【Objective】To provide data support for the evaluation of maize varieties suitable for mechanical grain harvest in Inner Mongolia,and to provide a reference for maize variety selection and timely harvest.【Methods】In the experiment,the representative maize varieties of extremely early,early,middle early,middle,middle late,and late maturity groups were used as experimental materials,and the mechanical grain harvest characters were studied in seven maize planting areas in Inner Mongolia. At physiological maturity,10,20 and 30 days after physiological maturity,the plant lodging rate,grain moisture content,grain breakage rate,grain fragmentation rate,impurity rate,and other indicators were measured. The yield of 60 000, 75 000,90 000 and 105 000 plants/hm² were compared by using the varieties suitable for mechanical grain harvest in Inner Mongolia.【Results】The plant lodging rate showed increasing trend with the increase of the number of days after physiological maturity. Grain moisture content and dehydration rate showed decreasing trend with the increase of the number of days after physiological maturity. The grain breakage rate,grain fragmentation rate and impurity rate decreased with the increase of the number of days after physiological maturity. The relationship between grain breakage rate,grain fragmentation rate, impurity rate and grain moisture content was unary quadratic curve. When the grain moisture content was 16.1%,17.0% and 15.6%,the corresponding grain breakage rate,grain fragmentation rate and impurity rate were the lowest,which were 1.3%,1.1% and 0.6% respectively. The relationship between dehydration rate and daily average temperature was a unary quadratic curve,when the daily average temperature was 0-5 ℃,the dehydration was slow,and the daily dehydration was 0.197-0.211 percentage points. The accumulated temperature from physiological maturity to grain moisture content reduced to 25.0% was 100-200 ℃. The suitable planting density of the varieties suitable for mechanical grain harvest in each region was 90 000 plants/hm².【Conclusion】The evaluation index of maize suitable for mechanical grain harvest as follows：The suitable planting density was 90 000 plants/hm²,and during the harvest,the suitable harvesting time was 10-20 days after physiological maturity with plant lodging rate≤5.0%,grain moisture content≤25.0%,grain breakage rate≤5.0%,grain fragmentation rate≤2.0%,impurity rate≤1.1%,yield loss rate≤5.0%.

【Objective】The drought tolerance and salt tolerance of 16 maize varieties at germination stage were evaluated.【Methods】Five treatments including 15% PEG-6000 drought stress,20% PEG-6000 drought stress,220 mmol/L NaCl salt stress,300 mmol/L NaCl salt stress and control（water）were set up. The drought tolerance and salt tolerance of 16 maize varieties were evaluated by weighted membership function value method. The GGE map was used to distinguish the tolerance of varieties. At the same time,the similarity and discrimination ability of different stress treatments in variety evaluation were analyzed.【Results】The weighted membership function value method evaluation results showed that,Yidan 131 and Zhenjin 308 were drought tolerant and Yidan 81 was salt tolerant;the GGE map was used to distinguish different stress treatments,the results showed that 15% PEG-6000,20% PEG-6000 and 300 mmol/L NaCl were positively correlated. The comprehensive evaluation of drought tolerance and salt tolerance of 16 maize varieties showed drought tolerance：Yidan 131,Yidan 81 and Zhenjin 308,and salt tolerance：Yidan 81,Yidan 507 and Shengfeng silage No.2.【Conclusion】Yidan 131 was a drought tolerant maize variety,and Yidan 81 was a drought and salt tolerant maize variety.

