Diaporthe/Phomopsis Species on Soybean in Serbia

A complex of soybean diseases is caused by species from the genus Diaporthe /Phomopsis.Diaporthe phaseolorum (anamorph Phomopsis phaseoli) and Phomopsis longicolla(teleomorph unknown) are described as soybean pathogens. The first species includesthree varieties: D. phaseolorum var. sojae, anamorph Phomopsis sojae, the causal agent ofpod and stem blight, and D. phaseolorum var. caulivora and D. phaseolorum var. meridionalis,agents of northern and southern stem canker. The species P. longicolla is the most commonand most damaging agent of soybean seed decay.The diseases caused by parasites from this genus were first observed and described onsoybean in the USA. Presently they are widespread in most soybean-growing regions aroundthe world. Soybean in Serbia is attacked by all pathogens mentioned above, except forD. phaseolorum var. meridionalis, the causal agent of the southern stem canker. D. phaseolorumvar. caulivora (northern stem canker) has the greatest economic importance becauseit causes wilt and drying of plants during pod development and grain filling. Most intensiveoutbreaks of the disease occurred in the 1980s in southern and southeastern Banat, southernBa ka and Srem. Prematurely wilted plants yielded 50% to 62% (depending on variety)less than healthy plants. Such heavy losses raised the question of the profitability ofsoybean growing. P. sojae and P. longicolla are less important in Serbia at the moment. Intensiveinfections of soybean seed break out occasionally. It was found that P. longicolla isthe primary agent of seed decay and latent infections of seed in our country, although theother members of this genus may cause identical symptoms.Sexual cycle of development (teleomorph stage) of the fungi of the genus Diaporthe/Phomopsis form perithecia with asci and ascospores, while in the asexual cycle (anamorphstage) various types of conidia (α and β) are formed in pycnidia. The species P. longicollahas no teleomorph stage.Infected harvest residues and soybean seeds are main sources of the inoculum. D. phaseolorumvar. caulivora forms perithecia with ascospores on overwintered harvest residues.During growing season, ascospores infect leaf laminas, petioles, or injured plant parts. P.sojae and P. longicolla form pycnidia (P. sojae sometimes forms perithecia), and they infectplants by means of conidia. Seed infection by conidia or ascospores unfolds via pods. Infectedcrop residues are the main source of the inoculum, while infected seeds help the parasitesspread over large distances. Humidity and temperature (soil and air) are the mainsfactors that a