Journal of Pure and Applied Agriculture (2020) 5(1): 30-38 ISSN (Print) 2617-8672, ISSN (Online) 2617-8680 http://jpaa.aiou.edu.pk/ RESEARCH PAPER Optimization of chitosan level to alleviate the drastic effects of heat stress in cucumber (Cucumis sativus L.) Mujahid Ali 1 *, Chaudhary Muhammad Ayyub 2 , Zahoor Hussain 1 , Rashid Hussain 2 and Shahla Rashid 1 1 Department of Horticulture, College of Agriculture, University of Sargodha, Sargodha, Pakistan 2 Institute of Horticultural Sciences, University of Agriculture, Faisalabad, Pakistan *Corresponding author: Mujahid Ali (mujahidali2263@gmail.com) Received: 21 February 2020; Accepted: 14 April 2020; Published online: 20 May 2020 Key Message: This study reveals the potential of chitosan to alleviate the drastic effects of heat stress on cucumber genotypes and optimization of chitosan for its effective and economical use. Abstract: Heat stress is a major concern during cucumber production. To explore its production potential, chitosan could play a vital role in alleviation of heat stress. This study was planned to evaluate the potential of chitosan in cucumber growth where it is more effective under high temperature with two factorial under Completely Randomized Design (CRD). Four genotypes were previously screened out; two were tolerant (L3466, Desi- cucumber) and two were sensitive (Suyo Long and Poinsett). These genotypes were grown in the growth room having a normal temperature (28 ° C/22 ° C day/night). One day before heat treatment (40 º C/32 º C day/night), chitosan foliar spray with different concentrations (0, 50, 100, 150, 200, 250, 300 ppm) was applied. It was found that 200 ppm of chitosan level revealed significantly better results on growth index (seedling length of shoot and root, the mass of fresh and dry seedlings and the number of leaves per seedling) and physiological index (chlorophyll contents and electrolyte leakage). It was also found that heat sensitive genotype Suyo Long gave the maximum seedling electrolyte leakage (74.03%) followed by Poinsett (69.35%) at control (0 ppm chitosan). The lowest seedling electrolyte leakage (28.85%) was noted in Desi-cucumber followed by L3466 (30.16%) with foliar application of 200 ppm of chitosan. So, chitosan spray at 200 ppm explored the maximum potential to alleviate the effect of heat stress in cucumber genotypes. © 2020 Department of Agricultural Sciences, AIOU Keywords: Abiotic stress, Chitosan, Cucumber, Heat stress, Optimization To cite this article: Ali, M., Ayyub, C. M., Hussain, Z., Hussain, R., & Rashid, S. (2020). Optimization of chitosan level to alleviate the drastic effects of heat stress in cucumber (Cucumis sativus L.). Journal of Pure and Applied Agriculture, 5(1), 30- 38. Introduction Cucumber (Cucumis sativus L.) has been playing a vital role in food security. Its world production is 80.6 MT (Food and Agricultural Organization Statistics [FAOSTAT], 2016). Although, it is warm season crop yet it is sensitive to heat stress (Zhang et al., 2012). Its annual production is 71.7 MT globally (Khater, 2017). Cucumber is native to subtropical and temperate zones and its best growth and development is observed at 15-32 ° C. However, high temperature above threshold level deteriorates cucumber yield and quality (Zhao et al., 2011). Characterization or screening of various genotypes of the species against heat stress is inevitable at seedling level (Shaheen et al., 2016; Sita et al., 2017) as heat stress is the main hindrance in agriculture production (Schauberger et al., 2017). Agriculture and global warming are directly correlated. The global temperature increased by 0.5 ° C in the last hundred years. The global temperature would elevate by 1.8 ° C to 4 ° C during the next century (Intergovernmental Panel on Climate Change [IPCC], 2014). The current climatic model predicts that environmental temperature would increase by 1.1-6.4 ° C if the CO 2 level doubles (Kim et al., 2007). Global warming is becoming a sever issue (Haworth et al., 2018). The high temperature is a principal cause of unwanted alterations in the growth, development, and physiology of plants (Shaked et al., 2004). The reproductive phase is more sensitive as compared to the vegetative phase because there are high losses at this stage (Meehl & Tebaldi, 2004). Heat stress proved to be the damaging effects during the pollination process in chilies (Shaked et al., 2004), comparable results were observed in bell pepper (Thuy & Kenji, 2015), bean plant growth, development and yield (Omae et al., 2012), and tomato yield and quality (Golam et al., 2012). When plants suffer from heat stress, they enable the development of reactive oxygen species that ultimately produce the oxidative stress (Hasanuzzaman et al., 2012). It causes alterations in the expression of genes that control heat tolerance potential (Shinozaki & Yamaguchi-Shinozaki, 2007). In response, the plants contest for the endurance of heat stress, such as adjustment by changes in gene expression which becomes a cause of heat tolerance to some extent (Moreno & Orellana, 2011). To avoid such situations in plants, foliar applications of