Application of oxygen sensing technology in seed vigor testing of Castanea mollissima

Abstract:【Objective】Castanea mollissima has a growing history of over 2 000 years in China and playsan important role in the economy.It is also one of the oldest edible seeds in the northern hemisphere, which has been extensively consumed in the past, suggesting that chestnut is a good source of bioactivesubstances including levels of vitamins, fibers, essential fatty acids and minerals.There is increasing evi-dence that the consumption of chestnuts is becoming more important in human nutrition due to the healthbenefits provided by the presence of antioxidants.Its seed vigor reflects field emergence performance andit is one of the most important indices of seed quality.Nowadays, standard germination experiments arestill the unique determination method for seed vigor of C.mollissima.However, the germination test takesa very long time (up to 35 days) .Oxygen-sensing technology is a new tool for seed vigor testing based onoxygen consumption during seed germination.Oxygen-sensing testing can be completed when the radiclebreaks through the testa.Our objective was to find the relationships among oxygen-sensing indices andgermination performances under laboratory and field conditions and then build a rapid seed vigor determi-nation method for C.mollissima.【Methods】Two varieties of C.mollissima, 'Zhezao No.1' and 'ZhezaoNo.2' were used for our experiment.For each variety, seeds of five mother plants were collected from Zhu-ji Forestry Institute in Zhejiang, China.Fifteen samples of 3 vigor levels were obtained by artificial agingtreatments (0 h, 24 h, 48 h) .An oxygen-sensing machine developed by the Netherlands ASTEC GlobalCompany was employed to measure the oxygen contents during seed germination of C.mollissima in adarkened closed system at 25℃.Four oxygen metabolism indices were calculated:oxygen consumptionindex (OCI) , oxygen consumption rate (OCR) , critical oxygen concentration (COC) and theoretical germinationtime (TGT) .In addition, laboratory standard germination tests and filed emergence tests were conducted asthe most direct indices of seed vigor were determined to be in Hangzhou and Wenzhou.【Results】Seed vig-or of C.mollissima began to decrease after seeds were subjected to artificial aging treatments.Germinationrate, emergence rate and oxygen metabolism indices used to describe seed quality of both cultivars wereranked in descending order as:aging for 0 h > aging for 24 h > aging for 48 h.Furthermore, seeds of thevariety'Zhezao No.1'generally had higher quality than did seeds of'Zhezao No.2', except for the COCvalue.The oxygen metabolism indices, except the TGTvalue and the COCvalue, were significantly correlatedwith the three germination indices of C.mollissima variety'Zhezao No.1'.The OCRvalue showed a signifi-cant positive correlation with the germination rate, whereas it was not significantly correlated with theemergence rates at both field locations.However, for the C.mollissima cultivar'Zhezao No.2', the OCIval-ue and the TGTvalue were significantly correlated with the three germination indices.The OCIvalue showeda significant positive correlation with the germination rate, but it was not significantly correlated with theemergence rate at both field locations, which was the same as'Zhezao No.1'.The COCvalue was signifi-cantly correlated with the germination rate, whereas it was not significantly correlated with the emergencerates at both locations.In general, only the OCIvalue was significantly correlated with the three germina-tion indices of both varieties and it was used to further evaluate seed quality during storage.The germina-tion rate of C.mollissima variety'Zhezao No.1'initially decreased with increasing storage time in all fourstorage conditions.The germination rate was 77.0% after low-temperature sand storage for 2 months.Af-ter low-temperature sand storage for 4 months, the germination rate decreased to 60.0%.Seeds stored atroom-temperature in dry storage had the lowest germination rate.After room-temperature dry storage for1 month, seed germination peaked at 62.0%, while the germination rate decreased to 6.0% after three-months of storage.The change trend of the germination rate was similar for the seeds treated with low-tem-perature dry storage and room-temperature sand storage.After seeds were stored under low temperatureand dry environmental conditions for 1 month, seed germination peaked at 69.0%, whereas the germina-tion rate decreased to 17.0% after three-months of storage.After seeds were treated with room-tempera-ture sand storage for 2 months or 4 months, the germination rate decreased to 63.0% and 20.0%, respec-tively.In addition, the effects of different storage treatments on the OCIvalue of the'Zhezao No.1'varietyshowed similar changes as those for the germination rate.The OCIvalue of'Zhezao No.1'gradually de-creased with prolonged storage time under the four storage conditions, suggesting that the seed respirationof C.mollissima always reduced after storage.Furthermore, seed respiration under the conditions of drystorage rapidly decreased while seed respiration under the conditions of sand storage was slowly reduced.All the above results suggest that the optimal method is low-temperature sand storage for C.mollissima.Above all, the results of the correlation analysis showed that OCIand OCRwere significantly correlated withstandard germination rates and field emergence rates in Hangzhou and Wenzhou of 'Zhezao No.1', and OCIand TGTwere significantly correlated with the above three indices of 'Zhezao No.2'.More importantly, the seed vigor of C.mollissima needs to be determined for 35 days by a standard germinations test, whileonly 10 days are required for the oxygen-sensing test.The determination time of the new technology wasgreatly shortened.【Conclusion】The results of variance analysis showed that through field emergence per-centages, the OCIvalue could significantly distinguish the seed vigor of 'Zhezao No.1' and 'Zhezao No.2' into 3 levels, respectively.In a word, the OCIvalue was the optimal index to assess seed vigor of both vari-eties of C.mollissima, which was validated in vigor monitoring of stored seeds.Compared with the stan-dard germination test, the seed vigor detection time of C.mollissima was greatly shortened by the OCIvalueand about 25 days were saved.