Effect of light on seed germination of succulent species from the southern Chihuahuan Desert: comparing germinability and relative light germination

Abstract

Light requirements for cactus seed germination have been considered to be associated with their life–form, but this has not been thoroughly studied for other succulent species. In this study, we performed a light and darkness experiment in 11 species: seven rosette species (Agavaceae) and two columnar, one barriliform, and one globose species (Cactaceae) from the Southern Chihuahuan Desert. The response variables were seed germination percentage or germinability and relative light germination (RLG). Following germinability analyses, only the barriliform cacti E. platyacanthus was positive photoblastic. All other species were neutral photoblastic, although we found three response patterns: species having similar seed germination in light and darkness conditions, species showing higher seed germination in darkness than in light, and species showing higher germination in light than in darkness. However, following the relative light germination (RLG) analyses, two columnar species had higher RLG than the other species, seven species showed intermediate RLG (RLG 0.49–0.67), and two species had low RLG, which indicates that they germinated best in darkness. Our results do not support the suggestion that columnar cacti are neutral photoblastic and that globose cacti are positive photoblastic. We suggest that RLG is a better expression of the species’ light requirement than seed germination percentage.