【Objective】The best planting density of spring wheat were selected among the full straw returning for no-tillage and no straw returning for real tillage,the effects of two tillage patterns on soil physical properties and spring wheat yield traits were compared under the optimal planting density.【Methods】Longmai No.30 as test material, the yield traits of nine planting densities[3.00 million（D1）,3.75 million（D2）,4.50 million（D3）,5.25 million（D4）,6.00 million（D5）,6.75 million（D6）,7.50 million（D7）,8.25 million（D8）,9.00 million plants per hm²（D9）] under two tillage patterns（full straw returning for no-tillage and no straw returning for real tillage） were compared and analyzed in 2019,and the effects of two tillage patterns on soil moisture content and soil bulk density and spring wheat yield were studied under the optimal planting density in 2020.【Results】The effects of planting density on plant height,panicle number,grain number per panicle,1 000-grain weight and yield of spring wheat reached extremely significant level（P<0.01）,and the effects of the interaction of tillage pattern and planting density on panicle number,grain number per panicle,1 000-grain weight and yield of spring wheat reached extremely significant level（P<0.01）. Under the two tillage patterns,the plant height,spike length,spikelet number,grain number per panicle and 1 000-grain weight of spring wheat decreased with the increase of planting density,showing a negative correlation;the number of invalid spikelets and panicle number increased with the increase of planting density,showing a positive correlation. Under the two tillage patterns,the yield increased steadily with the increase of planting density,and reached the highest under D6 density. Spring wheat yield under full straw returning for no-tillage was 5 601.3 kg/hm²,and that under no straw returning for real tillage was 5 097.2 kg/hm²,and then decreased gradually. Compared with the no straw returning for real tillage,spring wheat yield under D6 density increased by 9.9%. The soil moisture content and soil bulk density of 0-40 cm soil layer were significantly different before sowing and at different growth stages under the two tillage patterns. Compared with the no straw returning for real tillage,the full straw returning for no-tillage significantly improved the soil moisture content and soil bulk density of 0-40 cm soil layer. The yield of full straw returning for no-tillage increased by 433.8 kg/hm² compared with that of no straw returning for real tillage.【Conclusion】In Hulun Buir,Inner Mongolia,the best planting density of the full straw returning for no-tillage and no straw returning for real tillage were 6.75 million plants/hm². The full straw returning for no-tillage pattern effectively improved the soil moisture content and soil bulk density of 0-40 cm soil layer,and then increased spring wheat yield.

【Objective】To clarify the regulating effect of melatonin treatment on spring wheat yield under water deficit conditions.【Methods】In the experiment,the spring wheat irrigated varieties Nongmai2 and Yongliang4 were used as test materials. Using randomized complete block design,the effects of exogenous melatonin on the main phenotypic traits of spring wheat,such as chlorophyll content,photosynthetic rate,biomass per plant,spike number,grain number per spike,thousand kernel weight and grain yield,were studied under well-watered and water deficit treatments.【Results】Compared with well-watered treatment,water deficit treatment reduced the chlorophyll content and photosynthetic rate of functional leaves of spring wheat,hindered the accumulation of biomass per plant,reduced spike number,grain number per spike,and thousand kernel weight,reduced yield by 19.01%-20.35%. Under water deficit conditions,melatonin treatment could alleviate the damage to leaves caused by water deficit,maintain high chlorophyll content and photosynthetic rate,promote the accumulation of biomass per plant,inhibit the decrease of spike number,grain number per spike and thousand kernel weight,and increase yield by 13.19%-17.27%.【Conclusion】As a green growth regulator,melatonin played an important role in enhancing the adaptability of spring wheat and coping with frequent water deficit.

【Objective】To determine the optimum nitrogen application rate for soybean intercropping with double-plant maize in one hole in Hetao irrigation area.【Methods】Two rows of maize and three rows of soybean were intercropped. The width was 2.2 m,the spacing between maize and soybean was 60 cm. Maize planted by double-plant in one hole and soybean planted by one grain in one hole. Based on 420 kg/hm²（CK） of single nitrogen fertilizer for double-plant maize in one hole,the treatments with 10%,20%,30% and 40% reduction of nitrogen fertilizer were set up to compare and analyze the maize yield,soybean yield,maize agronomic traits and other indicators among the treatments,and calculate the input-output and efficiency.【Results】The yield results show that,under the intercropping pattern of double-plant maize in one hole and soybean in Hetao irrigation area,the highest yield of maize was 13 578.2 kg/hm² under the treatment with 10% reduction of nitrogen fertilizer;the highest yield of soybean was 1 094.3 kg/hm² under the treatment with 40% reduction of nitrogen fertilizer;the optimum nitrogen application rate for high yield of maize is 0-20% reduction of nitrogen fertilizer. Compared with CK,the benefit results showed that the treatment with 20% reduction of nitrogen fertilizer had the highest benefit,with an increase of 414.40 yuan/hm²,followed by the 10% reduction of nitrogen fertilizer,but the treatment with 30% and 40% reduction of nitrogen fertilizer was poor benefit.【Conclusion】Comprehensive yield and benefit showed that the optimum nitrogen application rate was 336 kg/hm²,20% reduction of nitrogen fertilizer for soybean intercropping with double-plant maize in one hole planting pattern in Hetao irrigation area.

