Effect of Plant Density on Some Physiological and Phenological Indices of Oat (Avena sativa L.) Genotypes in Climatic Conditions of Ahvaz

Abstract   Background and Objectives This study aimed at determining growth indices and temperature requirements at different stages of plant growth in order to optimize the ecology of plants to increase yield due to the availability of appropriate access to many agro technological issues, including appropriate planting dates, timely irrigation, appropriate time of harvesting, proper time to control the pests and diseases, the selection the appropriate cultivars, and achieving the highest yield of crops. The study also aimed at determining the growth indices and the growth rate of oat based on the BBCH scale.   Materials and Methods This experiment was conducted in the experimental field of Shahid Chamran University of Ahvaz during 2013-2014 growing season. Five oat genotypes (V1, V2, V3, V4, and V5) were grown under three different planting densities (including 300, 400, and 500 plants.m-2) using factorial experiment based on a randomized complete block design with three replicates. Growing Degree Days (GDD) of the different growing stages, according to the BBCH scale, and the daily temperature were calculated. Several physiological traits such as CGR, relative growth rate (RGR), net assimilation rate (NAR), SPAD value and total dry matter yield were evaluated.   Results The treatments had different effects on growth indices and physiological traits such as plant growth rate (CGR), relative growth rate (RGR), net assimilasion rate (NAR), leaf chlorophyll content, chlorophyll meter number, and dry matter yield. The results of the mean comparison showed that V2 had the highest level of NAR, RGR, CGR and TDW among oat genotypes, with an average of 1.40 g.m-2.day-1, 0.0015 g. g-1.da, 6.34 g.m-2.day and 39.87 g.m-2.day respectively, at a density of 300 plants / m2. In contrast, V1 had the lowest total dry matter yield with an average of 22.95 g.m-2 day. Among the genotypes, V2 had the lowest growth period with a density of 300 plants.m-2 with an average of 162 days of planting and 1899 days of growth (GDD in degrees C) and V4 had the highest growth period among the studied genotypes at a density of 500 plants.m-2 with the average of 175 days of sowing and 2178 days of growth. Discussion Reducing CGR at high densities can result in reduced photosynthetic energy in the growth of organs, or increased respiration or poor nutritional transmission of the growth of leaves from the root (Moradpour et al. 2013). Because of the decreasing RGR trend and the increasing density, dry matter accumulation was mainly attributed to undifferentiated tissues, as well as the shading of leaves on each other. Moreover, the increase in the age of the leaves can be considered effective in this decrease. Reductions in NAR during the increase in density can be attributed to the rapid addition of assimilates to seeds and the aging of the leaves. Considering the results of this research, it is suggested that using a GDD scale can lead to better at the growing season by estimating the time table as well as the time of phenological stages of oat in order to manage agricultural production, and therefore to determine the necessary conditions for plant growth.