Evalaluation Of Cold Tolerance Of Tropical Water Lily Varieties

Tropical water lily is a general term for the group of Nymphaea L.in Nymphaeaceae that is widely distributed in tropical regions.It is a world-famous ornamental flower.High ornamental value is widely used in garden waterscapes;it also has high medicinal value and economic value;since its introduction in China,it has been rapidly promoted and applied throughout the country,with broad market development prospects.Most tropical water lilies are not easy to survive when the temperature is below 0℃,and it is difficult to overwinter in the Yangtze River Basin and northern areas.Due to the lack of systematic research on the cold tolerance of tropical water lilies,the temperature required for their overwintering is not known.Usually,warmed greenhouses are used in production to protect their overwintering and seedling breeding,which consumes a lot of energy and causes waste.For this reason,it is very necessary to scientifically evaluate the cold tolerance of the main tropical water lily varieties to determine their safe wintering temperature,provide a scientific basis for protecting wintering,and guide their introduction.On the other hand,the selection of tropical water lily germplasms with strong cold tolerance can also provide important materials for the innovation of the cold-resistant tropical water lily germplasm.In this study,50 tropical water lily germplasm resources were used as the research object,the artificial leaves were subjected to artificial low temperature gradient treatment,and the semi-lethal temperature(LT50)was calculated by measuring the relative conductivity,and malondialdehyde(MDA),soluble sugar,Free proline content,SOD enzyme activity and other physiological and biochemical indicators,through comprehensive analysis of the significance,correlation and cluster analysis of the data,establish a tropical water lily cold tolerance evaluation system;in addition,observe some tropical water lily germplasm at natural low temperature The apparent morphological response of the following,the strength of cold tolerance is analyzed to verify the test results of artificial low temperature treatment,and finally the differences in cold tolerance of different tropical water lily varieties are finally obtained,which provides technical support for the protection of overwintering.Important practical value.The main findings are as follows:1 Physiological response of different tropical water lily varieties under artificial low temperatureThe low-temperature cycler was used to carry out low-temperature treatment of 4 gradients of 4℃,0℃,-6℃ and-12℃ on the detached leaves of 50 species of tropical water lilies,each gradient was maintained for 1.5h,and the relative conductivity was measured to calculate the semi-lethal temperature LT50 And determine the changes of MDA,soluble sugar,free proline content and SOD enzyme activity.The study found that during the entire cooling process,the relative conductivity values of various varieties increased with decreasing temperature.Among them,the varieties with poor cold resistance will reach a high level at the initial low temperature,and then increase slightly,reaching a peak at-12℃.However,the varieties with high cold resistance are not high at the initial low temperature,and there is often no obvious change in the first two stages,and they increase sharply when the temperature is subsequently lowered,and finally reach the peak.In addition,the LT50 value of the varieties with poor cold resistance is higher,and vice versa.Throughout the cooling process,the MDA content of varieties with different cold tolerances had different trends and ranges of change.Varieties with poor cold resistance have reached their peaks at the initial low temperature,and the MDA content continues to decrease due to the irreversible damage to the membrane permeability after continued cooling;while the MDA content of varieties with strong cold resistance exhibits a rise after the temperature decreases the trend of.Among them,the range of MDA content of varieties with strong cold tolerance is smaller than that of varieties with cold tolerance.Variations and ranges of soluble sugar content in varieties with different cold tolerances are also different.Among them,the varieties with poor cold tolerance have a high overall level,but as the stress deepens,the membrane structure is damaged,and the soluble content continues to decline.The varieties with strong cold tolerance showed a tendency to decrease after a small increase in the cooling process or no significant change,indicating that these varieties have accumulated