【Objective】To study the effects of different fertilization treatments on soil fertility and potato yield in the dry farming area at the northern piedmont of Yinshan Mountain,and to provide the basis for the construction of soil fertilization mode in the area.【Methods】In Wuchuan Dry Farming Experimental Station of Inner Mongolia,combining the positioning test and laboratory analysis,NPK,organic fertilizer,NPK+organic fertilizer and no fertilization（CK） treatments were set up to analyze soil physical properties,contents of soil organic matter,total nitrogen and available nutrients,potato yield and fertilizer contribution rate in 0-40 cm soil layer under different fertilization treatments.【Results】Different fertilization treatments could effectively decrease soil bulk density and increase soil total porosity. Among them,organic fertilizer and NPK+organic fertilizer had significant improvement effect on soil physical properties（P<0.05）. The soil bulk density decreased by 13.25% and 10.60% compared with CK,respectively,and the total porosity increased by 17.55% and 15.77% compared with CK,respectively. The effects of different fertilization treatments on soil nutrient contents in different soil layers were different. Organic fertilizer application alone could significantly increase soil organic matter and total nitrogen contents in 0-10 cm soil layer（P<0.05）,which were 42.96% and 38.68% higher than that of CK,respectively. NPK+organic fertilizer treatment could significantly increase soil organic matter and total nitrogen content in 0-10 cm and 10-20 cm soil layers by 70.70%-78.33% and 73.53%-82.08% compared with CK,respectively. Organic fertilizer and NPK+organic fertilizer had significant difference on soil rapid effect nutrient content（P<0.05）. Compared with CK,the content of alkali-hydrolyzable nitrogen,effective phosphorus and available potassium in 0-10,10-20 and 20-40 cm soil layers increased by 45.90%-157.84%,4.80-7.67 mg/kg and 59.66-179.66 mg/kg,respectively. NPK,organic fertilizer and NPK+organic fertilizer could significantly improve potato yield and marketable potato rate,and NPK+organic fertilizer was the best one. Potato yield and marketable potato rate increased by 171.64% and 50.87 percentage points respectively,and fertilizer contribution rate was 63.18%.【Conclusion】In order to improve soil fertility steadily,combined application of organic and inorganic fertilizers,and the organic fertilizer needed to be promoted in the dry farming area at the northern piedmont of Yinshan Mountain.

【Objective】To explore the effect of inorganic carbon fertilizer on wheat growth and carbon supplement.【Methods】Under the condition of ensuring the same nitrogen supply level,pot experiment was conducted to analyze the effects of ammonium bicarbonate application on wheat growth and total carbon accumulation by taking ammonium nitrate as control and sampling at 2,5,10 and 30 days after topdressing.【Results】Application of inorganic carbon fertilizer promoted the growth of wheat. Compared with the control,the plant height,leaf area,fresh weight and dry weight increased by 0.36%-9.45%,6.15%-19.95%,3.81%-20.80% and 3.13%-29.65% respectively at 5,10 and 30 days after topdressing. Application of inorganic carbon fertilizer had impacts on the total carbon accumulation in wheat plants. Compared with the control,the total carbon content in wheat increased by 0.17%-0.68% and the total carbon accumulation increased by 3.83%-28.82% at 5,10 and 30 days after topdressing.【Conclusion】The carbon in the inorganic carbon fertilizer ammonium bicarbonate could be absorbed and utilized by wheat,to participate in the process of carbon metabolism,and promote the growth of wheat.

【Objective】The colonization of arbuscular mycorrhizal fungi（AMF）and dark septate endophytic fungi（DSE）in the roots of three Artemisia argyi varieties（mengai,wanai and wild Artemisia argyi）and their interaction with soil physical and chemical factors were elucidated.【Methods】The colonization rates of AMF and DSE in roots of three Artemisia argyi varieties were analyzed by microscopy,and the correlation between AMF and DSE and soil physical and chemical factors was analyzed.【Results】The colonization rates of AMF and DSE were 78.44%,75.22%,75.86% and 27.22%,33.75%,27.67% respectively in three Artemisia argyi varieties roots. AMF colonization rate was significantly negatively correlated with soil alkali-hydrolyzable nitrogen content（P<0.01）;DSE colonization rate was positively correlated with soil moisture content（P<0.05）,and significantly negatively correlated with alkali-hydrolyzable nitrogen content（P<0.01）.【Conclusion】The colonization of root symbiotic fungi（AMF and DSE）in three Artemisia argyi varieties was different and correlated with soil physical and chemical factors.

