…It is adapted to drought, burns frequently, and is difficult to eradicate, which is why it is considered one of the most serious weeds where it occurs [18,23]. S. spontaneum was most likely introduced to the Republic of Panamá in 1939 with a United States Department of Agriculture (USDA) germplasm collection for sugarcane [24] and by the 1960s, had spread widely through disturbed areas [25]. Control of S. spontaneum is actively pursued throughout the country and is especially important in the watershed of the Panama Canal, where S. spontaneum is widespread and persistent [24,26].…”

“…S. spontaneum was most likely introduced to the Republic of Panamá in 1939 with a United States Department of Agriculture (USDA) germplasm collection for sugarcane [24] and by the 1960s, had spread widely through disturbed areas [25]. Control of S. spontaneum is actively pursued throughout the country and is especially important in the watershed of the Panama Canal, where S. spontaneum is widespread and persistent [24,26]. Fires promoted by abundant S. spontaneum reduce the germination and species richness of native trees and encourage additional growth and reproduction of S. spontaneum [17,18,27].…”

Predicting invasion risk of grasses in novel environments requires improved genomic understanding of adaptive potential

“…Though many nonnative and invasive grasses can quickly establish and persist asexually by rhizomatous reproduction and local spread, their ability to flourish and become widespread in new locations may depend on sexual reproduction and influx of novel genetic variation from other populations or species. Gene flow among introduced lineages and subsequent selection in new environments may have facilitated success of several established perennial grass invaders including Bromus tectorum (Novak and Mack, 1993 ) and Imperata cylindrica (Lucardi et al, 2014 ) throughout the United States and Saccharum spontaneum (Saltonstall et al, 2021 ) in Panama (Figure 1 ). These species have all had incredibly damaging impacts by altering fire regimes and displacing native communities in their invaded ranges (Hooper et al, 2005 ; Fusco et al, 2019 ).…”