Evaluation continues

Candidate

This is a known seed-borne disease in the literature. In Austria, D. phaseolorum var. sojae and D. phaseolorum var. caulivora (now known as D caulivora) were found and seed certification showed a significant influence of year and production area on infection rates of Diaporthe spp. There was a significant but very low correlation between infected soybean seeds and germination (Weingast & Weinhappel, 2015). Diaporthe phaseolorum (not specified to var.) has been found at levels of >30% in 8.5% of the seed samples analysed in Italy (Zecchinelli & Gaudenzi, 2002). In Iowa, USA, field emergence was shown to decline with increasing seed infection and sowing dates for both DP vars and P. longicola (Zorilla et al., 1994). Pedersen & Grau, 2010, found small differences in disease incidence between rotation sequences and tillage systems in 2000, but in 2001, the incidence of D. phaseolorum var. sojae was greater in no-tillage systems and in rotation sequences with continuous planted soybean. Although references to crop rotation and destruction of plants debris are made in various references on control methods, the proportion of field infection from infected debris compared to seed infection is not known. The SEWG concluded that other sources of inoculum may also be important but can be controlled through crop rotation.

Yes

D. phaseolorum var. sojae produces light-brown spots on the cotyledons and lower stem. Pod and stem blight later appear as pycnidia on the main stem, and broken upper and lower branches, petioles, leaves and pods after maturity (Athow and Laviolette, 1973; Dimitrijevic and Jurkovic, 1982). The most important aspect of pod and stem blight is its effect on seed. Infected seeds may exhibit varying degrees of cracking on the seed coat and shrivelling, and are frequently covered with white mould (Athow and Laviolette, 1973). Sometimes the seeds have brown or black spots on the seed coat (Ilyas et al., 1975). Seeds infected with D. phaseolorum var. sojae are frequently flattened, wrinkled, discoloured and smaller than non-infected seeds (Ellis et al., 1974a). Pedersen & Grau, 2010, concluded that D. phaseolorum var. sojae is a pathogen of subterranean basal stems and causes seed yield loss in soybean. In Canada, seed treatments were found to increase plant emergence and yield in a mixed population of Phomopsis longicolla (41% of isolates), D. phaseolorum var. caulivora (37%) and D. phaseolorum var. sojae (22%) (Xue et al., 2007). It was found that foliar fungicides are beneficial in reducing lodging, seed germination and for increasing yield due to infection by D. phaseolorum var. sojae (Chin MoonSup et al., 1994, Ploper et al., 2000, Vratarić et al., 2002).

Medium

No

Candidate

Pod and stem blight is caused by the fungus Diaporthe phaseolorum var. sojae. The imperfect (conidial) stage is Phomopsis phaseoli.This fungus along with other species of Diaporthe and Phomopsis causes significant yield loss and is commonly associated with low quality, poor germinating seed (Kucharek, 1981).

candidate

The diseases caused by the Diaporthe/Phomopsis complex can be partially controlled by cultural practices such as clean tillage and crop rotation with non-host crops. Knowledge of the inoculum sources is basic for these control strategies (Athow, 1987).
In Brazil, the incidence of D. phaseolorum var. sojae on seeds increased with delayed harvesting (Dhingra et al., 1979a). Heavy rainfalls during August in central Illinois, USA, favoured an epidemic of soyabean pod and stem blight. Even under these severe weather conditions, the quality of seeds harvested from the upper portions of soyabean plants was not reduced. Selective harvest would therefore be feasible and may avoid seed quality losses (Hepperly and Sinclair, 1980a).
Delayed planting decreased infection by D. phaseolorum var. sojae and increased germination rates. Late season cultivars showed less infection and greater germination of seeds than early season cultivars. As plant density increased, infection by D. phaseolorum var. sojae increased and germination decreased. Seeds treated with benomyl germinated better at 15°C than at 25°C. An increased level of N induced greater infection by D. phaseolorum var. sojae and lower germination. A delay in harvest caused a reduction of seed germination and increased the occurrence of abnormal germination and seed decay. This trend was more conspicuous in seeds from soyabean plants that had not been treated with benomyl than in those that had been sprayed with the fungicide (Chin et al., 1993a). Infection of seed by D. phaseolorum var. sojae, Glomerella glycines and Fusarium spp. was lowest, and germination percentages highest, on late-maturing cultivars that were harvested early (Alexander and Hinson, 1973). However, the physiological quality and health of seeds were decreased in Goias, Brazil, by early sowing due to adverse moisture conditions, mechanical damage at harvesting and fungal infection, mainly by D. phaseolorum var. sojae (Pereira et al., 2000).
Field sanitation, including the removal of host debris, fallen petioles and cotyledons from the field, reduced the infection of pods and seeds by Phomopsis spp.; however, seed infection was 28.7% in the sanitized field. Fields sanitized by the application of benomyl around the soyabean plant decreased seed infection by Phomopsis spp. Total seed infection caused by various pathogens was 75-79% without benomyl application compared to 34-42% with a routine fungicide application schedule. Field sanitation was effective in controlling Phomopsis seed decay when infection pressure was low. However, it did not significantly increase the yield of soyabean, whereas a routine fungicide application schedule did (Oh Jeung Haing, 1998).