Medicinal fungi refers to large fungi that are widely used in the field of traditional Chinese medicine and have certain therapeutic effects. Increasing and improving the yield and quality of medicinal fungi is an important goal of medicinal fungi breeding,and compared with other mutagenesis methods,physical mutagenesis has played an important role in the field of medicinal fungi mutagenesis breeding. This article reviews 9 different physical mutagenesis breeding methods including ultraviolet mutagenesis,ionizing radiation mutagenesis,laser mutagenesis,ion beam mutagenesis,ultrasonic mutagenesis,plasma mutagenesis,neutron mutagenesis,space mutagenesis,and compound mutagenesis and the research progress of physical mutagenesis technology in the field of medicinal fungi,and prospects for its application.

【Objective】In order to solve the increasingly serious problem of residual film pollution in maize field in the dry farming area of the southern foothills of Daxing′anling Mountains,the replacement and application prospect of degradable plastic film and thickened plastic film were explored.【Methods】In the experimental base of Hinggan League Institute of Agricultural and Animal Husbandry Sciences（Horqin Right Wing Front Banner）,three different types of film mulching experiments were set up,including national standard plastic film mulching,thickened plastic film mulching and degradable plastic film mulching. The difference of soil temperature,moisture and maize yield in different soil layers of maize fields under different types of film treatment were compared and analyzed.【Results】For soil temperature,the thermal insulation effect of degradable plastic film treatment from maize sowing to jointing stage was basically the same as that of national standard plastic film treatment,but the thermal insulation effect of degradable plastic film treatment after jointing stage was lower than that of national standard plastic film treatment;before the grouting stage,the thermal insulation effect of the thickened plastic film treatment was significantly lower than that of the national standard plastic film treatment（P<0.05）. After the grouting stage,the soil temperature of 0-5 cm soil layer of the thickened plastic film treatment was significantly higher than that of the national standard plastic film treatment（P<0.05）. For soil moisture,the change trend in different treatments from three leaf stage to jointing stage was basically the same,which showed thickened plastic film>national standard plastic film>degradable plastic film,and the difference was not significant（P>0.05）;from tasseling and silking stage to filling stage,the soil moisture content of 0-30 cm soil layer in the treatment of national standard plastic film and thickened plastic film was significantly higher than that in the treatment of degradable plastic film（P<0.05）. For maize yield,compared with the national standard plastic film treatment,the degradable plastic film treatment and thickened plastic film treatment could increase the maize yield. The maize yield of the degradable plastic film treatment increased by 12.37% compared with the national standard plastic film treatment,and the difference between the degradable plastic film treatment and the national standard plastic film treatment was significant（P<0.05）.【Conclusion】The thermal insulation effect of degradable plastic film treatment was basically the same as that of national standard plastic film treatment before maize jointing stage. With maize growing,the degradable plastic film gradually cracked and degraded,which reduced the residual pollution of soil plastic film and increased the soil permeability,which was conducive to the growth and development of maize in the later stage. Compared with the national standard plastic film treatment,the degradable plastic film treatment could significantly increase the maize yield,and degradable plastic film mulching had a good application effect on maize field in the dry farming area of the southern foothills of Daxing′anling Mountains.

【Objective】The effects of quercetin on the growth and development and main detoxification enzymes activities of Calliptamus abbreviatus were preliminarily determined,which provided the basis for the development and utilization of biological pesticides against Calliptamus abbreviatus.【Methods】The 3-year-old grasshoppers （female）were fed with 0（CK）,0.001%,0.01%,0.1% and 1% quercetin solution,respectively. It was measured that the 7-day survival rate,dry weight,growth rate,reactive oxygen species（ROS）levels,and the activities of cytochrome P450（CYP450）,glutathione S-transferase（GST）,superoxide dismutase（SOD）and catalase（CAT）.【Results】Compared with CK,after treated with 0.01%,0.1% and 1% quercetin,the 7-day survival rate decreased by 18.29%,37.69% and 53.68%,dry weight decreased by 23.74%,28.25% and 30.25%,and growth rate decreased by 58.02%,69.02% and 73.96%,respectively. The 7-day survival rate,dry weight and growth rate were significantly negatively correlated with quercetin concentration（P<0.05）. ROS levels increased by 95.66%,173.56% and 157.04%,the activities of CYP450 increased by 118.09%,142.61% and 174.87%,the activities of GST increased by 143.83%,194.41% and 235.62%,the activities of SOD increased by 75.47%,97.37% and 107.95%,the activities of CAT increased by 299.49%,282.23% and 333.74%. ROS levels,the activities of CYP450 and the activities of GST were significantly positively correlated with quercetin concentration（P<0.05）. The activities of SOD and the activities of CAT were showing positively correlated with quercetin concentration,but the correlation had no significant difference（P>0.05）.【Conclusion】Quercetin has a certain inhibitory effect on the growth of Calliptamus abbreviatus,and has potential application value in the biological pesticide for the green control of Calliptamus abbreviates.

