Studies On The Disease Causes Of Tobacco Pole Rot And Its Control Technology

Rhizopus oryzae causes tobacco pole rot during tobacco flue-curing,appears in the yellowing stage in yellow,regularly.This disease can spread rapidly through tobacco curing barns,leaf and stem rot of tobacco has the potential to cause considerable economic loss to farmers.The paper investigated the diseases of tobacco mildew disease during the baking period,analyzed the biological characteristics of the pathogens,analyzed the group structure and diversity of tobacco leaves,and screened the control agents.1.Rot disease during baking period of flue-cured tobacco leaf rot were identified as Rhizopus oryzae.biological characteristics of pathogens.The optimum growth temperature of R.oryzae were35?,and the lethal temperature was 65?for 10 min.It could metabolize in various hyperosmolytic solutions,including up to 1%-10%sodium chloride,and so on,with optimal p H around 7.0.The conidia germination ratio of the conidial suspension in 20%glycerol was 60%at 4?,.2.The results showed that tobacco pole rot occurred in all the planting areas of flue-cured tobacco in our province,and the detection ratios of R.oryzae from samples of tobacco leaves,tobacco baking stick and tobacco baking rope were all 100%.R.oryzae can cause disease temperature in the range of 20?38?,45?does not cause disease.It can cause disease in both petiole and petiole,and petioles wound is beneficial to its infection.The pathogenicity of parietal lobe was different,and the spread rate of parietal lobe was the slowest.The pathogenicity was the strongest for the mature leaves at the bottom,but the pathogenicity was weak for the young leaves at the top.The transmission vector of the disease is mainly conidia of pathogenic bacteria,and the main transmission medium is wind in the middle period of the closed grill room.3.The fungal community composition of both petiole and leaf samples from flue-cured tobacco leaves was analyzed based on high-throughput sequencing platform.It was showed that the fungi from MJ,MB,JQ,JZ,BQ,BZ were distributed in Ascomycota,and Basidiomycota,When at genus level for sample MJ,the dominant genus was Alternaria?31.65%?,Aspergillus?9.95%?and Neocamarosporium?1.34%?;For sample MB,dominant genus was Aspergillus?94.18%?,Penicillium?2.35%?and Rhizopus?0.77%?;For sample JQ,dominant genus was Aspergillus?40.13%?,Rhodotorula?31.81%?,Alternaria?16.75%?.For sample JZ,the dominant genus was Aspergillus?62.77%?,Alternaria?9.74%?,Rhodotorula?5.20%?.For sample BQ,dominant genus was Aspergillus was Aspergillus?89.46%?,Myrothecium?2.54%?and Rhodotorula?.48%?,For sample BZ,dominant genus was Aspergillus?96.93%?and Alternaria?1.92%?.Alpha index showed tha diversity of fungal communities and richness of fungal communities i is the highest for sample MJ,Lowest mildew in BZ.4.Fungal culturing and Ion S5^TMXL high-throughput sequencing techniques were used to reveal the fungal community of the petioles and lamina of tobacco leaves infected with pole rot during flue-curing.A total of 108 fungal isolates belonging to 5 genera and 10 species were isolated on media.The most common fungi isolated was R.oryzae,most often found equally on petioles and laminas in the color-fixing stage,followed by saprotrophs,mostly Aspergillus fumigatus and Aspergillus flavus.High-throughput sequencing revealed saprotrophs,Alternaria being the most abundant genus,followed by Phoma,Cercospora and Aspergillus,whereas Rhizopus was the tenth most abundant genus,which was mostly found on petioles at the yellowing stage.Both culturable fungal diversity and fungal sequence diversity was higher at stem-drying stage than the yellowing and color-fixing stages,and diversity was higher with leaf lamina than petioles revealing that the changes in fungal composition and diversity during the curing process were similar with both methods.5.All the seven fungicides showed different inhibitory activities against the mycelial growth of R.oryzae.The sensitivity of R.oryzae to six fungicides For the conidia germination,the highest inhibitions were found in the cases with fluazinam and boscalid,with EC₉₀ values of 0.67 mg/L and1.53 mg/L,For the disease control efficacy,the highest inhibition rate was observed in the group treated by azoxystrobin at 50 mg/L with the efficacy of 85%.Lower inhibition rate was detected after the boscalid treatment,which showed 83%efficacy at 200 mg/L,while a poor inhibition rate?48%?was observed by fluazinam treatment at the concentration of 1000 mg/L.And mancozeb,carbendazim and pyrimethanil all exhibited efficacy of<20%at their respectively highest dosages of 4000,800 and 800 mg/L.