Physiological Analysis of Genotypic Variations In Drought and Heat Tolerance for Creeping Bentgrass.

Drought and heat are both major abiotic stresses, which often lead to decline in turf growth and quality in various grass species. Creeping bentgrass (Agrostis Stolinefera), one of the widely-used species on golf courses, is sensitive to drought and heat stress. Improving tolerance to these abiotic stresses in creeping bentgrass is critically important for conserving resources and improving turf quality in water limiting and warm climatic regions. The genetic variation is an invaluable source for selecting tolerant germplasm that can persistent during stressful periods. The objectives of the study were to compare genetic variations in drought or heat tolerance among commercially available cultivars and to determine major physiological traits associated with the variations in either drought or heat tolerance. Eight cultivars of creeping bentgrass, ‘Kingpin' ‘Tyee' ‘Shark' ‘007' ‘Pro-a7' ‘Penncross' ‘Declaration' and ‘L-93', were subjected to drought by withholding irrigation or heat stress in a growth chamber with elevated temperature (35 C). Several physiological measurements were made, including turf quality, leaf relative water content (RWC), leaf photochemical efficiency (Fv/Fm), chlorophyll content, leaf electrolyte leakage (EL), and content of malondialdehyde, a product of lipid peroxidation. Using these parameters cultivars were grouped into three groups of varying drought or heat tolerance of high, medium or low levels, using cluster analysis. ‘Kingpin’, ‘Tyee’, and ‘Shark’ consistently performed poorly under drought stress; ‘Pro’, ‘Declaration’ and ‘007’ were the most tolerant.  For heat tolerance, ‘Declaration, ‘L93’ and ‘007’ performed the best while ‘Kingpin’ and ‘Penncross’ performed poorly under heat with the other cultivars being of intermediate tolerance.  Drought tolerance in creeping bentgrass was mainly associated with the ability of leaves to maintain cellular hydration or water retention and membrane stability whereas heat tolerance was closely related to the leaf senescence or stay-green trait. Those physiological parameters closed correlated to overall turf performance under drought or heat stress could be used as selection criteria for breeding stress tolerant germplasms.