soluble sugar levels that can cope with low temperature in the early stage of stress,so the difference is not significant during the cooling period.Judging from the change in free proline content,it showed a trend of rising first and then decreasing during the whole temperature lowering process.There is no obvious correlation between the proline level and the cold tolerance of tropical water lilies.Cold resistance with a high proline value is not necessarily strong.However,the variation range of proline is related to cold resistance.The larger the variation range,the easier it is to resist low temperature.From the change of SOD enzyme activity,during the whole cooling process,SOD enzyme activity showed a downward trend,but the varieties and periods with different cold tolerance had different periods and amplitudes.The varieties with poor cold tolerance began to have the highest SOD enzyme activity when they started to cool down,and then continued to decline,while the varieties with strong cold tolerance showed adaptability in the early stages,the cold protection system was activated,and the SOD enzyme activity increased.When the cold tolerance limit was reached,the SOD enzyme activity decreased.In addition,the cold tolerance of varieties with large changes was lower than those with less significant changes.2 Correlation analysis of 50 tropical water lilies under different temperature gradientsThe correlation results showed that there was a very significant positive correlation between LT50,MDA content,soluble sugar and free proline content,and a very significant negative correlation with SOD enzyme activity.Among them,SOD enzyme activity,MDA content,soluble sugar content,and LT50 are relatively closely related to the cold resistance of tropical water lilies,which can be used as screening factors for detecting the cold resistance of tropical water lilies.3 Multi-index comprehensive evaluation system of cold tolerance of tropical wa-ter liliesClustering analysis was carried out on the four important indicators for scree-ning cold resistance,such as LT50,SOD enzyme activity,MDA content,and soluble sugar content.The results showed that tropical water lilies can be divid-ed into 4 categories according to the cold tolerance:cold-resistant Weak cold resistant type,medium cold resistant type and high cold resistant type.There are 6 types of non-hardy types,including:N.’Fendai’,N.’Bull’s Eye’,N.’Wood’s Blue Goddess’,N.’St.Louis Gold’,N.Rubra,N.’Poonsub’.There are 14 types of weak and hardy types,including:N.’Alexis’,N.’Anne Emmet’,N.’Immutabilis sub sp.Immutabilis purple form,N.’Barbara Barnette’,N.’Tanzanite’,N.’Tina’,N.’Pink Flamingo’,N.’Fox Fire’,N.’Miami Rose’,N.’Rucell Presnell’,N.’Star of Siam’,N.’Ambrosia’,N.’micrantha’,N.’Avalanche’.There are 15 types of medium hardy,including:N.’Gigantea var.violace’,N.’PaulStetson’,N.’Anecphya hybrid’,N.’CharlesThomas’,N.’PinkDiamond’,N.’Red crab claw’,N.Eidorado’,N.’Yasuhiro’,N.’Blue Gold Crab Man’,N.’Paramee’,N.’Corona Red’,N.’Suwanna’,N.’King of Siam’,N.’MoonBeam’,N.’Colarata’.There are 15 types of high cold resistance types,including:N.lotus,N.’Southern Charm’,N.TropicPunch’,N.’whitecolorata’,N.’gary’,N.’Madame GannaWalska’,N.’Murasaki Shikibu’,N.’Rassameejan’,N.’Blue Aster’,N.’Ruby’,N.’Hilary,N.’Scarlet Flame’,N.’Islamorada’,N.’prolifera Wiersema’,N.’PurpleCloud’.4 Apparent morphological changes of tropical water lilies under natural low te-mperatureAccording to the observation of low temperature in the field,the cold injury symptoms of tropical water lilies are graded,the leaf cold injury index is calculated,and the defoliation rate,leaf color change,and defloration rate are taken as the representative indicators for evaluating cold tolerance.Outcome:The N.lotus at the observation point in Hangzhou has the highest cold tolerance,and the chilling stress index and the rate of defoliation are the lowest among all observed varieties.N.’Tina’ and N.’Wood’s Blue Goddess’ have poor cold tolerance,and the rate of defoliation and the index of cold damage stress are among the top of all varieties.It shows that the N.lotus has a strong cold resistance,and the N.’Tina’ and N.’Wood’s Blue Goddess’ have a weak cold resistance.This result is consistent with the result of the multi-index evaluation system.The cold damage index of the N.lotus at the Nanjing observation point is low,the N.’Tanzanite’chilling cold damage index is high,and N.’Colarata’ water lily cold damage index is somewhere in between.The cold tolerance ranks:N.lotus>N.’Colarata’>N.’Tanzanite’.The results are consistent,indicating that the experimental results are more reliable.