Pak. J. Bot., 54(2): 553-561, 2022. DOI: http://dx.doi.org/10.30848/PJB2022-2(30) BIO-STIMULATION AND YIELD RESPONSIVENESS IN MAIZE MUHAMMAD ASLAM 1 , MUHAMMAD ARSLAN AKHTAR 1* , MUHAMMAD YASEEN 2 , MUHAMMAD AMIR MAQBOOL 3 , WASEEM AKBAR 4 AND JAVERIA RAMZAN 5 1 Department of Plant Breeding and Genetics, University of Agriculture, Faisalabad, Pakistan 2 Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, Pakistan 3 International Maize and Wheat Improvement Center (CIMMYT), Islamabad, Pakistan 4 Maize and Millets Research Institute, Yusafwala, Sahiwal, Pakistan 5 Department of Plant Breeding and Genetics, UAF Sub-campus, Depalpur, Okara, Pakistan * Corresponding author's email: arslanpbg@gmail.com Abstract Since green revolution, synthetic fertilizers have been used extensively to enhance the crop productivity which posed harmful effects in various ecosystems. It is therefore needed to substitute or supplement the application of synthetic nutrients with organic ones for sustainable agricultural productivity. More recently, there is an increasing interest to organic bio- stimulants and if they are combined with synthetic nutrients, they have been reported to increase the crop productivity. Current investigation was planned to evaluate responsiveness of eleven commercial hybrids of maize against different combinations of a bio-stimulant (Plant Protector TM ) and synthetic fertilizer. Application of bio-stimulant increased plant biomass and chlorophyll contents, and reduced leaf temperature of the plants making them able to withstand high atmospheric temperratures. Treatment of bio-stimulant combined with 50% of prescribed synthetic fertilizer at 7 leaf stage showed 73.53% and 68.58% increase in the yield as compared to control and recommended fertilizer dose, respectively. Treatments, genotypes and their interactions contributed 35.97%, 26.23% and 27.79% of total variation for cob yield, respectively. Among the studied genotypes, FH-963, FH-985 and FH-988 were highest yielding. Results suggested that maize hybrids were highly responsive to nutrients at 7-leaf stage. It is recommended that for highest yield, dose of synthetic fertilizer could be reduced to half and supplemented with bio-stimulant at 7-leaf stage. Keywords: Plant Protector, Bio-stimulant, NPK, Maize, Contour plot, AMMI biplot Introduction Almost 18.5% Gross Domestic Product (GDP) of Pakistan is contributed from agricultural sector which employs about 38.5% of rural population and supports the whole population either directly or indirectly (Anon., 2019). Contributing as food and feed, maize has worldwide significance. Apart from usage as staple food in a number of countries, it is also used for the production of numerous industrial products including starch, oil, wax, syrup, dextrose and some cosmetics. One way or another, every part of maize plant is utilized in different industries (Haddadi et al., 2012; Aysin et al., 2020; Nawaz et al., 2020). This “Queen of Cereals” is cultivated in almost all altitudes of the country and throughout the year (Baloch et al., 2015). Maize is the third most cultivated crop worldwide covering an area of about 191.72 million hectares, yielding 5.86 tons per hectare (Anon., 2020). Maize is fourth most cultivated crop and third most cultivated cereal in Pakistan, which adds about 2.6% value in agriculture and 0.5% to the GDP. It is cultivated on about 1318 thousand hectares producing 6309 thousand tons of yield (Anon., 2019). Pakistan is ranked 19 according to maize production (Anon., 2019). Decrease in area under cultivation coupled with other biotic and abiotic factors contributed to the low production of maize in Pakistan (Dhungana et al., 2006; Walker & Schulze, 2008). Furthermore, Pakistani soils are generally calcareous and poor in nutrients and organic matter concentration. High temperature during kharif season makes situations even tougher for ideal crop yields (Sadiq et al., 2014). The primary strategy for increasing the production has always been the application of synthetic fertilizers which mainly comprise of nitrogen, phosphorus and potassium (NPK), and amounts of heavy metals including mercury, cadmium, arsenic, lead, copper and nickel accompanied by various radioactive isotopes of thorium, polonium or uranium etc. (Sönmez et al., 2007). The large scale application of synthetic fertilizers without understanding the crop requirements and soil fertility status have caused the degradation of soil profile, and pollution of surface and underground water bodies. In addition, deprived administration of organic matter causes loss in soil fertility causing disturbance in the activities of valuable microbes (Shah et al., 2009). Moreover, excessive nitrogen in fertilizers leaches and percolates contaminating the underground water which causes serious health issues (Cheema et al., 2010). On the other hand, accumulation of heavy metals and radioactive elements in the soil become part of the plant, which finally enter our food chain causing problems which might take generations to solve (Savci, 2012). Considering the above mentioned facts, it is high time we need to substitute the use of synthetic nutrients or supplement them with organic ones. Fageria et al., (2008) described that foliar application of bio -active nutrients could cut down the fertilizer requirement of the crop. Use of bio-stimulants can therefore be considered as a dependable option. Bio-stimulants have been studied to influence the growth and development of the