【Objective】To determine the indoor inhibitory effect of the tested microbial fertilizers on the four soil-borne disease pathogens of potato（Streptomyces galilaeus,Verticillium dahliae,Fusarium oxysporum and Rhizoctonia solani）.【Methods】By the method of mycelial growth rate,the inhibitory effect of four soil-borne disease pathogens of potato treated with different concentrations of microbial fertilizer（50,100,1 000 mg/L）was determined,and the effect of microbial fertilizer on the 4 pathogens toxicity was determined.【Results】The inhibition ratio of same pathogen was improved with the increase of concentration of microbial fertilizer;the greatest inhibitory effect showed when four pathogens treated with 1 000 mg/L microbial fertilizer,and the inhibition ratio of Streptomyces galilaeus and Verticillium dahliae were 97.44% and 85.01%,the inhibition ratio of Fusarium oxysporum and Rhizoctonia solani were 76.62% and 32.07%. The microbial fertilizer showed different toxicity effects on 4 pathogens,EC₅₀ of Verticillium dahliae and Streptomyces galilaeus were smaller and were 18.251 mg/L and 41.461 mg/L;EC₅₀ of Fusarium oxysporum was 140.939 mg/L,while EC₅₀ of Rhizoctonia solani was the biggest（18 632.649 mg/L）.【Conclusion】The tested microbial fertilizer had a strong inhibitory effect and toxicity against Verticillium dahliae and Streptomyces galilaeus,and has a certain inhibitory effect and toxicity against Fusarium oxysporum,but it has a lesser inhibitory effect and toxicity against Rhizoctonia solani.

【Objective】To clarify the occurrence of mung bean halo blight and the characteristics of pathogenic bacteria in Inner Mongolia.【Methods】The occurrence of halo blight in mung bean producing areas of 28 banners（counties） in Inner Mongolia from 2014 to 2018 was investigated. The pathogenic bacteria were isolated from the infected mung bean,and the morphology and colony characteristics of the pathogenic bacteria were observed. The pathogenicity,physiological and biochemical characteristics and carbon source utilization were determined,and the pathogenic bacteria were identified combined with molecular biological technology.【Results】The halo blight occurred in all the 28 banners（counties） and the incidence rate was 20%-100%. The strain was identified as Pseudomonas syringae pv. phaseolicola after phenotypic observation,physiological and biochemical identification and molecular biological identification. The utilization degree of carbon source was sucrose>inositol>glucose>lactose.【Conclusion】The halo blight occurred in all the 28 banners（counties） in Inner Mongolia,the pathogenic bacteria was Pseudomonas syringae pv. phaseolicola.

【Objective】To guide the efficient and safe use of herbicide in carrot field,and to screen the best use and application of herbicide in soil sealing before seedling.【Methods】To study the effect of different treatments on the control of weeds in carrot field,4 herbicides was used（450 g/L pendimethalin CS,330 g/L pendimethalin EC,480 g/L trifluralin EC,960 g/L refined metolachlor EC）,2 adjuvants and different application methods,with clean water spraying as a control,a total of 13 treatments in carrot field of Wusutu Town of Inner Mongolia.【Results】Among the 4 herbicides tested,the control effect of 960 g/L refined metolachlor EC on grassy weeds was significantly lower than that of 480 g/L trifluralin EC and 330 g/L pendimethalin EC（P<0.05）;3 000 mL/hm² 480 g/L trifluralin EC+300 mL/hm² adjuvant 1 had the best weed control effect compared different application doses. The control effect of grassy weeds was 93.12%,and the control effect of broad-leaved weeds was 87.88%;2 205 mL/hm² 450 g/L pendimethalin CS+300 mL/hm² adjuvant 1 treatment had the best weed control effect,and the control effect of grassy weeds and broad-leaved weeds was 99.10% and 92.51%,respectively.【Conclusion】Pre-seedling herbicide in carrot field was 2 205 mL/hm² 450 g/L pendimethalin CS+300 mL/hm² adjuvant 1.

