Australian Journal of Basic and Applied Sciences, 4(2): 160-170, 2010 ISSN 1991-8178 © 2010, INSInet Publication Corresponding Author: Amal M. El-Shraiy Nafeh, Agriculture Botany Department Faculty of Agriculture Ain Shams University E-mail: amalelshraiy3@yahoo.com. Fax: 002 02 44444460 160 Influence of JA and CPPU on Growth, Yield and á- Amylase Activity in Potato Plant (Solanum tuberosum L.) Amal M. El-Shraiy and Amira M. Hegazi Agriculture Botany Department Faculty of Agriculture Ain Shams University Abstract: Field experiment was carried out in the Experimental Farm, Faculty of Agriculture, Ain Shams University, Shoubra El-Kheima, Kalubia governorate, Egypt, to investigate the influences of bioregulators; Jasmonic acid (JA) at 5 and 10 ppm and N-(2-chloro-4-pyridyl)-N’-phenylurea (CPPU) at 10 and 20 ppm and their combinations on potato (Solanum tuberosum L.) plant growth, yield and á - amylase activity during the two successive seasons of 2007 & 2008. Bioregulators were applied as foliar spray at 55 and 75 days after planting. Application of CPPU(10 and 20 ppm) and the combination of CPPU at 20 ppm with JA at 5 and 10 ppm showed an improvement in plant growth as indicated by plant height, leaves number, branches number, plant fresh and dry weights. Application of CPPU and its combinations with JA significantly improved tubers number, tuber size, tubers weight/ plant and yield ton/fed comparing with control plants. CPPU at 20 ppm + JA at 5 ppm and CPPU at 20 ppm gave the best results of tubers number, size and the yield. These positive effects of CPPU at 20 ppm and its combination with JA at 5 ppm were correlated with significant increase in total chlorophylls in leaves and phenols, total soluble sugars and total soluble carbohydrates in tuber tissues. An enhancement in total soluble carbohydrates and á amylase activity at harvest and 2 weeks later followed by reduction in these measurements at 4 weeks after harvest were observed by CPPU at 10 and 20 ppm. Excluding JA, all combination treatments showed positive increase in total carbohydrates and á amylase activity at harvest, 2 and 4 weeks after harvest. While plants treated with JA showed significant increase in phenols at harvest and á- amylase activity at 4 weeks after harvest. Key words: Potato ( Solanum tuberosum L.) , bioregulators, Jasmonic acid (JA), N-(2-chloro-4- pyridyl)-N’-phenylurea (CPPU), yield, á- amylase activity. INTRODUCTION Potatoes are the most important kinds of vegetables which are the staple food in many parts of the world; also potato crop is one of the great economic importances as it is ranked second in export. Wherefore, potatoes cultivated widely in the world. Tuberization is a developmental process unique to some Solanum species , which under favorable conditions differentiate specialized underground propagation organs or tubers Rodr´ýguez- Falc´on et al 2006). Tuber induction is associated with several morphological changes in the plant (Ewing and Struik 1992). Coinciding with the rapid growth phase of the tubers. Such alterations in morphology, together with transmission of the inducing signal across a graft, led to the belief that the stimulus was of hormonal nature. Several hormones, i.e., gibberellin (Railton and wareing,1973; Xu, et al 1998), cytokinin (Hussey and Stacey, 1984, Palmer and smith, 1970), jasmonic and tuberonic acids (Koda, et al 1988, Van de Berg and Ewing 1991) or abscisic acid (menzel, 1980, Xu, et al 1998), reportedly play a role in tuberization, and changes in the endogenous levels of these hormones could be correlated with the tuberization onset. However, in the present study attempts were done to demonstrate a causal link between JA, CPPU and their combinations for tuberization and yield. JA derivatives in leaves turns to hydroxylated forms and these forms are then glucosidated and transported out of the leaves to initiate tuber formation (Helder et al,1993). Jasmonic acid (JA) was isolated from shoots of potato plants induced to tuberize (Koda, et al,1988). JA stimulate in vitro tuber formation when added to the agar medium (van den Berg and Ewing 1991) and increased levels of JA were detected in the stolons at tuberization onset (Abdala,et al 2002 ). Kris et al (2002) mentioned that microtubers produced either from JA preconditioned stock plants or on the JA-containing tuberization media were more uniform and larger than from other treatments. JA conditioning of stock plants