Development of reproductive structures of Phomopsis helianthi Munt.-Cvet. et al. and Phoma macdonaldii Boerema on sunflower seeds

Abstract

We investigated possibilities for the formation of reproductive structures of important sunflower pathogens, Phomopsis helianthi and Phoma macdonaldii , on the husk and kernels of naturally infected and inoculated seeds. Pycnidia were typically formed at the wider part of the husk in all sunflower lines and hybrids infected by P.helianthi and/or P.macdonaldii , partly immersed in the epidermis. The pycnidia of P.macdonaldii were larger than the pycnidia of P.helianthi . The kernels infected by P.helianthi showed slight structural changes in comparison with the non-infected achenes. An exception were the seeds of a line which, on infection by P.helianthi , showed a complete disintegration of the central part of the cotyledon while numerous pycnidia formed in the outer layers of the parenchyma. Seeds of lines infected by P.macdonaldii were considerably damaged. The cotyledonary tissue was disintegrated and pycnidia arranged in rows formed in the outer layers of the parenchyma.