| Junkekuo is a bioherbicide which was developed by Weed Research Laboratory, Nanjing Agricultural University with independent intellectual property rights. Its bioactive component is the mycelium of Sclerotium rolfsii strain SC64, which was isolated from malignant invasive weed Solidago canadensis L. Previous works show that the Sclerotium rolfsii has strong pathogenicity to main broadleaf weeds and Solidago canadensis L. It is safe to cereal crops such as rice and corn and turfgrass. It is easy for industrialized production, and can be potentially developed into a commercial bioherbicide. Mycelia of Junkekuo infected weeds and caused the weed diseased and died for 7 days after applied to dry direct-seeded rice field.However, residual mycelia developed into mature sclerotia which goes overwinter in the field and germinates, at 25?35?, and under relative humidity above 90%. New-gorwing mycelia can become the source of primary infection.and cause potential diseased risk to the next season of crops. The residue and vitality of sclerotia and the incidence of southern blight desease and yields of crops were observed in the previous paddy field after Junkekuo applied. In addition, a burial of sclerotia at different depth of soil was associatedly conducted to monitor sclerotium residue and vitality in paddy soil. The main purpose is to clarify sclerotia residual dynamics and impact on next season crop., This may provide a theoretical basis for the safe application of the bioherbicide in rice-wheat rape cropping system and rice-oilseed rape cropping system.From September 2013 to March 2014, a simulation test experiment was conducted about sclerotia which have initial germination rate of 100% buried under different-depth soil in order to study influence of sclerotia buried in soil on sclerotia vitality. The sclerotia buried in paddy soil for six months through summer, autumn and winter, were regularly taken out to check sclerotia activity changes in different burial depths. Results showed that the activity of sclerotia was associated with burial time and burial depth. Before December, under 2cm and 10cm deep soil, sclerotium activity demonstrated the same performance over time, that is first decreased and then increased, while the sclerotium activity under 5cm deep soil first decreased, then increased, and repeated this process once again. After December, the activity of the sclerotium under 2cm deep soil sharply declined to about 40%, while under 5cm and 10cm of soil, the sclerotium activity changed about the same and displayed a smooth, linear trend, and finally remained at about 90%.In August 2013, four different doses (600kg/ha?900kg/ha?1200kg/ha?1800 kg/ha) of JunKekuo were applied to control broadleaf weeds and sedges in paddy field. From September 2013 to June 2014, soil was regularly sampled to monitor sclerotium residue in the field with different bioherbicide dosage treatment plot in different soil depth through 1 /5 sampling-washing-soil method every two months. The results showed that in the four plots treated with different doses of JunKekuo, sclerotium residues and germination rate did not differ significantly except at intiation stage. Different soil depths and burial time had effect on sclerotium residue and germination rate. In September 2013, the average residual number of sclerotia in paddy soil under 2cm is 257/m2, significantly higher than that of soil under 5 cm (average residual number of 115/m2) and 10 cm (average residual number 72/m2). In December 2013, after mechanical tillage, the average number of sclerotium residues under 5 cm and 10 cm of the soil both increased and had no significant difference in.158/m2 and 147/m2 respectively, while those under 2cm of the soil dropped to 101/m2. After overwinter in April 2014, average residual number reduced to about 85/m2 was and had no significant difference among the three kinds of soil depth. To June 2014, the numble of sclerotia in three kinds of soil depth did not differ significantly and reduced to the lowest level in 47/m2. The activity of residual sclerotia is related with soil depth and time. In September 2013, the activity of residual sclerotia showed decreasing trend with the increase of soil depth. Sclerotium germination rate under 2 cm of soil was 58.29%, significantly higher than that of the soil under the 5cm (22.59%) and 10cm (0%).But in December 2013, March and June 2014, the activity of residual sclerotia did not showed decreasing trend with the increase of soil depth. In December 2013, Sclerotium germination rate under 2 cm, 5cm and 10cm of soil were 51.55%,50.32% and 60.55% separately.. But as time went on in March 2014, sclerotia germination rate in three soil depth were closely at around 29.66%. In June, sclerotium germination rate under 2 cm of soil was the lowest to 3.33%,sgnificantly lower than the germination rate under 5cm of soil (10.44%) and 10cm of soil (8.33%). In a word, residual number of sclerotia per unit area in both of different treatment plot or different layer of soil in dry direct-seeded rice for nine months later tended to homogenize (34.25-60.88 /m2), but sclerotia survival rate only was under16.67%. Therefore, infection of residual sclerotia to next season crops may be considered as a lower risk when Junkekuo is widely used in paddy fields.The safety test results of the next season crops showed in the rice-wheat and rice-rape cropping field, wheat and rape in the treated plots with Junkekuo grew naturely well compared to the control plot. And the height and yield of wheat and rape in the treated plots had no significant difference with the control plot. Before the crops harvested, the incidence of southern blight desease was found among oilrape or wheat in any plots. Therefore, Junkekuo can be safely applied to control broadleaf weed and sedge in direct-seeded rice under rice-wheat or oilrape cropping system. |
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