| Yam is Dioscorea of the Dioscoreaceae family.It is easy to grow and rich in nutrition with both edible and medicinal values.Climate change by global warming has become one of the important problems in the yam planting.Thus,it is urgent to develop yam varieties adopted with environmental stresses.Presently,most of yams planted in different regions are local varieties.The selection progresses of new varieties with better resistance against stresses are slow.In particular,the basis on stress physiology and biochemistry is rare.The objectives of this study were to study the physiological and biochemical parameters for environmental stresses of yams,and the selection indices for the differences in tolerance of various yam varieties were identified to explore the adaptability of various yam varieties to different planting environments and climate changes.These selection indices can be used in the future yam breeding and cultivations,and are expected for the scientific measuring of germplasm cultivation managements to reduce adversity damages from environmental stresses.Five yam varieties grown in Fujian,including Qingliuxueshu,Anshaxiaoyeshu,Shanshu,Minghuai NO.1,and Minghuai NO.3,were used in this study.Thirty-day-old seedlings were treated with low temperature and drought stresses in phytotron.For low temperature treatment,the seedlings were treated at 8 ? for 0,24 and 48 hours,and the drought treatment was performed at 25 ? for 0,15,25 days after watering.After the treatments,the leaf phenotypes of various cultivars under the stresses were observed and scored.Leaf stomatal density,stomatal opening,leaf water content,antioxidant system,and photosynthetic parameters of the seedlings were also measured for determining the promising physiological indices in response to each stress.The main results are as follows:1.Phenotypic analysis showed that(1)there were no obvious changes in the appearances of Minghuai NO.3 and Shanshu under drought stress,while Anshaxiaoyeshu had a slight lodging subjected todrought stress.In contrast,the symptoms of leaf yellowing,wilting,and curling occurred in Minghuai NO.1 under the drought stress for 25 days.Qingliuxueshu also appeared symptoms of leaf withering and yellowing when the plants were subjected to the drought stress.Based on the phenotypic scores,Shanshu and Minghuai NO.1 were drought-tolerance varieties,while Minghuai NO.1 and Qingliuxueshu were sensitive to drought stress.(2)Under low temperature stress,morphological appearances of Shanshu did not change significantly,but Anshaxiaoyeshu and Qingliuxueshu had a slight lodging.Notably,the leaves of Minghuai NO.1 and Minghuai NO.3 showed severe dehydration and wilting.Consequently,Shanshu was a low-temperature tolerance variety,while Minghuai NO.1 and Minghuai NO.3 were low-temperature intolerance varieties based on the phenotypic scores.2.The parameter analysis of water regulation system showed that the leaf water content of yam was positively and significantly correlated(r=0.892)to the tolerance under drought and low temperature conditions,indicating that both drought and low temperature stresses caused the leaves to lose water,and the water retention capacity of the leaves determined plant resistance to the stresses.In addition,stomatal opening was extremely related to the tolerance subjected to both drought(r =0.927)and low temperature stresses(r = 0.898).3.The results of photosynthetic parameters showed that the drought tolerance was significantly correlated to ETR(r = 0.723),Fv / Fm(r =0.744),and q P(r = 0.840),and SPAD value was also correlated to drought tolerance(r = 0.623).Low temperature tolerance was significantly correlated with ETR(r=0.909),Fv/Fm(r = 0.865,),NPQ(r= 0.753),and q P(r = 0.811)parameters,but no significant differences were observed between SPAD and tolerance under low temperature stress in yam.These results illustrat that drought and low temperature stresses had different chlorophyll destruction mechanism in yam.4.The parameter analysis of antioxidant system showed that the POD activity of Shanshu was significantly higher than other cultivars under drought stress.In addition,the accumulation of hydrogen peroxide caused by drought stress was significantly and negatively correlated(r =-0.538,p < 0.05)with drought resistance,suggesting that the POD activity of Shanshu might be related to the capacity to scavenge hydrogen peroxide,making it more resistant to drought stress.Furthermore,the hydrogen peroxide accumulation induced by low temperature stress was also significantly and negatively correlated(r =-0.62,p < 0.05)with the tolerance to low temperature,but no antioxidant enzymes associated with low temperature resistance were observed.Collectively,the tolerances to stresses in yam seedlings are significantly related to photosynthetic systems and water adjustment capacity.In addition,the accumulation of hydrogen peroxide is also an effective parameter in stress resistance of Shanshu.The POD activity of Shanshu may play a critical role in elimination of hydrogen peroxide.However,we did not identify any antioxidant enzymes related to the low temperature resistance.In near future,the stomatal regulatory mechanism,such as ABA hormone,needs to be studied in further detail.For antioxidant systems,the role of GR,GPX,and the non-enzymatic antioxidant system in resistance to stresses also needs to be further explored. |
PDF Full Text Request