Rice blast caused great loss to rice yield and severely restricted rice production. It was the safest,most effective and economical method to breed stable,effective,broad-spectrum and long-lasting varieties of rice blast resistance by using the host′s own disease-resistant genes. With the rapid development of molecular biotechnology,more rice blast resistance genes and QTLs were exploited to create stable,broad-spectrum and long-lasting disease-resistant materials. In this paper,the structure,function and disease-resistance mechanism of cloned disease-resistant genes and QTLs were reviewed,and the application of these disease-resistant genes combined with molecular marker selective breeding,polymerized disease-resistant genes and gene editing techniques in disease-resistant breeding was summarized,and the prospect of rice blast resistance breeding was also discussed.

【Objective】To study the effect of salt stress on processed tomato seedlings,to clarify the maximum salt concentration for normal growth of processed tomato,and to provide a reference for processed tomato cultivation and production and salt-tolerant breeding.【Methods】The seedlings of processed tomato Riegel 87-5 was used as test materials,and 0（CK）,50,100,150,200 mmol/L NaCl solution was irrigated at the seedling stage,to analyze the morphology,physiological indexes and the change of K⁺ and Na⁺ under different concentrations of NaCl solution of processed tomato.【Results】With the increase of NaCl concentration,the plant height and stem thickness of processed tomato seedlings decreased. Under NaCl stress,SOD activity,POD activity,CAT activity,MDA content,and Pro content in processed tomato leaves increased significantly（P<0.05）.Under different concentrations of NaCl stress,the K⁺ content in each organ was stem>leaf>root;when the NaCl concentration was less than 150 mmol/L,the Na⁺ content in each organ was root>stem>leaf,and when the NaCl concentration was greater than 150 mmol/L,it was the stem>root>leaf.【Conclusion】With the increase of NaCl concentration,the growth of processed tomato seedlings was inhibited,and the content of antioxidant enzyme increased with the increase of NaCl concentration;when the NaCl concentration was greater than 150 mmol/L,the cell membrane was damaged,the ion balance was broken,which affected the selective absorption of ions by the plant,and the plant cannot grow normally.

【Objective】To clarify the grain traits and accumulation rule of nutrient components during the growth and development of calabash-seed.【Methods】The variety “Jindi No.3” （Breeding by Inner Mongolia Academy of Agricultural and Animal Husbandry Sciences） was used as the test material. The grain size,weight and crude fat,protein,starch,soluble sugar of the grains were studied after 7 to 70 days of pollination.【Results】There was a great difference in grain traits and nutrient content at different growth stages. The first 14 days after pollination was the rapid growth period of the grain,and the seed morphology was mainly established in this stage. The length and width of the grains increased from 0.91 and 0.51 cm to 1.76 and 1.11 cm,and the increase amount accounted for 44.54% and 52.54% of the grain after completion. Fourteen days after pollination,grain size increased slowly,but the grain weight increased continuously until the grain was mature. From 14 to 70 days after pollination,grain length and width increased by 8.56% and 3.30% respectively. Grain weight per melon increased from 11.52 g to 67.31 g;the dry weight of 100-grain increased from 3.77 g to 20.93 g. During seed maturation,crude fat and protein contents increased gradually,and reached the highest values on 63^rd and 70^th day after pollination,which were 43.21% and 35.07%. Starch content and soluble sugar content decreased gradually on 28^th and 14^th day after pollination,respectively,and soluble sugar content could not be detected on 56^th day after pollination.【Conclusion】Seed maturation of calabash-seed divided into two stages：the first stage was the main stage of seed morphology formation within 14 days after pollination;the second stage was the accumulation stage of crude fat and protein at 21 days after pollination. The critical period for the accumulation of grain nutrients from 28 to 42 days after pollination.

