Effects Of Ammonium Nitrogen And Nitrate Nitrogen On Fusarium Wilt At Seedling Stage Of Cucumber

Cucumber（Cucums sativus L）,also known as king gourd and cucumber,is an annual herb of the Cucurbitaceae family,native to the warm and humid Himalayas,and now widely grown in temperate and tropical regions.NH₄⁺-N and NO₃^--N are the main nitrogen forms for plants absorption,and plants selectively absorb the NH₄⁺-N and NO₃^--N.the growth of plant is influenced by the differences in absorption and metabolism between the two nitrogen forms.Cucumber is one of the main vegetable under protected conditions in China,Fusarium wilt is one of the main soil-borne diseases that are easy to occur but difficult to prevent.The disease occurrence is closely related to seedlings growth.So it is important to provide suitable nitrogen forms for seedlings growth and disease resistance.In view of this,pot experiment was adopted in the paper and seedlings were supplied with NH₄⁺-N（AN）,NO₃^--N（NN）and half NH₄⁺-N and NO₃^--N（1/2A+1/2N）nutrient solutions on the premise of 15 mmol·L^-1 total nitrogen concentration.The effects of nitrogen forms on the growth and disease resistance were investigated,meanwhile,related mechanisms were discussed.It is helpful to provide theoretical basis for cucumber culture practice especially in greenhouse.The results are as follows:（1）In the absence of pathogen,the seedling’s indexes of cucumber seedlings treated with NN and 1/2A+1/2N were 2.75 times and 2.33 times than those of seedlings treated with AN respectively.However,Shoot dry weight and root dry weight of cucumber seedlings supplied with AN were significantly lower than those of seedlings treated with NN.At the same time,the nitrogen content in shoots of seedlings treated with NN were1.08 times and 1.15 times as much as AN and 1/2A+1/2N individually.Chlorophyll content of cucumber seedlings treated with NN and 1/2A+1/2N were 1.34 times and1.14 times as much as AN respectively.Soluble sugar content,free proline and MDA content in shoot of cucumber seedlings treated with AN were higher.（2）After the seedlings were infected by pathogen,the disease incidence of seedlings treated with AN was 8.3%,abut seedlings irrigated by NN and 1/2A+1/2N were healthy.The leaf area of seedlings treated with NN and 1/2A+1/2N were significantly larger than that of AN treatment,and the leaf area of cucumber seedlings treated with NN and 1/2A+1/2N were 1.74 times and 1.13 times than that of seedlings treated with AN separately.Meanwhile,for the NN and 1/2A+1/2N treatments the root dry weight of seedlings were 1.22 and 1.31 times than that of AN treatment respectively.In addition,nitrogen uptake by seedlings treated with NN and 1/2A+1/2N were significantly higher than those of seedlings treated with AN.（3）After the seedlings were infected by pathogen,the chlorophyll content of seedlings supplied with 1/2A+1/2N were 1.32 times and 1.31 times than those of seedlings supplied with NN and AN individually.The soluble sugar content in roots irrigated by AN solution was significantly higher than those of seedlings irrigated by NN and 1/2A+1/2N solution,and the soluble sugar content in roots of AN treatment were 2.84 times and 2.72 times than those of NN treatment and 1/2A+1/2N treatment respectively.In addition,free proline content in shoot of seedlings treated with NN was1.37 times than that of AN,and flavonoids and total phenol content in shoot of seedlings treated with NN and 1/2A+1/2N were more than that of AN.