Comparative Study on Growth, Physiological and Biotic Stress Resistance of Cucumber (Cucumis sativus L.) with Jasmonic Acid and Methyl Jasmonate under Greenhouse Conditions

Jasmonic acid (JA) is a defensive plant hormone, and its derivative methyl jasmonate (MeJA) is widely used in scientific research as an exogenous plant regulator for plants under biotic or abiotic stress. Differences between the response of JA compounds to biotic stress in cucumber under greenhouse conditions are not studied well. In this study, we studied the difference between two JA compounds in regulating cucumber’s physiological, growth and biotic stress resistance under greenhouse conditions. There are a total of 6 treatments in this experiment: CK (no JA compound spraying, no aphid inoculation), AS (no JA compound spraying, aphid inoculation), JA (JA spraying, no aphid inoculation), MeJA (MeJA spraying, no aphid inoculation), JA + AS (JA spraying, aphid inoculation), MeJA + AS (MeJA spraying, aphid inoculation). We have three key findings: (1) JA compounds could significantly enhance the antioxidant activity, defence of secondary metabolite accumulation and stress-resistance of cucumber. (2) MeJA increased the accumulation of lignin in cucumber leaves by elevating the activities of enzymes related to lignin biosynthesis (phenylalaninammo–nialyase, guaiacol peroxidase, laccase), which resulted in a lower value of plant stress rating than JA. (3) MeJA protects plant growth through stronger resistance to aphids, but its promotion of leaf lignification also leads to restricted leaves growth. Our research has provided suggestions and experience for relevant agricultural production and follow-up scientific research.