【Objective】To screen watermelon germplasm materials with low temperature tolerance,explore breeding physiological indexes,and provide materials and theoretical reference for breeding of low temperature tolerant watermelon varieties.【Methods】Using 30 watermelon varieties（lines） as experimental materials,the effects of low temperature stress on the chilling injury index and recovery index of watermelon seedlings were analyzed by simulating low temperature stress（7.5 ℃） in an incubator. Furthermore,Zaojia 8424 and Qianli No.4 were selected as the test materials to analyze the effects of long-term low temperature stress （8 ℃ for 15 days）,short-term low temperature stress （4 ℃ for 2 days） and normal temperature recovery growth（28/22 ℃ for 5 days） on antioxidant enzyme activity,malondialdehyde content,reactive oxygen species content and osmotic adjustment substance content of watermelon seedlings.【Results】There were significant differences（P<0.05） in chilling injury index and no significant difference（P>0.05） in recovery index among different watermelon materials under low temperature stress of 7.5 ℃. Five materials （Qianli No.2,Qianli No.3,Qianli No.4,18S-135-2 and 18S-145-1） selected from middle fruit type had significantly （P<0.05） stronger tolerance to low temperature than Zaojia 8424（CK1）. The ability of low temperature tolerance of 2 materials（17A-79×17A-82 and 17A-82×17A-79） selected from small fruit type was stronger than that of Xiaolan（CK2）. The changes of antioxidant enzyme activities,osmotic adjustment substance content and reactive oxygen species content of Zaojia 8424 and Qianli No.4 seedlings were different under different low temperature treatment（short-term low temperature stress and long-term low temperature stress）. Qianli No.4 had higher antioxidant enzyme activity,soluble protein content and soluble sugar content,and lower content of malondialdehyde,superoxide anion（O₂^-） and hydrogen peroxide（H₂O₂）,the content of proline of Zaojia 8424 and Qianli No.4 varies with different low temperature treatments.【Conclusion】Thirty watermelon varieties （lines） had different tolerance and physiological response to low temperature stress. Low temperature tolerant germplasm materials were Qianli No.2,Qianli No.3,Qianli No.4,18S-135-2,18S-145-1,17A-79×17A-82 and 17A-82×17A-79.

【Objective】To study the effects of appearance traits,yield and quality of commercial melons of Cucubita pepo L.under different growth regulators.【Methods】"Qianhu No.2"as the test materials,and the leaves of Cucubita pepo L. were sprayed with different growth regulators（4,5,6,10 mg/L Guafeng and 1 mg/L Qianshou）,and spraying water as a control,the effects of growth regulators on the appearance traits,yield and quality of commercial melons were analyzed,and the gray correlation method was used to analyze the correlation between each index and yield.【Results】The 1 mg/L Qianshou treatment significantly increased the single melon length and fruit transverse diameter of commercial melons of Cucubita pepo L.（P<0.01）;the number of melons per plant was lower than that of the control,and the yield decreased. Guafeng treatment had no significant effect on the single melon weight,single melon length and fruit transverse diameter of commercial melons of Cucubita pepo L.（P>0.05）,and the number of melons per plant was equal to or slightly increased compared to the control. 5 mg/L Guafeng treatment had the highest yield（67 242.9 kg/hm²）.The malformation rate of commercial melon under the treatment of growth regulator was 21.1%-77.8%,which was lower than that of the control.The gray correlation analysis showed that the correlation degree between each index and yield was as follows：the number of melons per plant>endogenous abscisic acid（ABA）>malformation rate> fruit transverse diameter>single melon length> single melon weight>fruit flesh thickness.【Conclusion】The use of growth regulators was beneficial to the development of commercial melons of Cucubita pepo L.;5 mg/L Guafeng treatment could reduce melons,increase fruit setting,and significantly increase yield.

【Objective】To study the effects of different concentrations of polyethylene glycol（PEG）on onion seed germination and seedling physiological indexes.【Methods】The seeds of 3 onion varieties,St.1-16,W465 and W433,were treated with 0（CK）,10%,20% and 30% PEG for 8 h under the dark condition of 20 ℃,and the germination and seedling growth and physiological indexes of each treatment were analyzed.【Results】Compared with the control,PEG treatment significantly（P<0.05）increased the germination rate,germination potential,dry weight,and fresh weight of onion seeds. The optimal PEG priming concentration was 30%. Under the treatment of 30% PEG,the SOD and POD activity of onion seedling increased by 3.84% to 15.23%,39.11% to 62.22%,MAD content decreased by 11.84% to 14.83%;the root activity of seedlings were significantly improved.【Conclusion】The germination effect of onion seeds after 30% PEG priming was better,and there was a significant role in the growth of its seedlings.