Wednesday, November 15, 2006

The quest for drought-tolerant tall fescue genotypes.

Francis Kirigwi, Jennifer Black, Andrew Hopkins, and Malay Saha. The Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401-1073

Tall fescue is a cool season perennial forage grass that is affected by drought stress during the hot, dry summers of the southern Midwest. The objective of this study was to identify genotypes with contrasting drought tolerance phenotypes to subsequently construct mapping populations. Our ultimate objective is to identify genomic regions associated with drought tolerance and markers of interest for marker-assisted selection. Initially, 1000 genotypes of a tall fescue population were evaluated in the greenhouse for drought tolerance. Twenty five genotypes each with high or low relative water content (RWC), osmotic potential (OP) or chlorophyll content were identified  A replicated trial with a non-stressed control treatment was planted in the greenhouse where RWC, OP, cell membrane stability after drought stress (CMS) and after both heat and drought stress (CMSDH), and canopy temperature were determined.  Genotypes differed (P<0.001) for all traits except canopy temperature in the control pots. A significant correlation was found between RWC and CMSDH (r=0.32). Biomass production was negatively correlated with chlorophyll content and CMS (r=-0.29, and -0.63, respectively) and positively correlated with canopy temperature (r=0.35 and r=0.38, for control and drought-stressed pots, respectively).  No significant correlation was found between RWC and OP, which might indicate that the variation in OP is genotypic in nature. Principle component analysis showed that both biomass-CMS and RWC-OP formed an obtuse angle, indicating that favorable levels of RWC-OP can be combined in one genotype. Contrasting genotypes from this study have been selected for root studies and the formation of mapping populations.