Can flower forms be indicators of pollen diversity and possible gametophytic selection in marigold breeding programs?

Abstract

Pollen shape has been utilized as a taxonomic attribute since it is thought to be the most constant trait within a plant species. The African marigold (Tagetes erecta L.) has substantial variability within the species due to its wider adaptability to various agroclimatic conditions; thus, from a palynological perspective, this species is interesting for studying the variation in its pollen grains. As a commercial flower crop, the breeding programme involves multiple flower forms within the species; hence, the objective of this study was twofold: first, to characterize the typical pollen grain features of marigold and second, to assess the potential variation in pollen morphology in different flower forms across marigold genotypes for possible gametophytic selection in breeding programmes. Nine African marigold plant genotypes with six different flower forms were imaged using a scanned electron microscope to study the characteristic features of the pollen grains. The pollen grains of Tagetes erecta were found to be radially symmetrical, isopolar monads that were oblate spheroidal and suboblate in shape with tricolpi apertures and with echinate erections on the pollen wall. Significant differences were recorded between the genotypes and flower forms for all the pollen morphological features studied. The variability observed among the pollen grain populations within the genotypes for certain morphometric traits also suggested the potential of using gametophytic selection in marigold breeding programs. Although it is important to establish pollen traits for commercial hybridization programs, little information is available, and to our knowledge, this is the first report on characteristic pollen grain features in African marigolds.