| Luculia pinceana belongs to the evergreen shrub or tree of Rubiaceae,which is one of the wild flowers with high ornamental value and market prospect.It has beautiful plant shape,a large number of branches and leaves,bright green,long florescence,large and dense inflorescence,beautiful and aromatic flowers,which is a summer and autumn ornamental flower with broad promotion prospects,but lack of horticultural varieties.Due to its poor cold resistance and susceptibility to diseases,its application is limited in gargens.As a way to cultivate resistant varieties,polyploid breeding has opened up a new idea for cultivating highly resistant varieties of L.pinceana.In this study,polyploid seedlings were used as experimental materials and diploid seedlings were used as control.The changes of its morphology,photosynthetic characteristics,physiologic indexes and its resistance to stem rot were studied in order to obtain excellent varieties with good horticultural characters and strong resistance to stem rot,and lay the foundation for breeding new varieties of L.pinceana.The main results are as follows:1.Based on the original polyploid materials,144 tetraploid plants with stable characters were screened by tissue culture,propagation,separation and purification.The chromosome number of diploid plants was 2n=44,and that of tetraploid plants was 4n=88.The DNA content of different ploidy plants was determined by flow cytometry.2.Compared with the control diploid,polyploid plant shape is shorter,leaves are rounder and thicker,leaf color are darker,leaf and stem hairs are longer and thicker.The length and width of guard cells in the stomata of polyploid plants were significantly larger than those of diploid plants,and the density of stomata was significantly smaller than that of diploid plants.Leaf length,leaf width,leaf area,leaf thickness,leaf shape index and plant height of polyploid plants were significantly different from those of diploid plants.Compared with diploid,tetraploid increased leaf width and thickness by 16.38% and 14.71%,while decreased leaf width,leaf area and plant height by 21.20%,3.46% and 54.86%,respectively.The diurnal curve of photosynthesis of Luculia pinciana was unimodal,with the highest diurnal value at about 10 o ’clock.Compared with diploid,tetraploid had higher maximum net photosynthetic rate,light saturation point and light compensation point.The activities of superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)and the contents of chlorophyll,soluble sugar(SS),soluble protein(SP)and proline(Pro)in polyploid seedlings were significantly higher than control plants.while the contents of malondialdehyde(MDA)were lower,suggesting that polyploid diploid had stronger resistance.3.The disease samples were isolated and purified by conventional tissue separation.The pathogens of these strains were identified by pathogenicity test,morphological and molecular biological methods.The pathogens of these strains were identified by pathogenicity test,morphological and molecular biological methods.Fusarium solani and F.oxysporum were identified as the pathogens causing stem rot of L.pinciana.The virulence of seven commonly used fungicides against the two pathogens was determined by the hypha growth rate method.The results showed that the concentration for 50% of maximal effect(EC50)of difenoconazole·azoxystrobin and propiconazole against F.oxysporum were 1.956μg/ml and 2.212 μg/ml,respectively.At the same time,propiconazole had a significant effect on F.solani,with an EC50 of 3.647 μg/ml.The results of comprehensive analysis showed that procycliazole and difenoconazole·azoxystrobin were the most effective drugs for preventing stem rot.4.To study the resistance of diploids and polyploids to pathogens by in vitro and in vivo inoculation.The results of in vitro inoculation showed that both pathogens could cause disease in diploid and polyploid stems,and the disease rate of both pathogens in diploid plants was 100%.And for tetraploid plants,the disease rates of F.solani and F.oxysporum were 78.78% and 88.89% respectively.The results of in vivro inoculation showed that the incidence of F.solani infection in diploid and tetraploid plants was 69.05% and 51.11%,respectively.After inoculation of diploid and tetraploid plants with F.oxysporum,the incidence rate was 86.68% and 62.22%,respectively,and the disease index after inoculation of diploid was significantly higher than that of tetraploid plants.In summary,diploid plants were extremely weak against both pathogens,while polyploid plants were better resistant to the disease. |
