Pericarp features of wild perennial Helianthus L. species as a potential source for improvement of technical and technological properties of cultivated sunflower

Abstract

Although the anatomy of the sunflower achene has been extensively studied, not enough attention is given to the research of the pericarp characteristics as potentially important parameters in the breeding programme. Therefore, we considered that it was important to make very detail comparative analysis of morpho-anatomical characteristics of achene as well as miromorphological and n-alkane characteristics of epicuticular wax of the 18 wild perennial Helianthus species. For anatomical analyses cross-sections were obtained from the middle part of pericarp using cryotechnique procedure. Micromorphological observation, morphological and anatomical analysis of pericarp were performed using Light and Scanning Electron Microscopy. The composition of the epicuticular n-alkanes was characterized by GC-FID and GC/MS analyses. Results showed differences in the distribution of phytomelanin pigment among the species. Denser phytomelanin network in the species H. salicifolius, H. resinous, H. tuberosus, and H. hirsutus may be connected with better resistance to insects and mechanical damages. Species H. resinosus, H. giganteus, and H. hirsutus are characterized by the highest percentage of cuticle and sclerenchyma thickness in the pericarp which can be a predictor of mechanical resistance to biotic and abiotic factors. Species H. strumosus, H. maximiliani, and H. grosseserratus are characterized with thin pericarp, poorly developed cuticle and epicuticle wax, as well as thin sclerenchyma tissue. In the pericarp waxes, C29 was the dominant alkane but several samples had n-alkanes longer than C33. These long-chain n-alkanes may be related to drought tolerance in some species. Obtained results of pericarp characteristics can be useful for improving technical and technological properties of the achene as well as for preservation of collection of wild sunflower species.